[Federal Register Volume 67, Number 194 (Monday, October 7, 2002)]
[Proposed Rules]
[Pages 62528-62588]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-25115]



[[Page 62527]]

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Part II





Department of Transportation





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National Highway Traffic Safety Administration



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49 CFR Part 575



Consumer Information Regulations; Federal Motor Vehicle Safety 
Standards; Rollover Resistance; Proposed Rule

  Federal Register / Vol. 67, No. 194 / Monday, October 7, 2002 / 
Proposed Rules  

[[Page 62528]]


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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 575

[Docket No. NHTSA-2001-9663; Notice 2]
RIN 2127-AI81


Consumer Information Regulations; Federal Motor Vehicle Safety 
Standards; Rollover Resistance

AGENCY: National Highway Traffic Safety Administration (NHTSA), DOT.

ACTION: Notice of proposed rulemaking.

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SUMMARY: The Transportation Recall Enhancement, Accountability, and 
Documentation Act of 2000 requires NHTSA to develop a dynamic test on 
rollovers by motor vehicles for the purposes of a consumer information 
program, to carry out a program of conducting such tests, and, as these 
tests are being developed, to conduct a rulemaking to determine how 
best to disseminate test results to the public. In response, this 
document discusses the results of NHTSA's evaluation of numerous 
driving maneuver tests for the dynamic rollover consumer information 
program that Congress mandated for the American public beginning in the 
2003 model year. This document also proposes several alternative 
methods for using the dynamic rollover test results in the agency's 
consumer information for vehicle rollover resistance.

DATES: Comment Date: Comments must be received by November 21, 2002.

ADDRESSES: All comments should refer to Docket No. NHTSA-2001-9663; 
Notice 2 and be submitted to: Docket Management, Room PL-401, 400 
Seventh Street, SW., Washington, DC 20590. Docket hours are 10 a.m. to 
5 p.m. Monday through Friday. For public comments and other information 
related to previous notices on this subject, please refer to DOT Docket 
Nos. NHTSA-2000-6859 and 8298 also available on the Web at http://dms.gov/search, and NHTSA Docket No. 91-68; Notice 3, NHTSA Docket, 
Room 5111, 400 Seventh Street, SW., Washington, DC 20590. The NHTSA 
Docket hours are from 9:30 a.m. to 4 p.m. Monday through Friday.

FOR FURTHER INFORMATION CONTACT: For technical questions you may 
contact Patrick Boyd, NPS-23, Office of Safety Performance Standards, 
National Highway Traffic Safety Administration, 400 Seventh Street, 
SW., Washington, DC 20590 and Dr. Riley Garrott, NRD-22, NHTSA Vehicle 
Research and Test Center, P.O. Box 37, East Liberty, OH 43319. Mr. Boyd 
can be reached by phone at (202) 366-6346 or by facsimile at (202) 493-
2739. Dr. Garrott can be reached by phone at (937) 666-4511 or by 
facsimile at (937) 666-3590.

SUPPLEMENTARY INFORMATION:

I. Executive Summary
II. Safety Problem
III. Background
IV. Comments to the Previous Notice
V. National Academy of Sciences Rollover Rating Study
VI. Choice of Maneuvers for Dynamic Rollover Resistance Tests
VII. Proposed Rollover Resistance Rating Alternatives
VIII. Intent to Evaluate Centrifuge Test
IX. Handling Tests
X. Assessment of Costs and Benefits
XI. Rulemaking Analyses and Notices
XII. Submission of Comments
Appendix I. Summary of Evaluation Test Results

I. Executive Summary

    Section 12 of the ``Transportation Recall, Enhancement, 
Accountability and Documentation (TREAD) Act of November 2000'' directs 
the Secretary to ``develop a dynamic test on rollovers by motor 
vehicles for a consumer information program; and carry out a program 
conducting such tests. As the Secretary develops a [rollover] test, the 
Secretary shall conduct a rulemaking to determine how best to 
disseminate test results to the public.'' The rulemaking must be 
carried out by November 1, 2002.
    On July 3, 2001, NHTSA published a Request for Comments notice (66 
FR 35179) discussing a variety of dynamic rollover tests that we had 
chosen to evaluate in our research program and what we believed were 
their potential advantages and disadvantages. It also discussed other 
possible approaches we considered but decided not to pursue. The 
driving maneuver tests to be evaluated fit into two broad categories: 
closed-loop maneuvers in which all test vehicles attempt to follow the 
same path; and open-loop maneuvers in which all test vehicles are given 
equivalent steering inputs. Other potential tests using a centrifuge or 
computational simulation were discussed but not included in our test 
plan. This notice discusses the comments we received and the results of 
our test program to date.
    The TREAD Act calls for a rulemaking to determine how best to 
disseminate rollover test results to the public, and this Notice of 
Proposed Rulemaking proposes alternatives for using the dynamic tests 
results in consumer information on the rollover resistance of new 
vehicles. The resulting rollover resistance ratings will be part of 
NHTSA's New Car Assessment Program (NCAP). The tests will be carried 
out and reported to the public by NHTSA. This program places no 
regulatory requirements on vehicle manufacturers. Past NCAP ratings 
have been developed using a procedure of public notice and comment, but 
there was no legal requirement to do so since no regulatory 
requirements were imposed on any party except NHTSA. Because the 
dissemination of information will pose no regulatory burden on 
manufacturers, we provided a brief statement on the potential benefits 
of this program and no regulatory evaluation.
    While the TREAD Act calls for a rulemaking to determine how best to 
disseminate the rollover test results, the development of the dynamic 
rollover test is simply the responsibility of the Secretary. Based on 
NHTSA's recent research to evaluate rollover test maneuvers, the 
National Academy of Sciences' study of rollover ratings, comments to 
the July 3, 2000 notice, extensive consultations with experts from the 
vehicle industry, consumer groups and academia, and NHTSA's previous 
research in 1997-8, the agency has chosen the J-turn and the Fishhook 
Maneuver as dynamic rollover tests. They are the limit maneuver tests 
that NHTSA found to have the highest levels of objectivity, 
repeatability and discriminatory capability. Vehicles will be tested in 
two load conditions using the J-turn at up to 60 mph and the Fishhook 
maneuver at up to 50 mph. Both maneuvers will be conducted with an 
automated steering controller, and the reverse steer of the Fishhook 
Maneuver will be timed to coincide with the maximum roll angle to 
create an objective ``worst case'' for all vehicles regardless of 
differences in resonant roll frequency. The light load condition will 
be the weight of the test driver and instruments, approximating a 
vehicle with a driver and one front seat passenger. The heavy load 
condition will add additional 175 lb manikins in all rear seat 
positions.
    The National Academy of Sciences recommended that dynamic maneuver 
tests be used to supplement rather than replace Static Stability Factor 
(the basis of our present rollover resistance ratings) in consumer 
information on rollover resistance. This notice proposes two 
alternatives for consumer information ratings on vehicle rollover 
resistance that include both dynamic maneuver test results and Static 
Stability Factor. The first alternative is to include the dynamic test 
results as vehicle variables along with SSF in a statistical model of 
rollover risk. This is conceptually similar to the present

[[Page 62529]]

ratings in which a statistical model is used to distinguish between the 
effects of vehicle variables and demographic and road use variables 
recorded for state crash data on a large number of single vehicle 
crashes. The National Academy of Sciences demonstrated the tight 
confidence limits that can be achieved using a logistic regression 
model for this purpose. Such a model would be used to predict the 
rollover rate in single vehicle crashes for a vehicle considering both 
its dynamic maneuver test performance and its Static Stability Factor 
for an average driver population (as a common basis of comparison).
    Under the first alternative, the ``star rating'' of a vehicle would 
be based on the rollover rate in single vehicle crashes predicted for 
it by a statistical model. The format would be the same as for the 
present rollover ratings (for example, one star for a predicted 
rollover rate in single vehicle crashes greater than 40 percent and 
five stars for a predicted rollover rate less than 10 percent). The 
present rollover ratings are based on a linear regression model using 
state crash reports of 241,000 single vehicle crashes of 100 make/model 
vehicles. We are proposing to replace the current rollover risk model 
with one that uses the performance of the vehicle in dynamic maneuver 
tests as well as its SSF to predict rollover risk. The performance of a 
vehicle in dynamic maneuver tests is simply whether it tipped-up or not 
in each of the four maneuver/load combinations. The lowest entry speed 
of maneuvers that caused tip-up will also be used if it improves the 
predictive fit of the model. In order to compute a logistic model of 
rollover risk, it is necessary to have large number of state crash 
reports of single vehicle crashes to establish rollover rates of 
vehicles for which the dynamic maneuver test performance and SSF are 
known. The agency is performing dynamic maneuver tests on about 25 of 
the 100 make/model vehicles for which we have SSF measurements and 
substantial state crash data. We believe this approach will ensure that 
the assigned NCAP ratings for rollover resistance correlate to the 
maximum extent possible with real-world performance. However, since the 
agency has not finished testing these 25 vehicles, we cannot yet say 
what the actual coefficients of the model relating dynamic maneuver 
test performance and SSF to predicted rollover rate will be. We are 
asking for comments on the validity of this concept only in this 
notice.
    The second alternative is to have separate ratings for Static 
Stability Factor and for dynamic maneuver test performance. Dynamic 
maneuver tests directly represent on-road untripped rollovers. The 
dynamic maneuver test performance would be used to rate resistance to 
untripped rollovers in a qualitative scale, such as A for no tip-ups, B 
for tip-up in one maneuver, C for tip-ups in two maneuvers, etc. Here 
again the results of ongoing dynamic testing of vehicles with 
established rollover rates would guide the establishment of a 
qualitative scale. A statistical risk model is not possible for 
untripped rollover crashes, because they appear to be relatively rare 
events and they cannot be reliably identified in state crash reports. 
The current Static Stability Factor based system would be used to rate 
resistance to tripped rollovers. Again we are asking for comments on 
the usefulness and validity of this concept in this notice. Until our 
testing of the 25 vehicles is finished, we will not know what 
particular NCAP rating will be assigned to a make/model under either of 
these two alternatives.

II. Safety Problem

    Rollover crashes are complex events that reflect the interaction of 
driver, road, vehicle, and environmental factors. We can describe the 
relationship between these factors and the risk of rollover using 
information from the agency's crash data programs. We limit our 
discussion here to light vehicles, which consist of (1) passenger cars 
and (2) multipurpose passenger vehicles and trucks under 4,536 
kilograms (10,000 pounds) gross vehicle weight rating.\1\
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    \1\ For brevity, we use the term ``light trucks'' in this 
document to refer to vans, minivans, sport utility vehicles (SUVs), 
and pickup trucks under 4,536 kilograms (10,000 pounds) gross 
vehicle weight rating. NHTSA has also used the term ``ALTVs'' to 
refer to the same vehicles.
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    According to the 2000 Fatality Analysis Reporting System (FARS), 
9,882 people were killed as occupants in light vehicle rollover 
crashes, which represents 31 percent of the occupants killed that year 
in crashes. Of those, 8,146 were killed in single-vehicle rollover 
crashes. Seventy-eight percent of the people who died in single-vehicle 
rollover crashes were not using a seat belt, and 65 percent were 
partially or completely ejected from the vehicle (including 53 percent 
who were completely ejected). FARS shows that 53 percent of light 
vehicle occupant fatalities in single-vehicle crashes involved a 
rollover event.
    Using data from the 1996-2000 National Automotive Sampling System 
(NASS) Crashworthiness Data System (CDS), we estimate that 274,000 
light vehicles were towed from a police-reported rollover crash each 
year (on average), and that 31,000 occupants of these vehicles were 
seriously injured (defined as an Abbreviated Injury Scale (AIS) rating 
of at least AIS 3).\2\ Of these 274,000 light vehicle rollover crashes, 
221,000 were single-vehicle crashes. (The present rollover resistance 
ratings estimate the risk of rollover if a vehicle is involved in a 
single-vehicle crash.) Sixty-two percent of those people who suffered a 
serious injury in single-vehicle towaway rollover crashes were not 
using a seat belt, and 48 percent were partially or completely ejected 
(including 41 percent who were completely ejected). Estimates from NASS 
CDS indicate that 81 percent of towaway rollovers were single-vehicle 
crashes, and that 84 percent (186,000) of the single-vehicle rollover 
crashes occurred after the vehicle left the roadway. An audit of 1992-
96 NASS CDS data showed that about 95 percent of rollovers in single-
vehicle crashes were tripped by mechanisms such as curbs, soft soil, 
pot holes, guard rails, and wheel rims digging into the pavement, 
rather than by tire/road interface friction as in the case of untripped 
rollover events.
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    \2\ A broken hip is an example of an AIS 3 injury.
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    According to the 1996-2000 NASS General Estimates System (GES) 
data, 61,000 occupants annually received injuries rated as K or A on 
the police KABCO injury scale in rollover crashes. (The police KABCO 
scale calls A injuries ``incapacitating,'' but their actual severity 
depends on local reporting practice. An ``incapacitating'' injury may 
mean that the injury was visible to the reporting officer or that the 
officer called for medical assistance. A K injury is fatal.) The data 
indicate that 212,000 single-vehicle rollover crashes resulted in 
50,000 K or A injuries. Fifty-one percent of those with K or A injury 
in single-vehicle rollover crashes were not using a seat belt, and 23 
percent were partially or completely ejected from the vehicle 
(including 20 percent who were completely ejected). Estimates from NASS 
GES indicate that 13 percent of light vehicles in police-reported 
single-vehicle crashes rolled over. The estimated risk of rollover 
differs by light vehicle type: 10 percent of cars and 10 percent of 
vans in police-reported single-vehicle crashes rolled over, compared to 
18 percent of pickup trucks and 27 percent of SUVs. The percent of all 
police reported crashes for each vehicle type that resulted in rollover 
was 1.7 percent for cars, 2.0 percent for vans, 3.7 percent for pickup 
trucks and 5.4 percent for SUVs as estimated by NASS GES.

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III. Background

    Section 12 of the ``Transportation Recall, Enhancement, 
Accountability and Documentation (TREAD) Act of November 2000'' directs 
the Secretary to ``develop a dynamic test on rollovers by motor 
vehicles for a consumer information program; and carry out a program 
conducting such tests. As the Secretary develops a [rollover] test, the 
Secretary shall conduct a rulemaking to determine how best to 
disseminate test results to the public.'' The rulemaking must be 
carried out by November 1, 2002.
    On July 3, 2001, NHTSA published a Request for Comments notice (66 
FR 35179) discussing a variety of dynamic rollover tests that we had 
chosen to evaluate in our research program and what we believed were 
their potential advantages and disadvantages. It also discussed other 
possible approaches we considered but decided not to pursue. The 
driving maneuver tests to be evaluated fit into two broad categories: 
closed-loop maneuvers in which all test vehicles attempt to follow the 
same path; and open-loop maneuvers in which all test vehicles are given 
equivalent steering inputs. Other potential tests using a centrifuge or 
computational simulation were discussed but not included in our test 
plan. This notice discusses the comments we received and the results of 
our test program to date.
    The TREAD Act calls for a rulemaking to determine how best to 
disseminate rollover test results to the public, and this Notice of 
Proposed Rulemaking proposes several alternatives for using the dynamic 
tests results in consumer information on the rollover resistance of new 
vehicles. The resulting rollover resistance ratings will be part of 
NHTSA's New Car Assessment Program (NCAP). The tests will be carried 
out and reported to the public by NHTSA. This program places no 
regulatory requirements on vehicle manufacturers. Past NCAP ratings 
have been developed using a procedure of public notice and comment, but 
there was no legal requirement to do so since no requirements were 
imposed on any party except NHTSA.
    NHTSA's NCAP program has been publishing comparative consumer 
information on frontal crashworthiness of new vehicles since 1979, on 
side crashworthiness since 1997, and on rollover resistance since 
January 2001. The present rollover resistance ratings are based on the 
Static Stability Factor (SSF) which is the ratio of one half the track 
width to the center of gravity (c.g.) height. (see http://www.nhtsa.dot.gov/hot/rollover/ for ratings and explanatory 
information).
    SSF was chosen over vehicle maneuver tests in the present ratings 
system because it represents the first order factors that determine 
vehicle rollover resistance in the 95 percent of rollovers that are 
tripped by impacts with curbs, soft soil, pot holes, guard rails, etc. 
or by wheel rims digging into the pavement. In contrast, untripped 
rollovers are those in which tire/road interface friction is the only 
external force acting on a vehicle that rolls over. Driving maneuver 
tests directly represent on-road untripped rollover crashes which are 
about 5 percent of the total, and test performance can be improved by 
vehicle changes that may not improve resistance to tripped rollovers. 
Other reasons for selecting the SSF measure are: driving maneuver test 
results are greatly influenced by SSF; the SSF is highly correlated 
with actual crash statistics; it can be measured accurately and 
inexpensively and explained to consumers; and changes in vehicle design 
to improve SSF are unlikely to degrade other safety attributes.
    Vehicle manufacturers generally oppose the present rollover 
resistance ratings because they believe that SSF is too simple since it 
does not include the effects of suspension deflections, tire traction 
and electronic stability control (ESC) and because they believe that 
the influence of vehicle factors on rollover risk is too slight to 
warrant consumer information ratings for rollover resistance. In the 
conference report dated October 23, 2000 of the FY2001 DOT 
Appropriation Act, Congress permitted NHTSA to move forward with the 
rollover rating proposal and directed the agency to fund a National 
Academy of Sciences study on vehicle rollover ratings. The study topics 
are ``whether the static stability factor is a scientifically valid 
measurement that presents practical, useful information to the public 
including a comparison of the static stability factor test versus a 
test with rollover metrics based on dynamic driving conditions that may 
induce rollover events.'' The National Academy's report was completed 
and made available in pre-publication form on February 21, 2002. 
Section IV discusses the findings and recommendations of the study.

IV. Comments to the Previous Notice

    In its July 3, 2001 Request for Comments notice (66 FR 35179), 
NHTSA solicited comment on the development of a dynamic test for 
vehicle rollover resistance and identified a number of tests it planned 
to evaluate. The notice posed the following five sets of questions for 
comments. Most commenters either supported one of the tests being 
evaluated, suggested another test, or described elements the commenter 
believed to be important for any test chosen for rollover resistance. 
In this way, most commenters responded to the substance of question 1. 
While only a few commenters responded specifically to the other 
questions, parts of the general comments of other commenters are 
discussed in the context of the questions.
    Question 1: NHTSA has decided to devote its available time and 
resources under the TREAD Act to develop a dynamic test for rollover 
based on driving maneuver tests. Is this the best approach to satisfy 
the intent of Congress in the time allotted? Are there additional 
maneuvers that NHTSA should be evaluating? Which maneuver or 
combination of maneuvers do you believe is the best for rollover 
rating? Are these other approaches well enough developed and validated 
that they could be implemented 18 months from now?
    Comments: In answer to this question many commenters either voiced 
a preference for one of the maneuvers in the test plan NHTSA announced 
in its July RFC Notice or made specific suggestions for other tests. 
Daimler-Chrysler (D-C), Continental-Teves, BMW, Mitsubishi and 
Volkswagen (VW) supported the use of the ISO 3388 Part 2 double lane 
change test (developed by VDA, the German vehicle manufacturers' 
association) as the dynamic rollover test. VW suggested that the 
ratings should include three components: (a) SSF for general overall 
rating of static stability, (b) the ISO 3388 Part 2 test with minimum 
entry of 60 kph without 2 wheel lift, and (c) a dynamic handling test 
that gives credit to ESC.
    Several commenters supported the variations of the fishhook test. 
Toyota suggested a fishhook test with fixed timing using the LAR 
(lateral acceleration at rollover [tip-up]) criterion as test for 
untripped rollover. Toyota's recommendation also suggested using the 
ISO 3388 PART 2 test as a stability/controllability test, with entry 
speed and peak to peak yaw rate as the measured criteria. Toyota also 
offered a hypothetical star rating breakdown for LAR as a rollover 
rating and a star rating chart relating entry speed and peak to peak 
yaw rate in the ISO 3388 PART 2 test as a separate controllability 
rating. TRW stated that rollover test maneuvers should excite worst 
case roll dynamics, but that some conditions on the vehicle path should

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be observed to keep handling tradeoffs in check. It expressed the 
opinion that a fishhook test with steering based on roll rate best 
approached the stated goal but that future developments in simulation 
could also be useful for rollover resistance ratings. Honda recommended 
a fishhook maneuver with a protocol for optimizing to the worst case 
timing for each vehicle as a test for untripped rollover resistance 
combined with the basic quasi-static centrifuge test to measure tripped 
rollover resistance. Nissan had previously suggested a fishhook test 
and its own optimization protocol, but in its comment to this notice, 
Nissan changed its position stating that the fishhook may be too severe 
for consumer information and that it has no data correlating it to real 
world accidents. It suggested that NHTSA should test for handling 
properties instead of rollover resistance.
    NHTSA's July RFC Notice announced a research plan that excluded the 
centrifuge test on the basis that it was not deemed sufficiently 
``dynamic'' for the requirements of the TREAD Act and for concern that 
a vehicle optimized for the centrifuge test may have more oversteer 
than the manufacturer would otherwise choose. Nevertheless, a number of 
commenters were in support of rollover resistance tests that included 
centrifuge testing. Ervin and Winkler of UMTRI suggested a number of 
possible test modes using a centrifuge including a basic quasi-static 
mode which adds suspension roll and shear effects to SSF, tether 
release modes which add roll inertial forces somewhat analogous to J-
turn and fishhook maneuvers, and a curb trip mode with a sliding table. 
They also suggested that a driving maneuver handling test for yaw 
stability be performed in addition to the centrifuge test. As noted 
above, a quasi-static centrifuge test for tripped rollover was part of 
Honda's recommendation. CU also suggested a centrifuge (or SSF as an 
alternative) as part of recommended suite of tests also including a 
dynamic maneuver test with steering reversal (like the fishhook) and 
handling tests for maximum lateral acceleration and yaw stability. 
Advocates commented that driving maneuver tests by themselves are not 
sufficient for rollover resistance tests because they only define 
untripped rollover resistance, and Advocates recommend that UMTRI's 
centrifuge tests should be investigated because they can be applied to 
both tripped and untripped rollover resistance.
    GM recommended that the centrifuge test be substituted for Side 
Pull Ratio or SSF in the Stability Margin concept it had recommended to 
NHTSA in comments to previous notices on rollover resistance ratings. 
It also supplied information addressing NHTSA's concern that the 
centrifuge test could reward undesirable changes in suspension roll 
stiffness distribution. The issue first arose in comments from Ford on 
a 1994 NHTSA proposal for rollover consumer information based on Tilt 
Table Ratio. Ford stated that a vehicle's score in a tilt table test is 
greatest if both the front and rear tires lift simultaneously when the 
table is inclined at the minimum angle for two wheel lift, and that the 
manufacturer could achieve the optimum score by stiffening the rear 
suspension relative to the front. If the manufacturer did so, the 
result would be a vehicle with less understeer as the trade-off for a 
better Tilt Table Ratio. The same optimization principal would apply to 
centrifuge tests. GM's comment included curves showing the point of 
optimization of Side Pull Ratio (theoretically the same as the 
centrifuge measurement) and its sensitivity to the proportion of total 
roll stiffness provided by the front suspension for a typical SUV and a 
typical car. GM compared the curves to the suspension characteristics 
of these production vehicles and found that (a) the suspension roll 
stiffnesses of the production vehicles were close to the optimized 
condition as designed with a very small sensitivity to further 
suspension changes and (b) the suspension changes to obtain the 
negligible improvement in rollover test score involved a relative 
stiffening at the front that would increase rather than decrease the 
understeer. GM concluded that manufacturers would have little to gain 
by suspension tuning for centrifuge test scores and that the tuning 
would be at least as likely to increase understeer as to decrease it. 
We believe that Ford's comment was correct in 1994, but NHTSA has 
recently reviewed data showing a trend toward less understeer in SUVs 
of more recent design. GM's dismissal of the issue may reflect more 
accurately the design of today's new vehicles.
    Toyota and GM were the only commenters to suggest how the results 
of their rollover and handling tests could be expressed in ratings. GM 
suggested that the following conditions be used to define ``good 
rollover resistance for light-duty vehicles'': (a) quasi-static 
centrifuge test tip-up threshold of at least 0.9g; (b) maximum lateral 
acceleration in a circular driving maneuver of at least 0.6g; and (c) a 
stability margin (a-b) at least 0.2g or 1.5/wheelbase [in meters] 
squared. GM estimated that a centrifuge measurement of 0.9g would 
correspond to a SSF of 1.06. However, we would estimate that centrifuge 
measurement as corresponding closer to a SSF of 1.00, based on 
comparisons with tilt table tests with an allowance for the vertical 
load error inherent with the tilt table.
    Based on its stability margin concept of good rollover resistance, 
GM suggested the following ``star rating'' system. A vehicle passing 
all three conditions for good rollover resistance would be rated with 
two stars. Failing any one of the conditions would reduce its rating to 
one star. Bonus stars above the two star level would be awarded for a 
centrifuge test measurement 1.0g or better, a maximum lateral 
acceleration measurement of 0.7g or better, or a stability margin 0.1 
or more above the minimum (0.2g or 1.5/wheelbase [in meters] squared). 
A vehicle satisfying all of these higher conditions would receive a 
five star rating. GM also suggested that NHTSA consider a symbol other 
than a star for rollover resistance ratings to differentiate them from 
frontal and side crashworthiness ratings. As previously mentioned, 
Toyota offered a hypothetical star rating breakdown for LAR in a 
Fishhook as a rollover rating.
    Previously, Ford had suggested a proprietary test method (Path 
Corrected Limit Lane Change (PCLLC)) involving a series of double lane 
change maneuvers controlled by a human driver and a mathematical 
technique for correcting the measurements of vehicle acceleration and 
wheel force to those expected if the vehicle perfectly adheres to a 
desired common path for vehicle comparisons. NHTSA agreed to evaluate 
this method but keep the details of the analytical technique 
confidential. Appendix I of this notice discusses the results of PCLLC 
testing using the same vehicles tested in other maneuver tests.
    In its comment to the July notice, Ford announced that the same 
test measurements could be made using a newly developed advanced path 
following steering controller to replace the human driver and the 
proprietary mathematical correction technique. Ford expected both 
implementations of the protocol to produce the same measurements. But 
it changed its recommendation to the path following steering controller 
because the face validity (realistic appearance) of the test would be 
enhanced by having the advanced steering controller actually drive the 
vehicles through nominally identical paths rather than rely on 
corrections to the unavoidably variable paths taken by skilled human 
test drivers. Ford's comment was made after

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NHTSA had run the PCLLC maneuvers in a cooperative effort with Ford to 
evaluate that test method. However, we believe that the results of the 
tests of our vehicles using the PCLLC mathematical corrections would be 
representative of same maneuver tests accomplished with a path 
following steering controller.
    Ford's path following steering controller is not the same as the 
automated steering controller NHTSA used to obtain repeatable steering 
inputs for open-loop maneuvers. Ford's steering controller is designed 
to drive different vehicles in the same repeatable path although the 
steering inputs to guide the various vehicles along the same path may 
be quite different. It uses a real-time computer simulation of the 
vehicle steering responses and a differential GPS position signal as 
feedback signals for closed-loop control.
    Unlike the other maneuver tests in NHTSA's evaluation, Ford's 
maneuvers are not intended to produce wheel lift or loss of control or 
invoke ESC operation. Ford suggests four lane change maneuvers (like 
those shown in Figure 9) varying in offset and length, each producing a 
maximum lateral acceleration of 0.7g at a single test speed of 45 mph, 
but varying in fundamental lateral acceleration frequency from 0.29 Hz 
to 0.40 Hz. The scoring metric is the maximum dynamic weight transfer 
measured as a 400 ms moving average. It refers to the percent reduction 
in vertical load for the two wheels on the side of the vehicle 
approaching tip-up. At tip-up, the dynamic weight transfer is 100 
percent, but dynamic weight transfer in the range of 50 to 80 percent 
would be typical in the Ford maneuver. A lower percent weight transfer 
score indicates a vehicle with higher rollover resistance. The tests 
are performed with the vehicle loaded to the gross vehicle weight 
rating and the rear axle load at the rear axle weight rating.
    Intrinsic advantages of this test method are its insensitivity to 
changes in pavement and tire friction because the tests are performed 
at lateral force levels below the friction limit and its continuous (as 
opposed to binary, tip-up or no tip-up) performance metric with a 
comparative score for all vehicles. Intrinsic disadvantages are its 
compression of vehicle differences as a result of tests restricted to a 
smaller range of lateral acceleration, the need for very accurate and 
repeatable vertical wheel force measurements to discriminate the 
compressed vehicle differences, and the question of whether non-limit 
dynamic tests can predict the comparative dynamic behavior of vehicles 
in limit maneuvers. Ford believes that non-limit results can be 
projected up to the limit, but it is certainly possible that anomalies 
in suspension behavior may occur only at the limit.
    Suzuki commented that driving maneuver tests should not be used as 
NHTSA's dynamic rollover test because they measure only resistance to 
untripped rollover, are unrealistic driving maneuvers and have many 
practical problems. Suzuki argued that a dynamic tripped rollover test 
should be used instead. In November 2001, Suzuki and its contractor 
Exponent made a suggestion how a ``dynamic tripped rollover test'' 
could be conducted. The test would use a braked sled with the vehicle 
placed transversely on the sled adjacent to tripping curb. From a 
constant speed of 25 mph, the sled would be braked at a relatively 
constant deceleration which produces a steady lateral acceleration on 
the test vehicle. Repeated runs of the sled at incrementally higher 
levels of deceleration would be made until the vehicle lifts and rolls 
at least 20 degrees to a position restrained by safety straps. Such a 
test imposes a step increase of lateral acceleration on the vehicle and 
measures the result of weight transfer due to the static rigid body 
(SSF) properties of the vehicle, to the c.g. movement due to quasi-
static body roll, and to the dynamic effects of roll inertia and 
suspension damping. This test is very similar to the ``straight 
tethered'' centrifuge test suggested by UMTRI in which the steady 
lateral acceleration imposed on the vehicle by the centrifuge is 
resisted by a tether until the tether is released and the vehicle 
experiences a step increase of lateral acceleration. Both are also 
analogous to a J-turn test with an extremely high level of tire 
adhesion.
    Question 2: How should NHTSA address the problem of long term and 
short term variations in pavement friction in conducting comparative 
driving maneuver tests of vehicle rollover resistance for a continuing 
program of consumer information?
    Comments: Toyota, D-C, and Ford addressed the question explicitly. 
Toyota had suggested a fishhook maneuver using the scoring metric LAR 
(lateral acceleration at roll). It believes that LAR is not very 
sensitive to changes in pavement friction, but if the pavement friction 
is too low it will become impossible for the vehicle to achieve 
sufficient lateral acceleration in the maneuver to reach LAR. Toyota 
also suggested a double lane change handling maneuver in which entry 
speed and peak to peak yaw rate were scoring metrics that it considers 
sensitive to pavement friction. It suggests strict limits on the course 
parameters to qualify the handling tests as valid, giving as an example 
the surface temperature limits (35C +/- 10C) used by the Japanese 
government NCAP protocol for braking tests.
    D-C suggested that a standard pavement friction monitoring trailer 
using a standard ASTM tire be used to define the nominal surface 
friction of a test track, and that at least five braking tests be 
conducted using the same anti-lock equipped vehicle with standard tires 
to qualify the surface before a test session. Limits for braking test 
measurements, temperature and wind velocity would be established to 
qualify the surface. VW made a similar recommendation of defined limits 
on temperature, humidity, wind speed and surface friction (presumably 
using a pavement friction monitoring trailer with a standard ASTM 
tire).
    Ford explained that its test protocol for the double lane change 
maneuvers performed either by a path-following robot or by mathematical 
path-correction of driver-controlled tests calls for comparing the side 
to side load transfer at a standard 0.7g lateral acceleration. Since 
almost all vehicles can achieve this level of lateral acceleration on 
ordinary dry pavement despite expected fluctuations in surface 
friction, the test method is not sensitive to ordinary pavement 
friction fluctuations.
    Likewise, fluctuations in pavement friction are not an issue for 
the centrifuge test suggested by UMTRI and the sled test suggested by 
Exponent/Suzuki because both tests use a curb-like structure rather 
than pavement friction to initiate an overturning moment.
    Question 3: Some ESC systems presently have two functions. One is 
yaw stability which uses one or more brakes to keep the vehicle headed 
in the right direction in a limit maneuver, and the other is simple 
brake intervention in excess of the braking required for yaw stability. 
It is expected that the presence of a brake intervention function in 
ESC will have a large effect on the rating of vehicles because the 
average speed through a given test maneuver for vehicles having this 
function will be much less than for vehicles without it (even if 
equipped with ESC for yaw stability) under the usual test protocols of 
coasting through maneuvers and using the entry speed as the test speed. 
Is the value given to the brake intervention function of ESC as opposed 
to the yaw stability function by potential rollover rating tests 
commensurate with its safety value to consumers? Please provide all the 
data

[[Page 62533]]

and reasoning that support your view. Should NHTSA measure the vehicle 
speed at the completion of the maneuver as well as vehicle speed at 
entry?
    Comments: Toyota commented that automatic braking in excess of what 
is required for yaw stability control to further lower the speed is a 
good strategy to mitigate harm in an emergency, but it recognizes 
NHTSA's concern that dynamic rollover tests could give the same credit 
to less sophisticated systems as to yaw control. Toyota believes that 
its suggestion of a separate handling test to accompany the dynamic 
rollover test would reward controllability and show the advantage of 
yaw control systems.
    D-C commented that ESC should operate during rollover maneuver 
tests with entry speed being the only criterion for the stringency of 
the maneuver. The exit speed should not be considered.\3\ Continental-
Teves also commented that only the entry speed is an appropriate 
measure because it best defines the obstacle avoidance situation facing 
the driver.
---------------------------------------------------------------------------

    \3\ NHTSA notes that if the stringency of a rollover maneuver 
test was determined by averaging the entry and exit speeds, a test 
in which the vehicle performed automatic braking would be considered 
less stringent than one in which the vehicle entered at the same 
speed and coasted through at a higher speed.
---------------------------------------------------------------------------

    TRW commented that ESC should be rewarded if it enhances roll 
dynamic behavior, and it also stated that ``Differential Braking Roll 
Prevention'' should be rewarded by the agency's rollover maneuver 
tests. It did not define the term ``Differential Braking Roll 
Prevention'', but we understand it to mean an automatic braking system 
in which selected brakes are applied for the purpose of reducing the 
lateral force generating capability of the selected tires rather than 
to augment yaw stability or to simply slow down.
    Ford also opposed using the average speed through a given test as a 
criterion and pointed out that its recommended test does not use speed 
as a comparative metric at all. It also stated that its test is 
unlikely to invoke ESC but would measure the effect of active 
stabilizer bars and electronically controlled shocks.
    Several other manufacturers share Ford's view that the operation of 
ESC is not essential to rollover resistance tests. GM suggested 
laboratory tests of rollover resistance using a centrifuge in which ESC 
would not operate. It stated that ``the rollover resistance of the 
underlying vehicle structure and suspension is a more important 
parameter than the possible use of ESC to mask poor rollover resistance 
of the foundation vehicle.'' Similarly, the recommendations from Suzuki 
and Exponent for a tripped rollover test do not involve the use of ESC. 
Honda suggested that if a vehicle is equipped with an on/off switch for 
ESC, it should be tested with the switch in the off position.
    One of the agency's reasons for posing this question was that ESC 
systems with a component of ordinary four wheel braking above the 
differential braking for yaw control are performing a braking action 
that the driver is also likely to do in an emergency. However, the 
usual test protocol for the maneuver tests being evaluated requires the 
driver to coast rather than brake. Therefore, there was a question 
whether the potential advantage of vehicles with automatic braking tied 
to ESC would be unrealistically amplified by a test protocol that would 
prevent driver braking in circumstances where actual drivers would be 
likely to brake. Our concern over this theoretical problem has been 
reduced by our observations during the recent maneuver test research 
that vehicles tip up early in rollovers maneuvers minimizing the effect 
of automatic braking.
    Question 4: If open-loop (defined steering input) maneuvers are 
used to determine whether a vehicle is susceptible to two wheel lift as 
a result of severe steering actions, superficial changes that reduce 
tire traction or otherwise reduce vehicle handling (but prevent wheel 
lift) would be rewarded the same as more fundamental or costly 
improvements. The same is true of closed loop (path following) 
maneuvers that use wheel lift as the sole criterion. Should measures of 
vehicle handling be reported so that consumers can be aware of possible 
trade-offs. What indicators of vehicles handling would be appropriate 
to measure, and how should this consumer information be reported?
    Comments: Many commenters recommended handling tests either in 
addition to rollover resistance maneuver tests or instead of rollover 
resistance maneuver tests. Nissan had earlier recommended a fishhook 
maneuver test for rollover resistance and had proposed a method of 
timing the steering reversal to achieve maximum severity for each test 
vehicle. However, in its comments to the July notice, Nissan 
recommended that NHTSA measure handling rather than rollover resistance 
on the basis that the fishhook test may be too severe for the purposes 
of consumer information and that Nissan had no data regarding the 
correlation of fishhook test performance to real-world crashes. It 
suggested a steady state lateral acceleration test and a lateral 
transient response test. D-C addressed the question directly by stating 
that its recommended ISO 3388 PART 2 test does not give incentives for 
negative trade-offs but rather encourages optimized cornering 
capability and ``limit condition performance'' by giving lower ratings 
for ``bad handling''. In its recommendation of the ISO 3388 PART 2 
test, Continental-Teves actually described it as a handling test.
    The combination of a rollover test and a separate handling test was 
recommended by many commenters. Toyota suggested that a closed loop 
stability and controllability test should be combined with an open loop 
rollover resistance test to deal with the trade-off issue for rollover 
tests. It suggested using the ISO 3388 PART 2 test as a handling test 
with both entry speed and peak-to-peak yaw rate as performance 
criteria. The peak-to-peak yaw rate would reflect on the yaw stability 
of the vehicle. UMTRI suggested the centrifuge test for a rollover 
resistance but recommended adding a driving maneuver test to 
characterize yaw controllability. GM also recommended the centrifuge 
test, but suggested combining its results with a driving test of steady 
state maximum lateral acceleration to create a stability margin and set 
a lower limit for handling. In addition to static and dynamic rollover 
resistance tests, CU recommended a steady state lateral acceleration 
test on a skip pad and ``track-type tests to assess the vehicle's 
controllability, response and grip.'' VW also suggested static and 
dynamic rollover resistance tests , but called for a handling test that 
``would give positive credit to ESP [ESC in generic parlance], since 
experience in Germany appears to substantiate the real world benefits 
of ESP. It did suggest a specific test, but tests of yaw stability 
would be expected to measure an aspect of handling benefited by ESC 
operation.
    Question 5: What criteria should NHTSA use to select the best 
vehicle maneuver test for rollover resistance? Should the maneuver that 
has the greatest chance of producing two wheel lift in susceptible 
vehicles be chosen regardless of its resemblance to driving situations? 
Is it more important that the maneuver resemble an emergency maneuver 
that consumers can visualize? How important is objectivity and 
repeatability?
    Comments: One issue is the potential conflict between the ability 
of a dynamic rollover test to produce tip-up in vulnerable vehicles 
(severity) and its resemblance to a driving maneuver consumers can 
imagine doing (face validity). Toyota commented that it

[[Page 62534]]

views severity as the more important property for a rollover resistance 
test and face validity as the more important property for a handling 
test. Ford and D-C took the opposite position. Ford stated that extreme 
maneuvers that cause two wheel lift of some vehicles on a paved road 
surface are unrelated to the vast majority of crashes. D-C said that 
resemblance to emergency maneuvers is more important than determining 
``artificial conditions'' under which a particular vehicle is likely to 
roll over.
    There were other comments about the general issue of criteria for 
selecting a rollover test. Continental-Teves stated that ``a dynamic 
test for vehicle rollover rating should assess whether the vehicle 
system (driver and vehicle) is capable of keeping the vehicle on the 
road'' which is consistent with the view that the ISO 3388 PART 2 test 
is more of a handling test than a rollover test. Advocates disagreed 
with NHTSA's conclusion that the TREAD Act called for a driving 
maneuver test as a rollover test, and suggested that UMTRI's ideas for 
a centrifuge test should be investigated. IIHS stated that ``although 
some of the test maneuvers may have considerably greater consumer face 
validity, the ultimate decision as to which maneuvers to use should 
rest on which provide the best correlation with real-world crash 
risk.''

Commenter's Recommended Approaches

    D-C, Mitsubishi, VW, BMW and Continental-Teves recommended the ISO 
3388 PART 2 closed-loop tight double lane change test as the best 
dynamic rollover test, but also described it as a handling test.
    Toyota, Honda, CU, and TRW recommended Fishhook tests optimized in 
various ways to present the worst-case timing to each vehicle as the 
best dynamic rollover test. Nissan had recommended the Fishhook earlier 
but decided that the Fishhook test may be too severe for consumer 
information, and recommended handling tests instead of a rollover test.
    UMTRI, GM, Advocates, CU and Honda recommended a centrifuge test as 
at least part of the rollover rating despite NHTSA's elimination of it 
from the research plan announced in July 2001.
    Honda, CU, and VW suggested the combination of a rollover maneuver 
test and the centrifuge test or SSF for rollover ratings.
    Toyota, UMTRI, Nissan, VW and Ford recommend a separate handling 
test distinct from the rollover rating with particular emphasis on yaw 
stability and ESC.
    Suzuki and Ford recommended tests other than those discussed in the 
July 2001 Notice. Suzuki recommended a dynamic tripped rollover test 
such as the sled test described by Exponent. Ford recommended using a 
new path following steering controller instead of the PCLLC 
mathematical path correction technique it previously recommended, but 
it continued to recommend the maneuvers and performance metric used in 
the PCLLC.
    NHTSA notes that although the Alliance criticized SSF for not 
measuring the effect of ESC, the tests recommended by Ford and GM do 
not measure the effect of ESC. Also, Honda recommended testing with ESC 
turned off if an on/off switch is provided.

V. National Academy of Sciences Study

    In the conference report dated October 23, 2000 of the FY 2001 DOT 
Appropriation Act, Congress directed the agency to fund a National 
Academy of Sciences study on vehicle rollover ratings. The study topics 
were ``whether the static stability factor is a scientifically valid 
measurement that presents practical, useful information to the public 
including a comparison of the static stability factor test versus a 
test with rollover metrics based on dynamic driving conditions that may 
induce rollover events.'' The National Academy's report was completed 
and made publicly available on February 21, 2002.
    The National Academy of Sciences made a number of findings and 
recommendations concerning NHTSA's present ratings of rollover 
resistance that we view as guidance for our efforts under the TREAD Act 
to improve the rating system.
    Finding 1: Through a rigid-body model, SSF relates a vehicle's 
track width, T, and center of gravity height, H, to a clearly defined 
level of the sustained lateral acceleration that will result in the 
vehicle's rolling over. The rigid-body model is based on the laws of 
physics and captures important vehicle characteristics related to 
rollover.
    Finding 2: Analysis of crash data reveals that, for higher-risk 
scenarios, SSF correlates significantly with a vehicle's involvement in 
single-vehicle rollovers, although driver behavior and driving 
environment also contribute. For these scenarios, the statistical 
trends in crash data and the underlying physics of rollover provide 
consistent insight: an increase in SSF reduces the likelihood of 
rollover.
    Finding 3: Metrics derived from dynamic testing are needed to 
complement static measures, such as SSF, by providing information about 
vehicle handling characteristics that are important in determining 
whether a driver can avoid conditions leading to rollover.
    The first three findings help resolve some very important questions 
facing NHTSA regarding the implementation of the TREAD Act to improve 
the rollover rating system. Namely, is SSF a scientifically valid 
measure of rollover resistance and should a dynamic rollover test 
replace SSF? The National Academy confirmed that SSF is a 
scientifically valid measure of rollover resistance for which the 
underlying physics and real-world crash data are consistent in the 
conclusion that an increase in SSF reduces the likelihood of rollover. 
It also found that dynamic tests should complement static measures, 
such as SSF, rather than replace them in consumer information on 
rollover resistance.
    The National Academy's report describes a rollover crash as an 
event having three phases: A phase in which the driver is in control of 
the vehicle, a transition phase in which loss of control develops, and 
a phase in which the vehicle is out of control. The report gives SSF 
(along with the terrain) as the dominant determinants of rollover in 
the final, out of control phase, of a crash leading to rollover. It is 
in the previous transition phase of the crash that other vehicle 
properties reflected in the ideal dynamic test can potentially 
influence whether the crash enters the final phase in which only the 
geometric properties of the vehicle matter.
    In its presentation to NHTSA of the findings and recommendations, 
the NAS study committee clarified that it envisions dynamic tests as 
limit maneuvers where loss of control and actual on-road vehicle tip-up 
can be expected for vulnerable vehicles. The NAS study panel also 
expressed a preference for combining static and dynamic vehicle 
information in a single rollover resistance rating, but it did not 
offer explicit suggestions for accomplishing the combination or 
conveying the rating to the consumer.
    The next series of findings involve the statistical relationship 
between SSF and rollover rate that NHTSA uses to interpret the rollover 
resistance ratings.
    Finding 4: NHTSA's implementation of an exponential statistical 
model lacks the confidence levels needed to permit discrimination among 
vehicles within a vehicle class with regard to differences in rollover 
risk.
    Finding 5: The relationship between rollover risk and SSF can be 
estimated accurately with available crash data and software using a 
logit model. For the

[[Page 62535]]

analysis of rollover crash data, this model is more appropriate than an 
exponential model.
    Finding 6: The approximation of the rollover curve with five 
discrete levels--corresponding to the five rating categories--is coarse 
and does not adequately convey the information provided by the 
available crash data, particularly at lower SSF values where the 
rollover curve is relatively steep.
    NHTSA calculated what it believed was an accurate trend line 
between the rollover rate in single vehicle crashes and SSF using data 
from over 221,000 single vehicle crashes of 100 vehicle make/model/
generations representing the range of SSFs and vehicle classes (cars, 
vans, pickup trucks and SUVs). It determined the average rollover rate 
for each of the 100 vehicles, corrected the rates for differences in 
demographic and road use variables (driver age, gender, alcohol use, 
road and weather conditions, etc) and performed a linear regression 
between SSF and the logarithm of the corrected average rollover rate of 
each vehicle. The NAS report refers to this approach as the exponential 
model because it creates an exponential regression line between SSF and 
rollover rate. NHTSA chose this approach because the exponential form 
of the regression line fits the rollover rate data well, and linear 
regression computes the R\2\ goodness of fit statistic that is familiar 
to many scientific readers who are not professional statisticians. 
However, the standard statistical technique for determining the 
confidence limits of the regression line (which estimate how well the 
line would be replicated with another sample of crash data for the same 
vehicles) only considers a data set of 518 points. The 518 data points 
are the rollover rates in each of six states for those vehicles in the 
100 make/model population for which more than 25 single vehicle crashes 
were reported. Consequently, the 95th percentile confidence limits 
computed for the exponential line are much larger than what would be 
expected for a data set of 221,000 points. This is the basis for 
Finding Number 4. Since each of the 518 data points on average 
represents 486 crashes, it stands to reason that the actual 
reproducibility of the line is much better than that computed on the 
basis of only 518 points. As the NAS study notes, the standard method 
of computing confidence limits for linear regression is the wrong 
method for our regression line, but it offered no other method of 
computing the confidence limits of our present model.
    In Finding Number 5, the National Academy offered an alternative 
solution to the confidence limits issue. It recommended that the logit 
model be used in place of the exponential model (linear regression on 
the logarithm of rollover rate). The logit model operates on the 
221,000 crash data samples individually rather than as 518 averages. 
Consequently, the confidence limits are extremely narrow as would be 
expected for a regression line representing a huge database. However, 
the change to logit model produces another problem. Each model 
incorporates an implicit assumption about the form of the regression 
line. We chose the exponential form because it appeared to follow the 
locus of data points. The form of the line produced by logit model in 
our application is closer to a straight line than to an exponential 
line. Consequently, it does not follow the locus of the raw data points 
as well. It appears to underestimate the rollover rate of vehicles at 
the low end of the SSF range by a substantial margin (36% versus about 
45% @ SSF=1.00). The NAS study acknowledged this shortcoming and gives 
the example of a nonparametric-based rollover curve it calculated on a 
subset of NHTSA data that represents the low end of the SSF range much 
better than the logit curve. We are investigating non-parametric models 
and logit models using various transformations of SSF to develop a 
model combining the demonstrated tight confidence limits of the logit 
model with the more accurate estimate of rollover risk of our 
exponential model.
    For the interpretation of vehicle measurements for consumer 
information on rollover risk, NAS concentrated exclusively on using 
statistical models relating measurements, such as SSF, to rollover risk 
in a single vehicle crash. Finding 5 concerns the choice of model 
within this methodology. Finding 6 suggests that a five interval system 
loses some of the power of the data to discriminate rollover risk 
between vehicles. The committee goes on to recommend that the agency 
look at a greater number of intervals or even a continuous risk scale.
    Finding 7: A gap exists between recommended practices for the 
development of safety information and NHTSA's current process for 
identifying and meeting consumer needs for such information. In 
particular:
    [sbull] The focus group studies used to develop the star rating 
system were limited in scope.
    [sbull] The agency has not undertaken empirical studies to evaluate 
consumers' use of the rollover resistance rating system in making 
vehicle safety judgments or purchase decisions.
    Focus group testing is the most appropriate tool we can use within 
our budget and time constraints. As mentioned in the response to 
Recommendation 3, below, we plan to use interviewing in conjunction 
with focus group testing to design second-tier information to be used 
by consumers who want more information than the star ratings. The 
agency has not undertaken empirical studies to evaluate consumer's use 
of the rollover rating system because the program was just initiated 
for the 2001 model year. Such a study would provide useful feedback for 
the development of additional consumer rollover information. However 
some history of use by the public needs to be acquired before the 
current system can be evaluated.
    Recommendation 1: NHTSA should vigorously pursue its ongoing 
research on driving maneuver tests for rollover resistance, mandated 
under the TREAD Act, with the objective of developing one or more 
dynamic tests that can be used to assess transient vehicle behavior 
leading to rollover.
    This notice describes the results of test program that is part of 
NHTSA's pursuit of the requirements of the TREAD Act to develop dynamic 
tests for rollover. We believe that the limit maneuver tests we are 
developing will provide the evaluation of the transient vehicle 
behavior that the NAS committee has recommended as a complement to the 
information from static measures. We also trying to develop tests of 
vehicle controllability to give consumers some information on the 
relative difficulty of keeping the vehicle on the road away from 
tripping mechanisms in the event of an emergency maneuver.
    Recommendation 2: In the longer term, NHTSA should develop revised 
consumer information on rollover that incorporates the results of one 
or more dynamic tests on transient vehicle behavior to complement the 
information from static measures, such as SSF.
    NHTSA will evaluate possible changes in its present consumer 
information on rollover resistance, based on SSF, as we develop the 
protocol for dynamic testing for rollover required by the TREAD Act. 
Part of our research planned for March to November 2002 will be to 
investigate the best way to present both static and dynamic information 
to consumers.
    Recommendation 3: NHTSA should investigate alternative options for 
communicating information to the public on SSF and its relationship to 
rollover. In developing revised consumer information, NHTSA should:

[[Page 62536]]

    [sbull] Use a logit model as a starting point for analysis of the 
relationship between rollover risk and SSF.
    [sbull] Consider a higher-resolution representation of the 
relationship between rollover risk and SSF than is provided by the 
current five-star rating system.
    [sbull] Continue to investigate presentation metrics other than 
stars.
    [sbull] Provide consumers with more information placing rollover 
risk in the broader context of motor vehicle safety.
    NHTSA is considering changing to a new model in conjunction with 
the incorporation of dynamic test results into the rollover resistance 
rating program. While the NAS prefers the logit model because it has 
tighter confidence bounds than the linear model we used, the logit 
model underestimates the risk of rollover for low-SSF vehicles. To 
attempt to overcome the drawbacks of both our original method and the 
logit model, while keeping tight confidence bounds, we will investigate 
the use of other statistical models to better estimate rollover risk in 
future model years at the same time that we improve our model to 
include dynamic test results.
    The NAS committee stated that it believed that NHTSA had documented 
the relationship between SSF and rollover risk in single-vehicle 
crashes so well that we were short-changing the public by reducing this 
information to five star-rating levels.\4\ The NAS committee 
recommended that we provide the public with additional rating levels in 
order to allow the public to better differentiate rollover risk between 
vehicles. The focus groups we conducted before implementing the current 
program indicated that consumers would prefer the five-star rating 
system. This star rating method is also consistent with the other parts 
of NCAP (frontal and side crash ratings). However, we will explore the 
use of greater differentiation of the data as well as alternative 
presentation formats in future consumer research. We will change our 
presentation of the second-level detailed information as soon as 
possible. We already provide the actual SSF number for each vehicle in 
NCAP in addition to the star rating, for those consumers who want more 
detailed information on the vehicles. This hierarchical approach was 
recommended in the 1996 NAS study, ``Shopping for Safety.'' We are 
considering refining this level of information by placing that SSF 
number in the context of all the other vehicles tested. We can also 
provide the public with the point estimate for the rollover risk 
associated with each value of the SSF using the logit curve. We will 
conduct interviews and focus groups this spring to determine the most 
effective way to communicate primary and secondary level information to 
consumers. Different communication methods may be developed for print 
and web site implementation.
---------------------------------------------------------------------------

    \4\ Finding 3-5, ``The current practice of approximating the 
rollover curve with five discrete levels does not convey the 
richness of the information provided by available crash data.'' ``An 
Assessment of the National Highway Traffic Safety Administration's 
Rating System for Rollover Resistance,'' TRB NRC, prepublication 
copy February 21, 2002, page 3-27.
---------------------------------------------------------------------------

    We agree that providing more information about rollover risk in the 
context of overall motor vehicle risk would be useful information to 
consumers. The agency presently includes an explanation of rollover 
resistance ratings, how they were derived, and safe driving tips on its 
web site.
    We intend to develop further consumer information on rollovers. In 
the short term, we are looking into providing consumers a better 
context for rollover risk by better describing the size of the rollover 
crash problem and its risk relative to other crash modes. In the long 
term, the agency is trying to develop a method of combining available 
information on the safety performance of each new vehicle model. The 
approach we are exploring uses the front, side, and rollover measures 
from NCAP combined with the safety benefits of rollover resistance and 
vehicle weight estimated from real-world crash data. We would like to 
combine the individual measures (for front, side, and rollover crashes) 
to reflect their relative frequency in the real world. However, a 
complete description of the safety of a new vehicle model should 
include the effect of that vehicle on other road users (including 
occupants of other vehicles on the road, pedestrians, and bicyclists). 
We are still performing research that will help us better understand 
the factors critical to vehicle aggressiveness and compatibility, and 
that will provide a basis for a comprehensive combined safety rating.

VI. Choice of Maneuvers for Rollover Resistance Tests

    Appendix I describes the candidate vehicle maneuver tests evaluated 
as possible tests for dynamic rollover resistance and presents the 
results of our evaluation program. The research to evaluate potential 
maneuver tests for rollover is fully documented in the NHTSA technical 
report ``Another Experimental Examination of Selected Maneuvers That 
May Induce On-Road Untripped, Light Vehicle Rollover--Phase IV of 
NHTSA's Light Vehicle Rollover Research Program''.
    Table 1 summarizes the observations in Appendix I about each of the 
nine Rollover Resistance maneuvers in the areas of Objectivity and 
Repeatability, Performability, Discriminatory Capability, and Realistic 
Appearance.

                                                                 Table 1.--Summary of Rollover Resistance Maneuver Observations
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                                               Consumers union
                                                     J-Turn with      Fixed timing        Roll rate                           Ford path      ISO 3888 part 2    short course    Open-loop pseudo
                                  NHTSA J-Turn      pulse braking       fishhook          feedback       Nissan fishhook   corrected limit     double lane       double lane      -double lane
                                                                                          fishhook                           lane change         change            change            change
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Objectivity and Repeatability.  Advantage.......  Advantage.......  Advantage.......  Advantage.......  Advantage.......  Disadvantage....  Disadvantage....  Disadvantage....  Advantage
Performability................  Advantage.......  Disadvantage....  Advantage.......  Advantage.......  Disadvantage....  Disadvantage....  Advantage.......  Advantage.......  Disadvantage
Discriminatory Capability.....  Advantage*......  Unacceptable....  Advantage.......  Advantage.......  Advantage.......  Advantage.......  Unacceptable....  Unacceptable....  Unacceptable
Realistic Appearance..........  Disadvantage....  Disadvantage....  Disadvantage....  Disadvantage....  Disadvantage....  Advantage.......  Advantage.......  Advantage.......  Advantage
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
*When limited to vehicles with low rollover resistance and/or disadvantageous load condition.

A. Closed-Loop Driver Controlled Rollover Resistance Maneuvers

    We continue to have substantial concerns about the use of maneuvers 
with driver generated steering inputs to develop NCAP rollover 
resistance ratings. Although fairly good driver-to-driver repeatability 
was seen during the Phase IV testing, this partially reflects the 
approximately equal skill levels of the test drivers. (This also 
partially reflects the small range of the rating metric, maneuver 
entrance speeds, that was seen.) A professional race driver

[[Page 62537]]

could probably drive cleanly through these maneuvers with higher 
entrance speeds. Conversely, an inexperienced driver who has never done 
any test driving could probably only manage lower speeds. We remain 
concerned that ratings generated with a driver-closed steering loop 
maneuver might not be fair or helpful to consumers if this year's test 
driver were not as good as last year's or the test driver was having an 
off day when a particular make-model was tested.
    A further problem for maneuvers with driver generated steering 
inputs is that of ``clean'' (none of the cones delimiting the 
maneuver's course were bypassed or struck) versus ``not clean'' runs. 
Only for a ``clean'' run do we know that the driver actually drove the 
prescribed maneuver. If the vehicle during a run bypasses or hits one 
or more of the delimiting cones, then there is no way to ensure that 
the driver was actually trying to steer the prescribed course. To give 
two extreme examples, a test driver could drive through the ISO 3888 
Part 2 Double Lane Change at a very high speed without a chance of two-
wheel lift occurring by going straight. Or, at the same speed, he could 
achieve two-wheel lift by performing a fishhook maneuver. For either 
case, a ``not clean'' run would be recorded.
    It is extremely difficult to generate two-wheel lift while having a 
``clean'' run. While Consumers Union has stated that on a rare occasion 
it managed to achieve two-wheel lift in a ``clean'' run, in general, 
two-wheel lift will result in the vehicle not following the prescribed 
course. Therefore, we must use maximum maneuver entrance speed for a 
``clean'' run as the rating metric instead of the more directly 
rollover related metric of when two-wheel lift first occurs. The 
relationship between maximum maneuver entrance speed and rollover 
resistance is not known.
    Although all Rollover Resistance maneuvers are influenced by both a 
vehicle's handling characteristics and its resistance to tip-up, it 
appears that handling dominates the Double Lane Change maneuvers but is 
less important for the J-Turn and Fishhook maneuvers. The Double Lane 
Change maneuvers are better for studying emergency vehicle handling 
than rollover resistance. Clean runs of the CU and ISO 3388 tests are 
not limit maneuvers in the sense of the J-Turn and Fishhook because 
they cannot measure tip-up after the vehicle's direction control is 
lost.
    One way to characterize maneuvers is by the number of major 
steering movements they involve. The J-Turn has just one major steering 
movement, the initial steer. A Fishhook has two major steering 
movements, the initial steer and the countersteer. As shown by Figures 
11 and 14, a Double Lane Change has four major steering movements, the 
initial lane change steer, the second lane change steer, the recovery 
steer, and the stabilization steer, plus some minor steering movements. 
We believe that these additional major steering movements increase the 
influence of handling for Double Lane Change results compared to J-Turn 
and Fishhook maneuvers.
    During the Phase IV Rollover Research there were a number of ``not 
clean'' runs of the CU Double Lane Change maneuver that resulted in 
two-wheel lift. These two-wheel lifts always occurred just after the 
completion of the second major steering movement, well before the 
third. In other words, the two-wheel lifts occurred while the Double 
Lane Change and Fishhook steering inputs were still similar and not 
after they had diverged. No two-wheel lifts in Double Lane Change 
maneuvers were seen after the third major steering movement. We believe 
that by the time of the third major steering movement, the severity of 
the steering has caused sufficient speed to be scrubbed-off to make 
two-wheel lifts at this point in the maneuver very unlikely.
    Double lane change maneuvers scored on the basis of highest 
``clean'' run speed had no value as dynamic tests of rollover 
resistance. For our sample of test vehicles, there was actually an 
inverse relationship between double lane change speed scores and the 
incidence of tip-up in more severe maneuvers that induced tip-up. The 
test vehicle that tipped-up the most often in other maneuvers and at a 
consistently lower tip-up speed than other test vehicles would be rated 
the best vehicle for rollover resistance by the CU Short Course or ISO 
3888 Part 2 double lane change on the basis of maximum clean run speed. 
These tests measure a type of handling performance but do not measure 
rollover resistance.

B. Sub-Limit Maneuvers Measuring Dynamic Weight Transfer

    Ford suggested two methods of implementing the same idea. It first 
suggested the Path Corrected Limit Lane Change method in which vertical 
wheel force measurements made in driver controlled runs over a number 
of nominal double lane change paths are corrected mathematically for 
variations due to the vehicle's departure from the ideal path. Appendix 
I reported the results of a demonstration of this method in which Ford 
assisted NHTSA in performing the test runs, and Ford performed the 
mathematical corrections and calculated the Dynamic Weight Transfer 
Metric (DWTM) for each of our test vehicles. In its subsequent comments 
to the docket, Ford announced that it had developed an advanced path 
following robot that could drive each test vehicle repeatably through 
the ideal path directly, eliminating the need for mathematical path 
correction. Ford expected both implementations to produce the same DWTM 
for a given vehicle, and the following remarks address both 
implementations.
    Four double lane change courses are run at 45 mph. They are each 
designed to produce a maximum lateral acceleration of 0.7g, but at a 
different frequency of motion due to their different combinations of 
length and offset. The performance metric for each test vehicle is 
highest dynamic weight transfer produced by any of the four double lane 
change courses.
    Ford's use of the double lane change is much more relevant to 
rollover resistance than the ISO 3888 or Consumers Union double lane 
change tests described above. Dynamic weight transfer is the mechanism 
that leads to tip-up. However, the Ford test is not a limit maneuver. 
It will not cause vehicles to tip-up, lose control, or even invoke ESC 
in most instances. From a theoretical point of view, this is the source 
of its greatest advantage and greatest limitation. Running the tests at 
sub-limit 0.7g lateral acceleration is a great advantage because any 
reasonable concrete or asphalt pavement should supply sufficient 
traction. It should eliminate concern about pavement traction variation 
at a designated test location, and even permit comparable tests at 
different locations. It should also eliminate the possibility of tire 
debeading during test conditions. However, sub-limit tests require that 
the comparison of dynamic performance between vehicles be extrapolated 
from a test condition that does not cause control problems to the 
extreme conditions that may actually produce rollover. Suspension 
effects that may be important at tip-up would not necessarily appear at 
the sub-limit test condition. While the swing-axle suspension design is 
not in current use, it offers a clear example of the theoretical 
problem of sub-limit tests. If a rear swing-axle vehicle enjoys a DWTM 
advantage over a vehicle with a beam rear axle at a sub-limit 
condition, it is easy to see how that advantage may not extrapolate to 
a limit condition where weight jacking and severe positive camber 
angles associated with swing-axle suspension manifest themselves.

[[Page 62538]]

    Sub-limit maneuver testing also may not predict vehicle rollover 
resistance at limit conditions. It is unclear how great a practical 
limitation on rollover resistance testing is presented by the inability 
of sub-limit tests to measure anomalies in suspension behavior that may 
occur only in limit conditions. However, in the case of the Ford test, 
the evaluation of the results for our test vehicles shows other 
practical limitations that are certainly important. We included the 2WD 
Chevrolet Blazer and the 4WD Ford Escape among our test vehicles 
because they represented a large difference in static stability factor 
(0.21) within the SUV class. In every test maneuver that produced tip-
up and in all load conditions, the Blazer had the worst performance and 
the Escape had the best. Under the PCLLC method, the Mercedes ML320 
with ESC enabled performed worse than the Blazer and significantly 
worse than the performance of the same ML320 with the ESC disabled. 
Since no other test showed a loss of rollover resistance due to the 
operation of ESC, we conclude that there was an error in the PCLLC 
method for this vehicle. Aside from the ML320 with ESC, the Blazer and 
Escape set the performance range among our test vehicles in the Ford 
test as well. However, the standard deviation of DTWM measurement is so 
large in comparison to the range of differences in DTWM between 
vehicles, that the large difference in rollover resistance between the 
2WD Blazer and the 4WD Escape barely attains statistical significance. 
Aside from the erroneous result for the ML320s with ESC, none of the 
other differences in DTWM between test vehicles were statistically 
distinguishable from random measurement variation. The measurement 
repeatability of the present form of the Ford test makes it not 
suitable for comparisons of vehicles within a class. The measurement 
variation of DWTM relative to the range of values across vehicle 
population is at least 20 times that of SSF measurements.
    A surprising limitation of the Ford test was that there was no 
discernable dynamic weight transfer component in the measured Dynamic 
Weight Transfer Metric. Except for the measurement of the ML320 with 
ESC that we consider erroneous, the ``dynamic'' weight transfer 
measurements were not different from the quasi-static weight transfer 
calculated from c.g height, track width, and an allowance for steady 
state body roll. This suggests that the same weight transfer would be 
measured if the vehicle were simply driven in a circle at 0.7g lateral 
acceleration.
    The centrifuge is a theoretically ideal way to make the same 
measurement. The weight transfer measurement could be made by placing 
the vehicle on stationary scales on the centrifuge platform. Stationary 
scales are a much more accurate way of measuring vertical load than the 
method used in the Ford test. Both the PCLLC method and the path-
following robot method of Ford's test rely on measurements of axle 
height and camber relative to the road to deduce vertical loads from 
separate studies of tire deflection versus vertical and lateral loads 
and camber angle. The centrifuge test could directly measure quasi-
static weight transfer at 0.7g, but it could also measure the lateral 
acceleration at tip-up for each vehicle which would increase the 
measurement range across the population of vehicles. We expect that the 
repeatability of centrifuge measurements would approach that of SSF 
measurements, and Section VIII describes our plans to investigate the 
potential of centrifuge testing. The ``straight tether release'' method 
of centrifuge testing suggested by UMTRI also provides for a dynamic 
component of load transfer that can be measured under laboratory 
conditions. It is identical in concept to the sled tests for tripped 
rollover suggested by Exponent.
    Although Ford's PCLLC test produces results that are more quasi-
static than dynamic, rollover resistance ratings based on quasi-static 
load transfer are useful if measured precisely, and they are likely to 
correlate very well with real-world crash statistics. However, only 
true limit maneuver tests measure the effects of ESC and potential 
anomalies in suspension behavior on rollover resistance. Unfortunately, 
limit maneuver tests are affected by pavement friction to a much 
greater degree than Ford's test or centrifuge tests that do not involve 
pavement friction. We do not expect pavement effects to be an 
insurmountable obstacle to practical limit maneuver tests, but should 
that occur, we believe that the centrifuge test has a great advantage 
in precision, simplicity, and cost of operation over the PCLLC method 
while sharing its advantage of pavement insensitivity.

C. Choice of the Fishhook Test With Roll Rate Feedback and the J-Turn 
as an Effective Pair of Dynamic Rollover Resistance Test Maneuvers

    The fishhook and J-turn maneuvers turned out to be the only true 
limit maneuvers in the test program. Unlike the other maneuvers they 
were capable of causing tip-up in vehicles susceptible to on-road 
untripped rollover. They were able to detect an increase in resistance 
to on-road untripped rollover as a result of ESC operation, and they 
place the vehicle in a circumstance where anomalies in suspension 
behavior will manifest themselves. They were very objective and 
repeatable because they were performed using a steering controller. We 
estimate that the speed at tip-up is repeatable within 2 mph on the 
same surface. A test performance criterion of tip-up or no tip-up would 
be absolutely repeatable except for vehicles with a tip-up speed within 
2 mph of the maneuver cut-off speed set by safety concern for test 
drivers. We are examining the repeatability of limit maneuver tests on 
different pavements and in different seasonal conditions on the same 
pavement.
    Our reasons for not choosing a Double Lane Change maneuver are 
summarized in Table 1, discussed in Appendix I of this notice and 
further clarified in subsections A and B above. However, to briefly 
repeat, our primary concerns with the Double Lane Change maneuvers are: 
(a) The Ford version appears to be a very complex and expensive way of 
measuring quasi-static load transfer with poor measurement precision; 
also it does not measure ESC effects or anomalies in suspension 
behavior at the limit; and (b) the ISO 3388 and CU Short Course simply 
do not measure rollover resistance under the performance criteria of 
maximum entry speed of a clean run, nor are they limit tests.
    Table 1 summarizes the observations that point to the Fishhook 
maneuver as the best choice for a dynamic rollover resistance test 
maneuver. We prefer the Roll Rate Feedback Fishhook to the Fixed Timing 
Fishhook because roll rate feedback feature adapts the timing of 
steering to characteristics of the vehicle being tested. This feature 
resolves long-standing criticism of double lane change maneuvers for 
rollover testing that the inherent timing of the course could favor the 
frequency response of some vehicles over others. (The Ford test used a 
variety of double lane change courses to address the same issue.) The 
Nissan Fishhook also contains a procedure to adjust the steering timing 
to the vehicle characteristic, but it is a more difficult test to 
perform than is the automated Roll Rate Feedback Fishhook maneuver.
    One of the problems with using the Roll Rate Feedback Fishhook (or 
any other Fishhook) maneuver for consumer information is that Fishhook 
does not give people an understanding as to how this maneuver occurs 
during driving. To help people understand this test, we

[[Page 62539]]

have decided to rename Fishhook maneuvers (all variants) as Road Edge 
Recovery Maneuvers. The Roll Rate Feedback Fishhook will be renamed the 
NHTSA Road Edge Recovery Maneuver.
    NHTSA analyses of crash databases have found that the most common 
scenario leading to untripped rollover is road edge recovery. This 
scenario begins with the vehicle dropping two wheels off the right edge 
of the paved roadway onto an unpaved shoulder. The reasons for this 
occurring include, among others, driver inattention, distraction and 
fatigue. The driver attempts to regain the paved roadway by steering to 
the left. Due to the lip between the pavement and the shoulder, a 
substantial steer angle is required to start the vehicle moving to the 
left. However, once the vehicle overcomes the lip and starts moving, it 
quickly threatens to depart from the left side of the road. Therefore, 
the driver rapidly countersteers to the right. This pattern of steering 
during a road edge recovery was discovered during research done by the 
Texas Transportation Institute.\5\
---------------------------------------------------------------------------

    \5\ Ivey, D.L., Sicking, D.L., ``Influence of Pavement Edge and 
Shoulder Characteristics on Vehicle Handling and Stability,'' 
Transportation Research Record 1084.
---------------------------------------------------------------------------

    The similarity between the characteristic pattern of steering used 
by drivers during a road edge recovery and a fishhook maneuver is 
apparent. We note that fishhook maneuvers do not simulate the lip 
between the pavement and the shoulder. However, we do not believe that 
this matters since the effects of this lip occur at the very beginning 
of the maneuver, well before the vehicle is likely to have two-wheel 
lift.
    The NHTSA J-Turn maneuver (without pulse braking) was the easiest 
limit maneuver to perform repeatably and objectively. However, it was 
not chosen as a stand-alone dynamic rollover resistance test because it 
is not severe enough. While our research has shown that the J-Turn can 
discriminate between vehicles that have a low rollover resistance, J-
Turns generally do not induce tip-up for modern production vehicles 
loaded only with a driver and instrumentation. Fishhook maneuvers 
induce two-wheel lifts for more production vehicles.
    The discriminatory power of the dynamic rollover test program will 
be maximized by having test maneuvers with different levels of 
stringency rather than just a single maneuver with tip-up speed as the 
only metric. The NHTSA J-Turn is our choice for a lower severity 
dynamic rollover resistance test maneuver. We have selected it because 
it has excellent objectivity and repeatability, is easy to perform, and 
has a well worked out test procedure. Having only a single major 
steering movement, it is a logical step down from the Fishhook. This 
maneuver has a long history of industry use. During NHTSA's discussions 
with the automotive industry, every manufacturer stated that they 
routinely perform J-Turn testing during vehicle development.
    Another way to increase the range of test severity is by testing 
vehicles in different load conditions. Ford suggested using the PCLLC 
tests with vehicles loaded to their Gross Vehicle Weight Rating with 
the rear axle carrying its maximum rated load. The tests described in 
this notice used a roof load as a second load configuration. The rating 
system alternatives described in the next section presume that the 
vehicles will be tested in two load conditions. We have tentatively 
decided that the light load condition will be just the driver and 
instruments and that the heavy load condition will be the equivalent of 
fiftieth percentile male dummies in all seating positions. Thus, we 
will test in four levels of stringency: J-turn with light and heavy 
loads; and Roll Rate Feedback Fishhook with light and heavy loads. The 
J-turn with light load is the least stringent, and the Fishhook with 
heavy load is the most stringent. The rating example in the next 
section assumes only four binary dynamic performance variables, namely 
did it tip-up or not in each of the four maneuver/load combinations. 
The speed at tip-up will be available as another level of stringency, 
but it is not clear whether it will be needed. A greater number of 
dynamic variables may not further improve the fit of the statistical 
model.

VII. Proposed Rollover Resistance Rating Alternatives

    While many commenters suggested or supported specific dynamic 
rollover tests, only two of them made suggestions about how to use the 
results of dynamic rollover tests in ratings of rollover resistance. GM 
defined minimum levels of performance for the centrifuge tip-up test, 
the constant radius driving maneuver test of maximum lateral 
acceleration, and the stability margin which is the difference between 
centrifuge test result and the constant radius maneuver test result. A 
vehicle meeting all three minimum levels of performance would be rated 
2 stars. It also defined a single higher ``bonus star'' level for each 
of the three performance criteria, making it possible to rate up to 3 
bonus stars for total rating of 5 stars. Toyota presented an example of 
a range of Lateral Acceleration for Rollover (LAR) in a fishhook 
maneuver (with pulse braking if necessary) for a number of hypothetical 
vehicles divided into 5 star levels of increasing LAR, noting that the 
actual star levels should be determined ``through NHTSA testing/data 
analysis.'' GM's suggestion is based on the idea of being directionally 
correct--a vehicle with better rollover stability attributes should 
earn a higher rating. Toyota's example is based on directional 
correctness as a minimum; it is unclear whether its reference to NHTSA 
data analysis refers to the analysis of test data to determine the 
likely extremes of LAR or to the analysis of rollover statistics for 
vehicles of known LAR.
    NHTSA's present rollover resistance ratings based on SSF are 
interpreted in terms of a predicted rollover rate for the vehicle if it 
is involved in a single vehicle crash. This goes far beyond the GM-
suggested minimum quality of directional correctness for a rating 
system. The NAS study strongly supported the use of SSF to predict 
rollover rate as long as the model relating SSF and rollover risk could 
be demonstrated to be repeatable across data sets (shown by a tight 
confidence limits about the regression line). While the logit model 
underestimates the rollover risk of vehicles with very low SSF, its 
tight confidence limits can be calculated by standard statistical 
software, and NAS concluded that the repeatability of the model would 
support the discrimination of more than 5 levels of rollover resistance 
for light vehicles.

Should Rollover Resistance Be Rated Using Dynamic Maneuver Tests Alone?

    The requirements of the TREAD Act refer only to a ``dynamic test on 
rollovers'' and are silent about rollover resistance information 
derived from static measures. However, the NAS study of the present 
rollover rating system recommended that ``NHTSA should vigorously 
pursue the development of dynamic testing to supplement the information 
provided by SSF'' [emphasis added]. NAS did not suggest that any 
combination of dynamic tests alone was sufficient for consumer 
information on rollover resistance, and its report explained that in 
the final out-of-control phase of a rollover crash ``SSF and the 
terrain over which the vehicle is moving are the dominant determinants 
of whether rollover will occur.''
    NHTSA agrees that the dynamic tests should supplement rather than 
replace the static measures for the reasons given by NAS, but also 
because ratings

[[Page 62540]]

derived only from dynamic driving maneuver tests would severely limit 
the scope of the consumer information. The terrain over which dynamic 
driving maneuver tests for rollover take place is smooth dry pavement, 
but the vast majority of rollovers take place on terrain that includes 
soft soil, curbs and other objects that can place higher tripping 
forces on the vehicle than can tire/pavement friction. There are a 
number of vehicle design strategies for preventing tip-up in maneuver 
tests. Those that involve lowering the center of gravity of the 
vehicle, increasing its track width or reducing body sway would be 
expected to increase the vehicle's general rollover resistance both on-
road and in the event of contact with a curb, soft soil or other 
tripping mechanism.
    There are also a number of vehicle design strategies to prevent 
tip-up in maneuver tests that involve reducing the lateral tire/
pavement friction. These strategies range from simply using low 
traction tires to sophisticated ``rollover prevention'' systems that 
can apply one or more brakes in response to sensing a potential 
rollover situation. When a tire is subjected to heavy braking, its 
capacity for lateral traction is greatly reduced. This principle can be 
used to cause the vehicle to skid rather than tip-up under control of a 
``rollover prevention'' system (that uses the brake intervention 
capability of ESC under control of a tip-up sensing rather than yaw 
sensing computer program). Design strategies that depend on the active 
or passive management of tire traction can be effective in reducing the 
risk of a vehicle rolling over on the road where tire traction matters. 
However, the on-road untripped rollover is a special and limited case 
of rollover crash; most rollovers are initiated by a tripping mechanism 
other than tire traction. NAS found that dynamic maneuver tests for 
rollover are important because they are sensitive to vehicle properties 
that are not reflected in static measures of rollover resistance. But, 
a dynamic maneuver test alone can only assure the measured level of 
rollover resistance in the case of on-road untripped rollover because 
tip-up in the dynamic test can be prevented by tire traction management 
strategies that have no effect when a tripping mechanism (other than 
tire traction) initiates the rollover. Using dynamic maneuver tests to 
supplement the information on rollover resistance obtained from static 
measurements represents a potential improvement in consumer 
information, but the use of dynamic maneuver tests alone would result 
in rollover resistance ratings that may not apply to the most common 
type of real-world rollover crash in which the vehicle strikes a 
tripping mechanism. That would significantly reduce the correlation of 
rollover resistance ratings to real-world rollover crashes.

Rollover Resistance Ratings Based on Both Static Measures and Dynamic 
Maneuver Tests

Alternative 1--Combine Static and Dynamic Vehicle Measurement in a 
Statistical Model of Rollover Risk

    The ideal rollover resistance rating system would give consumers 
information on the risk of rollover in a single vehicle crash taking 
into account both the static properties of a vehicle and its 
performance in dynamic maneuver tests. The risk based system is better 
than a system that is merely directionally correct. In addition to 
answering the question ``is the rollover risk lower for vehicle A or 
vehicle B?'', it can answer also the questions, ``how much lower?'' and 
``what is the absolute risk?''.
    The present rollover resistance ratings are based on a statistical 
model that considers about 221,000 single vehicle crashes of 100 
popular make/model vehicles for which we have SSF measurements. In 
addition, each state accident report provides a number of driver 
demographic variables (sex, age, sobriety), road characteristic 
variables (speed limit, hill, curve, slippery surface), and weather 
variables (storm, darkness). A statistical model can use the real-world 
crash data to determine the effect of any variable on the proportion of 
single vehicle crashes that result in rollover (rollover risk) in the 
presence of other variables that may also exert an influence. In the 
present case, the only vehicle variable is SSF, and the model predicts 
the risk of rollover as a function of SSF in the presence of the many 
combinations of confounding variables in the data sample of 221,000 
crashes. The predicted rollover risk of a vehicle in a single vehicle 
crash, based on its SSF, becomes its rollover resistance rating which 
is expressed in five discrete levels (less than 10%, 10% to 20%, 20% to 
30%, 30% to 40%, more than 40%) designated by one to five stars.
    As mentioned previously, the NAS recommended that we use a logistic 
regression model instead of the linear regression model in order to 
establish tight confidence limits on the repeatability of the model, 
and it found that the differences of rollover risk between vehicles 
predicted by the statistical model were significant enough to support 
more than five discrete levels. Also, the NAS study recommended that 
NHTSA develop a risk model that combines the SSF measurement with the 
results of one or more dynamic maneuver tests for a more robust 
consumer information rating on rollover resistance.
    The NAS study was not concerned with the distinction between 
tripped and untripped rollovers because it is the magnitude and 
duration of the forces that cause rollover in all circumstances. NHTSA 
has considered the distinction between tripped and untripped rollovers 
important in making a choice between a road maneuver test or a general 
rollover resistance indicator metric like SSF for consumer information 
because tripped rollovers are much more common occurrences. However, 
the NAS recommendation of including both SSF and road maneuver test 
results in a risk model makes the distinction between tripped and 
untripped rollovers unnecessary. The recommendation does not require a 
choice between the two types of rollover resistance measures because 
both are included. Also, the risk model will be calculated using all 
available rollover data including tripped and untripped rollovers from 
several states for a number of vehicles that we will test using J-Turn 
and Fishhook maneuvers and measure for SSF. The predictive power of 
both SSF and road maneuver tests determined by real-world data will be 
reflected in the risk model.
    We plan to conduct dynamic rollover tests of various levels of 
stringency. The J-turn maneuver with a driver and instruments (light 
load configuration) is the least stringent. It would be rare for this 
maneuver to cause tip-up of a modern vehicle. The same J-turn test 
performed with a passenger load in every seating position (heavy load 
configuration) is a more stringent test that is likely to cause tip-up 
for a few vehicles. The Fishhook test with roll rate feedback is more 
stringent than the J-turn test because it includes a steering reversal 
designed to occur at the least favorable instant for each vehicle. It 
would also be performed in both light and heavy vehicle load 
configurations for a total of four levels of test stringency. Each 
maneuver is repeated in a series of increasing speeds until it tips-up 
or reaches the maximum test speed. The speed at tip-up offers a 
discriminator within each stringency level if needed.
    We believe that this suite of dynamic rollover tests will identify 
vehicles vulnerable to rolling over without the presence of a tripping 
mechanism, and identify a relative rank order of vehicles

[[Page 62541]]

regarding this vulnerability. However, the vehicle's rank order alone 
does not predict the rollover risk associated with its level of 
vulnerability to tip-up in dynamic rollover tests. Also, the dynamic 
test program is not expected to distinguish between vehicles having an 
SSF of about 1.2 or greater because they are unlikely to tip-up in any 
dynamic maneuver test for rollover. This expectation is based upon 
NHTSA's rollover maneuver research from 1997 to present.
    Combining the dynamic rollover test results with SSF in a risk 
model should overcome the limitations discussed above. Consider two 
vehicles with a similar SSF. If one vehicle tips up during dynamic 
rollover tests but the second does not, we would expect this advantage 
to manifest itself in the rollover crash statistics of real vehicles. 
Likewise, a vehicle that tips-up only in high severity maneuvers should 
have better real-world performance than a vehicle of similar SSF that 
tips up in lower severity maneuvers as well. Even if the real-world 
reduction in rollover risk associated with better dynamic maneuver test 
performance proves to not be large, it is certainly reasonable to 
expect it to affect the statistical risk model when it is entered along 
with SSF as one or more additional vehicle variables.
    The logistic regression model recommended by NAS (referred to as 
the logit model) gives an example of how the dynamic and static 
information could be combined in a risk model. As presented in the NAS 
report, the model operated on three driver description variables, four 
road description variables, two weather variables, but only one vehicle 
variable. There is no obvious reason why the same model could not 
operate on additional vehicle variables. While we are particularly 
interested in differences in rollover risk between vehicles with 
different dynamic test performance but similar SSF, we recognize that 
dynamic test results and SSF are not independent variables. But some of 
the variables describing the driver, road and weather also were not 
independent. The hypothetical exercise described below seems to confirm 
that logistic regression can use interrelated variables without 
difficulty.
    The data base we have used to construct linear and logistic 
regression models for the existing rating program and to assist NAS in 
its study of rollover ratings contains the state crash data for 100 
vehicle make/models and their SSF measurements, but we do not have 
dynamic maneuver test results for these vehicles. In order to evaluate 
the logistic regression process when dynamic test results as well as 
SSF are used as vehicle variables, we selected 25 vehicles from our 100 
vehicle data base and tried to estimate their probable dynamic maneuver 
test results based on previous dynamic tests of similar make/models. In 
the absence of real test results these hypothetical maneuver test 
results allowed us to use the logistic regression software with vehicle 
multiple variables. The hypothetical dynamic maneuver test results were 
in the form of 4 binary (yes/no) variables representing whether the 
vehicle would tip-up in the four maneuver tests of differing stringency 
(J-turn/light load, J-turn/heavy load, Fishhook/light load, Fishhook/
heavy load). The possible sub-levels of performance defined by test 
speed at tip-up were not used. The data base included about 88,000 
single vehicle crashes of the 25 vehicle make/models with the real 
driver, road, weather and SSF data, but only our estimates for dynamic 
``data'.
    First, logistic regression was performed with SSF as the only 
vehicle variable. The result is presented by the dashed line in Figure 
1. It is essentially identical to the result of the ``logit model'' 
recommended by NAS that was constructed using a 221,000 crash data base 
of which the 88,000 crashes are a subset. The similarity of the results 
is consistent with the finding of very tight confidence limits for the 
model.
    Next, the logistic regression was repeated using the hypothetical 
dynamic maneuver test results in addition to SSF as vehicle variables. 
The points on the graph are the predicted rollover rates for each of 
the 25 vehicles considering both its static and dynamic measurements 
under the mean distribution of the driver, road and weather variables. 
The locus of points generally follows the line predicted by SSF alone 
but shows differences in predicted rollover rates as a result of 
hypothetical dynamic test performance, especially at the low end of the 
SSF range. We estimated in the hypothetical dynamic maneuver test 
results that, with one exception, none of the vehicles with an SSF 
greater than 1.17 would tip up in even our most severe dynamic maneuver 
test. However, even if a vehicle does not tip-up in our maneuver tests, 
its risk of rollover is not zero, and it is strongly related to SSF as 
shown in the model. The model also allows for the possibility that 
vehicles with the same SSF may have significant differences in dynamic 
test results that influence the real rollover risk. These are the 
characteristics we expect in a reasonable risk model. While this 
preliminary investigation of logistic regression as a means to combine 
static and dynamic measurements is encouraging, NHTSA will continue to 
examine the theoretical soundness and confidence limits of the model in 
keeping with the recommendations of NAS.\6\
---------------------------------------------------------------------------

    \6\ We noted that the predicted rollover risk of vehicles at the 
low end of the SSF range in Figure 1 was considerably larger for the 
model including dynamic maneuver results than for the logistic model 
using SSF only. This is due in part to an apparent limitation in the 
form of the risk prediction curve with a single independent variable 
inherent to the basic logistic regression procedure that prevents 
the line from having sufficient curvature to follow the trend in 
rollover risk versus SSF in the data set presented to the model. The 
exponential risk curve upon which our current SSF rollover 
resistance ratings are based agrees more closely with the logistic 
model operating on both the SSF and the hypothetical dynamic 
maneuver tests. Our current rating system also agrees more closely 
with the actual rollover rates of vehicles than does the basic 
logistic regression procedure operating on SSF alone. We expect to 
overcome the limitation in the form of the risk prediction curve of 
the logistic regression model operating on SSF alone by using 
transformations of SSF (log(SSF) for example) as the vehicle 
variable. Once we have achieved a model with the goodness of fit of 
our current exponential model and the narrow confidence limits of 
the logistic model recommended by NAS, we can add the dynamic 
maneuver test results with the certainty that we are refining the 
risk prediction rather than compensating for the deficiencies of the 
base model. In the example of Figure 1, we would not expect much 
change in the points representing the risk predictions of the 25 
vehicle with both SSF and dynamic maneuver test results. The use of 
multiple variables tends to free the model of the restrictions in 
form that are otherwise manifested in a single variable model by the 
need to represent an exponential risk relationship by single 
continuous line with a large change in curvature in our data range. 
However, we would expect the line representing an improved logistic 
model with SSF only to conform more closely to the actual vehicle 
rollover rates, and we would expect the spread between the SSF line 
and the vehicle points to represent only the effect of the dynamic 
performance of the vehicle.
---------------------------------------------------------------------------

    The relative value of static versus dynamic measurements for 
determining the rollover resistance of vehicles is a significant 
question. Certainly, the use of both types of information to determine 
rollover resistance should lead to the most accurate information, but 
one must determine the relative weighting of the static and dynamic 
measurements. The combination of the static and dynamic information in 
a statistical model of rollover risk is an objective way to let real-
world crash data determine the weighting that best represents the 
outcomes of crashes. Besides providing the best rollover risk 
estimates, the statistical model also has the advantage of not 
requiring judgments about appropriate data weighting from NHTSA or any 
of the interested parties. Regardless of the rating method, the NCAP 
program will make available the test results for SSF and for each of 
the dynamic maneuver

[[Page 62542]]

tests, so that consumers can see the basis of our rating and exercise 
their own judgments about their particular concerns.
    However, this method of rollover resistance rating has some 
drawbacks. Dynamic maneuver test results for vehicles with large 
samples of single vehicle crash data are needed to compute a robust 
risk model. In order to use dynamic test results in risk-based ratings, 
NHTSA must first test a number of older vehicles to correlate the 
combined vehicle information of dynamic test performance and SSF to 
rollover rate using a large crash database. Eventually the NCAP test 
results will supply the risk model with vehicle information, but 
sufficient corresponding crash data will trail the vehicle measurements 
by at least four years. State accident records are reported to NHTSA 
yearly, but they lag by about two model years. Even a high production 
vehicle requires about two years of exposure to accumulate sufficient 
single vehicle crash data in the few states with reliable reporting of 
both vehicle identification and rollover crashes. Consequently, it will 
be a number of years before the effects on rollover rate of traction 
management strategies and other technologies that improve dynamic 
maneuver test results are represented directly in the risk model. In 
the mean time, vehicle characteristics that improve rollover resistance 
only in the special case of on-road untripped rollover may be 
overvalued in the risk model in comparison to vehicle characteristics 
that improve resistance to both untripped and tripped rollover.
    Critics of the SSF-based rating system may view the combination of 
dynamic and static measurements in a risk model as an attempt by NHTSA 
to devalue the dynamic tests. That is not the case.\7\ It is true that 
SSF is a strong predictor of the risk of rollover especially in a 
tripping situation and that most rollovers are tripped. Consequently, 
we expect SSF to have a strong effect in a risk model even when dynamic 
test variables are also included. However, the strong effect of SSF is 
not likely to diminish the differences in rollover rate predicted for 
difference in dynamic performance. We note that the example of Figure 1 
is based only on estimates of dynamic test performance. We will not 
know until we have actual dynamic test results for some of the 100 
vehicles in our 221,000 crash database whether the effect of dynamic 
test performance on the rollover risk model is as great as expected.
---------------------------------------------------------------------------

    \7\ The example of Figure 1 shows substantial differences in 
risk prediction by standard logistic regression when hypothetical 
dynamic test results are added to a model using only SSF to describe 
the vehicle. This example demonstrates the potential value of adding 
dynamic test results to the logit model because the predictions that 
include the hypothetical dynamic test results more closely match the 
actual rollover rates.
---------------------------------------------------------------------------

Alternative 2: Separate Ratings for Dynamic Rollover Test Results and 
Static Vehicle Measurements

    An alternative rating system is proposed to address concerns that 
combining the dynamic and static information in a risk model could give 
the dynamic tests less influence than concerned parties would prefer. 
It is based on the idea that the dynamic rollover maneuver tests are a 
direct representation of an on-road untripped rollover. Therefore, the 
dynamic test results may be reported separately as ratings of 
resistance to untripped rollover. Likewise, the SSF measurements would 
be presented separately as ratings of resistance to tripped rollover.
    We believe that the vast majority of the rollovers in our 221,000 
single vehicle crash database are tripped rollovers. However, it is 
impossible to identify those that may be untripped because state 
accident reports are not concerned with that level of detail. About 95 
percent of the small number of rollover crashes investigated directly 
by NHTSA in great detail (the NASS-CDS program) were tripped. Assuming 
a similar distribution of tripped and untripped rollovers, our large 
database is a suitable basis for a risk model of tripped rollover using 
SSF. The tripped rollover risk predictions would be the same as the 
present risk predictions except for the changes in statistical 
methodology recommended by NAS.
    Unfortunately, the NASS-CDS database receives reports of only about 
10 untripped rollovers (and about 200 tripped rollovers) a year, 
precluding any possibility of risk prediction on a make/model basis for 
untripped rollover. Ratings of resistance to untripped rollover would 
have to be based simply on the principal of directional correctness. 
For instance, a vehicle that did not tip-up in any maneuver at any load 
condition would be rated ``A''; a vehicle that would tip-up in a 
maneuver test only when loaded at every seating position would be rated 
``B''; and a vehicle that would tip-up in a maneuver test even in the 
lightly loaded condition would be rated ``C''.
    This rating system also has some disadvantages. The use of two sets 
of ratings about the same general type of crash would be difficult to 
communicate effectively to consumers. It will also be hard to explain 
to consumers why the SSF rating may be expressed in terms of risk but 
not the dynamic rating. Since the only risk information in the rating 
system would be associated with the static measures, those most 
interested in the dynamic tests may find that more dismissive of the 
dynamic tests than the combination of both types of information in a 
single risk model. Since an unknown portion of our crash database does 
contain untripped rollovers, the risk model based on that data without 
the use of untripped rollover test data at hand may also be perceived 
as not the best use of all data available to NHTSA.
    Some of the parties most interested in dynamic tests have commented 
repeatedly that SSF should not be used in the rollover resistance 
rating of vehicles. However, consumer information based only on dynamic 
maneuver tests greatly reduces the assessment of the physical forces 
that cause real world rollovers. That would make the consumer 
information less useful to the public.
    SSF measures the steady, rigid body load transfer common to all 
rollovers. The quasi-static centrifuge test adds a measurement of the 
load transfer due to body roll which should also be common to all 
rollovers. The Exponent sled test and the straight tethered centrifuge 
test add roll momentum effects typical of tripped rollovers and 
possibly J-turn tests. The dynamic maneuver tests add to these only a 
measurement of the effect of ESC and other electronic ``rollover 
prevention'' systems and a measurement of dynamic suspension behavior 
that may detect unusual problems at limit conditions. However, the test 
conditions of dynamic maneuver tests are limited by on-road tire 
traction and represent only the special case of on-road untripped 
rollover. Hence, we believe the dynamic maneuver tests should be used 
to supplement in some way one of the other three types of tests with 
relevance to tripped rollovers because tripped rollovers represent the 
vast majority of real world rollovers.

Consumers Preferences for Presentation of Rollover Ratings

    In response to the NAS recommendations and in order to better 
refine approaches to developing and delivering consumer information on 
rollover, NHTSA recently initiated additional consumer research on 
rollover. This research was to further explore the perceptions, 
opinions, beliefs and attitudes of drivers about vehicle rollover, and 
to gather reactions

[[Page 62543]]

to different presentations of ratings and other rollover information.
    The consumer research conducted was iterative in that it utilized 
individual in-depth interviews as a first phase, and focus group 
testing as a second phase. The in-depth interviews were conducted with 
22 persons in Baltimore, MD in March, 2002. A total of 12 focus groups 
of 106 persons were conducted in Chicago, Dallas, and Richmond in 
April, 2002. Participants for both the interviews and focus groups had 
to have purchased or planned to purchase a vehicle within the year. 
They also had to rate safety as somewhat or very important in their 
vehicle purchase decisions. One-third of the participants also had to 
rate rollover as somewhat or very important in their purchase 
decisions.
    The in-depth interviews were conducted with the intention of 
exploring consumer beliefs and perceptions in a probing more detailed 
way than is possible in focus groups. The interviews also served to 
provide insights as to how the focus groups could be most effectively 
conducted to acquire the desired findings. The interview results 
provided the basis for modifying approaches and sample materials 
presented at the focus groups. This iterative process did not, however, 
render opposing or contradictory results. The findings of the 
interviews and focus groups were remarkably and consistently similar. 
The key findings are as follows:

Understanding of and Preference for Dynamic and/or Static Rating for 
Rollover

    [sbull] Virtually all participants were able to identify the 
difference between the tests for the Static Stability Factor (SSF) 
Rollover Rating and the Dynamic Test rollover rating, i.e., that the 
first is a vehicle measurement and that the latter involves maneuver 
tests.
    [sbull] Most participants preferred a combined rating, especially 
once they understood that 95% of real-world rollovers are accounted for 
by SSF. Those who said they should be presented separately thought they 
would provide consumers with more information; but they also thought 
that the different (5 pt vs.3 pt) rating scales presented would confuse 
people. Many thought that a dynamic test was more realistic.
    [sbull] Some participants had trouble understanding ``track width'' 
and ``center of gravity height'' in the description of SSF.
    [sbull] Even though most participants did not explain rollover in 
the same way it was described to them, most stated that the description 
of rollover they read (from NHTSA web-site information on rollover) was 
understandable.
    [sbull] Some of the rollover terminology; ``rollover resistance 
rating,'' ``tripped by'' and especially ``tripped by a ditch,'' were 
confusing or did not make sense to many of the participants.

Preferences for Presentation of Rollover Ratings and Information

    [sbull] Participants were presented with stars, numbers, letters 
and descriptive language as alternatives for presenting rollover 
ratings. Stars were overwhelmingly preferred by both interview and 
focus group participants. They clearly disliked number ratings, and 
were ambivalent about letters and descriptors. Graphics presented to 
participants are shown in Figure 2 and in the report ``Findings of 21 
In-Depth Interviews and 12 Focus Group Discussions Regarding Vehicle 
Rollover,'' which is available in the docket for this notice.
    [sbull] Participants accurately interpreted the star ratings, with 
and without the key that explained what each star meant and which was 
better. However, many did not fully grasp that the ratings were vehicle 
ratings and were therefore confused by or did not find credible the 
actual data sets that showed percentages from over 40% to under 10% for 
rollover risk.
    [sbull] When presented with a bar graph that showed an individual 
vehicle among all vehicles, most interview participants found the bar 
graph complicated and too vague. Some said it might be useful to decide 
between different vehicle classes. The bar graph was refined visually 
and presented as a way of checking an individual vehicle through the 
web-site for the focus groups. When shown this graph depicting where a 
certain vehicle ranked in relationship to other vehicles in it's class, 
and against all classes as well as where it fell in the star rating 
range, most participants understood it and thought it useful.

Preferences for Rating Levels for Rollover Ratings

    [sbull] Nearly all of the participants preferred five rating 
levels. Alternatives of three and ten ratings were presented through 
the use of numbers, letters, half-stars and narrative descriptors. Most 
said they did not like the half stars, but when probed said it might 
make a difference in whether or not they would consider a vehicle. 
Interestingly, many assigned different values to half-star ratings; 
e.g. 3\1/2\ stars was considered more important than 4\1/2\ stars.
    [sbull] Most participants felt three rating levels were too few. 
Very few felt that 10 rating levels were appropriate. Most thought it 
was too much information and unnecessary.
    The findings of this research will help NHTSA to develop 
appropriate and useful rollover ratings and consumer information in the 
future. NAS has recommended that the agency provide the public with 
additional rating levels in order to allow better differentiation of 
rollover risk between vehicles. While clearly there are improvements to 
be made in how rollover resistance and ratings are explained and made 
useful to the consumer, there does not seem to be any basis in our 
research to date for deviating from stars or from the five rating 
levels presently being used. However, for consumers who desire more 
information than just star-ratings, we will provide detailed 
information on each vehicle on the web-site. Consumers will also be 
able to differentiate between vehicles through use of the internet 
based bar-graph data that tested positively, and through other as yet 
undeveloped presentations.

VIII. Intent To Evaluate Centrifuge Test

    The test device for the centrifuge test is similar in concept to a 
merry-go-round. A person seated at the edge of the merry-go-round feels 
a lateral force pushing him or her away from the spinning surface that 
increases with the rotational speed of the merry-go-round. The 
centrifuge device test shown in Figure 3 consists of an arm attached to 
a powered vertical shaft. At the end of the arm is a horizontal 
platform upon which the test vehicle is parked. As the vertical shaft 
rotates, the parked vehicle is subjected to a lateral acceleration that 
can be precisely controlled and measured. The basic quasi-static 
measurement is the lateral acceleration at which the parked vehicle 
experiences two-wheel lift. The outside tires are restrained by a low 
curb so the measurement is independent of surface friction, and the 
vehicle is tethered for safety to prevent excessive wheel lift. This 
test method was suggested by the University of Michigan Transportation 
Research Institute (UMTRI) both in comments to our notice about the 
present rollover resistance ratings and more recently in the context of 
the TREAD Act. As discussed in Section III, the quasi-static centrifuge 
test was also recommended by GM, Honda, CU and Advocates as a possible 
improvement on SSF to measure general rollover resistance. The test 
method is directed primarily at tripped rollover, which UMTRI noted 
accounts for all but a small percentage of rollovers.

[[Page 62544]]

    The centrifuge test has many advantages. Like SSF, it is a 
measurement that that can be performed accurately, repeatably and 
economically (at least in labor costs). It is arguably more accurate 
than SSF in evaluating tripped rollover resistance because it includes 
the effect of the outward c.g. movement as a result of suspension and 
tire deflections. Its correlation to SSF would be high, and it would be 
expected to correlate well with the actual rollover rates of vehicles, 
because those statistics are largely driven by tripped rollovers. The 
quasi-static centrifuge measurement of a vehicle's lateral acceleration 
at two-wheel lift is expected to be roughly 10 percent less than the 
vehicle's SSF with about a +/-5 percent range to cover extremes in roll 
stiffness.
    Despite these advantages, we did not include the centrifuge test in 
the test evaluation plan that was the subject of our July 2001 notice. 
We stated the following reasons:

    Improvements in centrifuge test performance can be made by 
suspension changes that degrade handling. The best performance in 
the centrifuge test (and in the closely related but less accurate 
tilt table test) occurs when the front and rear inside tires lift 
from the platform at the same time. The tuning of the relative 
front/rear suspension roll stiffness to accomplish this will cause 
the vehicle to oversteer more than most manufacturers would 
otherwise desire. We do not want to tempt manufacturers to make this 
kind of trade-off. Further, we understood the intention behind TREAD 
to be that NHTSA should give the American public information on 
performance in a driving maneuver that would evaluate the 
performance of new technologies like ESC. The centrifuge test would 
not do so.

    As discussed in Section III of this notice, GM provided some data 
disputing our concern that improvements in centrifuge test scores could 
be obtained at the expense of changing the understeer/oversteer 
suspension tuning of vehicle from what the manufacturer would otherwise 
choose as optimum for handling and consumer satisfaction. We request 
that other manufacturers and vehicle designers review GM's information 
(comment 6 to docket NHTSA-2001-9663 notice 1) and comment on the 
validity of NHTSA's concern.
    In view of the interest expressed by several commenters in 
centrifuge testing and the potential importance GM's information, NHTSA 
intends to evaluate the practicability of centrifuge testing. To our 
knowledge, centrifuge tests for rollover resistance of vehicles have 
never been performed. The interest of commenters is based on 
theoretical advantages over SSF. NHTSA will develop a test fixture and 
test a number of vehicles in the quasi-static mode using a very large 
centrifuge at NASA's Goddard Space Flight Center in Greenbelt, 
Maryland.

IX. Handling Tests

A. The Need for Handling Testing and a Handling Rating

    NHTSA expects that implementation of a rollover rating system using 
dynamic tests will, over time, influence vehicle designs. Therefore, it 
is of the utmost importance that we do not encourage designers to 
maximize vehicle performance in rollover resistance tests by degrading 
other safety relevant areas of vehicle performance.
    Several possible ways to maximize vehicle performance in rollover 
resistance tests would degrade vehicle handling. For example, better 
performance in rollover resistance tests could be achieved by one or 
more of:
    [sbull] Making the vehicle have less turning capability. 
Unfortunately, this would make it harder, in difficult situations, for 
drivers to keep the vehicle on the road or to avoid colliding with 
other vehicles, pedestrians, animals, and other objects.
    [sbull] Equalizing the roll stiffnesses of the front and rear 
suspensions. Unfortunately, this may make the vehicle spin-out in limit 
maneuvers.
    [sbull] Making the vehicle respond slowly to steering inputs. 
Again, this would make it harder, in some situations, for drivers to 
keep the vehicle on the road or to avoid colliding with other vehicles 
or pedestrians.
    To discourage vehicle designers from maximizing rollover resistance 
at the expense of handling, NHTSA believes that if our rollover ratings 
are directly influenced by dynamic tests then we must also have a 
handling rating based on handling tests.
    In addition to discouraging vehicle designers from maximizing 
rollover resistance at the expense of handling, having a handling 
rating based on handling tests should also encourage the adoption of 
yaw stability control. While the crash prevention benefits of yaw 
stability control have not yet been proven, we anticipate that it may 
help prevent crashes. Based on NHTSA's Phase IV Rollover Research, we 
will see some improvement in a vehicle's rollover resistance rating due 
to yaw stability control. However, a handling rating provides another 
opportunity for showing the beneficial effects of yaw stability 
control.

B. Guiding Principles for NHTSA Handling Testing and Handling Rating

    What is handling? In this document, what we mean by handling is the 
lateral response of the vehicle to a driver's control inputs. Clearly 
steering inputs are the most important control inputs for handling, 
however, brake and throttle pedal inputs can also have an effect.
    Traditionally, handling assessments have been made subjectively. 
Several test drivers drive a vehicle for a period of time through a 
broad variety of maneuvers. The maneuvers range in severity from mild 
to severe to limit. After driving the vehicle, each driver 
independently assigns a numerical handling rating to the vehicle. 
Ratings from all of the test drivers are averaged to obtain an overall 
handling rating.
    We do not believe that a subjective handling rating is suitable for 
inclusion in the New Car Assessment Program. Government generated 
handling ratings must be objectively and repeatably determined.
    There are two perspectives for handling ratings. One perspective is 
how safe the vehicle is to drive. The other is how well the vehicle 
gives an enthusiast driver a pleasurable sense of control. Given its 
mission, a NHTSA generated handling rating can only assess how safe a 
vehicle is to drive, not how pleasurable it is to drive.
    What aspects of handling affect safety? NHTSA has identified the 
following four:
    1. Amount of turning capability. A vehicle that can turn more 
sharply should be easier for drivers to keep on the road and to avoid 
colliding with other vehicles, pedestrians, animals, and other objects.
    2. Graceful degradation at/near limits. When a driver approaches or 
tries to exceed the maximum turning capability of a vehicle the vehicle 
should plow-out (saturate traction on the front wheels first) instead 
of spin-out (saturate traction on the rear wheels first).
    3. Predictability. When the driver steers, brakes, or changes the 
throttle level, the vehicle should do what the driver expects the 
vehicle to do. Since all vehicles have delays between steering, 
braking, or throttle application and the response of the vehicle, 
drivers must predict the response of the vehicle to a control input. If 
the vehicle does not perform as expected, there may not be time for the 
driver to react to the unexpected motion before a crash occurs.
    4. Responsiveness. When the driver steers, brakes, or changes the 
throttle level, the vehicle should respond

[[Page 62545]]

quickly to the driver's inputs. A slowly responding vehicle would be 
harder for drivers to keep on the road or to avoid colliding with other 
vehicles, pedestrians, animals, and other objects.
    We have discussed the aspects of handling that affect safety with 
Consumers Union. In addition to the four aspects listed above, 
Consumers Union uses a fifth, appropriate feedback to the steering 
handwheel, in developing ratings for their magazine. While we do not 
dispute the importance of appropriate feedback to the steering 
handwheel, this seems to us to be such an inherently subjective 
assessment that we have not included it in the above list.
    We welcome comments as to the correctness of the above list of 
handling aspects that affect safety. Are the aspects that are listed 
appropriate? Have we left anything out?

C. Handling Tests Being Considered by NHTSA

    NHTSA is considering developing a handling rating based upon 
results from the three handling maneuvers. The handling maneuvers are:
    1. Slowly Increasing Steer maneuver. Using a programmable steering 
controller, the steering handwheel is turned slowly (13.5 degrees per 
second) from zero to well beyond the point at which the maximum lateral 
acceleration occurs (a handwheel steering angle of 270 degrees). The 
driver applies the throttle to keep the vehicle's speed as constant at 
50 mph as possible during the turn.
    The Slowly Increasing Steer maneuver provides data to assess the 
amount of turning capability of a vehicle (the Maximum Attainable 
Lateral Acceleration) and whether the vehicle's handling degrades 
gracefully at the limit (did the vehicle plow or spin when the maximum 
achievable turn was attained). We performed this maneuver for every 
vehicle tested during Phases II, III, and IV of NHTSA Rollover 
Research. Based on our experience we believe that this maneuver can be 
performed with excellent objectivity and repeatability. There is a well 
worked out and widely accepted procedure for the Slowly Increasing 
Steering maneuver that is contained in the Society of Automotive 
Engineers Standard J266.
    2. Dropped Throttle in a Turn maneuver. Using a programmable 
steering controller, the steering handwheel is turned quickly, and then 
held at, the angle required to attain 90 percent of the vehicle's 
maximum achievable lateral acceleration. The driver initially applies 
the throttle to keep the vehicle's speed as constant as possible during 
the turn. The throttle is then suddenly released and the resulting 
vehicle motion measured.
    The Dropped Throttle in a Turn maneuver provides data to assess the 
predictability of the vehicle. Desirable behavior is for the vehicle to 
either maintain the same radius of curvature or to ``tuck-in'' a bit 
(slightly decrease the radius of curvature). While we have not 
performed this maneuver in the past, we expect that this maneuver can 
be performed with excellent objectivity and repeatability. There is a 
well worked out and widely accepted procedure for the Dropped Throttle 
in a Turn maneuver that is contained in the International Standards 
Organization's Standard 9816.
    Multiple measures of vehicle performance are determined from this 
test. One is the Dropped Throttle Yaw Rate Ratio, defined as the 
maximum yaw rate attained at any time during the three seconds after 
the throttle was released divided by the initial yaw rate. The second 
is the Dropped Throttle Path Deviation, defined as the lateral 
displacement of the vehicle's center of gravity two seconds after the 
throttle has been released from the anticipated path if the throttle 
had not been released.
    3. The Step Steer maneuver. This maneuver is performed in the same 
manner as the NHTSA J-Turn except that the handwheel steering angle 
used is less. Instead of turning the steering handwheel to 8.0 times 
the angle needed to achieve 0.3 g lateral acceleration in the Slowly 
Increasing Steer maneuver (the angle used for the NHTSA J-Turn), for 
this maneuver the steering wheel is only turned to the angle needed to 
achieve 4.0 meters per second squared lateral acceleration. A handwheel 
steering rate of 1,000 degrees per second is used. The maneuver 
entrance speed is 50 mph (80 kph) and the throttle is held constant 
through the test.
    Multiple measures of vehicle performance are determined from this 
test. One is the Yaw Rate Response Time, defined as the time from when 
the steering handwheel reaches 50 percent of its final value to the 
time when the yaw rate reaches 90 percent of its steady-state value. 
The second is the Peak Yaw Rate Response Time, defined as the time from 
when the steering handwheel reaches 50 percent of its final value to 
the time when the yaw rate reaches it peak value. The third is Percent 
Overshoot, defined as the difference between the peak and steady state 
yaw rates divided by the steady state yaw rate.
    The Step Steer maneuver provides data to assess the predictability 
(from the Percent Overshoot measure) and the responsiveness (from the 
Yaw Rate Response Time and the Peak Yaw Rate Response Time measures) of 
the vehicle. We performed this maneuver for every vehicle tested during 
Phase IV of NHTSA Rollover Research; based on our experience we believe 
that this maneuver can be performed with excellent objectivity and 
repeatability. There is a well worked out and widely accepted procedure 
for the Step Steer maneuver that is contained in the International 
Standards Organization's Standard 7401.
    Each Handling Maneuver would be performed at two loading 
conditions, Nominal Load and Rear Load. The Nominal Load consists of 
the curb weight vehicle plus the driver plus NHTSA's instrumentation 
package plus NHTSA's titanium outriggers. The Rear Load adds to the 
Nominal Load ballast positioned such that the vehicles rear Gross Axle 
Weight Rating (GAWR) and Gross Vehicle Weight Rating (GVWR) are 
achieved simultaneously. The ballast is comprised of bags of lead shot, 
positioned as flat as possible across the rear cargo area of the test 
vehicle. The ballast will be secured in a manner that insures it does 
not shift during testing. We will use a `` inch enclosed plywood box to 
contain the ballast used in the Rear Load condition. Due to the wide 
range of shapes and sizes of light vehicle cargo areas, such boxes will 
need to be constructed on a per-vehicle basis.
    We welcome comments as to the appropriateness of the above list of 
handling maneuvers. What have we left out?
    NHTSA is seeking tests of handling and controllability both as way 
of dealing with potential trade-offs between handling properties and 
rollover tests and as a way of giving credit to technologies that 
improve controllability. We request comment on the value of such tests 
to resolve the concern for design compromises that could improve 
centrifuge test scores.
    One of our concerns is that yaw stability control is supposed to 
increase a vehicle's predictability; however, our Dropped Throttle in a 
Turn Maneuver test is may not be adequate for measuring the effects of 
yaw stability control. What other objective and repeatable tests exist 
for measuring vehicle predictability?

D. Combining Handling Test Results to Generate a Handling Rating

    As is the case for rollover resistance ratings, an ideal handling 
rating system would use data obtained from the above mentioned handling 
tests to predict the

[[Page 62546]]

risk, for a vehicle make/model assuming an ``average'' driver, of a 
single vehicle crash. The risk based ratings are better than ratings 
that are merely directionally correct because in addition to answering 
the question ``Is the single vehicle crash risk lower for Vehicle A or 
Vehicle B?'', it can also answer the questions, ``How much lower?'', 
and ``What is the absolute risk?''.
    The influence of drivers on whether or not a single vehicle crash 
occurs is very high. The driver demographic variables that are 
available in the crash data bases are believed not to be sufficient to 
quantify this influence (i.e., there is no variable quantifying a 
driver's aggressivity). Therefore, we believe that, unlike rollover 
resistance ratings, handling ratings will not be able to predict single 
vehicle crash risk. They can, at best, be directionally correct.
    We envision a three level handling rating system, tentatively, from 
best to worst, A, B, and C. A star rating system would not be used for 
handling ratings because they are not risk based but only directionally 
correct.
    The handling rating calculation method proposed below contains many 
constants whose values NHTSA will specify at a later date (e.g., 
aYMinN and aYRangeN). Our intention is to 
determine values for these constants based on data collected during the 
Phase VI testing. During Phase VI 25 vehicles for which we have state 
crash data on rollover will be tested using both rollover maneuver 
tests and handling tests concluding in Fall 2002. We have tried to 
choose the Phase VI test vehicles so as to cover the full range of 
handling that is seen in the current fleet, from excellent to average. 
(We do not believe that any current production vehicle has handling we 
would characterize as bad.) Once we have the Phase VI data, we will 
select values for the constants so that approximately one-third of the 
vehicles earn A ratings, one-third earn B ratings, and one-third earn C 
ratings.
    The handling rating would be determined from the measurements 
results of the handling tests as follows:
    1. Calculate a Handling Score, HS, from the formula:

HS = W1 * H1 + W2 * H2 + 
W3 * H3 + W4 * H4
+ W5 * H5 + W6 * H6 + 
W7 * H7 + W8 * H8
+ W9 * H9 + W10 * H10 + 
W11 * H11 + W12 * H12

where W1 through W12 are weights that NHTSA will 
select values for at a later date, H1 is the Maximum 
Attainable Lateral Acceleration at Nominal Load sub-score, 
H2 is the Dropped Throttle Yaw Rate Ratio at Nominal Load 
sub-score, H3 is the Dropped Throttle Path Deviation at 
Nominal Load sub-score, H4 is the Yaw Rate Response Time at 
Nominal Load sub-score, H5 is the Peak Yaw Rate Response 
Time at Nominal Load sub-score, and H6 is the Percent 
Overshoot at Nominal Load sub-score, H7 is the Maximum 
Attainable Lateral Acceleration at Rear Load sub-score, H8 
is the Dropped Throttle Taw Rate Ratio at Rear Load sub-score, 
H9 is the Dropped Throttle Path Deviation at Rear Load sub-
score, H10 is the Yaw Rate Response Time at Rear Load sub-
score, H11 is the Peak Yaw Rate Response Time at Rear Load 
sub-score, and H12 is the Percent Overshoot at Rear Load 
sub-score.
    2. Calculate the Maximum Attainable Lateral Acceleration at Nominal 
Load sub-score, H1, from the formulas:

If aYMaxN YMinN then H1 = 0
If aYMaxN (aYMinN + 
aYRangeN) then H1 = 1

Otherwise

    aBarN = (aYMaxN - aYMinN)/ 
aYRangeN
    H1 = aBarN*(2 -- aBarN)

where aYMaxN is the measured Maximum Attainable Lateral 
Acceleration at Nominal Load, and aYMinN and 
aYRangeN are constants that NHTSA will select values for at 
a later date.
    3. Calculate the Dropped Throttle Yaw Rate Ratio at Nominal Load 
sub-score, H2, from the formula:

If RMaxN RRangeN then H2 = 
0

Otherwise

    H2 = 1 - ((RMaxN -- 1) / 
RRangeN)\2\

where RMaxN is the measured Dropped Throttle Yaw Rate Ratio 
at Nominal Load, and RRangeN is a constant that NHTSA will 
select a value for at a later date. Note that RMaxN can 
never be less than one.
    4. Calculate the Dropped Throttle Path Deviation at Nominal Load 
sub-score, H3, from the formula:

If YDevN MinN then H3 = 0
If YDevN YMinN and YDevN <0 then
    H3 = 1--(YDevN/YMinN)\2\
If YDevN 0 and YDevN OkN then 
H3 = 1
If YDevN YOkN and YDevN 
MaxN then
    YBarN = (YDevN -- YOkN)/
(YMaxN--YOkN)
    H3 = YBarN*(2--YBarN)
If YDevN YMaxN then H3 = 0

where YDevN is the measured Dropped Throttle Path Deviation 
at Nominal Load, and YMaxN, YMinN, and 
YOkN are constants that NHTSA will select values for at a 
later date.
    5. Calculate the Yaw Rate Response Time at Nominal Load sub-score, 
H4, from the formula:

If trN rMinN then H4 = 1

If trN (trMinN + trRangeN) 
then H4 = 0

Otherwise

    H4 = ((trMinN + trRangeN) -
trN)/trRangeN

where trN is the measured Yaw Rate Response Time at Nominal 
Load, and trMinN and trRangeN are constants that 
NHTSA will select values for at a later date.
    6. Calculate the Peak Yaw Rate Response Time at Nominal Load sub-
score, H5, from the formula:

If tpN pMinN then H5 = 1
If tpN (tpMinN + tpRangeN) 
then H5 = 0

Otherwise

    H5 = ((tpMinN + tpRangeN)-
tpN)/tpRangeN

where tpN is the measured Yaw Rate Response Time at Nominal 
Load, and tpMinN and tpRangeN are constants that 
NHTSA will select values for at a later date.
    7. Calculate the Percent Overshoot at Nominal Load sub-score, 
H6, from the formula:

If OrN <0 then H6 = 1

Otherwise

    H6 = 1-(OrN/
OrRangeN)\2\

where OrN is the measured Percent 
Overshoot at Nominal Load, and OrRangeN is a constant that 
NHTSA will select a value for at a later date. Note that 
OrN can never be less than zero.
    8. Calculate the Maximum Attainable Lateral Acceleration at Rear 
Load sub-score, H7, from the formulas:

If aYMaxR YMinR then H7 = 0
If aYMaxR (aYMinR + 
aYRangeR) then H7 = 1

Otherwise

    aBarR = (aYMaxR-aYMinR) /
aYRangeR
    H7 = aBarR * (2-aBarR)

where aYMaxR is the measured Maximum Attainable Lateral 
Acceleration at Rear Load, and aYMinR and 
aYRangeR are constants that NHTSA will select values for at 
a later date.
    9. Calculate the Dropped Throttle Yaw Rate Ratio at Rear Load sub-
score, H8, from the formula:

If RMaxR RRangeN then H8 = 
0

Otherwise

    H8 = 1-((RMaxR-1)/RRangeR)\2\

where RMaxR is the measured Dropped Throttle Yaw 
Rate Ratio at Rear Load, and RRangeR is a constant that 
NHTSA will select a value for at a later date. Note that 
RMaxR can never be less than one.
    10. Calculate the Dropped Throttle Path Deviation at Rear Load sub-
score, H9, from the formula:

If YDevR MinR then H9 = 0
If YDevR YMinR and YDevR <0 then
    H9 = 1-(YDevR/YMinR)\2\
If YDevR 0 and YDevR OkR then 
H9 = 1
If YDevR YOkR and YDevR 
MaxR then
    YBarR = (YDevR - YOkR)/
(YMaxR -

[[Page 62547]]

YOkR)
    H9 = YBarR * (2-YBarR)
If YDevR YMaxR then H9 = 0

where YDevR is the measured Dropped Throttle Path Deviation 
at Nominal Load, and YMaxR, YMinR, and 
YOkR are constants that NHTSA will select values for at a 
later date.
    11. Calculate the Yaw Rate Response Time at Rear Load sub-score, 
H10, from the formula:

If trR rMinR then H10 = 1
If trR (trMinR + trRangeR) 
then H10 = 0

Otherwise
    H10 = ((trMinR + trRangeR )-
trR)/trRangeR

where trR is the measured Yaw Rate Response Time at Rear 
Load, and trMinR and trRangeR are constants that 
NHTSA will select values for at a later date.
    12. Calculate the Peak Yaw Rate Response Time at Rear Load sub-
score, H11, from the formula:

If tpR pMinR then H11 = 1
If tpR (tpMinR + tpRangeR) 
then H11 = 0

Otherwise

    H11 = ((tpMinR + tpRangeR)-
tpR)/tpRangeR
where tpR is the measured Yaw Rate Response Time at Rear 
Load, and tpMinR and tpRangeR are constants that 
NHTSA will select values for at a later date.
    13. Calculate the Percent Overshoot at Rear Load sub-score, 
H12, from the formula:

If OrR <0 then H12 = 1

Otherwise

    H12 = 1 - (OrR/
OrRangeR)\2\

where OrR is the measured Percent 
Overshoot at Rear Load, and OrRangeR is a constant that 
NHTSA will select a value for at a later date. Note that 
OrR can never be less than zero.
    14. Calculate the provisional Handling Rating from the Handling 
Score, HS, as follows:

If HS HSA then the provisional Handling Rating is 
an A
If HS C then the provisional Handling Rating is a C
Otherwise the provisional Handling Rating is a B

where HSA and HSC are constants that NHTSA will 
select values for at a later date.

    15. If the vehicle spins when determining the Maximum Attainable 
Lateral Acceleration at Nominal Load, then reduce the provisional 
Handling Rating by one letter (but never below a C).
    16. If the vehicle spins when determining the Maximum Attainable 
Lateral Acceleration at Rear Load, then reduce the provisional Handling 
Rating by one letter (but never below a C).
    17. The provisional Handling Rating now becomes the final Handling 
Rating.
    We welcome comments as to the appropriateness of the above 
technique for determining handling ratings. How can it be improved? One 
possibility would be to have two handling ratings, one for Nominal Load 
and one for Rear Load. Would this be better? Or should we consider the 
ratings for the different loadings to be an additional level of detail 
available to interested persons who want more than just the one rating?

X. Assessment of Costs and Benefits

    The costs are Federal Government costs for developing the test 
protocol and rating system, conducting the tests, and disseminating the 
information. The benefits are information to consumers. Consumers want 
additional information. It is impossible for us to quantify the effect 
on consumer behavior or on manufacturer behavior.

XI. Rulemaking Analyses and Notices

A. Executive Order 12866

    Executive Order 12866, ``Regulatory Planning and Review'' (58 FR 
51735, October 4, 1993), provides for making determinations whether a 
regulatory action is ``significant'' and therefore subject to Office of 
Management and Budget (OMB) review and to the requirements of the 
Executive Order. The Order defines a ``significant regulatory action'' 
as one that is likely to result in a rule that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or Tribal governments or 
communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations of recipients 
thereof; or
    (4) Raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    NHTSA has considered the impact of this action under Executive 
Order 12866 and the Department of Transportation's regulatory policies 
and procedures. This action has been determined to be economically not 
significant. However, because it is a subject of Congressional 
interest, this rulemaking document was reviewed by the Office of 
Management and Budget under Executive Order 12866, ``Regulatory 
Planning and Review.''

B. Regulatory Flexibility Act

    The Regulatory Flexibility Act of 1980 (5 U.S.C. Sec.  601 et seq.) 
requires agencies to evaluate the potential effects of their proposed 
and final rules on small business, small organizations and small 
governmental jurisdictions. I hereby certify that the proposed 
amendment would not have a significant economic impact on a substantial 
number of small entities. The proposed action does not impose 
regulatory requirements on any manufacturer or other party.

C. National Environmental Policy Act

    NHTSA has analyzed this proposal for the purposes of the National 
Environmental Policy Act. The agency has determined that implementation 
of this action would not have any significant impact on the quality of 
the human environment.

D. Executive Order 13132 (Federalism)

    The agency has analyzed this rulemaking in accordance with the 
principles and criteria contained in Executive Order 13132 and has 
determined that it does not have sufficient federal implications to 
warrant consultation with State and local officials or the preparation 
of a federalism summary impact statement. The proposal would not have 
any substantial impact on the States, or on the current Federal-State 
relationship, or on the current distribution of power and 
responsibilities among the various local officials.

E. Unfunded Mandates Act

    The Unfunded Mandates Reform Act of 1995 requires agencies to 
prepare a written assessment of the costs, benefits and other effects 
of proposed or final rules that include a Federal mandate likely to 
result in the expenditure by State, local or tribal governments, in the 
aggregate, or by the private sector, of more than $100 million annually 
(adjusted annually for inflation with base year of 1995). Adjusting 
this amount by the implicit gross domestic product price deflator for 
the year 2000 results in $109 million (106.99/98.11 = 1.09). The 
assessment may be included in conjunction with other assessments, as it 
is here.
    The proposed action does not impose regulatory requirements on any 
manufacturer or other party.

F. Civil Justice Reform

    This proposal would not have any retroactive effect. Under 49 
U.S.C. 21403, whenever a Federal motor vehicle safety standard is in 
effect, a State may not adopt or maintain a safety standard applicable 
to the same aspect

[[Page 62548]]

of performance which is not identical to the Federal standard, except 
to the extent that the state requirement imposes a higher level of 
performance and applies only to vehicles procured for the State's use. 
49 U.S.C. 21461 sets forth a procedure for judicial review of final 
rules establishing, amending or revoking Federal motor vehicle safety 
standards. That section does not require submission of a petition for 
reconsideration or other administrative proceedings before parties may 
file suit in court.

G. Paperwork Reduction Act

    This proposal does not contain ``collections of information,'' as 
that term is defined in 5 CFR Part 1320 Controlling Paperwork Burdens 
on the Public.

H. Plain Language

    Executive Order 12866 and the President's memorandum of June 1, 
1998, require each agency to write all rules in plain language. This 
action will not result in regulatory language.

XII. Submission of Comments

How Can I Influence NHTSA's Thinking on This Proposed Rule?

    In developing this proposal, we tried to address the concerns of 
all our stakeholders. Your comments will help us improve this rule. We 
invite you to provide views on options we propose, to suggest new 
approaches we have not considered, provide new data, indicate how this 
proposed rule may affect you, or provide other relevant information. We 
welcome your views on all aspects of this proposed rule, but request 
comments on specific issues throughout this document. We grouped these 
specific requests near the end of the sections in which we discuss the 
relevant issues. Your comments will be most effective if you follow the 
suggestions below:
    [sbull] Explain your views and reasoning as clearly as possible.
    [sbull] Provide solid technical and cost data to support your 
views.
    [sbull] If you estimate potential costs, explain how you arrived at 
the estimate.
    [sbull] Tell us which parts of the proposal you support, as well as 
those with which you disagree.
    [sbull] Provide specific examples to illustrate your concerns.
    [sbull] Offer specific alternatives.
    [sbull] Refer your comments to specific sections of the proposal, 
such as the units or page numbers of the preamble, or the regulatory 
sections.
    [sbull] Be sure to include the name, date, and docket number with 
your comments.

How Do I Prepare and Submit Comments?

    Your comments must be written and in English. To ensure that your 
comments are correctly filed in the Docket, please include the docket 
number of this document in your comments.
    Your comments must not be more than 15 pages long. (49 CFR 553.21). 
We established this limit to encourage you to write your primary 
comments in a concise fashion. However, you may attach necessary 
additional documents to your comments. There is no limit on the length 
of the attachments.
    Please submit two copies of your comments, including the 
attachments, to Docket Management at the address given above under 
ADDRESSES.
    Comments may also be submitted to the docket electronically by 
logging onto the Dockets Management System Web site at http://dms.dot.gov. Click on ``Help & Information'' or ``Help/Info'' to obtain 
instructions for filing the document electronically.

How Can I Be Sure That My Comments Were Received?

    If you wish Docket Management to notify you upon its receipt of 
your comments, enclose a self-addressed, stamped postcard in the 
envelope containing your comments. Upon receiving your comments, Docket 
Management will return the postcard by mail.

How Do I Submit Confidential Business Information?

    If you wish to submit any information under a claim of 
confidentiality, you should submit three copies of your complete 
submission, including the information you claim to be confidential 
business information, to the Chief Counsel, NHTSA, 400 Seventh Street, 
SW., Washington, DC 20590. In addition, you should submit two copies, 
from which you have deleted the claimed confidential business 
information, to Docket Management at the address given above under 
ADDRESSES. When you send a comment containing information claimed to be 
confidential business information, you should include a cover letter 
setting forth the information specified in our confidential business 
information regulation. (49 CFR part 512.)

Will the Agency Consider Late Comments?

    We will consider all comments that Docket Management receives 
before the close of business on the comment closing date indicated 
above under DATES. To the extent possible, we will also consider 
comments that Docket Management receives after that date. If Docket 
Management receives a comment too late for us to consider it in 
developing a final rule (assuming that one is issued), we will consider 
that comment as an informal suggestion for future rulemaking action.

How Can I Read the Comments Submitted by Other People?

    You may read the comments received by Docket Management at the 
address given above under ADDRESSES. The hours of the Docket are 
indicated above in the same location.
    You may also see the comments on the Internet. To read the comments 
on the Internet, take the following steps:
    (1) Go to the Docket Management System (DMS) Web page of the 
Department of Transportation (http://dms.dot.gov/).
    (2) On that page, click on ``search.''
    (3) On the next page (http://dms.dot.gov/search/), type in the 
four-digit docket number shown at the beginning of this document. 
Example: If the docket number were ``NHTSA-1998-1234,'' you would type 
``1234.'' After typing the docket number, click on ``search.''
    (4) On the next page, which contains docket summary information for 
the docket you selected, click on the desired comments. You may 
download the comments. However, since the comments are imaged 
documents, instead of word processing documents, the downloaded 
comments are not word searchable.
    Please note that even after the comment closing date, we will 
continue to file relevant information in the Docket as it becomes 
available. Further, some people may submit late comments. Accordingly, 
we recommend that you periodically check the Docket for new material.

    Issued on: September 27, 2002.
Stephen R. Kratzke,
Associate Administrator for Safety Performance Standards.
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Appendix I.--Summary of Maneuver Evaluation Test Results

    Prior to the initiation of this research, NHTSA met with the 
Alliance of Automobile Manufacturers, Daimler-Chrysler, BMW, 
Volkswagen, Mitsubishi, Ford, Nissan, Toyota, Consumers Union of the 
United States, MTS Systems Corporation, Heitz Automotive Inc., and 
other interested parties to gather information on possible 
approaches for dynamic rollover tests. NHTSA also corresponded with 
the University of Michigan Transportation Research Institute. These 
parties made specific suggestions about approaches to dynamic 
testing of vehicle rollover resistance. Based on these suggestions 
plus NHTSA's experience in this area, a set of nine rollover 
resistance maneuvers were selected for evaluation. These nine 
maneuvers were listed in the July 2001 notice.
    The research to evaluate potential maneuver tests for rollover 
is fully documented in the NHTSA technical report ``Another 
Experimental Examination of Selected Maneuvers That May Induce On-
Road Untripped, Light Vehicle Rollover--Phase IV of NHTSA's Light 
Vehicle Rollover Research Program''. A number of test results and 
principal observations about the maneuvers are discussed here under 
the following four general headings:
    1. Objectivity and Repeatability, i.e., whether a maneuver could 
be performed objectively with repeatable results for the same 
vehicle.
    2. Discriminatory Capability, i.e., whether a maneuver 
demonstrated poorer performance for vehicles that have less 
resistance to rollover. Although of obvious importance, a maneuver's 
ability to discriminate between different levels of vehicle handling 
was not considered.
    3. Performability i.e., how difficult each maneuver is to 
objectively perform while obtaining repeatable results, how well 
developed are the test procedures for each maneuver, and whether the 
test procedure includes adequate means for adapting to differing 
vehicle characteristics.
    4. Realistic Appearance, i.e., whether a test maneuver looks 
like a maneuver consumers might imagine performing in an emergency.
    The headings are useful for organizing the information, but they 
are not mutually exclusive. For example, the discussion of whether 
the performance of a vehicle in a particular maneuver is influenced 
more by handling properties than by rollover resistance would be 
under the heading of Discriminatory Capability. But the 
repeatability of the performance measurement discussed under 
Objectivity and Repeatability also influences the discriminatory 
capability of the maneuver. Similarly, Performability is a catch-all 
category that includes discussions of topics outside of the more 
specific headings.
    Realistic Appearance helps consumers visualize the test 
maneuvers, but it is less important than the other three categories 
of test attributes because we are interested in anything that the 
vehicle is capable of doing. What we desire are ``worst case'' 
maneuvers, not necessarily ones that drivers try to perform. For 
example, drivers would not try to drive in a fishhook pattern, but 
the steering movements are similar to what occurs in an unsuccessful 
road edge recovery attempt. The maneuver only looks like a fishhook 
path if the vehicle does not tip-up. If the vehicle tips-up, it 
occurs shortly after the counter-steer when a driver in a road edge 
recovery attempt would still be on the pavement.
    The specific reasons for the choice of maneuvers we are 
proposing for rollover resistance ratings are discussed in Section 
VI. The reasons are a consequence of the observations made in this 
section plus other practical considerations such as the desirability 
of multiple maneuvers to create a range of test severity were taken 
into account.
    Four sport utility vehicles were tested during the summer of 
2001 to obtain the data needed to perform this maneuver evaluation 
(the Phase IV Rollover Research). Two of the vehicles tested during 
the Phase IV research (the 1999 Mercedes ML320 and the 2001 Toyota 
4Runner) came with yaw stability control systems as original 
equipment. Both of these vehicles were treated, for the purposes of 
maneuver evaluation, as two vehicles, one with yaw stability control 
and one without.
    Therefore, the six test vehicles were:

1. 2001 Chevrolet Blazer without yaw stability control
2. 2001 Ford Escape without yaw stability control.

    Note: The Automotive News Truck Market classifications classify 
this vehicle as a Sport Wagon instead of a Sport Utility Vehicle.

3. 1999 Mercedes ML320 with yaw stability control disabled
4. 1999 Mercedes ML320 with yaw stability control enabled
5. 2001 Toyota 4Runner with yaw stability control disabled
6. 2001 Toyota 4Runner with yaw stability control enabled

    Each of the above test vehicles was tested in three 
configurations. Only two of these configurations will be discussed 
in this notice; test data from the Modified Handling configuration 
were not used for the maneuver evaluations discussed in this notice. 
The test configurations of interest were:
    Nominal Vehicle. The vehicle load consisted of one occupant (the 
driver), instrumentation, and outriggers in/on the vehicle.
    Reduced Rollover Resistance Vehicle. In addition to the Nominal 
Vehicle load, sufficient weight was placed on the roof to reduce the 
vehicle's SSF by 0.05. The weight on the roof was positioned so that 
the longitudinal/lateral position of the center of gravity did not 
change.
    The Reduced Rollover Resistance Vehicle was used as a check on 
the sensitivity of the test maneuvers. A 0.05 reduction in SSF 
equates, for sport utility vehicles, to approximately a one star 
reduction in the vehicle's rollover resistance rating. (A larger 
reduction in SSF is necessary to achieve a one star rating reduction 
for vehicles, such as passenger cars, that have higher SSFs.) NHTSA 
believes that a one star reduction in the rollover resistance rating 
should make a vehicle substantially easier to rollover. Maneuvers 
with good discriminatory capability should measure substantially 
worse performance for this vehicle configuration than for the 
Nominal Vehicle configuration.
    Data collected during the Phase IV Rollover Research was used to 
evaluate eight of the rollover resistance maneuvers (all except the 
J-Turn with Pulse Braking). For each of these eight maneuvers, 
vehicles were tested in the Nominal Vehicle configuration. For 
maneuvers which we deemed appropriate, testing was also performed 
using the Reduced Rollover Resistance configuration. For the J-Turn 
with Pulse Braking, we decided that we had sufficient data from 
prior testing (Phases II and III of the Rollover Research program) 
to evaluate this maneuver.
    The results of the evaluation for each rollover resistance 
maneuver follows. For each maneuver, a brief description of the 
maneuver is given followed by its scores in each of the four 
evaluation factors. Each evaluation factor score is followed by a 
discussion as to how that particular score was decided upon.

A. NHTSA J-Turn

Maneuver Description

    To perform this maneuver, the programmable steering controller 
input the handwheel commands described by Figure 1.
    The NHTSA J-Turn handwheel angle is eight times the handwheel 
angle that produces a quasi-static 0.3 g lateral acceleration at 50 
mph for each particular test vehicle. The handwheel rate of the 
handwheel ramp was 1000 degrees per second.
    J-Turn tests were performed with two directions of steer, to the 
left and to the right. Vehicle speed was increased in 5 mph 
increments from 35 to 60 mph, unless at least two inches of 
simultaneous two-wheel lift was observed. If such wheel lift was 
detected, entrance speeds were iteratively reduced by 1 mph until it 
was no longer apparent.

Objectivity and Repeatability

    The NHTSA J-Turn is the most objective and repeatable of all of 
the rollover resistance maneuvers. Figure 2 shows the Handwheel 
Angle, Vehicle Speed, Lateral Acceleration, and Roll Angle as 
functions of time for three tests of the Toyota 4Runner with yaw 
stability control enabled that were run at approximately the same 
speed (59.4, 58.1, and 58.6 mph). The Handwheel Angle graph shows 
that, by using the programmable steering controller, the steering 
control input can be precisely replicated from run-to-run (there are 
three traces in this graph). Test drivers can repeatably achieve 
input speeds within +/-2 mph of the target speed. The vehicle speed, 
lateral acceleration and roll angle traces clearly show the very 
high repeatability of this maneuver.
    Data from these runs is typical of our experience with the 
maneuver, with one exception. For runs that are either result in 
two-wheel lift or are very near to the point at which it first 
occurs, the roll angle repeatability becomes much worse. This is

[[Page 62561]]

the case for all rollover resistance maneuvers that induce tip up 
because the vehicle either falls over or it does not. As a result, 
small fluctuations in test performance can lead to large changes in 
roll angle in this situation. This results in a variability of 
approximately +/-2 mph in determining the lowest speed at which two-
wheel lift occurs. As such, roll angle variability at the tip-up 
threshold did not lower the Objectivity and Repeatability rating for 
this maneuver.

Performability

    The NHTSA J-Turn is the easiest of all of the rollover 
resistance maneuvers to perform. Objective and repeatable NHTSA J-
Turn maneuvers can easily be performed using a programmable steering 
controller. Having only one major steering movement maximizes 
maneuver repeatability. The test procedure is well developed. 
Procedures have been developed to adapt the NHTSA J-Turn maneuver to 
the characteristics of the vehicle being tested.

Discriminatory Capability

    None of the vehicles tested had two-wheel lift during NHTSA J-
Turn tests in their Nominal Vehicle configuration. However, all of 
the vehicles except the Ford Escape and the Toyota 4Runner with its 
yaw stability control enabled did have two-wheel lift when tested in 
their Reduced Rollover Resistance configuration. The NHTSA J-Turn is 
not a severe enough maneuver to discriminate between typical, 
current generation, sport utility vehicles loaded with a driver and 
passenger only. However, it was very sensitive to the decrease in 
rollover resistance attributable to a decrease in SSF of 0.05. Also 
the speed at tip-up could discriminate between our individual test 
vehicles when the entire group was loaded to produce a decrease in 
SSF of 0.05. We used a roof load of about 200 lb to reduce the SSF 
by 0.05, but the addition of 5 to 6 passengers causes a similar 
reduction in SSF for typical current generation SUVs, vans and 
pickup trucks.

Realistic Appearance

    Drivers perform NHTSA J-Turns during actual driving on 
cloverleaf entrance/exit ramps and other, essentially constant 
radius, curves that are driven at substantial speeds. This maneuver 
is not given an excellent rating in this category, however, because 
for light vehicles, actual drivers are very unlikely to use the 
large steering magnitudes needed to induce two-wheel lift without 
also applying sustained braking.
    During NHTSA's discussions with the automotive industry, every 
manufacturer stated that they routinely perform J-Turn testing 
during vehicle development. This maneuver has a long history of 
industry use.

B. J-Turn With Pulse Braking

Maneuver Description

    To perform this maneuver, the programmable steering and braking 
controller input the handwheel steering and braking commands as 
shown in Figure 3. Figure 3 also shows a typical vehicle roll rate 
response resulting from the steering input so as to explain the 
timing of the brake pulse. Pulse braking was initiated at the first 
zero crossing (determined by the roll rate being between +1.5 
degrees per second and -1.5 degrees per second) of the roll rate 
after the initiation of steering (i.e., at the time when the maximum 
roll angle occurs).
    The handwheel magnitudes used for the J-Turn with Pulse Braking 
maneuver were always 330 degrees. The handwheel rate of the 
handwheel ramp was 1000 degrees per second.
    The maximum brake pedal force used for the J-Turn with Pulse 
Braking maneuver was 200 pounds. The brake pulse durations ranged 
from 0.25 to 0.55 seconds.
    J-Turn with Pulse Braking tests were performed with two 
directions of steer, to the left and to the right. Vehicle speed was 
increased in 2 mph increments from 36 to 60 mph, unless simultaneous 
two-wheel lift was observed.

Objectivity and Repeatability

    The J-Turn with Pulse Braking is not as objective and repeatable 
as the J-Turn due to the pulse braking. Research has shown that the 
results of this test depend upon the precise timing and magnitude of 
the brake pulse. Therefore, to perform this maneuver with reasonable 
objectivity and repeatability, both tightly controlled steering and 
braking are required. The programmable steering controller needed 
for the J-Turn has now become a programmable steering and braking 
controller with a corresponding increase in testing complexity, 
difficulty, and cost.
    Figure 4 shows the Handwheel Angle, Brake Pedal Force, Lateral 
Acceleration, Longitudinal Acceleration, Roll Angle, and Vehicle 
Speed, as functions of time for two tests of a 1998 Chevrolet 
Tracker (this vehicle did not have either antilock brakes or yaw 
stability control) that were run at approximately the same speed 
(31.1 and 31.3 mph). Unlike the rest of the data presented in this 
section, the J-Turn with Pulse Braking data was collected during the 
summer of 2000 as part of the Phase III-B Rollover research.
    Like the NHTSA J-Turn, due to the use of the programmable 
steering controller, the steering control input was precisely 
replicated from run-to-run. The apparent non-repeatability in the 
steering input (and lateral acceleration and roll angle) is actually 
after the test is over and the driver has retaken control of the 
vehicle.
    Similarly, the Brake Pedal Force graph shows that, by using the 
programmable braking controller, the braking control input can be 
precisely replicated from run-to-run. The precisely overlaid lateral 
acceleration, longitudinal acceleration, roll angle, and vehicle 
speed traces clearly show the very high repeatability achieved for 
these two runs.
    We caution, however, that data from these two runs is not 
typical of our experience with maneuver. In general, we saw somewhat 
more variability in the brake pedal force than is shown in Figure 4. 
Also, as was discussed above for the NHTSA J-Turn, for runs that are 
near the point at which two-wheel lift first occurs, roll angle 
repeatability becomes much worse.

Performability

    The addition of pulse braking substantially reduces the 
performability of this maneuver relative to the NHTSA J-Turn. The 
addition of a programmable braking controller, which is necessary to 
achieve the precise pulse brake timing required for repeatable 
performance, makes this test significantly harder and more costly to 
run. Issues remain as to the brake pulse timing needed to achieve 
worst case rollover performance.
    Through the use of roll rate feedback, the timing of the brake 
pulse can be adapted to the characteristics of the vehicle being 
tested. The magnitude of the steering input can also be adapted from 
vehicle-to-vehicle (although this was not done during the Phase III 
research).

Discriminatory Capability

    The J-Turn with Pulse Braking is a very bad maneuver for 
measuring the rollover resistance of different vehicles. For 
vehicles equipped with antilock braking systems (ABS), it does not 
appear to give any additional information beyond that obtained from 
the NHTSA J-Turn maneuver (unless the ABS is disabled; not a 
realistic situation). For vehicles without ABS, it can be a very 
severe test vehicle provided the timing of the brake pulse is just 
right. If this test were used for NCAP, it would discriminate more 
on the basis of ABS equipment than rollover resistance.

Realistic Appearance

    Drivers could perform J-Turns with Pulse Braking during actual 
driving on cloverleaf entrance/exit ramps and other, essentially 
constant radius, curves that are driven at substantial speeds. 
However, we think that the occurrence of this maneuver is unlikely. 
With the large steering magnitudes needed to induce two-wheel lift, 
we believe it to be far more probable that drivers will apply 
sustained braking (which discourages rather than encourages two-
wheel lift) instead of pulse braking.

C. Fixed Timing Fishhook

Maneuver Description

    To perform this maneuver, the programmable steering controller 
input the handwheel commands described by Figure 5.
    Fixed Timing Fishhook handwheel angle is 6.5 times the handwheel 
angle that produces a quasi-static 0.3 g lateral acceleration at 50 
mph for each particular test vehicle. The commanded dwell (amount of 
time after the first steer for which handwheel position was 
maintained) for the Fixed Timing Fishhook was 0.25 seconds. The 
handwheel rates of the initial steer and countersteer ramps were 720 
degrees per second.
    Fixed Timing Fishhook tests were performed with both initial 
directions of steer, to the left and to the right. Vehicle speed was 
increased in 5 mph increments from 35 to 50 mph, unless at least two 
inches of simultaneous two-wheel lift was observed. If such wheel 
lift was detected, entrance speeds were iteratively reduced by 1 mph 
until it was no longer apparent.

[[Page 62562]]

Objectivity and Repeatability

    The Fixed Timing Fishhook can be performed with excellent 
objectivity and repeatability. Figure 6 shows the Handwheel Angle, 
Vehicle Speed, Lateral Acceleration, and Roll Angle as functions of 
time for three tests of the Chevrolet Blazer that were run at 
approximately the same speed (37.8, 37.8, and 37.3 mph). Data from 
these runs is typical of our experience with this maneuver.
    The vehicle speed and lateral acceleration traces clearly show 
the very high repeatability of this maneuver. The roll angle traces 
show the non-repeatability in roll angle that occurs around the 
point of two wheel lift. All three of these runs had two wheel lift 
approximately three seconds into the test. The amount of two-wheel 
lift was substantially less for one run than for the other two. Near 
the initiation of two-wheel lift, the roll angle becomes 
mathematically unstable because the vehicle either falls over or it 
does not. As was discussed above for the NHTSA J-Turn, this roll 
angle non-repeatability occurs for all maneuvers that generate two-
wheel lift.

Performability

    Objective and repeatable Fixed Timing Fishhook maneuvers can 
easily be performed using a programmable steering controller. The 
test procedure is well developed. Procedures have been developed to 
adapt the steering magnitude used for the Fixed Timing Fishhook 
maneuver for the characteristics of the vehicle being tested.

Discriminatory Capability

    The Fixed Timing Fishhook is excellent maneuver for measuring 
the rollover resistance of different vehicles. The Chevrolet Blazer 
and the Mercedes ML320 (with the stability control both enabled and 
disabled) had two-wheel lift when tested in their Nominal Vehicle 
configuration. All vehicles (with the stability control, if present, 
both enabled and disabled) had two-wheel lift when tested in their 
Reduced Rollover Resistance configuration. (The Mercedes ML320 was 
not tested in its Reduced Rollover Resistance configuration. 
However, we are certain that it would have had two-wheel lift in 
this configuration because it had two-wheel lift in its Nominal 
Vehicle configuration and raising its center of gravity height is 
going to encourage, not prevent, two-wheel lifts.) The maneuver 
initial speed (a severity measure for the Fixed Timing Fishhook) at 
which two-wheel lifts first occurred varied about as expected.
    While the Fixed Timing Fishhook does an excellent job of 
discriminating between vehicles for typical, current generation, 
sport utility vehicles, it will not do as good a job for the entire 
vehicle fleet. It is doubtful that any two-wheel lifts will occur 
during testing of vehicles that have a Static Stability Factors of 
1.2 or greater (e.g., most vehicles that earn three or more stars 
under NHTSA's current rollover rating program). That said, no 
driving maneuver known to NHTSA is expected to cause two-wheel lifts 
for vehicles in the 1.20 SSF range. However, as the name of this 
maneuver implies, the timing of this maneuver does not change from 
vehicle-to-vehicle. This will result in some vehicles not being 
tested with the timing needed to achieve worst case rollover 
performance.

Realistic Appearance

    The Fishhook maneuver's steering input, no matter whether it's 
the Fixed Timing, Roll Rate Feedback, or Nissan variant, 
approximates the steering that a driver might perform in an effort 
to resume traveling in the correct lane of a two lane road after 
dropping two-wheels off of the road. None of the Fishhooks simulate 
the effects of the road-edge drop-off.

D. Roll Rate Feedback Fishhook

Maneuver Description

    This maneuver is performed similarly to the Fixed Timing 
Fishhook except for the timing of the steering reversal. Figure 7 
shows the handwheel steering input, as a function of time, used for 
this maneuver. Note that the magnitude of the steering is identical 
to that of the Fixed Timing Fishhook. However, the steering dwell 
time (amount of time after the first steer for which handwheel 
position was maintained) is no longer kept at 0.25 seconds. Instead, 
this dwell time is varied so as to maximize the severity of the 
maneuver.
    Figure 7 also shows a typical vehicle roll rate response 
resulting from the steering input so as to explain the timing of the 
steering reversal. The steering reversal was initiated at the first 
zero crossing (determined by the roll rate being between +1.5 
degrees per second and -1.5 degrees per second) of the roll rate 
after the initiation of steering (i.e., at the time when the maximum 
roll angle occurs).

Objectivity and Repeatability

    The Roll Rate Feedback Fishhook can be performed with excellent 
objectivity and repeatability. Occasionally, when performing this 
maneuver, the measured roll rate does not return to zero for a 
substantial period of time (1 to 2 seconds) resulting in a greatly 
delayed countersteer and an invalid test. However, this happens 
quite rarely, and it is obvious to the test driver when this delay 
causes the need to repeat the test run. Therefore, from a practical 
point of view, the objectivity and repeatability of this maneuver 
was not different from that of the Fixed Timing Fishhook.
    Figure 8 shows the Handwheel Angle, Vehicle Speed, Lateral 
Acceleration, and Roll Angle as functions of time for three tests of 
the Toyota 4Runner with stability control disabled that were run at 
approximately the same speed (39.9, 40.3, and 39.5 mph). Data from 
these runs is typical of our experience with this maneuver.
    The vehicle speed and lateral acceleration traces show the high 
repeatability of this maneuver. The roll angle traces show the non-
repeatability in roll angle that occurs around the point of two 
wheel lift. As the traces show two of these runs had two wheel lift 
approximately three seconds into the test while one did not. Near 
the initiation of two-wheel lift, the roll angle becomes 
mathematically unstable because the vehicle either falls over or it 
does not. As was discussed above for the NHTSA J-Turn, this roll 
angle non-repeatability occurs for all maneuvers that generate two-
wheel lift.

Performability

    Objective and repeatable Roll Rate Feedback Fishhook maneuvers 
can easily be performed using a programmable steering controller 
equipped to handle roll rate feedback. The test procedure is well 
developed. Procedures have been developed to adapt both the steering 
magnitude and the steering reversal timing used for the Roll Rate 
Feedback Fishhook maneuver for the characteristics of the vehicle 
being tested.

Discriminatory Capability

    The Roll Rate Feedback Fishhook is excellent maneuver for 
measuring the rollover resistance of different vehicles. The 
Chevrolet Blazer and the Mercedes ML320 (with the stability control 
both enabled and disabled) had two-wheel lift when tested in their 
Nominal Vehicle configuration. All vehicles (with the stability 
control, if present, both enabled and disabled) had two-wheel lift 
when tested in their Reduced Rollover Resistance configuration. (The 
Mercedes ML320 was not tested in its Reduced Rollover Resistance 
configuration. However, we are certain that it would have had two-
wheel lift in this configuration because it had two-wheel lift in 
its Nominal Vehicle configuration and raising its center of gravity 
height is going to encourage, not prevent, two-wheel lifts.) The 
maneuver initial speed (a severity measure for the Roll Rate 
Feedback Fishhook) at which two-wheel lifts first occurred varied 
about as expected.
    While the Roll Rate Feedback Fishhook does an excellent job of 
discriminating between vehicles for typical, current generation, 
sport utility vehicles, as explained above for the Fixed Timing 
Fishhook, it will not do as good a job for the entire vehicle fleet.

Realistic Appearance

    See the Fixed Timing Fishhook maneuver Realistic Appearance 
discussion.

E. Nissan Fishhook

Maneuver Description

    The Nissan Fishhook adds to the Fixed Timing Fishhook a 
procedure for adjusting the steering reversal timings to the vehicle 
being tested. This adjustment process has the same goal as the 
adjustment process used for the Roll Rate Feedback Fishhook, i.e., 
to test each vehicle with the steering reversal timing required for 
the vehicle to have its worst case rollover performance. While the 
Roll Rate Feedback Fishhook maneuver accomplishes this by using roll 
rate feedback resulting in only one test run per initial maneuver 
speed, the Nissan Fishhook uses an iterative procedure to determine 
the timing.
    First, a J-Turn is performed followed by a series of Fixed 
Timing Fishhooks (with different timings). Typically, two to four 
runs will be made for each initial maneuver speed. The procedure 
used to determine the final timing is too complex to give here but 
is fully described in the NHTSA technical report ``Another 
Experimental Examination of Selected Maneuvers That May Induce On-
Road Untripped, Light Vehicle Rollover--Phase IV of NHTSA's Light 
Vehicle Rollover Research Program.'' However, the final dwell times 
(the length of the pause between

[[Page 62563]]

completion of the first steer and the initiation of the 
countersteer, shown as time, T1, in Figures 5 and 7) 
generated were close to those of the Roll Rate Feedback Fishhook.

Objectivity and Repeatability

    The Nissan Fishhook was performed with good objectivity and 
repeatability. By using the programmable steering machine, handwheel 
inputs were precisely executed, and able to be replicated from run-
to-run. Test drivers were able to achieve maneuver entrance speeds 
an average of +/- 0.9 mph from the desired target speed.
    Note that the Objectivity and Repeatability rating of the Nissan 
Fishhook maneuver was reduced from that assigned to the Fixed Timing 
Fishhook. This was due to roll rate zero-crossing variability 
observed in response to the step steer used in determining the 
timing of the maneuver. The Nissan Fishhook requires accurate 
determination of the third roll rate zero-crossing following input 
of the step steer. This is because zero crossing variability 
directly affects what dwell time duration will ultimately satisfy 
Nissan's requirements. If the third roll rate zero crossing is 
delayed (e.g., due to an anomalous response produced during the step 
steer) an inappropriate dwell time extension will result.
    Generally speaking the vehicle speed, lateral acceleration, and 
roll angle data observed during Nissan Fishhook tests were highly 
repeatable. However, as was discussed above for the NHTSA J-Turn, 
for runs that are near the point at which two-wheel lift first 
occurs, roll angle repeatability becomes much worse.

Performability

    The Nissan Fishhook has a well worked out test procedure. It 
does not have a procedure to adapt the steering magnitude for the 
characteristics of the vehicle being tested although this could 
probably be added to the current test procedure without difficulty. 
The steering reversal timings used for the Nissan Fishhook maneuver 
are adjusted for the vehicle being tested.
    The primary advantage of the Nissan Fishhook over the Roll Rate 
Feedback Fishhook is that by not using roll rate feedback you avoid 
the occasional need for repetitions caused by anomalies in the roll 
rate measurement and the extra expense of a programmable steering 
controller that can handle roll rate feedback.
    The primary disadvantage of the Nissan Fishhook over the Roll 
Rate Feedback Fishhook is that the Nissan procedure requires three 
to four times as many test runs than does the Roll Rate Feedback 
Fishhook. As a result, greater tire wear occurs which has been shown 
to affect the results of Fishhook testing. It also increases testing 
time and costs.
    The Nissan Fishhook, as proposed by Nissan, uses a very high 
steering wheel angle rate (1,080 degrees per second). Our 
programmable steering controller has some difficulty with such a 
high rate. Changing to the lower steering wheel angle rate (720 
degrees per second) used for the Fixed Timing and Roll Rate Feedback 
Fishhooks would probably only minimally affect maneuver results. 
Reduction of the magnitude of the countersteer to the amount used 
for the Fixed Timing and Roll Rate Feedback Fishhooks should 
slightly increase maneuver severity. Our experience has been that 
the large countersteer used by the Nissan Fishhook slows the vehicle 
down more rapidly, decreasing maneuver severity.

Discriminatory Capability

    The Nissan Fishhook was an excellent maneuver for measuring the 
rollover resistance of different vehicles. The dynamic rollover 
propensity of only the Chevrolet Blazer and Ford Escape was assessed 
using the Nissan Fishhook, and all tests were performed in the 
Nominal Load condition. Two-wheel lift was produced during tests 
performed with the Chevrolet Blazer.
    The results obtained with Nissan's methodology were in good 
agreement with those produced during Fixed Timing and Roll Rate 
Feedback Fishhook testing. That said, the entrance speed of the 
Nissan Fishhook test for which two-wheel lift occurred was 
approximately 6 mph higher than that of either of the other 
Fishhooks.
    While the Nissan Fishhook does an excellent job of 
discriminating between vehicles for typical, current generation, 
sport utility vehicles, as explained above for the Fixed Timing 
Fishhook, it will not do as good a job for the entire vehicle fleet.

Realistic Appearance

    See the Fixed Timing Fishhook maneuver Realistic Appearance 
discussion.

F. Ford Path Corrected Limit Lane Change

Maneuver Description

    Ford's procedure is a path specific method composed of an array 
of double lane change courses and a data-normalizing technique used 
to address driver variability. It results in a metric based on 
dynamic weight transfer.
    Ford believes that a path specific method, wherein test vehicles 
navigate a standard set of paths, is preferable to maneuvers that 
employ open loop steering. Ford states that a specific path provides 
a basis for comparison of the resulting metrics. By ensuring that 
all vehicles experience the same magnitude of lateral acceleration, 
the effects of surface variability on test results are negated. Ford 
suggests that 0.7g is an appropriate target for lateral 
acceleration. Its suite of specific paths exercises vehicles through 
a range of frequencies and amplitudes at the proposed target lateral 
acceleration.
    Three markers (short traffic cones) placed on the pavement 
delimit the path's lane change apertures with the middle marker 
representing an avoidance obstacle. Varying the position of the 
obstacle laterally and longitudinally (with corresponding 
longitudinal repositioning of the exit marker) produces an array of 
steering input amplitudes and frequencies. A test vehicle approaches 
the course at 45 mph. The driver releases the throttle at the course 
entrance and coasts while steering through the course. Figure 9 
portrays the suite of double lane change paths to the left used for 
this maneuver. A similar suite of double lane change paths to the 
right is also tested.
    Ford addresses driver and test surface variability with the Path 
Corrected Limit Lane Change (PCLLC) normalizing technique. The 
mathematical procedure is executed during post-processing of test 
data and is used ``to normalize the varying results of physical 
tests to a uniformly based metric.'' \8\ The results indicate how 
the various vehicles would perform had they followed the exact same 
path.
---------------------------------------------------------------------------

    \8\ Copied from Page 4 of Ford Motor Company's submission of 
August 16, 2001 in response to NHTSA notice Consumer Information 
Regulations; Rollover Resistance, Docket No. NHTSA-2001-9663 (66 
Fed. Reg. 35179-35193, July 3, 2001). Referred to subsequently as 
Ford's 2001 Rollover Comments.
---------------------------------------------------------------------------

    Ford states, ``Post-test computer aided normalizing techniques 
have been sufficiently developed that we have high confidence in 
their applicability to this issue. The PCLLC technique uses physical 
test data to define a vehicle-specific transfer function. These 
functions are then used to normalize metric values, such as dynamic 
weight transfer, to a specific vehicle path common to all vehicles 
evaluated. The data suggests that use of these normalizing 
techniques eliminates concerns that may arise because of test driver 
variability and by subjecting the vehicles to the same path, help to 
eliminate track surface variability, thus providing the only dynamic 
test method and metric unaffected by these sources of variability. 
We [Ford] believe this is a technically sound method to achieve 
reliable, repeatable and objectively stated results that will 
improve upon SSF based star ratings.'' \9\
---------------------------------------------------------------------------

    \9\ Copied from Page 5 of Ford's 2001 Rollover Comments.
---------------------------------------------------------------------------

    Ford reports that an analysis of the results of the normalizing 
technique shows that, despite varying styles of driving indicated by 
measurement of peak steering wheel angles and rates, the differences 
in the mean values of Dynamic Weight Transfer Metric (DWTM) among 
four test drivers driving the same vehicle are not statistically 
significant.
    Ford has allowed NHTSA to evaluate the PCLLC technique under a 
confidentiality agreement. Thus, details of the procedure are not 
available for this notice. NHTSA expects that Ford would make the 
details of the procedure public if it proposed that Ford's test 
protocol as the dynamic rollover test mandated by the TREAD Act.
    Ford proposes a rollover resistance metric based on dynamic 
lateral weight transfer. Ford defines dynamic weight transfer as the 
``percentage of weight that is removed from a vehicle's two inside 
tires during a severe lane change.'' \10\ The Dynamic Weight 
Transfer Metric (DWTM) is the maximum percent of dynamic weight 
transfer averaged over a minimum specific time. Ford recommends a 
minimum specific time of 400 milliseconds.
---------------------------------------------------------------------------

    \10\ Copied from Page 1 of a Ford Motor Company memorandum 
titled ``Dynamic Weight Transfer Results from Path-Corrected Limit 
Lane Change Joint Testing with NHTSA.'' Referred to subsequently as 
Ford's PCLLC Report.
---------------------------------------------------------------------------

Objectivity and Repeatability

    The Path Corrected Limit Lane Change maneuver consists of a 
series of closed-loop

[[Page 62564]]

(test driver generated steering inputs) double lane changes. Data 
collected during these double lane changes is then processed ``to 
assure that all vehicles follow the same path and are subject to the 
same acceleration demands.'' \11\ For reasons that are discussed 
below in the Discriminatory Capability subsection for this maneuver, 
Ford Motor Company (Ford) recommends the calculation of a Dynamic 
Weight Transfer Metric (DWTM) at 0.7 g lateral acceleration for this 
maneuver. ``Because different vehicle designs will react differently 
to forces of varying magnitude and time duration, a suite of various 
paths should be analyzed in determining an overall dynamic weight 
transfer metric (DWTM), based on values of maximum weight 
transfer.'' \12\ Note that higher values of DWTM are worse than 
lower values.
---------------------------------------------------------------------------

    \11\ Copied from Page 3 of Ford's 2001 Rollover Comments.
    \12\ Copied from Page 1 of Appendix III of Ford's 2001 Rollover 
Comments.
---------------------------------------------------------------------------

    Ford has performed a substantial amount of Path Corrected Limit 
Lane Change maneuver testing. While we do not have access to this 
data, Ford has summarized this data as follows: ``Ford's overall 
standard deviation for the DWT metric is 4.4 from multiple tests 
made on a variety of vehicles with a variety of drivers, over a time 
span of several months and using a new set of tires fitted for each 
test.'' \13\ To understand the meaning of this standard deviation, 
we need to know the expected range of the dynamic weight transfer 
metric.
---------------------------------------------------------------------------

    \13\ Copied from Page 2 of Ford's PCLLC Report.
---------------------------------------------------------------------------

    The most basic way to estimate this range is to approximate the 
vehicle as a rigid block in a steady state curve at 0.7g lateral 
acceleration. Using this approximation, the expected range of DWTM 
values is from 46.7 percent (corresponding to a vehicle with a 
static stability factor of 1.50) to 70.0 percent (corresponding to a 
static stability factor of 1.00).
    Real vehicles, of course, are not rigid bodies. They have 
compliant suspensions and tires. This increases the DWTM values from 
those of rigid vehicles. Based on NHTSA's Tilt Table data and 
assumptions about the difference between tilt table and flat track 
testing, we estimate an addition of about 4% to 8% DWTM to the rigid 
body calculations as a result of quasi-static body roll at 0.7 g. 
Applying the average addition of 6% DWTM makes the expected range of 
DWTM approximately 53 percent to 76 percent. Therefore, Ford's 
standard deviation of 4.4 for DWTM is 19 percent of the entire 
expected range of DWTM values.
    Another way to understand the meaning of this standard deviation 
is to analyze the values of DWTM that were measured by Ford and 
NHTSA during joint testing of the Phase IV rollover test vehicles. 
Table 1 lists these values, along with the number of observations 
that these values are based on, the calculated dynamic weight 
transfer at 0.7 g lateral acceleration based on a rigid body model, 
and the difference between these two dynamic weight transfer values.
    Consider the Chevrolet Blazer and the Ford Escape. The Blazer 
receives one star; the lowest rating a for sport utility vehicle 
from NHTSA's current rollover rating system (which is based on 
Static Stability Factor). The Ford Escape has an SSF at the high end 
of the three star range; one of the higher ratings for sport utility 
vehicles. Most sport utility vehicles have Static Stability Factors 
between these two vehicles.

                                             Table 1.--Measured and Calculated Dynamic Weight Transfers \14\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                               2001                       1999  Mercedes   1999 Mercedes    2001 Toyota    2001  Toyota
                                                             Chevrolet      2001  Ford    ML320 with ESC  ML320 with ESC   4Runner with    4Runner with
                                                              Blazer          Escape            on              off           ESC on          ESC off
--------------------------------------------------------------------------------------------------------------------------------------------------------
PCLLC Measured DWTM (in percent)........................            70.3            62.9            74.8            68.2            66.2            66.6
Number of Observations..................................               4               4               4              10               4               4
Steady State Rigid Body WT Calculated from SSF (in                  67.3            55.6            60.9            60.9            63.1            63.1
 percent)...............................................
Difference (in percent).................................             3.0             7.3            13.9             7.3             3.1             3.5
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Now compare the DWTM values of these vehicles as measured using 
the Path Corrected Limit Lane Change and shown in Table 1. For the 
Chevrolet Blazer the measured DWTM value is 70.3. However, based on 
Ford's standard deviation and the number of samples, we have 95 
percent confidence that the DWTM for this vehicle is between 66.0 
and 74.6. Similarly, for the Ford Escape we have 95 percent 
confidence that the DWTM is between 58.6 and 67.2. Note that these 
ranges overlap. However, the difference between these two vehicles 
DWTM values is statistically significant (although just barely 
having a t-value of 2.38 versus the critical t-value of 2.37).
---------------------------------------------------------------------------

    \14\ Values taken from Page 2 of Ford's PCLLC Report.
---------------------------------------------------------------------------

    A measurement standard deviation for which the difference 
between a sport utility vehicle with high rollover resistance and 
one with low rollover resistance is only marginally statistically 
significant is too large for generating vehicle ratings.
    Table 1 shows another problem with the measured DWTM values. 
When we estimated the expected range of DWTM as 53 percent to 76 
over the entire range of vehicles from SUVs to sport sedans, we 
considered only the quasi-static load transfer due to the vehicle's 
rigid body geometry (SSF) and to its steady state body roll. We 
neglected the dynamic weight transfer that occurs as a result of 
body roll acceleration in an abrupt maneuver. However, when the 
calculated steady state, rigid body weight transfer in Table 1 is 
subtracted from the measured DWTM, the difference is no more than 
that expected for the steady state body roll in all but one case. It 
would appear that the Dynamic Weight Transfer Metric produced by 
PCLLC generally measures quasi-static rather than dynamic weight 
transfer. Quasi-static weight transfer is what occurs when a vehicle 
is driven in a circle at a constant speed without abrupt changes in 
speed or direction.
    The exception is the DWTM measurement for the Mercedes ML320 
with yaw stability control enabled. While the DTWM for this vehicle 
with yaw stability control disabled is no more than the expected 
quasi-static load transfer, the DTWM increases by 6.6 percent when 
the yaw stability control is enabled. The difference between these 
two values is statistically significant and would seem to represent 
a dynamic weight transfer component missing in the other PCLLC 
results in Table 1. However, it is hard to understand why stability 
control should lower the rollover resistance of this vehicle. 
Fishhook testing indicates just the opposite; that yaw stability 
control increases the rollover resistance of this vehicle. 
Therefore, we believe that the measured DWTM value for the Mercedes 
ML320 with yaw stability control enabled is incorrect.
    In conclusion, the objectivity and repeatability of the Path 
Corrected Limit Lane Change has not yet attained an acceptable level 
for rating the rollover resistance of vehicles. Future improvements 
to the objectivity and repeatability of this maneuver can probably 
be made, but there are other tests with more potential for making 
highly objective and repeatable measurements of quasi-static weight 
transfer.

Performability

    The procedure for performing this test is straight-forward. 
However, substantial additional instrumentation, over and above that 
required to perform a Fishhook maneuver, are required. The costs and 
additional testing time associated with this equipment is expected 
to exceed the costs and additional testing time saved by not having 
to use a programmable steering controller. An additional test, on a 
tire testing machine, is also required.
    Ford has ideas for reducing the additional instrumentation 
required for the Path Corrected Limit Lane Change procedure. 
However, this is a future enhancement and cannot be evaluated at 
this time.

[[Page 62565]]

    Since Ford processed the data collected during our testing, we 
are unable to say how difficult the data processing is to perform. 
However, with experience and the correct software it is expected to 
approximately equal the effort required to process data from a 
Fishhook or J-Turn test. There may be issues in making Ford's data 
processing software publicly available.
    Due to the use of a suite of paths for calculating DWTM values, 
the Path Corrected Limit Lane Change procedure should adequately 
adapt to differing vehicle characteristics.
    We also have concerns about determining dynamic weight transfer 
as an average value over a 400 millisecond window. The use of this 
broad a window may filter out dynamic effects that may be important 
in actual vehicle rollovers.

Discriminatory Capability

    No two-wheel lifts occurred during Path Corrected Limit Lane 
Change testing for any of the test vehicles. However, unlike the J-
Turn and Fishhook maneuvers, the occurrence/non-occurrence of two-
wheel lift is not used as a measure of vehicle performance for this 
maneuver. The DWTM measured in PCLLC testing produces a continuous 
measure of rollover resistance that, like SSF, that allows 
discrimination even among vehicles that are not susceptible to on-
road untripped rollover.
    Ford recommends the calculation of a Dynamic Weight Transfer 
Metric (DWTM) at 0.7 g lateral acceleration as a measure of vehicle 
performance for this maneuver. Data collected during testing is 
processed to remove driver effects by having all vehicles always 
follow the same specified paths and be subject to the same 
acceleration demands. ``Because different vehicle designs will react 
differently to forces of varying magnitude and time duration, a 
suite of various paths should be analyzed in determining an overall 
dynamic weight transfer metric (DWTM), based on values of maximum 
weight transfer.'' \15\ Ford's reasons for making this 
recommendation are as follows:
---------------------------------------------------------------------------

    \15\ Copied from Page 1 of Appendix III of Ford's 2001 Rollover 
Comments.
---------------------------------------------------------------------------

    ``For a given velocity change, various vehicle related factors 
determine the magnitude of dynamic weight transfer for events that 
can lead to both tripped or un-tripped rollover. Obviously, the 
higher the center-of-gravity, the greater the transfer for a given 
travel velocity change. Similarly, the smaller the track width, the 
greater the transfer. As is well known, many factors other than 
these two affect dynamic weight transfer and it is because of this 
that SSF is a narrow and inadequate concept. For example, if 
deflections occur in suspensions, tires, or other parts that control 
overall body movements such as active stabilizer bars or 
electronically controlled shock absorbers, when dynamic forces are 
applied, the magnitude of the dynamic weight transfer will also 
change. Inertial values, yaw plane motions, vertical motions and 
pitch plane motions that arise because of a vehicle's design details 
or features can affect force and moment balances and can change 
vehicle configurations to affect the magnitude of the dynamic weight 
transfer. It is a directionally correct proposition that the greater 
the magnitude of the dynamic weight transfer in a given high 
severity event, the less margin, reserve, or resistance remains to a 
rollover occurring. Based on these principles, Ford believes that 
dynamic weight transfer is a metric of value in a dynamic test.'' 
``Our preliminary work has confirmed that this metric will 
discriminate among specific vehicles within a class and between 
classes of vehicles. We submit that DWTM is a more reliable metric 
than SSF alone.'' \16\
---------------------------------------------------------------------------

    \16\ Copied from Pages 5 and 6 of Ford's 2001 Rollover Comments.
---------------------------------------------------------------------------

    DWTM has the theoretical advantage over SSF of including load 
transfer due to quasi-static body roll and true dynamic load 
transfer due to body roll accelerations, but its measurement by the 
PCLLC method seems to be lacking the dynamic load transfer 
component. The PCLLC test also is not able to test for the effect of 
yaw stability control. In its comment to the docket of the last 
notice, Ford suggested that the same 0.7g lane change maneuvers and 
DTWM could be implemented directly with an advanced path following 
robot rather than with the PCLLC method, but it cautioned that the 
test would not evaluate the effect of yaw stability control. In 
light of this comment, it is not surprising that the PCLLC test 
measured no effect of yaw stability control of Toyota 4Runner, but 
it remains troubling that it measured a significant loss of rollover 
resistance for yaw stability control of the Mercedes ML320 contrary 
to its effect measured in other rollover maneuver tests.
    As discussed above, we do not believe that dynamic weight 
transfer values determined using this maneuver have, so far, 
attained an acceptable level of repeatability. We are also concerned 
about not exercising vehicles to the limits of their performance. By 
not taking vehicles to their limits, some important limit 
performance problems could be overlooked.

Realistic Appearance

    In general, double lane change maneuvers have an excellent 
appearance of reality. These are the emergency obstacle avoidance 
maneuvers that people think of first when they consider untripped 
rollover. While the Path Corrected Limit Lane Change trajectories 
are idealized, rather than actual, this distinction would likely not 
be noticed by consumers.

G. ISO 3888 Part 2 Double Lane Change

Maneuver Description

    To perform ISO 3888 Part 2 Double Lane Change testing, the 
vehicle was driven through the course shown in Figure 10. The driver 
released the throttle 6.6 ft (2.0 m) from the entrance of the first 
lane. No throttle input or brake application occurred during the 
remainder of maneuver.
    Drivers iteratively increased maneuver entrance speed from 
approximately 35 mph in 1 mph increments. The iteration continued 
until valid tests could no longer be performed (lane position could 
not be maintained without striking cones). Each driver was required 
to perform three valid runs at their maximum speed. This was to 
assess input and output variability for tests performed by the same 
driver with the same entrance speed.
    The manner in which the 1 mph iterations were implemented was 
somewhat driver-dependent. Some drivers preferred to increase speed 
until they could no longer achieve a valid test. Once this threshold 
was reached, the driver would reduce speed slightly and perform 
three valid tests. Other drivers would perform three valid tests at 
one speed before proceeding to the next iteration. Both methods 
produced similar results.
    So as to examine driver-to-driver differences, during the Phase 
IV research, this maneuver was performed for each vehicle by three 
drivers. To reduce any confounding effect tire wear may have on ISO 
3888 Part 2 Double Lane Change test results, a new tire set was 
installed on each vehicle, for each driver.

Objectivity and Repeatability

    Since steering inputs for the ISO 3888 Part 2 Double Lane Change 
maneuver are generated by the test driver, vehicle performance in 
this maneuver depends upon the skill of the test driver, the 
steering strategy used by the test driver, plus random run-to-run 
fluctuations.
    The ISO 3888 Part 2 Double Lane Change maneuver attempts to 
minimize this variability through the use of an in-between lane of 
substantial length and very tight entry, exit, and in-between lanes, 
thereby minimizing a driver's steering options for getting through 
the course without striking delineating cones.
    Figure 11 shows the range of handwheel steering angles used by 
three different test drivers while performing this maneuver multiple 
times while Figure 12 shows the range of handwheel steering angles 
used by these drivers at selected times during this maneuver. As 
these figures show, there are both substantial driver-to-driver 
differences and substantial within driver run-to-run differences in 
the steering inputs. These differences tend to increase as the 
maneuver progresses.
    Arguably, the differences in steering inputs shown in Figure 11 
and 12 do not really matter for the purposes of determining Rollover 
Resistance Ratings. What really matters are driver-to-driver 
differences in vehicle outputs, specifically the vehicle rating 
metrics.
    The rating metric suggested by the Daimler-Chrysler Corporation 
is the maximum entry speed into the test course at which a driver 
successfully achieved a ``clean'' run. (A ``clean'' run is one 
during which none of the cones delineating the course were struck.)
    Table 2 shows the maximum achievable ``clean'' run speeds for 
three test drivers for the Nominal Vehicle configuration for each of 
the Phase IV rollover test vehicles. (While each vehicle was tested 
by three drivers, four drivers actually participated in this 
testing.) Note that higher values of this metric indicate a better 
performing vehicle.

[[Page 62566]]



          Table 2.--Maximum Achievable ``Clean'' Run Speeds for the ISO 3888 Part 2 Double Lane Change Maneuver--Nominal Vehicle Configuration
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                           1999 Mercedes   1999 Mercedes    2001 Toyota     2001 Toyota
                       Test driver                        2001 Chevrolet     2001 Ford    ML320 with ESC  ML320 with ESC   4Runner with    4Runner with
                                                           Blazer (mph)    Escape (mph)      on (mph)        off (mph)     ESC on (mph)    ESC off (mph)
--------------------------------------------------------------------------------------------------------------------------------------------------------
GF/RS...................................................            39.0            36.9            38.0            37.2            37.6            35.9
LJ......................................................            40.0            36.6            37.0            36.7            36.7            35.3
RL......................................................            41.0            38.0            36.8            37.8            35.8            37.0
Range...................................................             2.0             1.4             1.2             1.1             1.8             1.7
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Table 3 shows a rank ordering of the Phase IV rollover test 
vehicles based on the maximum ``clean'' run speeds achieved by the 
test drivers. Note that 1 is the best rank and 6 the worst.

    Table 3.--Vehicle Rankings Based on Maximum Achievable ``Clean'' Run Speeds for the ISO 3888 Part 2 Double Lane Change Maneuver--Nominal Vehicle
                                                                      Configuration
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                           1999 Mercedes   1999 Mercedes    2001 Toyota     2001 Toyota
                       Test driver                        2001 Chevrolet     2001 Ford    ML320 with ESC  ML320 with ESC   4Runner with    4Runner with
                                                              Blazer          Escape            on              off           ESC on          ESC off
--------------------------------------------------------------------------------------------------------------------------------------------------------
GF/RS...................................................               1               5               2               4               3               6
LJ......................................................               1               5               2               3               3               6
RL......................................................               1               2               5               3               6               4
--------------------------------------------------------------------------------------------------------------------------------------------------------

    As Table 2 shows, for the drivers used, the range of maximum 
achievable ``clean'' run entry speeds varied from 1.2 mph for the 
1999 Mercedes ML320 with yaw stability control enabled to 2.0 mph 
for the 2001 Chevrolet Blazer. The average range was 1.5 mph. While 
these may seem like small ranges, the entire best-to-worst range in 
Table 2 is only 5.7 mph. Since we tested a fairly broad range of 
sport utility vehicles during the Phase IV research, the maximum 
achievable ``clean'' run speeds for most sport utility vehicles are 
expected to be in this 5.7 mph range. Therefore, driver-to driver 
variability averages 27 percent of the range of the rating metric 
and can be as much as 35 percent.
    The problem caused by driver-to-driver variability combined with 
the small range of metric values is clearly shown by Table 3. While 
the Chevrolet Blazer attained the best ranking from all three test 
drivers, the ranking for the Mercedes ML320 with yaw stability 
control enabled varied from second best to second worst.
    Driver skills and abilities vary with time. Although we did not 
do such testing, if we retested the Phase IV rollover test vehicles 
with the same test drivers performing the ISO 3888 Part 2 Double 
Lane Change maneuver we anticipate that our results would not 
exactly match those shown in Tables 2 and 3. Since we have such a 
small range for the rating metric day-to-day (or even hour-to-hour) 
changes in test driver performance would probably change the maximum 
achievable ``clean'' run entry speeds by a substantial percentage of 
the overall range.
    Due to the problems associated with driver-to-driver variability 
and run-to-run for the same driver variability, the objectivity and 
repeatability of this maneuver is poor.

Performability

    The procedure for performing this test is straight-forward. 
However, as discussed above, this maneuver has objectivity and 
repeatability issues. Resolving these issues adds difficulty and 
complexity to performing these tests.
    For example, one possibility for improving objectivity and 
repeatability is to use multiple drivers to perform the testing 
(three drivers were used during the Phase IV testing). While this 
should help, there are still potential problems. One exceptionally 
skilled test driver could generate very good performance metrics for 
a mediocre vehicle. If this exceptionally skilled driver did not 
test some other vehicle, that vehicle's performance metrics might, 
incorrectly, be lower than they should be. Therefore, in addition to 
using multiple drivers, procedures would need to be developed to 
ensure that every vehicle is tested by drivers of approximately 
equal skill.
    The ISO 3888 Part 2 Double Lane Change test procedure includes 
adjustments to lane width and lane change gate length for differing 
vehicle sizes. These should adequately adapt this maneuver for 
differing vehicle characteristics.

Discriminatory Capability

    No two-wheel lifts occurred during any ``clean'' run of ISO 3888 
Part 2 Double Lane Change testing for any of the test vehicles. (A 
``clean'' run is one during which none of the cones delineating the 
course were struck.) While some two-wheel lifts did occur during 
runs that were not ``clean'', these should not be considered for the 
determination of our rollover resistance ratings. The reason is that 
when a run is not ``clean'', there is no way to determine whether 
the vehicle comes close to following the test course. For example, a 
driver could perform a fishhook maneuver or simply drive straight 
through. Either case would simply be recorded as not a ``clean'' 
run.
    Unlike the J-Turn and Fishhook maneuvers, the occurrence/non-
occurrence of two-wheel lift cannot be used as a measure of vehicle 
performance for this maneuver because two-wheel lifts during a clean 
run appear very unlikely for any NCAP vehicle. The rating metric 
suggested by the Daimler-Chrysler Corporation (Daimler) is the 
maximum entry speed into the test course at which a driver 
successfully achieved a ``clean'' run.
    Table 4 shows the maximum achievable ``clean'' run speeds 
attained by any of the test drivers for both the Nominal Vehicle and 
Reduced Rollover Resistance configuration for each of the Phase IV 
rollover test vehicles. Note that higher values of this metric 
indicate a better performing vehicle.
    The Reduced Rollover Resistance configuration vehicles have had 
weights placed on the roof so as to raise the center of gravity 
height. Their Static Stability Factors have been reduced by 0.05. A 
0.05 reduction in SSF equates, for sport utility vehicles, to 
approximately a one star reduction in the vehicle's rollover 
resistance rating. As was previously stated, NHTSA believes that a 
one star reduction in the rollover resistance rating should make a 
vehicle substantially easier to rollover. Maneuvers with good 
discriminatory capability should measure substantially worse 
performance for Reduced Rollover Resistance the configuration than 
for the Nominal Vehicle configuration.

[[Page 62567]]



    Table 4.--Maximum Achievable ``Clean'' Run Speeds by Any Driver for the ISO 3888 Part 2 Double Lane Change Maneuver--Nominal Vehicle and Reduced
                                                           Rollover Resistance Configurations
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                           1999 Mercedes   1999 Mercedes    2001 Toyota     2001 Toyota
                       Test driver                        2001 Chevrolet     2001 Ford    ML320 with ESC  ML320 with ESC   4Runner with    4Runner with
                                                           Blazer (mph)    Escape (mph)      on (mph)        off (mph)     ESC on (mph)    ESC off (mph)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Nominal Vehicle Configuration...........................            41.0            38.0            38.0            38.9            37.6            37.0
Reduced Rollover Resistance Configuration...............            39.0            37.3            37.4            37.1            39.3            38.0
Difference..............................................             2.0             0.7             0.6             1.8            -1.7            -1.0
--------------------------------------------------------------------------------------------------------------------------------------------------------

    This expected substantial change in rollover resistance ratings 
is not seen for the ISO3888 Part 2 Double Lane Change maneuver. For 
three of the vehicles the maximum achievable ``clean'' run speeds 
attained by any of the test drivers in the Reduced Rollover 
Resistance configuration vehicles did decrease slightly compared to 
the Nominal Configuration vehicles while for the 2001 Toyota 4Runner 
they increased slightly. The average change was only 0.4 mph, far 
less than the average driver-to-driver variability of 1.5 mph.
    The expected substantial change in rollover resistance 
measurement was not observed for the ISO3888 Part 2 Double Lane 
Change maneuver apparently because the sensitivity of the test to 
handling properties is predominant compared to its sensitivity to 
rollover resistance. Placing weight on a vehicle's roof raises its 
center of gravity height which reduces its rollover resistance. 
However, doing this also increases a vehicle's mass and roll moment 
of inertia, resulting in changes to a vehicle's handling that are 
not well understood. Since handling and rollover resistance are 
inextricably intertwined in the rating produced by this maneuver, 
the rating generated can improve even though the rollover resistance 
of a vehicle is getting worse.
    Results from both J-Turn and Fishhook testing are, of course, 
also influenced by the handling characteristics of the vehicle. 
However, handling has less of a chance to dominate these maneuvers 
because they involve fewer major steering movements (one for a J-
Turn, two for a Fishhook, and three for a Double Lane Change).
    The above reasoning also explains an apparent anomaly in Table 
3. In this table, the Chevrolet Blazer has the best ranking of any 
of the vehicles. However, based on its one star rating and 
performance in the NHTSA J-Turn and Fishhooks, we believe it to have 
the lowest rollover resistance of any of the Phase IV rollover test 
vehicles. The apparent contradiction is resolved once we realize 
that the ISO3888 Part 2 Double Lane Change maneuver measures mostly 
the handling rather than rollover resistance of vehicles.

Realistic Appearance

    In general, double lane change maneuvers have an excellent 
appearance of reality. These are the emergency obstacle avoidance 
maneuvers that people think of first when they consider untripped 
rollover.

H. Consumers Union Short Course Double Lane Change

Maneuver Description

    To perform Consumers Union Short Course Double Lane Change 
testing, the vehicle was driven through the course shown in Figure 
13. As the vehicle approached the course entrance, the driver 
released the throttle so as to achieve a desired target speed as the 
vehicle passed over a timing strip 35 feet from the entrance of the 
first lane. Otherwise, the procedure for this maneuver was identical 
to that used for the ISO 3888 Part 2 Double Lane Change testing.

Objectivity and Repeatability

    Since steering inputs for the Consumers Union Short Course 
Double Lane Change maneuver are generated by the test driver, 
vehicle performance in this maneuver depends upon the skill of the 
test driver, the steering strategy used by the test driver, plus 
random run-to-run fluctuations.
    Figure 14 shows the range of handwheel steering angles used by 
three different test drivers while performing this maneuver multiple 
times while Figure 15 shows the range of handwheel steering angles 
used by these drivers at selected times during this maneuver. As 
these figures show, there are both substantial driver-to-driver 
differences and substantial within driver run-to-run differences in 
the steering inputs. These differences tend to increase as the 
maneuver progresses.
    Arguably, the differences in steering inputs shown in Figures 14 
and 15 do not really matter for the purposes of determining Rollover 
Resistance Ratings. What really matters are driver-to-driver 
differences in vehicle outputs, specifically the vehicle rating 
metrics.
    The rating metric used by NHTSA is the maximum entry speed into 
the test course at which a driver successfully achieved a ``clean'' 
run. (A ``clean'' run is one during which none of the cones 
delineating the course were struck.) Note that this is not the 
rating metric used by Consumers Union for this maneuver; Consumers 
Union performs subjective rating of the emergency handling 
capability of vehicles with vehicles that have large amounts of two-
wheel lift in this maneuver receiving an ``unacceptable'' safety 
rating.
    Table 5 shows the maximum achievable ``clean'' run speeds for 
three test drivers for the Nominal Vehicle configuration for the 
Phase IV rollover test vehicles. Note that higher values of this 
metric indicate a better performing vehicle.

    Table 5.--Maximum Achievable ``Clean'' Run Speeds for the Consumers Union Short Course Double Lane Change Maneuver--Nominal Vehicle Configuration
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                           1999 Mercedes   1999 Mercedes    2001 Toyota     2001 Toyota
                       Test driver                        2001 Chevrolet     2001 Ford    ML320 with ESC  ML320 with ESC   4Runner with    4Runner with
                                                           Blazer (mph)    Escape (mph)      on (mph)        off (mph)     ESC on (mph)    ESC off (mph)
--------------------------------------------------------------------------------------------------------------------------------------------------------
GF......................................................            39.3            37.0            38.8            36.7            36.5            37.7
LJ......................................................            38.1            37.1            37.1            36.6            37.4            35.7
RL......................................................            40.7            40.5            39.2            38.3            37.8            37.8
Range...................................................             2.6             3.5             1.7             1.7             1.3             2.1
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Table 6 shows a rank ordering of the Phase IV rollover test 
vehicles based on the maximum ``clean'' run speeds achieved by the 
three test drivers. Note that 1 is the best rank and 6 the worst.

[[Page 62568]]



  Table 6.--Vehicle Rankings Based on Maximum Achievable ``Clean'' Run Speeds for the Consumers Union Short Course Double Lane Change Maneuver--Nominal
                                                                  Vehicle Configuration
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                               2001                       1999  Mercedes  1999  Mercedes  2001  Toyota 4  2001  Toyota 4
                       Test driver                           Chevrolet      2001  Ford    ML320 with ESC  ML320 with ESC    Runner with     Runner with
                                                              Blazer          Escape            on              off           ESC on          ESC off
--------------------------------------------------------------------------------------------------------------------------------------------------------
GF......................................................               1               4               2               5               6               3
LJ......................................................               1               3               3               5               2               6
RL......................................................               1               2               3               4               5               5
--------------------------------------------------------------------------------------------------------------------------------------------------------

    As Table 5 shows, for three test drivers used, the range of 
maximum achievable ``clean'' run entry speeds varied from 1.3 mph 
for the 2001 Toyota 4Runner with yaw stability control enabled to 
3.5 mph for the 2001 Ford Escape. The average range was 2.2 mph. 
While these may seem like small ranges, the entire best-to-worst 
range in Table 5 is only 5.0 mph. Since we tested a fairly broad 
range of sport utility vehicles during the Phase IV research, the 
maximum achievable ``clean'' run speeds for most sport utility 
vehicles are expected to be in this 5.0 mph range. Therefore, 
driver-to driver variability averages 44 percent of the range of the 
rating metric and can be as much as 70 percent.
    The problem caused by driver-to-driver variability combined with 
the small range of metric values is clearly shown by Table 6. While 
the Chevrolet Blazer attained the best ranking from all three test 
drivers, the ranking for the Toyota 4Runner with yaw stability 
control enabled varied from second best to worst.
    Driver skills and abilities vary with time. Although we did not 
do such testing, if we retested the Phase IV rollover test vehicles 
with the same test drivers performing the Consumers Union Short 
Course Double Lane Change maneuver we anticipate that our results 
would not exactly match those shown in Tables 4 and 5. Since we have 
such a small range for the rating metric day-to-day (or even hour-
to-hour) changes in test driver performance would probably change 
the maximum achievable ``clean'' run entry speeds by a substantial 
percentage of the overall range.
    Due to the problems associated with driver-to-driver variability 
and run-to-run for the same driver variability, the objectivity and 
repeatability of this maneuver are poor. However, it is important to 
recognize that NHTSA's objective for this maneuver, the 
determination of rollover resistance ratings, is not the same as 
Consumers Union's objective, the evaluation of a vehicle's emergency 
handling capabilities. Handling evaluation has always been a 
subjective process. This appears to be a better maneuver for what 
Consumers Union wants to accomplish than for what the NHTSA wants to 
accomplish.

Performability

    The procedure for performing this test is straight-forward. 
However, as discussed above, this maneuver has objectivity and 
repeatability issues. Resolving these issues adds difficulty and 
complexity to performing these tests.
    For example, one possibility for improving objectivity and 
repeatability is to use multiple drivers to perform the testing 
(three drivers were used during the NHTSA testing). While this 
should help, there are still potential problems. One exceptionally 
skilled test driver could generate very good performance metrics for 
a mediocre vehicle. If this exceptionally skilled driver did not 
test some other vehicle that vehicle's performance metrics might, 
incorrectly, be lower than they should be. Therefore, in addition to 
using multiple drivers, procedures would need to be developed to 
ensure that every vehicle is tested by drivers of approximately 
equal skill.
    The Consumers Union Short Course Double Lane Change test 
procedure does not change from vehicle-to-vehicle. This reflects 
Consumers Union's reason for developing this maneuver; as a test of 
emergency handling. On an actual road, if an obstacle suddenly 
intrudes into a vehicle's lane requiring emergency maneuvering to 
avoid, the parameters of the intrusion (distance ahead of oncoming 
vehicle at which the intrusion begins, amount of intrusion) do not 
depend on the characteristics of the oncoming vehicle. In other 
words, if a child runs out in front of you, they do not run out 
sooner because your vehicle is bigger or wider.
    However, NHTSA has a different purpose. We are trying to rate a 
vehicle resistance to rollover. As such, we would like to test with 
worst case lane geometry. This may well change with vehicle size or 
other characteristics. Therefore, for NHTSA's purpose, we believe 
that a test maneuver should adapt for differing vehicle 
characteristics.

Discriminatory Capability

    No two-wheel lifts occurred during any ``clean'' run of 
Consumers Union Short Course Double Lane Change testing for any of 
the test vehicles. (A ``clean'' run is one during which none of the 
cones delineating the course were struck.) While some two-wheel 
lifts did occur during runs that were not ``clean'', these should 
not be considered for the determination of our rollover resistance 
ratings. The reason is that when a run is not ``clean'', there is no 
way to determine whether the vehicle comes close to following the 
test course. For example, a driver could perform a fishhook maneuver 
or simply drive straight through. Either case would simply be 
recorded as not a ``clean'' run.
    Unlike the J-Turn and Fishhook maneuvers, the occurrence/non-
occurrence of two-wheel lift cannot be used as a measure of vehicle 
performance for this maneuver because two-wheel lifts during clean 
run appear unlikely for NCAP vehicles. The rating metric use by 
NHTSA is the maximum entry speed into the test course at which a 
driver successfully achieved a ``clean'' run.
    We did not perform testing of the Reduced Rollover Resistance 
configurations of the Phase IV test vehicles with this maneuver; so, 
we cannot make the comparisons shown in Table 4 for this maneuver. 
However, the discussion following Table 4 likely applies to this 
maneuver as well as to the ISO 3888 Part 2 Double Lane Change. 
Again, this maneuver tests both the handling and rollover resistance 
of vehicles. In fact, since Consumers Union developed this maneuver 
to examine the emergency handling of vehicles, and because this 
maneuver is not as tightly constrained as is the ISO 3888 Part 2 
Double Lane Change, we believe that this maneuver focuses more on 
handling than does the ISO maneuver. Since handling and rollover 
resistance are inextricably intertwined in the rating produced by 
this maneuver with handling dominating, the rating generated can 
easily improve even though the rollover resistance of a vehicle is 
getting worse.
    The above reasoning explains the apparent anomaly in Table 6. In 
this table, the Chevrolet Blazer has the best ranking of any of the 
vehicles. However, based on its one star rating and performance in 
the NHTSA J-Turn and Fishhooks, we believe it to have the lowest 
rollover resistance of any of the Phase IV rollover test vehicles. 
The apparent contradiction is resolved once we realize that the 
Consumers Union Double Lane Change maneuver measures both the 
handling and rollover resistance of vehicles with handling 
dominating.
    Due to the fact that this maneuver is not focused solely on a 
vehicle's rollover resistance but instead measures some combination 
of their handling and rollover resistance properties, its 
discriminatory capability for rollover resistance (not emergency 
handling) is poor.

Realistic Appearance

    See the ISO 3888 Part 2 Double Lane Change maneuver Realistic 
Appearance discussion.

I. Open-Loop Pseudo-Double Lane Change

Maneuver Description

    Driver-based, path-following double lane changes have 
historically been associated with considerable handwheel 
variability. This was in evidence during the ISO 3888 Part 2 and 
Consumers Union Short Course

[[Page 62569]]

testing performed during the Phase IV research. Although the ISO 
3888 Part 2 Double Lane Change course layout attempts to minimize 
this variability by relating lane width to vehicle width, handwheel 
variability observed during this maneuver continues to exceed that 
typically observed during steering machine-based maneuvers.
    Aside from the handwheel variability issues, double lane changes 
have a certain appeal. It is foreseeable that the inputs of either 
double lane change used in Phase IV could emulate a driver's 
reaction to a variety of crash avoidance scenarios. Furthermore, 
examination of what effects the third steering input (second 
reversal) has on dynamic rollover propensity is of interest. To 
facilitate examination of third steer effects without the 
confounding effect of handwheel variability, open-loop handwheel 
inputs executed with the steering machine that approximated a double 
lane change were performed.
    Two open-loop pseudo-double lane changes were performed during 
the Phase IV research: ISO 3888 Part 2 and Consumers Union Short 
Course simulations. For each maneuver, handwheel inputs were chosen 
to approximate those observed during closed-loop, path-following 
tests performed at VRTC by three test drivers. Specifically, 
steering recorded during the three tests begun with the highest, yet 
most similar, entrance speeds was considered for each driver, per 
maneuver. Using these data, handwheel input composites were 
developed. Open-loop double lane changes were performed in the 
Nominal load condition, with the Toyota 4Runner and Chevrolet Blazer 
only. The Ford Escape and Mercedes ML320 were not evaluated with 
these maneuvers.
    Upon completion of the path-following double lane changes, the 
three highest, most consistent valid maneuver entrance speeds 
attained by each driver were determined. A valid test was one in 
which no vehicle-to-cone contact was detected. This produced a total 
of nine valid runs for each vehicle (recall the 4Runner with enabled 
stability control was considered to be separate vehicle from the 
4Runner with disabled stability control).
    Double lane change simulation began by plotting of the handwheel 
angles for all drivers of a particular vehicle. The plots were 
overlaid and centered about the middle peak of the maneuver in the 
time domain. After each of the nine tests was centered, the data 
were averaged to form a preliminary composite.
    Once the preliminary composite was created, averages for each of 
the three primary handwheel peaks were calculated. These averages 
were based on peak value data (independent of time) from each of the 
nine driver-based tests. Each average was then divided by the 
appropriate preliminary composite value to produce a ratio. The 
three ratios were averaged to produce a final, overall ratio. This 
final ratio was multiplied by preliminary composite data to yield a 
final handwheel input composite.\17\
---------------------------------------------------------------------------

    \17\ Determination of the final composite was necessary because 
the peak handwheel input of a particular test did not necessarily 
occur at the same time as the others. The preliminary composite was 
used to establish trends (e.g., timing, rates, etc.) in the 
handwheel position data. The final composite increased handwheel 
magnitudes, so as to insure maneuver severity was preserved.
---------------------------------------------------------------------------

    Piecewise approximation was used to construct ramp-based 
handwheel profiles representative of the final handwheel composites. 
The approximation was programmed into the steering machine, and the 
maneuver performed.
    Figure 16 presents the suite of piecewise approximations used to 
define the Consumers Union Short Course simulations for the Toyota 
4Runner (enabled and disabled stability control) and Chevrolet 
Blazer.
    Generally speaking, closed-loop Consumers Union Short Course 
tests performed with the 4Runner (disabled stability control) and 
Blazer contained four significant steering inputs (i.e., third 
reversals). The drivers used the fourth steering inputs to preserve 
lateral stability and insure exit lane position. These inputs were 
included in Consumers Union Short Course approximations for the 
4Runner with disabled stability control and for the Blazer, but were 
not required for approximation of 4Runner steering observed during 
tests performed with enabled stability control.
    Due to the length of the second lane in the ISO 3888 Part 2 
course, each driver made steering adjustments after the second 
handwheel peak to maintain lane position. As a result, each ISO 3888 
Part 2 simulation contained five significant handwheel peaks. Figure 
17 presents the open-loop steering inputs used to simulate the ISO 
3888 Part 2 Double Lane Change maneuver for each vehicle.
    During testing, runs of the Open-Loop Pseudo-Double Lane Change 
were performed beginning with a maneuver entry speed of 35 mph. 
Vehicle speed was iteratively increased in 5 mph increments to 50 
mph or until two-wheel lift occurred. Additionally, tests were 
performed at the average maximum entrance speed attained by test 
drivers at VRTC during closed-loop tests without the steering 
machine. No downward speed iterations were used to isolate the 
lowest entrance speed capable of producing two-wheel lift.

Objectivity and Repeatability

    The Open-Loop Pseudo-Double Lane Change can be performed with 
excellent objectivity and repeatability. Figure 18 shows the 
Handwheel Angle, Vehicle Speed, Lateral Acceleration, and Roll Angle 
as functions of time for two tests of the Chevrolet Blazer that were 
run at approximately the same speed (40.3 and 40.7 mph). Data from 
these runs is typical of our experience with this maneuver.
    Since this maneuver uses the programmable steering controller, 
the steering control input is once again precisely replicated from 
run-to-run. However, the lateral acceleration becomes slightly less 
repeatable when the vehicle is in the recovery portion (i.e., while 
trying to straighten out after performing the return lane change).
    As was discussed above for the NHTSA J-Turn, for runs near the 
point at which two-wheel lift first occurs, roll angle repeatability 
becomes much worse.

Performability

    Objective and repeatable Open-Loop Pseudo-Double Lane Change 
maneuvers can easily be performed using a programmable steering 
controller.
    While running this maneuver is straight-forward, we have 
substantial concerns about the maneuver itself. Unfortunately, due 
to lack of development time, we doubt that the steering inputs used 
during the Phase IV Rollover Research correspond to worst case 
conditions. Work is needed as to how to adapt this maneuver for 
different vehicles sizes or characteristics. Probably at least one 
year of effort would be required to develop and refine this 
maneuver.

Discriminatory Capability

    Testing for the Open-Loop Pseudo-Double Lane Change maneuver was 
only performed using two vehicles, the 2001 Chevrolet Blazer and the 
2001 Toyota 4Runner (both with the yaw stability control enabled and 
disabled). Two different steering inputs were used for this Open-
Loop Pseudo-Double Lane Change testing, one that simulated the ISO 
3888 Part 2 Double Lane Change and one that simulated the Consumers 
Union Short Course Double Lane Change.
    For the simulated ISO 3888 Part 2 Double Lane Change, the 
Chevrolet Blazer had two-wheel lift while the Toyota 4Runner with 
yaw stability control enabled and disabled did not. However, the 
maneuver entry speed at which the Chevrolet Blazer had two-wheel 
lift was substantially (5 mph) higher than the maximum speed at 
which Toyota 4Runner testing was stopped. When yaw stability control 
was disabled, the speed at which Toyota 4Runner testing was stopped 
was determined by when spin-out occurred. When yaw stability control 
was enabled, the speed at which Toyota 4Runner testing was stopped 
was determined by test driver concerns about possible loss of 
control. So two-wheel lift was seen for the Chevrolet Blazer but not 
the Toyota 4Runner because the Blazer was able to perform this 
maneuver at higher speeds than was the 4Runner. As was the case for 
the actual ISO 3888 Part 2 Double Lane Change, handling and rollover 
resistance appear to be inextricably intertwined in the ratings 
produced by this maneuver.
    For the simulated Consumers Union Short Course Double Lane 
Change, the Chevrolet Blazer and the Toyota 4Runner with yaw 
stability control disabled had two-wheel lift while the Toyota 
4Runner with yaw stability control enabled did not. The maneuver 
entry speed at which the Chevrolet Blazer had two-wheel lift was 
higher than the maximum speed at which Toyota 4Runner two-wheel lift 
occurred. However, based on its one star rating and performance in 
the NHTSA J-Turn and Fishhooks, we believe the Chevrolet Blazer to 
have the lowest rollover resistance of any of the Phase IV rollover 
test vehicles. The explanation for this apparent anomaly is that, as 
was the case for the actual Consumers Union Short Course Double Lane 
Change, handling and rollover resistance appear to be inextricably 
intertwined in the ratings produced by this maneuver.
    Because this maneuver is not focused solely on a vehicle's 
rollover resistance but

[[Page 62570]]

instead measures some combination of handling and rollover 
resistance properties, its discriminatory capability for rollover 
resistance is poor.

Realistic Appearance

    The Realistic Appearance discussion from the Ford Path Corrected 
Limit Lane Change again applies.
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[FR Doc. 02-25115 Filed 10-1-02; 8:45 am]
BILLING CODE 4910-59-C