[Federal Register Volume 68, Number 198 (Tuesday, October 14, 2003)]
[Rules and Regulations]
[Pages 59250-59304]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-25360]



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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; New Car Assessment Program; Rollover Resistance; 
Final Rule

  Federal Register / Vol. 68, No. 198 / Tuesday, October 14, 2003 / 
Rules and Regulations  

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 575

[Docket No. NHTSA-2001-9663; Notice 3]
RIN 2127-AI81


Consumer Information; New Car Assessment Program; Rollover 
Resistance

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

ACTION: Final policy statement.

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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. This document modifies 
NHTSA's rollover resistance ratings in its New Car Assessment Program 
(NCAP) to include dynamic rollover tests after considering comments to 
our previous document. The changes described in this document will 
improve consumer information provided by NHTSA, but will not place 
regulatory requirements on vehicle manufacturers.

DATES: NCAP rollover resistance ratings in the 2004 model year will be 
determined using the system established by this document.
    Petitions: Petitions for reconsideration must be received by 
November 28, 2003.

FOR FURTHER INFORMATION CONTACT: For technical questions you may 
contact Patrick Boyd, NVS-123, Office of Rulemaking, National Highway 
Traffic Safety Administration, 400 Seventh Street, SW., Washington, DC 
20590 and Dr. Riley Garrott, NVS-312, 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
    A. Existing NCAP Program and the TREAD Act
    B. National Academy of Sciences Study
IV. Notice of Proposed Rulemaking
V. Results of Dynamic Maneuver Tests of 25 Vehicles
    A. J-Turn Maneuver
    B. Fishhook Maneuver
    C. Loading Conditions
    D. Test Results
VI. Rollover Risk Model
VII. Comments to the Previous Notice
    A. Combined or Separate Rollover Resistance Ratings
    B. Crash Avoidance Technologies
    C. The J-Turn and Fishhook Maneuvers
    D. Tire Wear
    E. Pavement Temperature
    F. Surface Friction
    G. Steering Reversal
    H. Fifteen-Passenger Vans
    I. Tip-up Criterion
    J. Testing of Passenger Cars vs. Light Trucks
    K. Testing with Electronic Stability Control Systems
VIII. Final Form for Rollover Resistance Ratings `` Alternative I
    A. Combined Ratings
    B. Dynamic Testing
    C. Demonstration Program
IX. Cost Benefit Statement
X. Rulemaking Analyses and Notices
    A. Executive Order 12866
    B. Regulatory Flexibility Act
    C. National Environmental Policy Act
    D. Executive Order 13132 (Federalism)
    E. Unfunded Mandates Act
    F. Civil Justice Reform
    G. Paperwork Reduction Act
    H. Plain Language
Appendix I. Fishhook Test Protocol
Appendix II. Development of Logistic Regression Risk Model

I. Executive Summary

    While the total number of highway fatalities has remained 
relatively stable over the past decade, the number of rollover deaths 
has risen substantially. According to NHTSA's National Center for 
Statistics and Analysis, from 1991 to 2001 the number of passenger 
vehicle occupants killed in all motor vehicle crashes increased 4 
percent, while fatalities in rollover crashes increased 10 percent. In 
the same decade, passenger car occupant fatalities in rollovers 
declined 15 percent while rollover fatalities in light trucks increased 
43 percent. In 2001, 10,138 people died in rollover crashes, a figure 
that represents 32 percent of occupant fatalities for the year.
    In response to that trend, NHTSA has been evaluating rollover 
testing since 1993. In 2001, NHTSA began publishing rollover rating 
information for consumers, supplementing New Car Assessment Program 
(NCAP) frontal crashworthiness ratings that began in 1979 and side 
impact ratings that began in 1997.
    When Congress approved the ``Transportation Recall, Enhancement, 
Accountability and Documentation (TREAD) Act of November 2000'', 
Section 12 directed the Secretary of Transportation 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.''
    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.
    We published a Notice of Proposed Rulemaking on October 7, 2002 (67 
FR 62528) that proposed alternative ways of using the dynamic maneuver 
test results in consumer information on the rollover resistance of new 
vehicles.
    Beginning with rollover ratings for the 2004 model year, NHTSA will 
combine a vehicle's Static Stability Factor (SSF) measurement with its 
performance in the so-called ``Fishhook'' maneuver. The so-called ``J-
Turn'' dynamic test maneuver discussed in previous notices will be not 
be used by NHTSA for rating rollover resistance. Our analysis has found 
that the J-Turn maneuver test does not add any meaningful information 
to what is obtained from the fishhook maneuver test alone (see Appendix 
II.B). The predicted rollover rate will be translated into a five-star 
rating system that is the same as the one now in use: One star is for a 
rollover rate greater than 40 percent; two stars, between 30 and 39 
percent; three stars, between 20 and 29 percent; four stars, between 10 
and 19 percent; and five stars for 10 percent or less.
    This decision maximizes the vehicle information used to make the 
rollover rate prediction and will allow us to ensure that rollover NCAP 
information corresponds even more closely to real-world rollovers. We 
have also decided to present our rollover information as a single 
combined rollover rating that most commenters agreed would be more 
understandable to consumers.
    This document also includes a test procedure (Appendix I) for 
conducting vehicle maneuver tests, and discusses testing regimes that 
have been incorporated to minimize variability in test data.

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,

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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 ``LTVs'' to 
refer to the same vehicles.
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    According to the 2001 Fatality Analysis Reporting System (FARS), 
10,138 people were killed as occupants in light vehicle rollover 
crashes, which represent 32 percent of the occupants killed that year 
in crashes. Of those, 8,407 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 64 percent were 
partially or completely ejected from the vehicle (including 53 percent 
who were completely ejected). FARS shows that 54 percent of light 
vehicle occupant fatalities in single-vehicle crashes involved a 
rollover event.
    Using data from the 1997-2001 National Automotive Sampling System 
(NASS) Crashworthiness Data System (CDS), we estimate that 281,000 
light vehicles were towed from a police-reported rollover crash each 
year (on average), and that 30,000 occupants of these vehicles were 
seriously injured or killed (defined as any fatality or an injury with 
an Abbreviated Injury Scale (AIS) rating of at least AIS 3).\2\ Of 
these 281,000 light vehicle rollover crashes, 225,000 were single-
vehicle crashes. (The NCAP rollover resistance ratings estimate the 
risk of rollover if a vehicle is involved in a single-vehicle crash.) 
Sixty-one percent of those people who suffered a serious injury in 
single-vehicle towaway rollover crashes were not using a seat belt, and 
49 percent were partially or completely ejected (including 40 percent 
who were completely ejected). Estimates from NASS CDS indicate that 80 
percent of towaway rollovers were single-vehicle crashes, and that 83 
percent (168,000) 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 with splintering of the bone is an example of an 
AIS 3 injury.
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    According to the 1997-2001 NASS General Estimates System (GES) 
data, 62,000 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 215,000 single-vehicle rollover crashes resulted in 
49,000 K or A injuries. Fifty percent of those with K or A injury in 
single-vehicle rollover crashes were not using a seat belt, and 24 
percent were partially or completely ejected from the vehicle 
(including 21 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 percentages of 
all police-reported crashes for each vehicle type that resulted in 
rollover were 1.7 percent for cars, 2.0 percent for vans, 3.8 percent 
for pickup trucks and 5.5 percent for SUVs as estimated by NASS GES.

III. Background

A. Existing NCAP Program and the TREAD Act

    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 (66 FR 3388). This notice does not establish a new 
consumer information program on rollover resistance ratings. Rather, it 
refines our existing rollover resistance rating program in accordance 
with the requirements of the TREAD Act and the recommendations of the 
National Academy of Sciences.
    The present NCAP rollover resistance ratings are based on the 
Static Stability Factor (SSF) of a vehicle, which is the ratio of one 
half its track width to its center of gravity (c.g.) height (see http://www.nhtsa.dot.gov/hot/rollover/ for ratings and explanatory 
information). After an evaluation of some driving maneuver tests in 
1997 and 1998, we chose to use SSF instead of any driving maneuvers to 
characterize rollover resistance. As we explained in our notices 
establishing rollover NCAP, we chose SSF as the basis of our ratings 
because it represents the first order factors that determine vehicle 
rollover resistance in the vast majority of rollovers which 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, but such crashes 
represent less than five percent of rollover crashes.\3\
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    \3\ NHTSA Reseach Note, ``Passenger Vehicles in Untripped 
Rollovers,'' September 1999.
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    At the time, we believed it was necessary to choose between SSF and 
driving maneuver tests as the basis for rollover resistance ratings. 
SSF was chosen because it had a number of advantages: it 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. 
We also considered the fact that an improvement in SSF represents an 
increase in rollover resistance in both tripped and untripped 
circumstances while maneuver test performance can be improved by 
reduced tire traction and certain implementations of electronic 
stability control that we believe are unlikely to improve resistance to 
tripped rollovers.
    Congress funded NHTSA's rollover NCAP program, but directed the 
agency to enhance the program. 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 
was to be carried out by November 1, 2002.
    On July 3, 2001, NHTSA published a Request for Comments notice (66 
FR 35179) regarding our research plans to assess a number of possible 
dynamic rollover tests. The notice discussed the possible advantages 
and disadvantages of various approaches that had been suggested by 
manufacturers, consumer groups, and NHTSA's prior research. 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. The

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principal theme of the comments was a sharp division of opinion about 
whether the dynamic rollover test should be a closed loop maneuver test 
like the ISO 3388 double lane change that emphasizes the handling 
properties of vehicles or whether it should be an open loop maneuver 
like a J-Turn or Fishhook that are limit maneuvers in which vulnerable 
vehicles would actually tip up. Ford recommended a different type of 
closed loop lane change maneuver in which a path-following robot or a 
mathematical correction method would be used to evaluate all vehicles 
on the same set of paths at the same lateral acceleration. It used a 
measurement of partial wheel unloading without tip-up at 0.7g lateral 
acceleration as a performance criterion in contrast to the other closed 
loop maneuver tests that used maximum speed through the maneuver as the 
performance criterion. Another unique comment was a recommendation from 
Suzuki to use a sled test developed by Exponent Inc. to simulate 
tripped rollovers.
    The subsequent test program (using four SUVs in various load 
conditions and with and without electronic stability control enabled on 
two of the SUVs) showed that open-loop maneuver tests using an 
automated steering controller could be performed with better 
repeatability of results than the other maneuver tests. The J-Turn 
maneuver and the Fishhook maneuver (with steering reversal at maximum 
vehicle roll angle) were found to be the most objective tests of the 
susceptibility of vehicles to maneuver-induced on-road rollover. Except 
for the Ford test, the closed loop tests were found not to measure 
rollover resistance. Instead, the tests of maximum speed through a 
double lane change responded to vehicle agility. None of the test 
vehicles tipped up during runs in which they maintained the prescribed 
path even when loaded with roof ballast to experimentally reduce their 
rollover resistance. The speed scores of the test vehicles in the 
closed loop maneuvers were found to be unrelated to their resistance to 
tip-up in the open-loop maneuvers that actually caused tip-up. The test 
vehicle that was clearly the poorest performer in the maneuvers that 
caused tip-ups achieved the best score (highest speed) in the ISO 3388 
and CU short course double lane change, and one vehicle improved its 
score in the ISO 3388 test when roof ballast was added to reduce its 
rollover resistance.
    Due to the non-limit test conditions and the averaging necessary 
for stable wheel force measurements, the wheel unloading measured in 
the Ford test appeared to be more quasi-static (as in driving in a 
circle at a steady speed or placing the vehicle on a centrifuge) than 
dynamic. Sled tests were not evaluated because we believed that SSF 
already provided a good indicator of resistance to tripped rollover.

B. National Academy of Sciences Study

    During the time NHTSA was evaluating dynamic maneuver tests in 
response to the TREAD Act, the National Academy of Sciences (NAS) was 
conducting a study of the four SSF-based rollover resistance ratings 
and was directed to make recommendations regarding driving maneuver 
tests. We expected the NAS recommendations to have a strong influence 
on TREAD-mandated changes to NCAP rollover resistance ratings.
    When NHTSA proposed the present SSF rollover resistance ratings in 
June 2000 (65 FR 34998), vehicle manufacturers generally opposed it 
because they believed that SSF as a measure of rollover resistance is 
too simple since it does not include the effects of suspension 
deflections, tire traction and electronic stability control (ESC). In 
addition, the vehicle manufacturers argued that the influence of 
vehicle factors on rollover risk is too slight to warrant consumer 
information ratings for rollover resistance. In the conference report 
of the FY2001 DOT Appropriations Act, Congress permitted NHTSA to move 
forward with its rollover rating program, but directed the agency to 
fund a National Academy of Sciences (NAS) 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 available at the end 
of February 2002.
    The NAS study found that SSF is a scientifically valid measure of 
rollover resistance for which the underlying physics and real-world 
crash data are consistent with 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 dynamic tests 
the NAS recommended would be driving maneuvers used to assess 
``transient vehicle behavior leading to rollover.''
    The NAS study also made recommendations concerning the statistical 
analysis of rollover risk and the representation of ratings. It 
recommended that we use logistic regression rather than linear 
regression for analysis of the relationship between rollover risk and 
SSF, and it recommended that we consider a higher-resolution 
representation of the relationship between rollover risk and SSF than 
is provided by the current five-star rating system.
    We published a Notice of Proposed Rulemaking on October 7, 2002 (67 
FR 62528) that proposed alternative ways of using the dynamic maneuver 
test results in consumer information on the rollover resistance of new 
vehicles. We chose the J-Turn and Fishhook maneuver (with roll rate 
feedback) as the dynamic maneuver tests because they were the type of 
limit maneuver tests that could directly lead to rollover as 
recommended by the NAS. We also proposed to use a logistic regression 
analysis to determine the relationship between vehicle properties and 
rollover risk, as recommended by the NAS. The resulting rollover 
resistance ratings were proposed to be part of NHTSA's New Car 
Assessment Program (NCAP). Also, we proposed two methods for presenting 
rollover resistance ratings for consumer information.

IV. Notice of Proposed Rulemaking

    The TREAD Act calls for a rulemaking to determine how best to 
disseminate rollover test results to the public, and our Notice of 
Proposed Rulemaking (NPRM) of October 7, 2002 (67 FR 62528) proposed 
two alternatives for using the dynamic test results in consumer 
information on the rollover resistance of new vehicles. In this case 
the term ``rulemaking'' refers more to the process than to the product. 
This document does not amend the Code of Federal Regulations, but 
establishes NHTSA's policy on consumer information regarding the 
rollover resistance program. As mentioned above, this program places no 
requirements on vehicle manufacturers, only some on NHTSA.
    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

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previous research in 1997-8, the agency chose the J-Turn and the 
Fishhook maneuvers as dynamic rollover tests. They are the limit 
maneuver tests that NHTSA found to have the highest levels of 
objectivity, repeatability and discriminatory capability. The document 
announced that vehicles would 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 would be conducted with an automated steering 
controller, and the reverse steer of the Fishhook maneuver would 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. Figures 1 and 2 illustrate the open-loop steering wheel 
motions characterizing these maneuvers. The light load condition would 
be the weight of the test driver and instruments, approximating a 
vehicle with a driver and one front seat passenger. The notice 
announced that the heavy load condition would 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 
in consumer information on rollover resistance. NHTSA proposed two 
alternatives for consumer information ratings on vehicle rollover 
resistance that included both dynamic maneuver test results and Static 
Stability Factor. The first alternative was to include the dynamic test 
results as vehicle variables along with SSF in a statistical model of 
rollover risk that would combine their predictive power. This is 
conceptually similar to the present 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 recommended 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 its rollover rate in single-vehicle crashes predicted 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 proposed 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 would be simply whether it tipped up or not in 
each of the four maneuver/load combinations.
    In order to compute this logistic model for rollover risk, it is 
necessary to have the dynamic maneuver test results as well as SSF for 
a number of vehicles with rollover rates established by state crash 
reports of single-vehicle crashes. We had the SSF measurements and 
established rollover rates for the 100 make/model vehicles upon which 
we based the static rating system but not their dynamic maneuver test 
results. Thus, we asked for comment on the suitability of a rating 
method that combines static and dynamic vehicle properties in a single 
rating and on the validity of logistic regression analysis for the risk 
model that combines the properties in a way that is predictive of real-
world crash experience.
    The NPRM notice announced that we were going to perform the dynamic 
maneuver tests on about 25 of the 100 make/model vehicles for which we 
had SSF measurements and substantial state crash data. Time and budget 
constraints would not permit testing all 100 vehicles. With these 
dynamic maneuver test results and our existing crash and SSF 
information we would be able to compute the new risk model using a 
standard statistical package of computer programs (SAS) for logistic 
regression analysis. This final document presents the dynamic maneuver 
test results for 24 of the 100 vehicles, chosen to span the SSF range 
and to represent high production vehicles of each type (passenger car, 
van, pickup truck and sport utility vehicle (SUV)). An additional SUV 
with a lower SSF than found among the 100 vehicles was also included. 
The resulting risk model is presented in this document.
    The second alternative we proposed was to have separate ratings for 
Static Stability Factor and for dynamic maneuver test performance. 
Dynamic maneuver tests directly represent on-road untripped rollovers. 
Under this alternative, the dynamic maneuver test performance would be 
used to rate resistance to untripped rollovers in a qualitative scale. 
Barring unforeseen results of the dynamic maneuver tests of the 25 
vehicle group, the obvious qualitative scale would be: A for no tip-
ups, B for tip-up in one maneuver, C for tip-ups in two maneuvers, D 
for tip-ups in three maneuvers and E for tip-ups in all four maneuvers/
load combinations.
    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. For this 
alternative, the current Static Stability Factor based system would be 
used to rate resistance to tripped rollovers (since we believe most of 
the rollovers reported in the state crash reports are tripped). Again 
we asked for comments on the usefulness and validity of the concept in 
the NPRM notice, but we could not offer examples of actual vehicle 
ratings because the tests had not yet been conducted.

V. Results of Dynamic Maneuver Tests of 25 Vehicles

    This section presents an overview of the test maneuvers and the 
results for 25 vehicles that were used to develop the logistic 
regression risk model. A more extensive account of the test program is 
contained in the Phase VI and VII Report that has been placed in Docket 
NHTSA-2001-9663. A detailed description of how we will perform the 
maneuver tests for NCAP ratings is contained in Appendix I.
    The NHTSA J-Turn and Fishhook (with roll rate feedback) maneuver 
tests were performed for 25 vehicles representing four vehicle types 
including passenger cars, vans, pickup trucks and SUVs. We chose mainly 
high production vehicles that spanned a wide range of SSF values, using 
vehicles NHTSA already owned where possible. Except for four 2001 model 
year vehicles NHTSA purchased new, the vehicle suspensions were rebuilt 
with new springs and shock absorbers, and other parts as required for 
all the other vehicles included in the test program.

A. J-Turn Maneuver

    The NHTSA J-Turn maneuver represents an avoidance maneuver in which 
a vehicle is steered away from an obstacle using a single input. The 
maneuver is similar to the J-Turn used during NHTSA's 1997-98 rollover 
research program and is a common maneuver in test programs conducted by 
vehicle manufacturers and others. Often the J-Turn is conducted with a 
fixed steering input (handwheel angle) for all test vehicles. In its 
1997-98 testing, NHTSA used a fixed handwheel angle of 330 degrees. In 
the testing that preceded the NPRM notice, we developed an objective 
method of specifying equivalent handwheel angles

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for J-Turn tests of various vehicles, taking into account their 
differences in steering ratio, wheelbase and linear range understeer 
properties. (See NHTSA's Phase IV report docketed with the NPRM notice 
as item 38 in Docket No. NHTSA 2001-9663). Under this method, one first 
measures the handwheel angle that would produce a steady-state lateral 
acceleration of 0.3 g at 50 mph on a level paved surface for a 
particular vehicle. In brief, the 0.3 g value was chosen because the 
steering angle variability associated with this lateral acceleration is 
quite low and there is no possibility that stability control 
intervention could confound the test results. Since the magnitude of 
the handwheel position at 0.3 g is small, it must be multiplied by a 
scalar to have a high maneuver severity. In the case of the J-Turn, the 
handwheel angle at 0.3 g was multiplied by eight. When this scalar is 
multiplied by the average handwheel angle at 0.3 g (observed during 
NHTSA's 1997-98 rollover research program), the result is approximately 
330 degrees. Figure 1 illustrates the J-Turn maneuver in terms of the 
automated steering inputs commanded by the programmable steering 
machine. The rate of the handwheel turning is 1000 degrees per second.
    To begin the maneuver, the vehicle was driven in a straight line at 
a speed slightly greater than the desired entrance speed. The driver 
released the throttle, coasted to the target speed, and then triggered 
the commanded handwheel input. The nominal maneuver entrance speeds 
used in the J-Turn maneuver ranged from 35 to 60 mph, increased in 5 
mph increments until a termination condition was achieved. Termination 
conditions were simultaneous two inch or greater lift of a vehicle's 
inside tires (two-wheel lift) or completion of a test performed at the 
maximum maneuver entrance speed without two-wheel lift. If two-wheel 
lift was observed, a downward iteration of vehicle speed was used in 1 
mph increments until such lift was no longer detected. Once the lowest 
speed for which two-wheel lift could be detected was isolated, two 
additional tests were performed at that speed to monitor two-wheel lift 
repeatability.

B. Fishhook Maneuver

    The second maneuver test, the fishhook maneuver, uses steering 
inputs that approximate the steering a driver acting in panic might use 
in an effort to regain lane position after dropping two wheels off the 
roadway onto the shoulder. In the NPRM notice, we described it as a 
road edge recovery maneuver. As pointed out by some commenters, it is 
performed on a smooth pavement rather than at a road edge drop-off, but 
its rapid steering input followed by an over-correction is 
representative of a general loss of control situation. The original 
version of this test was developed by Toyota, and variations of it were 
suggested by Nissan and Honda. NHTSA has experimented with several 
versions since 1997, and the present test includes roll rate feedback 
in order to time the counter-steer to coincide with the maximum roll 
angle of each vehicle in response to the first steer.
    Figure 2 describes the Fishhook maneuver in terms of the automated 
steering inputs commanded by the programmable steering machine and 
illustrates the roll rate feedback. The initial steering magnitude and 
countersteer magnitudes are symmetric, and are calculated by 
multiplying the handwheel angle that would produce a steady state 
lateral acceleration of 0.3 g at 50 mph on level pavement by 6.5. The 
average steering input is equivalent to the 270 degree handwheel angle 
used in earlier forms of the maneuver but, as in the case of the J-
Turn, the procedure above is an objective way of compensating for 
differences in steering gear ratio, wheelbase and understeer properties 
between vehicles. The fishhook maneuver dwell times (the time between 
completion of the initial steering ramp and the initiation of the 
countersteer) are defined by the roll motion of the vehicle being 
evaluated, and can vary on a test-to-test basis. This is made possible 
by having the steering machine monitor roll rate (roll velocity). If an 
initial steer is to the left, the steering reversal following 
completion of the first handwheel ramp occurs when the roll rate of the 
vehicle first equals or goes below 1.5 degrees per second. If an 
initial steer is to the right, the steering reversal following 
completion of the first handwheel ramp occurs when the roll rate of the 
vehicle first equals or exceeds -1.5 degrees per second. The handwheel 
rates of the initial steer and countersteer ramps are 720 degrees per 
second.
    To begin the maneuver, the vehicle was driven in a straight line at 
a speed slightly greater than the desired entrance speed. The driver 
released the throttle, coasted to the target speed, and then triggered 
the commanded handwheel input described in Figure 2. The nominal 
maneuver entrance speeds used in the fishhook maneuver ranged from 35 
to 50 mph, increased in 5 mph increments until a termination condition 
was achieved. Termination conditions included simultaneous two inch or 
greater lift of a vehicle's inside tires (two-wheel lift) or completion 
of a test performed at the maximum maneuver entrance speed without two-
wheel lift. If two-wheel lift was observed, a downward iteration of 
vehicle speed was used in 1 mph increments until such lift was no 
longer detected. Once the lowest speed for which two-wheel lift could 
be detected was isolated, two additional tests were performed at that 
speed to check two-wheel lift repeatability.

C. Loading Conditions

    The vehicles were tested in each maneuver in two load conditions in 
order to create four levels of stringency in the suite of maneuver 
tests. The light load was the test driver plus instrumentation in the 
front passenger seat, which represented two occupants. A heavier load 
was used to create a higher level of stringency for each test. In our 
NPRM, we announced that the heavy load would include 175 lb 
anthropomorphic forms (water dummies) in all rear seat positions. 
During the test of the 25 vehicles, it became obvious that heavy load 
tests were being run at very unequal load conditions especially between 
vans and other vehicles (two water dummies in some vehicles but six 
water dummies in others). While very heavy passenger loads can 
certainly reduce rollover resistance and potentially cause special 
problems, crashes at those loads are too few to greatly influence the 
overall rollover rate of vehicles. Over 94% of van rollovers in our 
293,000 crash database occurred with five or fewer occupants, and over 
99% of rollovers of other vehicles occurred with five or fewer 
occupants. The average passenger loads of vehicles in our crash 
database was less than two: 1.81 for vans; 1.54 for SUVs; 1.48 for 
cars; and 1.35 for pickup trucks. In order to use the maneuver tests to 
predict real-world rollover rates, it seemed inappropriate to test the 
vehicles under widely differing loads that did not correspond to the 
real-world crash statistics. Therefore, the tests used to develop a 
statistical model of rollover risk were changed to a uniform heavy load 
condition of three water dummies (representing a 5-occupant loading) 
for all vehicles capable of carrying at least five occupants. Some 
vehicles were loaded with only two water dummies because they were 
designed for four occupants. For pickup trucks, water dummies were 
loaded in the bed at approximately the same height as a passenger in 
the front seat.
    To avoid disruption, the tests were completed under the original 
loading

[[Page 59255]]

plan. Then we conducted tests at a 5-occupant heavy load only for those 
vehicles in which loading differences might influence tip-up. If the 
vehicle had completed the maneuver without tip-up with more than three 
water dummies in the rear it was not necessary to retest at a lighter 
load. Likewise, if the vehicle tipped up in the light load (no water 
dummies) condition, it was not necessary to retest with three water 
dummies in the rear. We have never observed a vehicle for which a 
greater passenger load improved performance in a tip-up test.

D. Test Results

    The test results in Table 1 reflect the performance either measured 
or imputed as described for a heavy-load condition representing 5 
occupants except for the Ford Explorer 2DR, the Chevrolet Tracker and 
Metro that were designed for only four occupants, and the Honda CRV, 
Honda Civic and Chevrolet Cavalier that could not be loaded to the 5 
occupant level without exceeding a gross axle weight rating because of 
the additional weight of the outriggers.
    Note that Table 1 includes some results collected during tests 
performed with alternative steering angles. Although the steering 
angles used during these tests were still based on the handwheel angle 
that would produce a steady-state lateral acceleration of 0.3 g at 50 
mph on a level paved surface, the scalars used to calculate the 
steering angles were smaller. These tests were performed because, for 
some vehicles, the methods used to calculate the steering inputs used 
in the J-Turn and/or Fishhook maneuvers can produce ``excessive'' 
steering--steering angles so great that maneuver severity is actually 
reduced (i.e., the lateral force capability of the tires is exceeded). 
As an example, consider the Ford Ranger 4WD and Aerostar. These 
vehicles required a reduction of the J-Turn steering scalar from 8.0 to 
7.0 (Ranger 4WD) or 6.0 (Aerostar) before J-Turn steering was able to 
produce two-wheel lift.

               Table 1.--Dynamic Maneuver Test Results (the Check Mark Indicates Tip-Up Observed)
----------------------------------------------------------------------------------------------------------------
                                               Nominal
                          Model range/make/     static      Fishhook      Fishhook    J-turn light  J-turn heavy
   Veh. group number            model         stability    light (FL)    heavy (FH)      (JL) (2       (JH) (5
                                                factor      (2 occ.)      (5 occ.)        occ.)         occ.)
----------------------------------------------------------------------------------------------------------------
                         '92-'00 Mitsubishi         0.95     [bcheck]      [bcheck]   ............     [bcheck]
                          Montero 4WD.
47.....................  '95-'03 Chevrolet          1.02     [bcheck]      [bcheck]   ............     [bcheck]
                          Blazer 2WD.
43.....................  '95-'01 Ford               1.06  ............  ............  ............  ............
                          Explorer 2dr 2WD.
44.....................  '95-'01 Ford               1.06  ............     [bcheck]   ............  ............
                          Explorer 4dr 4WD.
66.....................  '96-'00 Toyota             1.06  ............     [bcheck]   ............  ............
                          4Runner 4WD.
89.....................  '93-'97 Ford               1.07     [bcheck]      [bcheck]      [bcheck]      [bcheck]
                          Ranger p/u 4WD.
58.....................  '88-'97 Jeep               1.08  ............  ............  ............  ............
                          Cherokee 4WD.
59.....................  '95-'02 Acura SLX/         1.09     [bcheck]      [bcheck]      [bcheck]      [bcheck]
                          Isuzu Trooper 4WD.
70.....................  '88-'98 Ford               1.10     [bcheck]      [bcheck]      [bcheck]      [bcheck]
                          Aerostar 2WD.
74.....................  '88-'02 Chevrolet          1.12  ............     [bcheck]   ............  ............
                          Astro 2WD.
53.....................  '89-'98 Chevrolet/         1.13  ............     [bcheck]   ............  ............
                          Geo Tracker 4WD.
91.....................  '88-'98 Chevrolet          1.14  ............  ............  ............  ............
                          K1500 p/u 4WD.
88.....................  '93-'97 Ford               1.17  ............     [bcheck]   ............     [bcheck]
                          Ranger p/u 2WD.
85.....................  '97-'02 Ford F-150         1.18  ............  ............  ............  ............
                          p/u 2WD.
54.....................  '97-'01 Honda CR-V         1.19     [bcheck]      [bcheck]   ............     [bcheck]
                          4WD.
83.....................  '88-'96 Ford F-150         1.19  ............  ............  ............  ............
                          p/u 2WD.
67.....................  '88-'95 Dodge              1.21  ............  ............  ............  ............
                          Caravan/Plymouth
                          Voyager 2WD.
90.....................  '88-'98 Chevrolet          1.22  ............  ............  ............  ............
                          C1500 p/u 2WD.
68.....................  '96-'00 Dodge              1.23  ............  ............  ............  ............
                          Caravan/Plymouth
                          Voyager 2WD.
73.....................  '95-'98 Ford               1.24  ............  ............  ............  ............
                          Windstar 2WD.
22.....................  '95-'01 Chevrolet/         1.29  ............  ............  ............  ............
                          Geo Metro.
19.....................  '88-'94 Chevrolet          1.32  ............  ............  ............  ............
                          Cavalier.
18.....................  '91-'96 Chevrolet          1.40  ............  ............  ............  ............
                          Caprice.
7......................  '88-'95 Ford               1.45  ............  ............  ............  ............
                          Taurus.
26.....................  '92-'95 Honda              1.48  ............  ............  ............  ............
                          Civic.
                                            --------------
Total Tip-ups..........  ..................  ...........            6            11             3             7
----------------------------------------------------------------------------------------------------------------

    During some Fishhook tests, excessive steering caused some vehicles 
to reach their maximum roll angle response to the initial steering 
input before it had been fully completed (this is essentially 
equivalent to a ``negative'' T1 in Figure 2). Since dwell 
time duration can have a significant effect on how the Fishhook 
maneuver's ability to produce two-wheel lift, we believe that excessive 
steering may stifle the most severe timing of the counter steer for 
some vehicles. In an attempt to better insure high maneuver severity, a 
number of vehicles that did not produce two-wheel lift with steering 
inputs calculated with the 6.5 multiplier were also tested with lesser 
steering angles by reducing the multiplier to 5.5. This change reduced 
the likelihood of excessive steering, and increased the dwell times 
observed during the respective maneuvers. In the case of the Ford 
Ranger 4x2, Fishhook maneuvers with steering inputs based on the 
reduced multiplier were able to produce two-wheel lift. Such lift was 
not observed when the original steering was used (i.e., when a 
multiplier of 6.5 was used). We have modified the Fishhook test 
procedure to include tests at the steering angle determined by the 5.5 
multiplier for vehicles that do not tip up using the original steering 
angle determination.
    Each test vehicle in Table 1 represented a generation of vehicles 
whose model year range is given. Twenty-four of the vehicles were taken 
from 100 vehicle groups whose 1994-98 crash statistics in six states 
were the basis of the present SSF based rollover resistance ratings. 
The vehicle group numbers used to identify these vehicles in the prior 
notices (65 FR 34998 and 66 FR 3388) are given for convenience. The 
nominal SSFs used to describe the vehicle groups in the prior 
statistical studies are given. While there were some variations between 
the SSFs of the

[[Page 59256]]

individual test vehicles and the nominal vehicle group SSF values, the 
nominal SSFs were retained for the present statistical analyses because 
they represent vehicles produced over a wide range of years in many 
cases and provide a simple comparison between the risk model presented 
in this document and that discussed in the previous notices.
    The check marks under the various test maneuver names indicate 
which vehicles tipped up during the tests. Eleven of the twenty-five 
vehicles tipped up in the Fishhook maneuver conducted in the heavy 
condition. The heavy condition represented a five-occupant load for all 
vehicles except the six mentioned above that were limited to a four-
occupant load by the vehicle seating positions and GVWR. All eleven 
were among the sixteen test vehicles with SSFs less than 1.20. None of 
the vehicles with higher SSFs tipped up in any test maneuver. The 
fishhook test under the heavy load clearly had the greatest potential 
to cause tip-up. The groups of vehicles that tipped up in other tests 
were subsets of the larger group of eleven that tipped up in the 
fishhook heavy test. There were seven vehicles in the group that tipped 
up in the J-Turn heavy test, six of which also tipped up in the 
Fishhook light test. The J-Turn light test had the least potential to 
tip up vehicles. Only three vehicles tipped up, all of which had tipped 
up in every other test.

VI. Rollover Risk Model

    In its study of our rating system for rollover resistance 
(Transportation Research Board Special Report 265), the National 
Academy of Sciences (NAS) recommended that we use logistic regression 
rather than linear regression for analysis of the relationship between 
rollover risk and SSF. Logistic regression has the advantage that it 
operates on every crash data point directly rather than requiring that 
the crash data be aggregated by vehicle and state into a smaller number 
of data points. For example, we now have state data reports of about 
293,000 single-vehicle crashes of the hundred vehicle make/models 
(together with their corporate cousins) whose single-vehicle crashes we 
have been tracking in six states. The logistic regression analysis of 
this data would have a sample size of 293,000, producing a narrow 
confidence interval on the repeatability of the relationship between 
SSF and rollover rate. In contrast, the linear regression analysis 
operates on the rollover rate of the hundred vehicle make/models in 
each of the six states. It produces a maximum sample size of only 600 
(100 vehicles times six states) minus the number of samples for which 
fewer than 25 crashes were available for determining the rollover rate 
(a data quality control practice). Confidence limits computed for a 
data sample size of 600 will be much greater than those based on a 
sample size of 293,000. On average, each sample in the linear 
regression analysis was computed from over 400 crash report samples. 
However, ordinary techniques to compute the confidence intervals of 
linear regression results do not take into account the actual sample 
size represented by aggregated data. The statistical model created to 
combine SSF and dynamic test information in the prediction of rollover 
risk was computed by means of logistic regression as recommended by the 
NAS. Logistic regression is well suited to the correlation with crash 
data of vehicle properties that include both continuous variables like 
SSF and binary variables like tip-up or no tip-up in maneuver tests.
    We had previously considered logistic regression during the 
development of the SSF based rating system (66 FR 3388, January 12, 
2001, p.3393), but found that it consistently under-predicted the 
actual rollover rate at the low end of the SSF range where the rollover 
rates are high. The NAS study acknowledged this situation and gave the 
example of another analysis technique (non-parametric) that made higher 
rollover rate predictions at the low end of the SSF scale. In the NPRM, 
we discussed our plan to first examine ways to improve the fit of the 
logistic regression model to the actual rollover rates in the simpler 
model with SSF as the only vehicle attribute before expanding the 
logistic regression model to predict rollover rates using maneuver test 
results and SSF as vehicle attributes. In this way, the addition of 
maneuver test results is more likely to have an effect that reflects 
the additional information they represent on rollover causation.
    Appendix II discusses the details of seeking a mathematical 
transformation of SSF to improve the accuracy of logistic regression 
models. We found that logistic regression on the transformation 
``Log(SSF-0.9)'' rather than on SSF directly computed a risk model 
whose predictions of rollovers per single-vehicle crash more closely 
matched the relationship between vehicle SSF and actual rollover rates 
observed in state crash data. We sought to optimize the accuracy of the 
predictions in the SSF range between 1.0 and 1.25 that includes the 
vehicles with the highest rollover rates, even at the expense of 
accuracy in predicting the low rollover rates at high end of the SSF 
scale. The risk model that resulted from this exercise is equivalent to 
the SSF-based rating system used for 2001-2003 NCAP rollover resistance 
ratings except that it was computed using logistic regression rather 
than linear regression as the statistical technique. Figure 3 compares 
the logistic regression model and linear regression model formerly used 
for NCAP ratings. The linear regression model is not in the form of a 
straight line because it also operated on a transformation of SSF 
(Log(SSF) in this case). The logistic regression model is the more 
accurate at lower half of the SSF range, and the linear regression 
model is the more accurate at the upper half of the SSF range. The two 
curves are quite similar.
    A good logistic regression risk model using SSF only was the 
starting point for models using dynamic variables together with SSF. 
The dynamic maneuver test results (tip-up or no tip-up in each 
maneuver/load combination in Table 1) were used as four binary dynamic 
variables in the logistic regression analysis. The dynamic variables 
were entered in addition to SSF to describe the vehicle. The same 
driver and road variables from state crash reports discussed above were 
used. The state crash report data for twenty four of the vehicles used 
in the logistic regression analysis with dynamic maneuver test 
variables was a subset of the database of 293,000 single-vehicle 
crashes described above. One extra vehicle was added for the maneuver 
tests that was not among the 100 vehicle groups we had studied 
previously, but state crash report data from the same years and states 
was obtained for it. However, the database with SSF and dynamic 
maneuver test was much smaller than the 293,000 sample size available 
for the logistic regression model with SSF only. Its sample size was 
96,000 single-vehicle crashes of 25 vehicles including 20,000 
rollovers. Appendix II contains a more detailed discussion.
    First, we tried each dynamic variable separately in conjunction 
with SSF. The models using variables for performance in the Fishhook 
heavy and J-Turn heavy maneuvers predicted a greater rollover risk for 
those vehicles that tipped up in the maneuver test. However, the models 
using variables for performance in the Fishhook light and J-Turn light 
maneuvers predicted a greater rollover risk for vehicles that did not 
tip up.
    We do not believe vehicles that tip up in the least severe 
maneuvers are actually safer than those that do not tip up. A more 
rational interpretation is that the numbers of vehicle tipping up

[[Page 59257]]

in these maneuvers were too few to establish a definitive correlation. 
Only three vehicles tipped up in the J-Turn light maneuver, and six 
vehicles tipped up in the Fishhook light maneuver. Only one more 
vehicle tipped up in the J-Turn heavy maneuver than in the Fishhook 
light, and the prediction of the model with J-Turn heavy was consistent 
with expectations that tip-up in the test predicts greater rollover 
risk. However, the extra vehicle in the J-Turn heavy tip-up group was 
the Ford Ranger 2 WD with a very large sample size of over 8,000 
single-vehicle crashes (nearly 10 percent of the entire data base).
    Next we computed a logistic regression model combining SSF with the 
dynamic variables for both maneuvers, Fishhook heavy and J-Turn heavy, 
that were observed to have a directionally correct result when entered 
into the model individually. The variable for J-Turn heavy was rejected 
by the logistic regression program as not statistically significant in 
the presence of the Fishhook heavy variable. In other words, the 
predictions based on tip-up in the Fishhook heavy maneuver do not 
change whether or not the vehicle also tips up in the J-Turn heavy 
maneuver.
    Figure 4 shows the final model that uses Fishhook heavy as the only 
necessary dynamic variable. This model has a risk prediction for 
vehicles that tip up in the dynamic maneuver tests based on the 
greatest number of vehicles possible in our 25 vehicle data base. All 
11 vehicles that tipped up in any maneuver are represented on the tip-
up curve, and the 14 vehicles without tip-up are represented on the 
other curve. The risk curve in Figure 4 representing vehicles that 
tipped up in the Fishhook heavy maneuver is very similar to the 
logistic regression model based on SSF only in Figure 3 (that was based 
on the rollover rates of 100 vehicles). This result is logical because 
the SSF only model was optimized for best fit in the 1.00 to 1.25 SSF 
range that included all vehicles tipping up in dynamic maneuver tests. 
Also, the fact that the risk curve of the logistic regression model in 
Figure 3 that was based on the SSF of 100 vehicles closely matches the 
risk curve in Figure 4 that was based on 11 vehicles that tipped up in 
the dynamic tests suggests that the curve in Figure 4 is robust. 
However, the small difference in Figure 4 between the risk curve for 
vehicles that tip up in the dynamic test and the risk curve for those 
that do not tip up suggests that the predictive power of tip-up in the 
dynamic test may not be great.
    Our testing and logistic regression analysis was sufficient to 
assign a greater rollover risk to vehicles that tipped up in the most 
severe maneuver than to those that did not tip up at all. However, the 
extra risk was small, and we were not able to distinguish a rollover 
risk difference between vehicles that tipped up in the less severe 
Fishhook maneuver with a two occupant load from those that tipped up 
only with a five occupant load. In general, vehicles that tip up in the 
Fishhook maneuver with a two occupant load also tip up at a slower 
entry speed in the Fishhook maneuver with a five occupant load than 
those that do not. Therefore, our data does not allow us to distinguish 
rollover risk differences between vehicles on the basis of maneuver 
entry speed for tip-up. The objective of using different load 
conditions and different maneuvers instead of different speeds in a 
single maneuver to provide a range of test severity was to reduce the 
sensitivity of the result to extraneous factors such as tire wear.
    It is noteworthy that the final rollover risk model required 
results from only the fishhook maneuver. This is an advantage from the 
standpoint of minimizing the practical problems of the effects of tire 
wear during a test series and of deviations from uniformity of surface 
friction at a test facility. The fishhook maneuver produces less wear 
on the test tires and requires only about 2 or 3 lane widths of uniform 
test surface versus 10 or more lane widths for the J-Turn maneuver. The 
commenters also considered it more representative of a real driving 
situation than the J-Turn.

VII. Comments to the NPRM Notice and Agency Response

    We received 39 comments to the NPRM notice from vehicle 
manufacturers, equipment suppliers, test labs, public interest groups, 
the National Transportation Safety Board, the Insurance Institute for 
Highway Safety, attorneys, and members of the public. Mainly, the 
comments addressed whether the static and dynamic measurements should 
be used for separate ratings of rollover resistance or for a combined 
rating based on a risk model. The nature of the dynamic maneuver tests, 
testing of 15-passenger vans, and several practical testing issues such 
as the extraneous effects of tire wear, surface condition and ambient 
temperature were also addressed. The notice also introduced the related 
subject of handling ratings that was not part of the TREAD Act 
requirements. We received a number of valuable comments on handling 
tests, and we are still soliciting information. However, the subject of 
this notice is confined to the TREAD Act requirements for dynamic 
rollover ratings.

A. Combined or Separate Rollover Resistance Ratings

    The main question posed in the NPRM notice was whether the rollover 
resistance ratings should reflect the combined statistical power of SSF 
and dynamic tests for predicting rollover risk or whether ratings of 
rollover risk using SSF alone should continue, supplemented with a 
qualitative comparison of dynamic test performance. The document gave 
alternative A as a risk model determined by logistic regression 
analysis of state crash reports of single-vehicle crashes for about 25 
vehicles with known SSF and dynamic test results. That process led to 
the risk model described in Section VI, however the mathematical 
calculation of the model could not be performed until the completion of 
a lengthy dynamic test program. Alternative B in the notice was a 
continuation of rollover risk prediction using SSF-only plus 
qualitative separate dynamic scores of A, B, C, D, or E signifying the 
number of maneuvers in which the vehicle tripped up without a risk 
interpretation.
    Commenters representing TRW Automotive, National Automobile Dealers 
Association (NADA), General Motors (GM), Alliance of Automobile 
Manufacturers (Alliance), Association of International Automobile 
Manufacturers (AIAM), Insurance Institute for Highway Safety (IIHS), 
Bosch, Consumers Union, Advocates for Highway and Auto Safety 
(Advocates), Toyota, Continental-Teves and Public Citizen remarked 
directly on the question of combined versus separate use of SSF and 
dynamic maneuver tests in rollover resistance ratings. Except for 
Continental-Teves and Bosch, the commenters were in favor of ratings 
that combined the SSF and dynamic maneuver tests in a single rating. 
Consumers Union specifically supported the logit risk model operating 
on a moderate risk scenario (in which rollover rates vary in the 
approximate range of 0.075 to 0.55 across the range of vehicles) as a 
way of combining the SSF and dynamic maneuver tests. It commented that 
using the risk model it described was consistent with the 
recommendations of the NAS study. We believe the risk model we have 
developed is consistent with recommendation of NAS and Consumers Union. 
It is the logit model with the risk scenario (of demographic and road 
condition variables) that represents the average crash conditions of 
293,000 actual single-vehicle crashes.

[[Page 59258]]

It produces predicted rollover rates in the range of 0.09 to 0.50 for 
vehicles ranging from tip-up to no tip-up in maneuvers and from 1.0 to 
1.55 in SSF.
    The other commenters in favor of combined ratings were primarily 
concerned that separate ratings would be too confusing to serve as 
consumer information. They believed a combined rating was the only 
viable option, but they did not comment specifically on the means used 
by NHTSA to develop the combined risk model. IIHS and the Alliance 
(along with Carr Engineering) suggested that another comment period 
following the notice containing the actual model (as opposed to the 
example given in the NPRM notice) would be necessary. GM suggested that 
the risk model be developed through a collaborative effort along the 
lines of the Motor Vehicle Safety Research Advisory Committee, and the 
Alliance suggested a working-level dialog between NHTSA and the auto 
industry to develop the risk model. TRW supported a single rating that 
would be computed on the basis of the SSF only model with a 
predetermined number of stars added or subtracted for dynamic maneuver 
performance (determined without a statistical relationship to risk). 
Advocates expressed wariness that the combined rating could be 
misleading to consumers unless it corresponded to real-world rollover 
rates. Public Citizen preferred the combined rating developed from a 
risk model. It was concerned that consumers would focus more attention 
on the dynamic maneuvers in separate ratings although the tests 
represent an event (on-road untripped rollover) that occurs in less 
than 5 percent of actual rollover crashes.
    Continental-Teves and Bosch prefer separate ratings for SSF and 
dynamic maneuver tests. Continental-Teves stated that ``the relative 
effects of SSF and dynamic performance are not well understood, and may 
not be the same for every vehicle or every driver.'' Bosch stated that 
``static and dynamic ratings should be separate, as they are both 
equally important with regards to indicating stability and safety of 
the vehicle.'' Bosch further explained that `` a combined rating may 
not adequately show the influence of such systems [Electronic Stability 
Control and Rollover Mitigation] which in turn would not encourage 
manufacturers to add systems to vehicles that increase overall vehicle 
safety in potential rollover as well as many other situations.''

B. Crash Avoidance Technologies

    Some of the stated expectations of the commenters about rollover 
resistance ratings are unrealistic. The rollover resistance ratings 
predict the likelihood of a single-vehicle crash becoming a rollover. 
They do not predict the likelihood of the vehicle becoming involved in 
a single-vehicle crash. Similarly, the frontal and side NCAP 
crashworthiness ratings do not predict the likelihood of the vehicle 
striking an object head-on or being struck from the side. The Alliance 
comment anticipates the dilemma. While conceding that SSF is strongly 
correlated with a tripped rollover once the vehicle is already off-
road, it states that `` the likelihood of being involved in a single-
vehicle crash in the first place `` particularly one involving off-road 
excursion `` is influenced much more by demographic and environmental 
influences than is the scenario examined for SSF purposes.'' The 
scenario used in the combined risk model is the same scenario used in 
the SSF model, namely the average demographic and environmental 
variables reported by the states for the entire 293,000 single-vehicle 
crash data base we have collected. We think this is the best scenario 
to characterize single-vehicle crashes.
    The Alliance is concerned that our model ``may fail to account for 
potentially beneficial technologies for avoiding single-vehicle and 
rollover crashes, such as electronic stability control and variable 
ride high suspension systems.'' Its concern is unnecessary for variable 
ride-height suspension systems, which will be tested in the highway 
rather than off-road height for both SSF and dynamic maneuver tests, 
and the technology will certainly improve the rating of vehicles so 
equipped.
    However, the Alliance is right that the model does not predict the 
risk of a single-vehicle crash. NHTSA has been very clear in public 
notices, consumer information and web site presentations that neither 
the SSF risk model nor the proposed combined SSF and dynamic maneuver 
risk model predict the risk of having a single-vehicle crash. From the 
standpoint of rollover resistance, single-vehicle crashes are a measure 
of exposure. The prediction is of the risk of a rollover resulting from 
the exposure of the vehicle to a single-vehicle crash. The risk of 
rollover in the event of a single-vehicle crash is strongly influenced 
by vehicle properties, but the vehicle properties of modern vehicles 
have far less influence in comparison to demographic and environmental 
factors regarding the risk of a single-vehicle crash in the first 
place. However, electronic yaw stability control may provide a real-
world reduction in single-vehicle crashes.
    We have been optimistic about the potential of electronic yaw 
stability control to reduce single-vehicle crashes. NHTSA's consumer 
information identifies its availability as standard or optional 
equipment on individual vehicles and explains how it operates to help a 
driver maintain control in extreme circumstances. One of the reasons we 
are exploring the possibility of NCAP handling ratings is to describe 
the effect of yaw stability control on handling predictability. 
However, the technology has not been in widespread use long enough to 
produce much crash evidence for the evaluation of its real-world 
effectiveness in preventing single-vehicle crashes. Our previous 
attempts at evaluating its effectiveness were thwarted by insufficient 
data.
    Part of the motivation for the NAS study of NHTSA's SSF-based 
rollover resistance ratings was the Alliance's concern that yaw 
stability control was not being considered. In its public oral 
presentation to the NAS study committee in May 2001, NHTSA said it did 
not expect yaw stability control to have a large effect on the risk of 
rollover given a single-vehicle crash. In its view, the large majority 
of rollovers were the result of various types of tripping, and SSF 
represented the most important vehicle attributes in those 
circumstances. NHTSA believes that the greatest potential effect of yaw 
stability control was in reducing single-vehicle crashes in the first 
place. Therefore, we suggested to the committee that rather than trying 
to predict rollovers per single-vehicle crash with dynamic maneuver 
tests, we should keep SSF for that purpose and adjust the comparative 
risk for vehicles with yaw stability control by the effect of yaw 
stability control to reduce exposure to single-vehicle crashes. 
However, establishing the effectiveness of yaw stability control would 
require data not available for at least two or three more years. 
Neither the NAS committee nor the Alliance, which was active in 
providing the committee information, expressed interest in this 
suggestion. But the present comments indicate that finding a way to 
include the crash avoidance potential of yaw stability control is a 
principal concern of the Alliance and several suppliers of these 
systems.
    IIHS's comment also shows an expectation of more than what is 
possible for a rollover resistance rating. It discusses a comparison of 
the 1997 Jeep Grand Cherokee and 1997 Toyota 4Runner made in one its 
reports. In that report, the Toyota had four times the number of fatal 
rollovers per 100,000

[[Page 59259]]

registered vehicles as the Jeep, but they had very similar SSFs. They 
also had very similar rollover rates in terms of rollovers per single-
vehicle crash that were consistent with their SSFs. IIHS expects a good 
dynamic rating to show a large difference between the Grand Cherokee 
and the 4Runner. That will not be possible because differences in 
dynamic maneuver test performance predict only small differences in 
rollover rate, and, in fact, there is not a large difference in 
rollover rate between these vehicles in terms of rollovers per single-
vehicle crash in our six state crash data base. The difference is in 
the definition of rollover rate. A rollover rate in terms of fatal 
rollovers per 100,000 vehicles depends on the rate of single-vehicle 
crashes per 100,000 vehicles and on the occurrence of a fatality in the 
rollover as well as on the rate of rollover per single-vehicle crash. 
The first two of these factors depend primarily on demographic and 
environmental influences and can mask actual differences or 
similarities between vehicles as in this case. Neither vehicle had yaw 
stability control, which would have created a plausible vehicle-related 
difference in single-vehicle crash rate. The difference in fatality 
rate could involve crashworthiness features, or particularly in the 
case of rollover, it could merely reflect the seat belt wearing habits 
of a risk taking demographic that also experienced a higher rate of 
single-vehicle crashes. The rate of rollovers per single-vehicle crash 
is much less sensitive to demographic influences than is the rate of 
fatal rollovers per 100,000 vehicles.
    Carr Engineering and Suzuki commented that the agency was not 
following the recommendations of the NAS study by performing J-Turn and 
Fishhook maneuver tests. They believe that the NAS recommended handling 
tests to assess loss of control potential rather than limit maneuvers 
to assess the resistance of the vehicle to actual on-road tip-up. We 
agree that the language of the NAS study report is somewhat ambiguous. 
That is why we included in our NPRM notice the clarification the NAS 
study panel gave us during the presentation of the report to NHTSA in 
response to our direct questions about J-Turn and Fishhook tests versus 
handling tests. The NAS study committee clarified that it envisioned 
dynamic maneuver 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 stated it was not in a position to recommend a 
specific test because that would require study of discriminatory 
capability, repeatability and other properties, but J-Turns and 
Fishhooks were of the type of tests it had in mind. Two outside experts 
in vehicle dynamics and testing reviewed our test plan before the Phase 
VI test of the 25 vehicles. One had been a member of the NAS study 
committee. Once again, we were assured that our tests were consistent 
with the NAS recommendations.
    We believe that both our test selection and our analysis method of 
developing a rollover risk model to combine SSF and dynamic test 
results are entirely consistent with the recommendations of the NAS 
study and therefore appropriate to satisfy the requirements of the 
TREAD Act. We agree that it is important to inform consumers of the 
effectiveness of yaw stability control in reducing single-vehicle 
crashes, and we will determine its effectiveness from crash report data 
as sufficient data becomes available.

C. The J-Turn and Fishhook Maneuvers

    There were a number of comments regarding the J-Turn and Fishhook 
test protocols from the Alliance, GM, Toyota, Honda, Nissan, Renfroe 
Engineering, Carr Engineering, Mechanical Systems Analysis Inc, and 
Automotive Testing Inc. In addition, Ford made a detailed presentation 
elaborating on some of the subjects introduced in the Alliance comment. 
The Ford presentation material was placed in Docket NHTSA-2001-9663.
    A number of the commenters objected to the J-Turn maneuver because 
they thought it was not representative of real driving, involved too 
fast a steering movement, or was redundant. Since its results were not 
used in the risk model, we agree that it is redundant. As a result, we 
are no longer planning to use it in the NCAP testing program.
    Except for Suzuki, Carr Engineering and Ford, those who commented 
on the maneuver tests supported the Fishhook maneuver. Carr Engineering 
and Advocates objected to calling the Fishhook maneuver a road edge 
recovery test as we had done in the NPRM notice. While the Fishhook 
maneuver includes steering commands like a crash involving road edge 
recovery, it is performed on a smooth uniform surface instead of one 
with vertical drop-offs and friction coefficients differences that 
exist at road edges. To accommodate these concerns, we will refer to 
the maneuver as the Fishhook.

D. Tire Wear

    The effect of tire wear on test results and the tire changing 
protocol was addressed by several commenters. Tire shoulder wear during 
limit maneuver tests is much more severe than in ordinary driving and 
has the effect of increasing the lateral acceleration capability of the 
vehicle. After a number of tests, the tire wear causes the vehicle to 
tip up more easily, and there is concern that a vehicle with test-worn 
tires does not represent a typical street driven vehicle. In the 25 
vehicle tests, new tires were used for each maneuver (FH, FL, JH, JL) 
which limited the tires to no more than 6 runs in each direction (4 for 
Fishhooks) before detecting tip-up if it occurred.
    Ford gave an example using a Ford Ranger 4WD that was apparently 
known to tip up at 53 mph with worn tires in a J-Turn test. The vehicle 
was equipped with new tires and tested repeatedly at 53 mph. It did not 
tip up during the first three runs, but during the fourth run a large 
increase in lateral acceleration and sideslip angle occurred and the 
vehicle tipped up. It continued this behavior for two subsequent runs, 
and the tires exhibited a large amount of shoulder wear after only six 
runs. We have noticed similar tire wear effects, but not in so few 
runs. The J-Turn tests are of much longer duration than Fishhook tests 
and produce more wear per run. Also tests run at lower speeds 
approaching tip-up speed produce less wear than tests performed at a 
higher speed just below the tip-up speed. Ford's example of a worst 
case in which the tire wear of just three runs changed vehicle behavior 
from no tip to tip-up is an effective illustration of the tire wear 
problem.
    We believe this problem is much less acute for Fishhook tests. We 
performed a similar experiment using a 2001 Ford Explorer 4 door 4WD 
that we knew would tip up at 40 mph on worn tires in a Fishhook 
maneuver. We performed 18 test runs without tip-up and then experienced 
a 20 degree tip-up against the outriggers on the nineteenth run. We 
performed three more runs and experienced two more tip-ups. Renfroe 
Engineering also commented about tire wear effects citing an UMTRI 
study in which lateral tire forces remained steady for about 10 runs 
and then increased to a maximum force at about 20 runs.
    Ford suggested a tire change protocol to limit tire wear. We intend 
to test a number of vehicles in the summer of 2003. During these tests 
we will use the tire change protocol of Appendix I because we believe 
this appropriately limits the effect of tire wear. However, we intend 
to confirm tip-ups using new (broken in but not worn) tires when 
appropriate to make sure that the

[[Page 59260]]

vehicle scores have not been affected by tire wear. We will consider 
the results of this exercise in deciding whether any changes in the 
tire change protocol are necessary.

E. Pavement Temperature

    The Alliance and Toyota commented on the potential effect of 
pavement temperature on Fishhook maneuver results. Toyota has observed 
increases in pavement friction as an apparent consequence of increases 
in pavement temperature. It also supplied a computer simulation of 
Fishhook tests that showed a large decrease in the speed at tip-up with 
increases in surface friction. Taken together, Toyota's information 
predicts a decrease in tip-up speed in a Fishhook maneuver of over 15 
mph for a 70 degree F increase in pavement temperature. While the risk 
model for ratings does not depend on tip-up speed, the temperature 
effects predicted by Toyota would prevent most of the vehicles that 
tipped up in a summer test from having tip-up in a winter test. NHTSA 
ran a number of tests to evaluate the temperature sensitivity of J-Turn 
and Fishhook tests (NHTSA Technical Report ``Testing to Determine the 
Effects of Ambient Temperature on Dynamic Rollover Testing'', docketed 
with this notice). We tested the 2001 Toyota 4Runner 4WD (with and 
without yaw stability control enabled) and the 2001 Chevrolet Blazer 
2WD on the same test track during cold, moderate and hot ambient 
temperature. The difference between cold and hot ambient temperature 
was about 60 degrees F. We do not have pavement temperatures, but there 
is no reason to believe that the range of pavement temperature is less 
than the range of ambient temperature. The whole test procedure 
including the determination of handwheel angles based on the 0.3g 
steady state curve was repeated at each temperature. The results are 
given in Table 2. Every test that failed to cause tip-up in cold 
weather also failed to cause tip-up in hot weather, and the two tests 
that caused tip-up in hot weather also caused tip-up in cold weather. 
Thus, the temperature effect predicted by the commenters did not occur. 
The tip-up speeds for the Blazer in the right and left Fishhooks 
repeated to within 1 mph despite differences in ambient temperature of 
60 degrees F, seasonal differences in pavement surface, and the use of 
three different sets of tires. The only temperature effect observed was 
that the Blazer tipped up in the J-Turn in cold weather but did not in 
the moderate and hot weather tests. This is the opposite of the 
temperature effect predicted by the commenters and occurred during a 
maneuver we no longer intend to use. We do not think it is necessary to 
set tight surface temperature limits on the test protocol as suggested 
by the commenters.

                            Table 2.--Results From NHTSA J-Turn and Fishhook Tests at Various Ambient Temperature Conditions.
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                        Initial Steer Left        Initial Steer Right
                                                                                                   -----------------------------------------------------
                                                                             Ambient     Commanded    Wheel lift,                Wheel Lift,
  Test vehicle and configuration      Test maneuver       Test condition   temperature   handwheel    front/rear     Maneuver    front rear     Maneuver
                                                                             ([deg]F)      angle       (inches)      entrance     (inches)      entrance
                                                                                         (degrees) ----------------   speed   ----------------   speed
                                                                                                     Front   Rear     (mph)     Front   Rear     (mph)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Toyota 4Runner, VSC disabled.....  NHTSA..............  Cold.............          30          345       0       0       62.1       0       0       61.7
                                   J-Turn\1\..........
                                                        Moderate.........          79          354       0       0       60.4       0       0       60.0
                                                        Hot..............          87          358       0       0       61.8       0       0       60.3
                                   Fishhook\2\........  Cold.............          32          280       1       0       51.1       0       1       51.7
                                                        Moderate.........       74-73          287       0       0       48.0       0       0       48.5
                                                        Hot..............          89          290       1       0       51.4       0       0       50.8
Toyota 4Runner, VSC enabled......  NHTSA..............  Cold.............          28          345       0       0       61.8       0       0       62.4
                                   J-Turn\1\..........
                                                        Moderate.........          75          354       0       0       59.4       0       0       58.2
                                                        Hot..............          90          358       0       0       61.9       0       0       61.6
                                   Fishhook\2\........  Cold.............          31          280       0       0       51.3       0       0       51.7
                                                        Moderate.........          72          287       0       0       48.8       0       0       50.1
                                                        Hot..............          90          290       0       0       50.7       0       0       51.3
Chevrolet Blazer.................  NHTSA..............  Cold.............          29          381     5-8     5-8       58.0     5-8     5-8       54.8
                                   J-Turn\1,3\........
                                                        Moderate.........          83          401       0       0       60.9       0       0       62.2
                                                        Hot..............          86          392       0       0       60.3       0       0       59.4
                                   Fishhook\2,3\......  Cold.............          30          309     5-8     5-8       40.2     2-3     2-3       39.1
                                                        Moderate.........          74          326     3-4     3-4       40.3     4-5     4-5       40.1
                                                        Hot..............          90          319     2-3     2-3       39.4     2-3     2-3      38.8
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ NHTSA J-Turn maximum nominal entrance speed was 60 mph.
\2\ Fishhook maximum nominal entrance speed was 50 mph.
\3\ Two-wheel lift =2 inches was observed during tests highlighted in bold.

F. Surface Friction

    A practical problem for the repeatability of any limit maneuver 
test is the possibility that the surface friction properties of the 
test track will change. Ford commented that computer simulations of 
several of its SUVs showed that a change in surface coefficient of 0.05 
would change the tip-up speed in a fishhook test by as much as 12 mph 
in one example (6 mph and 4 mph respectively for two other example 
vehicles). It also commented that a seasonal variation in surface 
coefficient of 0.05 could be typical of test tracks, and that its own 
test track exhibited a long-term trend of an increase in coefficient of 
0.02 per year (which would change the tip-up speed of the first example 
vehicle by 8 mph in Ford's simulation). Ford's simulations are even 
more pessimistic than Toyota's regarding the possibility of repeatable 
Fishhook tip-up speeds given normal variations in surface properties 
and temperatures. However, we have not observed these large variations 
in tip-up speed in actual tests. The very close repeatability of tip-up 
speed for the Blazer in Table 2 extended over likely

[[Page 59261]]

seasonal changes in the pavement as well as changes in ambient 
temperature.
    Additionally, NHTSA performed a study using the same 4Runner and 
Blazer mentioned above for J-Turn and Fishhook tests at Daimler 
Chrysler's Arizona Proving Grounds (APG) and General Motors Desert 
Proving Grounds (DPG) as well as TRC of Ohio, where our maneuver test 
development has been conducted (NHTSA Technical Report ``Testing to 
Determine the Effects of Surface Variability on Dynamic Rollover 
Testing'', docketed with this notice). Table 3 shows the peak and slide 
braking coefficients (multiplied by 100) measured at these facilities.

                               Table 3.--Friction Numbers for all Test Facilities
----------------------------------------------------------------------------------------------------------------
                                            Peak braking coefficient                     Skid number
            Test facility            ---------------------------------------------------------------------------
                                             Dry                Wet                Dry                Wet
----------------------------------------------------------------------------------------------------------------
TRC.................................              94-96              69-83              81-84              47-54
DPG.................................              86-93              74-77              83-85              60-64
APG.................................              90-93              75-80              81-84              56-59
----------------------------------------------------------------------------------------------------------------

    Table 4 shows the results of the maneuver tests. As in Table 2, the 
vehicles were loaded with the equivalent of a 2-occupant load, like the 
light load condition of the 25 vehicle test. The 4Runner did not tip up 
at TRC and it did not tip up at the other facilities. The Blazer did 
not tip up in the J-Turn at TRC, but it did at the other facilities. We 
do not think that this is a result of the surface coefficient of 
friction (due to the similarities of the ranges) but rather due to the 
greater degree of vertical irregularities and pavement cracks at DPG 
and APG than at TRC. Tip-up is often triggered by vertical oscillations 
of the vehicle suspension during high cornering forces in maneuver 
tests. DPG had the most vertical surface irregularities that caused the 
Blazer to tip up most easily. The Blazer tipped up in the Fishhook at 
TRC, and it also tipped up in the Fishhook at the other facilities. 
Again, the tip-up speeds were lower at APG and DPG, which would be 
expected due to the greater surface irregularities.

                                                 Table 4.--Results From NHTSA J-Turn and Fishhook Tests
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                               Initial steer left              Initial steer right
                                                                                       -----------------------------------------------------------------
                                                                            Commanded     Moderate or major    Maneuver    Moderate or major    Maneuver
  Test vehicle and configuration        Test maneuver      Test facility    handwheel           lift           entrance          lift           entrance
                                                                            angle, deg ----------------------   speed,  ----------------------   speed,
                                                                                               Yes/No            mph            Yes/No            mph
--------------------------------------------------------------------------------------------------------------------------------------------------------
Toyota 4Runner, VSC enabled.......  NHTSA...............  TRC                      354  No..................      58.21  No..................      59.29
                                    J-Turn \1\..........
                                                          DPG                      402  No..................      61.56  No..................      61.21
                                                          APG                      362  No..................      61.68  No..................      62.11
                                    Fishhook \2\........  TRC                      287  No..................      48.75  No..................      50.13
                                                          DPG                      327  No..................      53.05  No..................      50.94
                                                          APG                      294  No..................      52.63  No..................      51.44
Toyota 4Runner, VSC disabled......  NHTSA...............  TRC                      354  No..................       60.4  No..................      60.00
                                    J-Turn \1\..........
                                                          DPG                      402  No..................      60.97  No..................      61.63
                                                          APG                      362  No..................      62.38  No..................      62.27
                                    Fishhook \2\........  TRC                      287  No..................      49.84  No..................      49.79
                                                          DPG                      327  No..................      52.20  No..................      51.93
                                                          APG                      294  No..................      51.04  No..................      51.14
Chevrolet Blazer..................  NHTSA...............  TRC                      401  No..................      60.90  No..................      62.27
                                    J-Turn \1\..........
                                                          DPG                      382  Yes.................      49.80  Yes.................      44.90
                                                          APG                      395  Yes.................      57.36  Yes.................      58.68
                                    Fishhook \2\........  TRC                      326  Yes.................      40.32  Yes.................      40.09
                                                          DPG                      311  Yes.................      37.80  Yes.................      38.01
                                                          APG                      321  Yes.................      35.52  Yes.................     38.54
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ NHTSA J-Turn maximum nominal entrance speed is 60 mph.
\2\ Fishhook maximum nominal entrance speed is 50 mph.

    We recognize the potential difficulties caused by changes in 
surface friction coefficient, and we have tried to minimize them. We 
have observed the Fishhook maneuver to be less sensitive to surface 
conditions than the J-Turn, and we have used changes in vehicle load 
condition rather than changes in tip-up speed to signify degrees of 
test severity in a way least likely to be influenced by surface 
coefficient. None of the changes of pavement and temperature in our 
test experience has caused a change in the Fishhook result (tip-up or 
no tip-up) for a vehicle. We believe the comments based on computer 
simulation overstate the sensitivity observed in our actual tests.

G. Steering Reversal

    Honda commented that using a roll rate measurement within 1.5 
degrees/sec of a zero crossing as shown in Figure 2 to trigger the 
reverse steering in a fishhook maneuver occasionally leads to an 
unusually long dwell time (T1) for certain vehicles at 
certain load conditions. It suggested setting a default value for dwell 
time to force a reverse

[[Page 59262]]

steering action if the absolute value of the vehicle roll rate stayed 
too long at a value that was very low but not low enough to trigger 
reversal. It explained that tests in which excessive dwell times 
occurred would be less severe and possibly not cause a tip-up that 
would have occurred with a shorter dwell.
    Automotive Testing Inc. commented at length on the same phenomenon. 
It observed that the low but steady roll rate above 1.5 degrees/sec 
that can delay the triggering of steering reversal is a result of tire 
deflections continuing the roll motion of the whole vehicle after the 
point of maximum roll of the suspension system. It believes that a 
default trigger negates the design of the maneuver to let the vehicle 
motions select the steering response, but describes some ways of using 
filtering of the roll rate signal to cause the steering to trigger 
earlier in these cases. But it acknowledges that letting the vehicle 
react to the actual roll motion of the whole vehicle rather than to a 
roll signal distorted by signal processing may be preferable.
    At this point we are preserving the consistent application of the 
fishhook steering algorithm. We do not believe that commenters have 
presented us a substantive reason to depart from this application. If 
the vehicle tips up despite a long dwell time, there is no change in 
test result. If the vehicle does not tip, it will be retested with a 
reduced steering angle according to the current procedure, which may 
change the roll frequency harmonics and dwell time. We will observe the 
steering reversal dwell times during the first group of tests and, if 
necessary, reconsider the commenter's observations on this issue.

H. Fifteen-Passenger Vans

    The National Transportation Safety Board, Public Citizen and others 
commented on the rollover issues surrounding fifteen-passenger vans. 
NHTSA agrees that it is important to investigate the commenters' 
concerns about the rollover susceptibility of fifteen-passenger vans. 
To do this, we will conduct an evaluation of fifteen-passenger vans' 
rollover susceptibility at different loading conditions and evaluate 
available electronic stability control systems on these vehicles.

I. Tip-up Criterion

    Mechanical Systems Analysis, Inc. and several other commenters 
suggested that the tip-up criterion of 2 inches simultaneous wheel lift 
is too conservative. It recommended a criterion of 20 degrees body roll 
instead because suspension bouncing on test surface irregularities 
could influence performance under our criterion. Other similar 
recommendations were given for body roll angles between 15 and 20 
degrees. The 2 inch wheel lift criterion is met at about 11 degrees of 
body roll on average.
    NHTSA's tests were performed on a very smooth test area at TRC of 
Ohio. The tip-up criterion maximized driver safety and minimized tire 
wear by allowing us to increase speed in 5 mph increments with a 
reasonable expectation of avoiding sudden violent tip-ups that could 
``pole-vault'' the vehicle on its outriggers. However, we observed tip-
ups at lower than expected speeds during tests at other facilities (DPG 
and APG as described above) that were probably influenced by surface 
irregularity as described by the commenter. We believe that our tip-up 
criterion is appropriate for an excellent facility like TRC, but we 
agree that the criterion should be revisited if NCAP tests were to take 
place at a facility with a more irregular surface.

J. Testing of Passenger Cars v. Light Trucks

    Consumers Union and IIHS recommended that we not test passenger 
cars in order to devote all the available time and resources for 
maneuver tests to light trucks. We agree that it is very unlikely that 
passenger cars will tip up in the maneuver test. We have tested 
passenger cars at the low end of the SSF range for passenger cars 
without observing any tip-ups. It seems reasonable to rate passenger 
cars using the ``no tip-up'' curve of the risk model along with SSF 
measurements. However, we prefer to track whether this continues to be 
true. Hence, we will continue to test a few passenger cars each year at 
the low end of the SSF range to reinforce the ``no tip-up'' assumption. 
Therefore, two passenger cars are listed in Table 5.

K. Testing With Stability Control Systems

    Toyota suggested that NHTSA should selectively choose vehicles with 
optional equipment that assists the driver in controlling the vehicle 
such as electronic yaw stability control, while in a previous comment 
Honda suggested the opposite policy. Honda believed that even a vehicle 
with standard stability control should be tested with it turned off if 
the vehicle has an ``off'' switch. It has been NHTSA's policy for 
rollover resistance ratings that we test vehicles most representative 
of those sold. Also, we are interested in the potential safety benefits 
of electronic yaw stability control and have alerted consumers to its 
purpose and availability on individual models in our present consumer 
information. Therefore, when it is standard equipment or optional 
equipment found on the majority of vehicles of a particular model, we 
will test with stability control turned on and report that the test 
vehicle was so equipped. Also, if the market penetration of a stability 
control option is too low for NHTSA to choose it for inclusion on our 
test vehicle, we will consider optional NCAP tests at the 
manufacturer's expense.

VIII. Final Form for Rollover Resistance Ratings--Alternative I

A. Combined Ratings

    NHTSA will use the statistical model shown in Figure 4 to combine 
the vehicle's SSF measurement and its performance in the Fishhook 
maneuver with 5-occupant loading as a prediction of its rollover rate 
per single-vehicle crash. The predicted rollover rate will be 
translated into a star rating in the same way used in the present 
rollover resistance ratings: one star for a rollover rate greater than 
40 percent; two stars, greater than 30 percent; three stars, greater 
than 20 percent; four stars, greater than 10 percent; five stars, less 
than or equal to 10 percent.
    The decision to combine the static (SSF) and the dynamic (maneuver 
test) vehicle measurements in a single rollover resistance rating is 
consistent with the view of most commenters that separate ratings would 
be confusing to consumers. It is also the best way of achieving NHTSA's 
goal of presenting risk-based ratings because it maximizes the vehicle 
information used to make the prediction of the rate of rollovers per 
single-vehicle crash. Those who favored separate static and dynamic 
ratings expressed concern that the influence of electronic stability 
control would be small in the combined rating. It is true that 
electronic stability control will not have a great influence on 
rollover resistance ratings because the dynamic test result has less 
predictive power than the static measurement on rollover rate and the 
effect of electronic (yaw) stability control on the dynamic test is 
also modest. We believe that the potential benefit of electronic 
stability control lies in helping drivers to stay on the road and away 
from tripping devices rather than providing much increase in rollover 
resistance, especially regarding tripped rollovers. Rather than reduce 
the rate of rollovers in single-vehicle crashes, electronic stability 
control may reduce the number of single-vehicle crashes in the first 
place. However, its effectiveness in reducing single-vehicle

[[Page 59263]]

crashes remains to be demonstrated by crash statistics.
    For the present time, we will retain the use of five stars to 
express rollover resistance ratings. Focus groups consistently find 
that presentation understandable. However, the NAS and a number of 
commenters were in favor of presentations that are able to show smaller 
differences between vehicles, contrast the range of ratings between 
types of vehicles and show the relative position of a vehicle's rating 
among other vehicles of the same type. NHTSA is performing additional 
consumer research to determine the best approach to providing consumers 
with more detailed information to supplement the star ratings. Several 
presentation methods are being tested, and we will consider those test 
results and propose appropriate changes to how we present rollover 
information to consumers.

B. Dynamic Testing

    The Fishhook maneuver test will be conducted according to the 
procedure in Appendix I, and we will discontinue the J-Turn maneuver 
test. This decision is a consequence of the logistic regression 
analysis of the crash data, SSF and results of the J-Turn and Fishhook 
tests at two load conditions for 25 vehicles. From a statistical point 
of view, the J-Turn test results were redundant in the presence of the 
Fishhook test results. The J-Turn test also seems to be more sensitive 
to irregularities in pavement surface and friction and changes in 
ambient temperature than the Fishhook test. It also causes more concern 
about tire wear effects than the Fishhook, and it was criticized by 
some commenters as less representative of ``real-world'' driving 
situations.
    We have decided to change the heavy load condition from an 
anthropomorphic dummy (water dummy) in every rear seating position 
(along with the test driver and instruments of approximately a 
passenger weight in the front) to a standard load representing five 
occupants in all vehicles capable of at least that loading. During the 
test of the 25 vehicles, it became obvious that heavy load tests were 
being run at very unequal conditions especially between vans and other 
vehicles (two water dummies in some vehicles but six water dummies in 
others). While very heavy passenger loads can certainly reduce rollover 
resistance and potentially cause special problems, crashes at those 
loads are too few to greatly influence the overall rollover rate of 
vehicles. Over 94% of van rollovers in our 293,000 crash database 
occurred with five or fewer occupants, and over 99% of rollovers of 
other vehicles occurred with five or fewer occupants. The average 
passenger load of vehicles in our crash database was less than two: 
1.81 for vans; 1.54 for SUVs; 1.48 for cars; and 1.35 for pickup 
trucks. In order to use the maneuver tests to predict real-world 
rollover rates rather than investigate possible poor performance at 
high occupancy levels, it is not useful to test the vehicles under 
widely differing loadings while there is much less loading variation 
represented in the crash statistics. Consequently, the maneuver test 
data used in the logistic regression analysis involving the 25 dynamic 
test vehicles in the heavy load condition represented performance with 
a 5-occupant loading (obtained using three water dummies in the rear 
seating positions) for all vehicles capable of carrying at least that 
load.
    The use of dynamic maneuver tests creates the need for a policy 
regarding tire de-beading. The tests are conducted using the tire 
pressure recommended by the vehicle manufacturer and labeled on the 
vehicle. We have experienced a number of instances in which the tire 
bead became unseated from the rim, resulting in total air loss and rim 
contact with the paved surface. This causes damage to the test facility 
and the possibility of a rollover of the test vehicle. For at least a 
year, we have been using inner tubes in all tires placed on rollover 
test vehicles. This action reduces the instances of total de-beading, 
but does not eliminate them entirely. In some instances, a tire with a 
tube that is not pinched during the process can experience a partial 
de-bead in which the rim makes contact with the pavement surface and 
then the tire becomes remounted on the rim by the pressure of the tube. 
It has been NHTSA's experience on the test track that if a maneuver 
results in rim contact without destroying the tube, the next run at a 
higher speed will destroy the tube and cause a complete de-beading of 
the tire and hard contact of the rim with risk to the driver, test 
surface and vehicle.
    In the case of rim contact without total de-beading, it is a near 
certainty that total de-beading would have occurred without the tube, 
and total de-beading despite the tube is highly likely at the next 
speed increment. Thus, we consider rim contact to indicate de-beading, 
and it will be NHTSA's policy to terminate the test if rim contact with 
the pavement is observed even if the tube prevents total de-beading.
    The vehicle did not actually tip up in the maneuver if the test is 
terminated as a result of rim contact indicating tire de-beading. 
However, debeading is a bad outcome for the test because tire de-
beading is associated with on-road tripped rollovers that actually 
outnumber on-road untripped rollovers. Therefore, it would be improper 
to ignore tire debeading and predict the vehicle's rollover rate as if 
it had completed the test without tip-up or de-beading. The only 
alternative in the case of rim contact is to simply not compute a 
rollover resistance rating of the vehicle because the test was not 
completed. It will be reported that the dynamic test could not be 
completed because of tire debeading, but the SSF measurement will be 
retained in the detailed consumer information.

C. Demonstration Program

    In April 2003, NHTSA's VRTC began the Demonstration Test program at 
TRC of Ohio using the test protocol of Appendix I for Fishhook maneuver 
tests of 18 new vehicles. Table 5 lists the vehicles in this group. We 
will verify tip-ups using new tires as explained in our answer to 
Ford's comments in Section VII. Unless we discover serious procedural 
problems, these vehicles will be given 2004 NCAP rollover resistance 
ratings according to the system established in this final notice.

                                Table 5.--Vehicles Included in Demonstration Test
----------------------------------------------------------------------------------------------------------------
                                Make                                  Model                        Bodystyle
----------------------------------------------------------------------------------------------------------------
1...............  Chevrolet......................  Silverado 4x2.............................  PU ext. cab.
2...............  Chevrolet......................  Silverado 4x4.............................  PU ext. cab.
3...............  Chevrolet......................  Trailblazer 4x2...........................  4-dr Utility.
4...............  Chevrolet......................  Trailblazer 4x4...........................  4-dr Utility.
5...............  Ford...........................  Explorer 4x2..............................  4-dr Utility.
6...............  Ford...........................  Explorer 4x4..............................  4-dr Utility.
7...............  Ford...........................  Explorer SportTrac 4x2....................  4-dr Utility.
8...............  Ford...........................  Explorer SportTrac 4x4....................  4-dr Utility.

[[Page 59264]]

 
9...............  Ford...........................  Focus.....................................  4-dr wagon.
10..............  Jeep...........................  Liberty 4x2...............................  4-dr Utility.
11..............  Jeep...........................  Liberty 4x4...............................  4-dr Utility.
12..............  Subaru Outback (4x4)...........  4-dr wagon................................
13..............  Toyota.........................  Echo......................................  4-dr sedan.
14..............  Toyota.........................  4Runner 4x2...............................  4-dr Utility.
15..............  Toyota.........................  4Runner 4x4...............................  4-dr Utility.
16..............  Toyota.........................  Tacoma 4x2................................  PU ExCab.
17..............  Toyota.........................  Tacoma 4x4................................  PU ExCab.
18..............  Volvo..........................  XC90 (4x4)................................  4-dr Utility.
----------------------------------------------------------------------------------------------------------------

X. Assessment of Costs and Benefits

    Since this is a consumer information program, no Regulatory 
Evaluation was developed for this notice. Adding the dynamic maneuver 
tests to the Rollover NCAP will not require vehicle manufacturers to 
take any action. 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 amendment will 
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 will 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 action will 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 2002 results in $113 million (110.66/98.11 = 1.13). The 
assessment may be included in conjunction with other assessments, as it 
is here.
    The action does not impose regulatory requirements on any 
manufacturer or other party.

F. Civil Justice Reform

    This action will 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 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 document 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 requires each agency to write all rules in 
plain language. This action will not result in regulatory language.


[[Page 59265]]


    Issued on: October 2, 2003.
Jeffrey W. Runge,
Administrator.

BILLING CODE 4910-59-P
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[GRAPHIC] [TIFF OMITTED] TR14OC03.001


[[Page 59267]]


[GRAPHIC] [TIFF OMITTED] TR14OC03.002


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[GRAPHIC] [TIFF OMITTED] TR14OC03.003


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Appendix I. Fishhook Maneuver Test Procedure

1.0 Introduction

1.1 General

    This document describes the test procedure used by the National 
Highway Traffic Safety Administration's (NHTSA) New Car Assessment 
Program (NCAP) to evaluate light vehicle dynamic rollover 
propensity. The procedure is comprised of one characterization 
maneuver and one rollover resistance maneuver.

1.2 Rollover Resistance Requirements of the TREAD Act

    Section 12 of the ``Transportation Recall, Enhancement, 
Accountability and Documentation (TREAD) Act of November 2000'' 
reflects the desire of Congress to supplement SSF [Static Stability 
Factor] with a dynamic stability test using vehicle maneuvers. 
Congress directed NHTSA to ``develop a dynamic test on rollovers by 
motor vehicles for a consumer information program; and carry out a 
program conducting such tests.'' NHTSA's NCAP Light Vehicle Dynamic 
Rollover Propensity Test Procedure described in this document was 
developed as part of NHTSA's effort to fulfill the requirements of 
the TREAD Act.

1.3 Recent NHTSA Light Vehicle Dynamic Rollover Propensity Research

    During the spring through fall of 2001 NHTSA performed an 
extensive assessment of many test track maneuvers potentially 
capable of quantifying on-road, untripped rollover propensity. In 
brief, five vehicle characterization and nine dynamic rollover 
propensity maneuvers were studied. Each maneuver was either 
discarded or retained for subsequent program phases. The 2001 
research project is documented in [1].
    During the spring through fall of 2002 NHTSA performed a 
comprehensive evaluation of rollover resistance for a broad spectrum 
of twenty-six light vehicles. The test vehicles were evaluated with 
one Characterization maneuver and two Rollover Resistance maneuvers. 
Up to two load configurations per vehicle were used. The 2002 
research project is documented in [2].

2.0 Test Equipment

2.1 Vehicle Load Configurations

    NHTSA's dynamic rollover propensity test procedure uses one of 
two loading configurations: Nominal or Multi-Passenger. A 
description of each configuration is provided below.
    Both vehicle load configurations include instrumentation, a 
steering machine, and outriggers.
    Test vehicle bumper assemblies are removed for outrigger 
installation. The reduction in vehicle weight due to the removal of 
the bumpers is offset by the additional weight of the outriggers and 
their mounting system. The outrigger system typically outweighs the 
bumper assemblies.

2.1.1 Nominal Load Configuration

    The Nominal Load Configuration consists of the driver, 
instrumentation, steering machine, outriggers, and full tank of 
fuel. Weight and location specifications for the data acquisition 
system and steering machine are presented in Table I.1 and Figure 
I.1.

                                    Table I.1.--Equipment Location and Weight
----------------------------------------------------------------------------------------------------------------
                                                                                                Weight, typical
                  Equipment                                       Location                           (lbs)
----------------------------------------------------------------------------------------------------------------
Data Acquisition System......................  Front passenger seat.........................                  58
Steering Machine.............................  Handwheel....................................                  31
Steering Machine Electronics Box.............  Passenger row foot well behind the front                       39
                                                passenger seat. If vehicle does not have a
                                                rear passenger row foot well, the
                                                Electronics Box should be placed in the
                                                front passenger seat foot well.
----------------------------------------------------------------------------------------------------------------

    Non-pickup truck vehicles with only front designated seating 
positions use the Nominal Load Configuration.

2.1.2 Multi-Passenger Configuration

    The Multi-Passenger Configuration includes all elements of the 
Nominal Load Configuration plus ballast in the form of water 
dummies. Water dummies are installed as follows:
    For vehicles with three or more designated rear seating 
positions, three 175 lb water dummies are used. The water dummies 
shall be positioned on the rear seats (second seating row) closest 
to driver and front passenger seats (first seating row). If there 
are only two seating positions in the second seating row, the third 
water dummy shall be placed in the center of the third seating row, 
provided it is a designated seating position. Refer to Figure I.2.
    For vehicles with two designated rear seating positions, two 175 
lb water dummies shall be positioned in the rear seats. Refer to 
Figure I.3.
    For pickups with only front designated seating positions, three 
175 lb water dummies will be used. The water dummies shall be 
positioned behind the cab in a manner that emulates a second seating 
row. If it is not possible to fit three water dummies directly 
behind the cab, the third water dummy shall be placed in the center 
of a simulated third seating row. Refer to Figure I.4.
    For pickups with two seating rows, three 175 lb water dummies 
will be used. If the second seating row includes three designated 
seating positions, each water dummy shall be placed in these 
positions. If the second seating row includes two designated seating 
positions, two 175 lb water dummies shall be positioned in the 
second seating row of the cab, and the third water dummy shall be 
positioned behind the cab in a manner that emulates the center 
seating position of a third seating row. Refer to Figure I.5.
    For all vehicles, if the Multi-Passenger Configuration results 
in the vehicle exceeding its Gross Vehicle Weight Rating (GVWR) and/
or rear Gross Axle Weight Rating (GAWR), the weight of each dummy 
will be equally reduced until the GVWR and/or rear GAWR are no 
longer exceeded. The weight of the water dummies shall not be 
reduced if only the front GAWR is exceeded and the front axle weight 
does not exceed the front GAWR by more that 50 pounds, i.e., if the 
Multi-Passenger Configuration results in the vehicle exceeding its 
front GAWR, and its GVWR and/or rear GAWR, the weight of each dummy 
will be equally reduced until the GVWR and rear GAWR are no longer 
exceeded and the front GAWR is not exceeded by more that 50 pounds.
    For non-pickup truck vehicles with only front designated seating 
positions, the Multi-Passenger Configuration is omitted from the 
test matrix.

2.2 Safety Outriggers

    Safety outriggers are installed on all test vehicles during all 
test maneuvers. NHTSA uses outriggers machined from 6Al-4V titanium. 
NHTSA's ``short'' outriggers are used for vehicles with baseline 
weights under 3,500 pounds in a baseline condition (as delivered); 
``standard'' outriggers are used for vehicles with baseline weights 
from 3,500 and 7,000 pounds; and ``long'' outriggers are used for 
vehicles with baseline weights from 7,001 to 10,000 pounds. 
Information on NHTSA's titanium outrigger system is documented in 
[3].

2.3 Tires

    All tires must be new, and of the same make, model, size, and 
DOT specification of those installed on vehicles when purchased new. 
Tire inflation pressures are to be in accordance with the 
recommendations indicated on each vehicle's identification placard.

2.3.1 Tire Mounting Technique

    When mounting tires to the rims used for testing, no tire 
mounting lubricant should be used. Lubricant is not used due to 
uncertainty surrounding the occurrences of tire debeading observed 
during NHTSA's rollover research. To eliminate the possibility of 
tire lubricant contributing to this phenomenon, it should not be 
used. Because no lubricant is used, care must be taken to confirm 
that the tire is fully seated on the

[[Page 59270]]

wheel rim at the completion of the mounting procedure.

2.3.2 Frequency of Tire Changes

    To minimize the effects of tire wear on vehicle response and 
rollover propensity, rollover research requires frequent tire 
changes. For each loading condition, the following guidelines must 
be followed:
    [sbull] One set of tires is to be used for each Slowly 
Increasing Steer test series. Each series is comprised of left and 
right steer tests.
    [sbull] Up to two tire sets are to be used for the Fishhook 
maneuver test series. The actual number of tire sets used is 
dependent on the response of each vehicle. The tire change protocol 
is presented in the Fishhook maneuver test procedure (Section 3.2). 
Note: A tire change between the completion of the Slowly Increasing 
Steer maneuver and initiation of Fishhook testing is not required 
provided the abbreviated Slowly Increasing Steer procedure described 
in Section 3.1.2 is used. If the abbreviated procedure is not used 
(i.e., the maneuver is performed such that maximum lateral 
acceleration is achieved), a tire change between the completion of 
the Slowly Increasing Steer maneuver and initiation of Fishhook 
testing is required, as tire wear associated with these tests may 
potentially confound Fishhook test outcome.

2.3.3 Use of Inner Tubes

    Fishhook maneuvers have been shown to produce debeading of the 
outside front and rear tires. The occurrence of debeads can result 
in significant damage to the test surface. NHTSA research has 
concluded the easiest, most cost effective way to minimize debeading 
is the use of inner tubes designed for radial tires. Inner tubes 
must be installed prior to any Fishhook test `` one inner tube for 
each of the vehicle's tires. Inner tubes should be appropriately 
sized for the test vehicle's tires.
    Installation of inner tubes is not required prior to Slowly 
Increasing Steer tests, regardless of vehicle or load condition.

2.4 Data Collection

    All data is to be sampled at 200 Hz. NHTSA's signal conditioning 
consists of amplification, anti-alias filtering, and digitizing. 
Amplifier gains are selected to maximize the signal-to-noise ratio 
of the digitized data. Filtering is performed with two-pole low-pass 
Butterworth filters with nominal cutoff frequencies selected to 
prevent aliasing. The nominal cutoff frequency is 15 Hz (calculated 
breakpoint frequencies are 18 and 19 Hz for the first and second 
poles respectively).
    Data collection is initiated manually by the test driver 
immediately before the start of the maneuver or automatically by 
``Handwheel Command Flag'' signal from the steering machine (refer 
to Section 3.2.4.2.2, Handwheel Command Flag).

2.5 Instrumentation

    Each test vehicle is to be equipped with sensors, a data 
acquisition system, and a programmable steering machine. Equipment 
location and weight specifications are presented in Table I.1 and 
Figure I.1.

2.5.1 Sensors and Sensor Locations

    Table I.2 lists the sensors required by NHTSA's dynamic rollover 
propensity test procedure. A brief description of these sensors is 
provided in this section.

                                  Table I.2.--Recommended Sensor Specifications
----------------------------------------------------------------------------------------------------------------
              Type                      Output               Range            Resolution           Accuracy
----------------------------------------------------------------------------------------------------------------
Multi-Axis Inertial Sensing       Longitudinal,       Accelerometers: +/- Accelerometers:     Accelerometers:
 System.                           Lateral, and        2 g.                <=10 ug.            <=0.05% of full
                                   Vertical                                                    range.
                                   Acceleration.
                                  Roll, Yaw, and      Angular Rate        Angular Rate        Angular Rate
                                   Pitch Rate.         Sensors: +/-100     Sensors: <=0.004    Sensors: 0.05% of
                                                       deg/s.              deg/s.              full range.
Angle Encoder...................  Handwheel Angle...  +/-800 deg........  0.25 deg..........  +/-0.25 deg.
Ultrasonic Distance Measuring     Left and Right      5-24 inches.......  0.01 inches.......  +/-0.25% of
 System.                           Side Vehicle                                                maximum distance.
                                   Height.
Load Cell.......................  Brake Pedal Force.  0-300 lbf.........  N/A...............  N/A.
Radar Speed Sensor..............  Vehicle Speed.....  0.1-125 mph.......  0.009 mph.........  +/-0.25% of full
                                                                                               scale.
Infrared Distance Measuring       Wheel Lift........  13.75-33.5 inches.  0.10 in., short     +/-1% of full
 System.                                                                   range.              scale
                                                                          0.3 in., long
                                                                           range.
Data Flag (Handwheel Command      Pauses in           0--10 V...........  N/A...............  Flag should
 Flag).                            commanded                                                   respond within 10
                                   steering inputs.                                            ms.
Data Flag (Roll Rate Flag)......  Indication of +/-   0-10 V............  N/A...............  Flag should
                                   1.5 deg/s roll                                              respond within 10
                                   rate.                                                       ms.
----------------------------------------------------------------------------------------------------------------

2.5.1.1 Handwheel Angle

    Handwheel position is measured via an angle encoder integral 
with the programmable steering machines.

2.5.1.2 Vehicle Speed

    Vehicle speed is measured with a non-contact speed sensor placed 
at the center rear of each vehicle.
    NHTSA has had good experiences with the use of Doppler radar 
based sensors. Sensor outputs are to be transmitted not only to the 
data acquisition system, but also to a dashboard display unit. This 
allows the driver to accurately monitor vehicle speed.

2.5.1.3 Chassis Dynamics

    A multi-axis inertial sensing system is used to measure linear 
accelerations and roll, pitch, and yaw angular rates. The position 
of the multi-axis inertial sensing system must be accurately 
measured relative to the C.G. of the vehicle in the Nominal Load and 
Multi-Passenger Configurations. These data are required to translate 
the motion of the vehicle at the measured location to that which 
occurred at the actual C.G to remove roll, pitch, and yaw effects. 
NHTSA uses an independent laboratory to measure the C.G. of its test 
vehicles.
    The following equations are used to correct the accelerometer 
data in post-processing. They were derived from equations of general 
relative acceleration for a translating reference frame and use the 
SAE Convention for Vehicle Dynamics Coordinate Systems. The 
coordinate transformations are:
[GRAPHIC] [TIFF OMITTED] TR14OC03.038


[[Page 59271]]


where,

x''corrected, y''corrected, and 
z''corrected = longitudinal, lateral, and vertical 
accelerations, respectively, at the vehicle's center of gravity
x''accel, y''accel, and z''accel = 
longitudinal, lateral, and vertical accelerations, respectively, at 
the accelerometer location
x''disp, y''disp, and z''disp = 
longitudinal, lateral, and vertical displacements, respectively, of 
the center of gravity with respect to the accelerometer location
[phis]' and [phis]''=roll rate and roll acceleration, respectively
[Theta]' and [Theta]'' = pitch rate and pitch acceleration, 
respectively
[Psi]' and [Psi]'' = yaw rate and yaw acceleration, respectively

    NHTSA does not use inertially stabilized accelerometers for this 
test procedure. Therefore, lateral acceleration must be corrected 
for vehicle roll angle during data post-processing. This is 
discussed in Section 4.12.

2.5.1.4 Roll Angle

    An ultrasonic distance measurement system is used to collect 
left and right side vertical displacements for the purpose of 
calculating vehicle roll angle. One ultrasonic ranging module is 
mounted on each side of a vehicle, and is positioned at the 
longitudinal center of gravity. With these data, roll angle is 
calculated during post-processing using trigonometry.

2.5.1.5 Wheel Lift

    Wheel lift is measured individually with two height sensors 
attached to spindles installed at the wheel. Using trigonometry, the 
output of the two sensors can be used to resolve the camber angle of 
the wheel, and remove its influence from the uncorrected height 
sensor output. Information on NHTSA's wheel lift measurement system 
is documented in [4].

2.5.1.6 Brake Application

    Brake pedal force is measured with a load cell transducer 
attached to the face of the brake pedal. While brake pedal force is 
not explicitly required by this test procedure, it is important to 
monitor the driver's braking activity during testing. No test 
included in this procedure requires brake application. If the driver 
applies force to the brake pedal before completion of a test, that 
test is not valid, and should not be considered in further analyses.

2.5.2 Additional Mnemonics

2.5.2.1 Handwheel Command Flag

    Refer to Section 3.2.4.2.2, Handwheel Command Flag.

2.5.2.2 Roll Rate Flag

    Refer to Section 3.2.4.2.3, Roll Rate Flag.

2.6 Steering Machine

    A programmable steering machine is used to generate handwheel 
steering inputs for all test maneuvers. The machine must provide at 
least 35 lbf-ft of torque at a handwheel rate of 720 deg/
sec, be able to move each vehicle's steering system through its full 
range, and accept angular rate sensor feedback input for roll rate-
induced steering reversals (refer to section 3.2.4). It is 
recommended that the steering machine be capable of initiating 
steering programs at a preset road speed, and have the convenience 
of changing the steering program during test sessions.

3.0 Test Maneuvers

3.1 Slowly Increasing Steer

    The Slowly Increasing Steer maneuver is used to characterize the 
lateral dynamics of each vehicle, and is based on the ``Constant 
Speed, Variable Steer'' test defined in SAE J266 [5]. The maneuver 
is used to determine the steering that produces a lateral 
acceleration of 0.3 g. This handwheel angle is used to define the 
magnitude of steering to be used for the NHTSA Fishhook maneuver.

3.1.1 Maneuver Description (Option 1)

    To begin this maneuver, the vehicle is driven in a straight line 
at 50 mph. The driver must attempt to maintain this speed during and 
briefly after the steering is input using smooth throttle 
modulation. At time zero, handwheel position is linearly increased 
from zero to 270 degrees at a rate of 13.5 degrees per second. 
Handwheel position is held constant at 270 degrees for two seconds, 
after which the maneuver is concluded. The handwheel is then 
returned to zero as a convenience to the driver. The maneuver is 
performed three times to the left and three times to the right for 
each load configuration. Figure I.6 presents a description of the 
handwheel angles to be used during Slowly Increasing Steer, Option 
1 tests.

3.1.2 Maneuver Description (Option 2, Preferred)

    Historically, NHTSA has used Slowly Increasing Steer tests to 
measure linear range and maximum quasi steady state lateral 
acceleration. While maximum lateral acceleration data is 
interesting, it is not a required metric when determining a 
vehicle's NCAP rollover resistance rating. For this reason, NHTSA 
recommends use of an ``abbreviated'' Slowly Increasing Steer 
maneuver. The handwheel angles used in this abbreviated procedure 
only steer the vehicle enough to assess its linear range lateral 
acceleration performance.
    To determine the most appropriate Slowly Increasing Steer 
handwheel angle for a given vehicle, a preliminary left steer test 
is performed. The test speed during this test was held constant at 
50 mph via throttle modulation, and the steering input ranged from 0 
to 30 degrees, applied at 13.5 degrees per second. The magnitude of 
this input was selected because it was believed to be capable of 
producing a steady state lateral acceleration within the linear 
range for any light vehicle. Using the ratio of steady state 
handwheel position and lateral acceleration established by this 
test, the maximum steering input for the abbreviated Slowly 
Increasing Steer test was derived using the below equation:
[GRAPHIC] [TIFF OMITTED] TR14OC03.032

where,
ay,30 degrees was the raw lateral acceleration produced 
with a constant handwheel angle of 30 degrees during a test 
performed at 50 mph
dSIS was the steering input that, if the relationship of 
handwheel angle and lateral acceleration was linear, would produce a 
lateral acceleration of 0.55 g during a test performed at 50 mph

    Note: ay,30 degrees is ``raw'' data, not corrected 
for the effects of roll, pitch, and yaw. NHTSA acknowledges the 
relationship of handwheel angle and corrected lateral acceleration 
data is often not linear at 0.55 g. However, previously collected 
data indicates the magnitude of raw 0.55 g acceleration data is 
typically reduced by approximately 9.6 percent to 0.497 g, when 
corrected for roll, pitch, and yaw, just outside of the linear range 
for most vehicles. Removing the effect of accelerometer offset 
(error due to the accelerometer not being positioned at the 
vehicle's actual center of gravity) typically reduces the magnitude 
of these data by an additional 0.07 percent. The importance of 
Equation 3.1 is that it simply provides experimenters with a direct, 
``in-the-field'' way of determining an appropriate steering input 
for which to proceed with further tests for a given vehicle.

    Figure I.7 presents a description of the handwheel angles to be 
used during the abbreviated Slowly Increasing Steer, Option 
2 tests.

3.1.3 Measured Parameters

    Analyses of Slowly Increasing Steer tests output overall average 
handwheel position at a specified lateral acceleration
    When lateral acceleration data collected during Slowly 
Increasing Steer tests is plotted with respect to time, a first 
order polynomial best-fit line accurately describes the data from 
0.1 to 0.375 g. NHTSA defines this as the linear range of the 
lateral acceleration response. A simple linear regression is used to 
determine the best-fit line, as shown in Figures I.8 and I.9.
    Using the slope of the best-fit line, the average of handwheel 
position at 0.3 g is calculated using data from each of the six 
Slowly Increasing Steer tests performed for each vehicle. This 
average handwheel position is used to calculate NHTSA Fishhook 
maneuver steering inputs, as described in Section 3.2.

3.2 NHTSA Fishhook Maneuver

3.2.1 Maneuver Overview

    To begin the maneuver, the vehicle is driven in a straight line 
at a speed slightly greater than the desired entrance speed. The 
driver releases the throttle, and when at the target speed, 
initiates the handwheel commands described in Figure I.10 using a 
programmable steering machine. Following completion of the 
countersteer, handwheel position is maintained for three seconds. As 
a convenience to the test driver, the handwheel is then returned to 
zero.
    Each Fishhook maneuver test series contains two sequences (with 
exceptions noted in the following sections): Tests performed with 
left-right steering (first sequence), and tests performed with 
right-left

[[Page 59272]]

steering (second sequence). The sequence of left-right tests always 
precedes those performed with right-left steering.

3.2.2 Default Procedure

    Fishhook maneuver handwheel angles are calculated with lateral 
acceleration and handwheel angle data ([delta]) collected during a 
series of six Slowly Increasing Steer tests (a total of three left-
steer and three right-steer tests are performed). For each Slowly 
Increasing Steer test, a linear regression line is fitted to the 
lateral acceleration data from 0.1 to 0.375 g. Using the slopes of 
these regression lines, the handwheel angles at 0.3 g are determined 
for each individual test ([delta]0.3 g). The six 
handwheel angles are then averaged to produce an overall value 
([delta]0.3 g, overall).

[GRAPHIC] [TIFF OMITTED] TR14OC03.037

    The Fishhook maneuver steering angles are calculated by 
multiplying [delta]0.3 g, overall by a steering scalar 
(SS). The default steering scalar is 6.5.

[delta]Fishhook (Default) = 6.5 x 
[delta]0.3 g, overall

    3.2.2.1 Maneuver Entrance Speed
    For the sake of driver safety, and as a final step in the tire 
scrub-in procedure, each Default Procedure sequence begins with a 
Maneuver Entrance Speed (MES) equal to 35 mph. The MES is measured 
at the initiation of the first steering ramp, and is increased until 
a termination condition is satisfied. The order of MES for a 
sequence is, in mph: 35, 40, 45, 47.5, 50. For each test run, the 
actual MES must be within 1 mph of the target MES.

    Note: NHTSA's experience with the Fishhook maneuver indicates 
that an incremental increase in MES of 5 mph, up to 45 mph, 
minimizes tire wear without compromising test driver safety. 
However, when a MES greater than 45 mph is used, the severity of the 
responses produced with some vehicles can increase substantially 
from that observed at lesser entrance speeds. This is especially 
true if a vehicle has a propensity to oscillate in roll, and/or is 
able to produce two-wheel lift slightly less than NHTSA's threshold 
criterion of two inches. In some of these cases, the driver and/or 
experimenter may not be comfortable with a final 5 mph upwards 
increment in MES, and might, for the sake of driver safety, deviate 
from a test procedure that requires it. Generally speaking, such a 
deviation typically involves the experimenter's use of a more 
gradual 2.5 mph increase in MES.

    To promote driver safety while also eliminating inconsistencies 
in the way NHTSA's Fishhook maneuvers are performed, the test 
procedure requires a MES increment equal to 2.5 mph be used above 45 
mph if a test performed at 45 mph does not produce two-wheel lift, 
regardless of the vehicle being evaluated.

3.2.2.2 Outrigger Contact

    If either safety outrigger contacts the pavement without two-
wheel lift during a Fishhook maneuver test run, the affected 
outrigger is raised 0.75 inches and the test is repeated at the same 
MES. If both safety outriggers contact the pavement without two-
wheel lift, both outriggers are raised 0.75 inches and the test is 
repeated at the same MES.

3.2.2.3 Termination and Conclusion Conditions

    A test sequence is terminated if the MES capable of producing 
two-wheel lift is observed and the MES is 45 mph or lower. If two-
wheel lift is observed during a left-right sequence at 45 mph or 
lower, the [entire] series is terminated. If no two-wheel lift is 
observed during a left-right sequence, right-left tests are 
performed. If two-wheel lift is observed during a right-left 
sequence performed with a MES of 45 mph or lower, the test series is 
terminated.
    If the MES capable of producing two-wheel lift during a left-
right or right-left sequence is 47.5 mph or higher, a new set of 
tires is installed on the vehicle and the procedure described in 
Section 3.2.3.1 is implemented.
    A test series is terminated if rim-to-pavement contact or tire 
debeading is observed during any test performed with either test 
sequence.
    A test series is deemed complete if both test sequences within a 
given series have been performed at the maximum maneuver entrance 
speed without two-wheel lift, rim-to-pavement contact, tire 
debeading, or outrigger-to-pavement contact. If the Default 
Procedure is completed without encountering a termination condition, 
Supplemental Procedure Part 2, described in Section 3.2.3.2, is 
implemented.
    The flowchart presented in Figure I.11 describes the sequence of 
events for the Default Test Series.

3.2.3 Supplemental Procedures

    Note: If the results of the Default Test Series require the 
implementation of the Supplemental Procedure Part 1, neither 
Supplemental Procedure Part 2 nor Part 3 is used.


    Note: Depending on the response of test vehicles to elements of 
the Fishhook maneuver protocol, Supplemental Procedure, Parts 1, 2, 
and 3 may require a change in the steering scalar. The steering 
machine used by NHTSA has the capability for making such changes in 
vehicles during test sessions via selection of a pre-programmed 
steering schedule and the adjustment of overall steering angles.

3.2.3.1 Supplemental Procedure Part 1

    Following the tire scrub-in procedure outlined in Section 4.6, 
tests are performed with handwheel angles equal to 
[delta]Fishhook (Default), as explained in Section 3.2.2. 
The steering combination (i.e., either left-right or right-left) 
that produced two-wheel lift in the Default Test Series is used. The 
first test is to be performed at a MES of 35 mph. This test is 
performed to ensure any mold sheen remaining from the tire break-in 
procedure has been removed from the tires. The second test is to be 
performed at the MES at which two-wheel lift had been previously 
observed (i.e., with the previous tire set). If two-wheel lift is 
produced during the test performed with handwheel angles equal to 
[delta]Fishhook (Default), the tip-up will be reported in 
the vehicle's NCAP Rollover Resistance Rating and the test series is 
deemed complete. If two-wheel lift is not produced and the MES is 
47.5 mph, the MES is increased to 50 mph. If two-wheel lift is 
produced during the test performed with MES equal to 50 mph, the 
tip-up will be reported in the vehicle's NCAP Rollover Resistance 
Rating and the test series is deemed complete.
    If two-wheel lift is not produced at 50 mph with handwheel 
angles equal to [delta]Fishhook (Default), tests are 
performed with steering angles calculated by multiplying 
[delta]0.3 g. overall by a steering scalar of 5.5.

[delta]Fishhook (Supplemental) = 5.5 x 
[delta]0.3 g, overall

    After the application of the reduced scalar, a test is to be 
performed, using the same steering combination (i.e., either left-
right or right-left), at the MES at which two-wheel lift had been 
observed in the Default Test Series. If two-wheel lift is produced 
during the test performed with handwheel angles equal to 
[delta]Fishhook (Supplemental), the tip-up will be 
reported in the vehicle's NCAP Rollover Resistance Rating and the 
test series is deemed complete. If two-wheel lift is not produced 
and the MES is 47.5 mph, the MES is increased to 50 mph. If two-
wheel lift is produced during the test performed with MES equal to 
50 mph, the tip-up will be reported in the vehicle's NCAP Rollover 
Resistance Rating and the test series is deemed complete. If two-
wheel lift is not produced at 50 mph, the test series is deemed 
complete and no tip-up will be reported in the vehicle's NCAP 
Rollover Resistance Rating.
    A test series is terminated if rim-to-pavement contact or tire 
debeading is observed during any Supplemental Procedure Part 1 test. 
The flowchart presented in Figure I.12 describes the sequence of 
events for the Supplemental Procedure Part 1.

3.2.3.2 Supplemental Procedure Part 2

    If two-wheel lift is not produced during tests performed with 
the Default Procedure, the steering scalar is reduced from 6.5 to 
5.5. Using the same tires used for tests performed with the Default 
Test Series, tests are performed with steering angles calculated by 
multiplying [delta]0.3 g. overall by a steering scalar of 
5.5.

[delta]Fishhook (Supplemental) = 5.5 x 
[delta]0.3 g, overall

    For the sake of driver safety, the first test of the left-right 
sequence with the reduced steering scalar applied is to be performed 
at a MES of 45 mph. If this test does not

[[Page 59273]]

produce two-wheel lift, the MES is increased to 47.5 mph. If the 
test with MES equal to 47.5 mph does not produce two-wheel lift, the 
MES is increased to 50 mph (the maximum MES used for Fishhook 
maneuver testing). If no two-wheel lift is observed during the left-
right sequence, the right-left test sequence is initiated using the 
same process as the left-right sequence. If any test in the 
Supplemental Procedure Part 2 test series produces two-wheel lift, a 
new set of tires is installed on the vehicle, and the procedure 
described Section 3.2.3.3 is implemented.
    A test series is terminated if rim-to-pavement contact or tire 
debeading is observed during any test performed with either test 
sequence. A test series is deemed complete if both test sequences 
within the series have been performed at the maximum maneuver 
entrance speed without two-wheel lift. The flowchart presented in 
Figure I.13 describes the sequence of events for the Supplemental 
Procedure Part 2.

3.2.3.3 Supplemental Procedure Part 3

    Following the tire scrub-in procedure outlined in Section 4.6, 
two tests are performed with handwheel angles equal to 
[delta]Fishhook (Supplemental). The steering combination 
that produced two-wheel lift during Supplemental Procedure Part 2 
testing is used (i.e., either left-right or right-left). The first 
test is to be performed at a MES of 35 mph. This test is performed 
to ensure any mold sheen remaining from the tire break-in procedure 
has been removed from the tires. The second test is to be performed 
at the MES that had produced two-wheel lift during Supplemental 
Procedure Part 2 testing (i.e., with the previous tire set). If two-
wheel lift is produced during the test performed with handwheel 
angles equal to [delta]Fishhook (Supplemental), the tip-
up will be reported in the vehicle's NCAP Rollover Resistance Rating 
and the test series is deemed complete. If two-wheel lift is not 
produced and the MES is 45 mph, the MES is increased to 47.5 mph. If 
two-wheel lift is not produced and the MES is 47.5 mph, the MES is 
increased to 50 mph. If two-wheel lift is produced during any test 
performed during Supplemental Procedure Part 3, the tip-up will be 
reported in the vehicle's NCAP Rollover Resistance Rating and the 
test series is deemed complete. If two-wheel lift is not produced 
during Supplemental Procedure Part 3, the test series is deemed 
complete and no tip-up will be reported in the vehicle's NCAP 
Rollover Resistance Rating.
    A test series is terminated if rim-to-pavement contact or tire 
debeading is observed during any Supplemental Procedure Part 3 test. 
The flowchart presented in Figure I.14 describes the sequence of 
events for the Supplemental Procedure Part 3.

3.2.4 Handwheel Inputs

3.2.4.1 Steering Rate

    The handwheel rates of the initial steer and countersteer 
steering ramps are always to be performed with nominal steering 
rates of 720 degrees per second, regardless of what steering scalar 
is used.

3.2.4.2 Dwell Time

    The Fishhook maneuver is designed to maximize the roll motion of 
the test vehicle. When left-right steering is used, this is 
accomplished by:

1. Steering the vehicle with an input equal to 
[delta]Fishhook (Default) or 
[delta]Fishhook (Supplemental)
2. Waiting until the vehicle achieves maximum roll angle.
3. Reversing the direction of steer
4. Steering the vehicle with an input equal to -
[delta]Fishhook (Default) or -
[delta]Fishhook (Supplemental)

    When right-left steering is used, the sign conventions indicated 
in Steps 1 and 4 above are switched from positive to negative (i.e., 
for Step 1) or from negative to positive (i.e., for Step 4).
    Dwell time is defined as the time from the completion of the 
initial steering ramp to the initiation of the steering reversal. A 
roll rate ``Window Comparator'' is used to determine when the 
vehicle has achieved maximum roll angle. Since the programmable 
steering machine used by NHTSA has a mechanical overshoot after 
completion of the initial steer, dwell time is not measured directly 
with handwheel angle data. Rather, two signals output from the 
steering machine are used: ``Handwheel Start'' and ``Roll Flag''.

3.2.4.2.1 Steering Machine Window Comparator

    As indicated in Figure I.10, Fishhook maneuver steering 
reversals are commanded after the completion of the initial steering 
ramp and when the roll rate of the vehicle is very close to zero 
(because it is the derivative of roll angle, when roll rate is equal 
to zero at this point, roll angle is at its maximum). To minimize 
the likelihood of erroneous reversals, the reversals occur when the 
roll rate signal transmitted from a sensor positioned near the test 
vehicle's center of gravity enters the window comparator. The window 
comparator is defined as +/-1.5 degrees per second, regardless of 
what steering scalar was used.
    Examples: If an initial steer to the left is input, the reversal 
is initiated when the roll velocity of the vehicle is equal to 1.5 
degrees per second. If an initial steer to the right is input, the 
reversal is initiated when the roll velocity of the vehicle is equal 
to -1.5 degrees per second.

3.2.4.2.2 Handwheel Command Flag

    The programmable steering machine used by NHTSA outputs a 
``Handwheel Command Flag'' signal based on the machine's internal 
clock. The output of the Handwheel Command Flag signal ranges from 0 
to 10 volts, and is binary. The signal is high (10 volts) when the 
steering machine is in the process of executing a commanded input, 
or low (0 volts) when the machine is not in use or a pause is 
commanded during the execution of a commanded input, as shown in 
Figure I.10. When the pause ends, and execution of the commanded 
steering inputs are resumed, the Handwheel Command Flag signal is 
once again set high. In a Fishhook maneuver, the duration of the 
pause is the dwell time.

3.2.4.2.3 Roll Rate Flag

    The ``Roll Rate Flag'' signal output by the programmable 
steering machine used by NHTSA is monitored. Like that of the 
Handwheel Command Flag channel, the Roll Rate Flag output ranges 
from 0 to 10 volts, and is binary. The signal is high (10 volts) 
when the roll rate of the test vehicle is within the window 
comparator, or low (0 volts) when roll rate is outside the window 
comparator, as shown in Figure I.10.
    Fishhook maneuver steering reversals are to be initiated by the 
steering machine within 10 milliseconds of the roll rate entering 
the window comparator. Initiation of the steering reversal is 
defined as the instant the steering machine sets the Roll Rate Flag 
signal high.

    Note: After completion of the initial steer, the instants that 
the steering machine sets the Roll Rate Flag and Handwheel Command 
Flag signals high should coincide.

3.2.4.3 Excessive Steering

    In some cases, the magnitude of 
[delta]Fishhook (Default) used during the Default 
Procedure may be so great that the vehicle reaches maximum roll 
angle before completion of the initial steer. This is defined as 
excessive steering; i.e., the vehicle cannot respond to the entire 
commanded steering input.
    Excessive steering is also said to occur if the dwell time of a 
Fishhook test performed with the Default Procedure results in a 
dwell time less than 80 milliseconds. The mechanical overshoot of 
the steering machine that occurs after completion of the initial 
steer can prohibit the machine from accurately executing dwell times 
less than approximately 80 milliseconds. In such cases, the effect 
of the overshoot is that the actual dwell time is equal to zero (an 
immediate steering reversal).
    NHTSA's experience with the Fishhook maneuver has demonstrated 
the effect of excessive steering on dynamic rollover resistance is 
vehicle-dependent. While it may not allow the roll motion of some 
test vehicles to be maximized, excessive steering has been shown to 
contribute to an increased tip-up propensity in others. For this 
reason, a test sequence for which excessive steering is observed 
should not be terminated. Testing should proceed as outlined in 
Section 3.2.2, Default Procedure. If two-wheel lift is not observed 
during either Default Procedure test sequence, the Supplemental 
Procedure beginning at Part 2, described in Section 3.2.3.2, is 
performed.

4.0 Items Pertaining to Test Conduct

4.1 Definition of Two-Wheel Lift

    Two-wheel lift is defined as the occurrence of at least two 
inches of simultaneous lift of the inside wheels from the test 
surface. NHTSA does not consider two-wheel lift less than two inches 
when calculating a vehicle's NCAP rollover resistance rating. Two-
wheel lift great enough to require outriggers to suppress further 
roll motion is to be reported simply as ``two-wheel lift'' as long 
as at least two inches of simultaneous two-wheel lift occurs before 
outrigger contact with the ground is made.

4.2 Vehicle Test Configurations

4.2.1 Load Configurations

    All vehicles are to be evaluated with one of the two load 
configurations previously defined in Section 2.1.

[[Page 59274]]

4.2.2 Fuel Tank Loading

    Prior to beginning a Slowly Increasing Steer or Fishhook 
maneuver test series, the fuel tank of the vehicle is to be 
completely filled at the beginning of testing and may not be less 
than 75% of capacity during any part of the testing. This criterion 
is in agreement with that defined in FMVSS 135.

4.2.3 Stability Control System

    If equipped, vehicles are tested with stability control systems 
active. Stability control is not to be deactivated for any Slowly 
Increasing Steer or Fishhook maneuver.

4.3 Road Test Surface

    Tests are conducted on a dry, uniform, solid-paved surface. 
Surfaces with irregularities, such as dips and large cracks, are 
unsuitable, as they may confound test results.

4.3.1 Pavement Friction

    All maneuvers are to be performed on a dry, high-mu road test 
surface.
    Unless otherwise specified, the road test surface produces a 
peak friction coefficient (PFC) of approximately 0.9 when measured 
using an American Society for Testing and Materials (ASTM) E1136 
standard reference test tire, in accordance with ASTM Method E 1337-
90, at a speed of 64.4 km/h (40 mph), without water delivery. This 
criterion is in agreement with that defined in FMVSS 135.

4.3.2 Slope

    The test surface has a consistent slope between level and 2%. 
All tests are to be initiated in the direction of positive slope 
(uphill).

4.4 Ambient Conditions

4.4.1 Ambient Temperature

    The ambient temperature shall be between 0[deg] C (32[deg] F) 
and 40[deg] C (104[deg] F). This criterion is in agreement with that 
defined in FMVSS 135.

4.4.2 Wind Speed

    The maximum wind speed shall be no greater than 10 m/s (22 mph).

4.5 Calibration Data

    It is strongly recommended that calibration data be collected 
prior to tests of each configuration to assist in resolving 
uncertain test data. NHTSA typically records the following data at 
the beginning of each test day for each test vehicle configuration.
    [sbull] The distance measured by the speed sensor along a 
straight line between the end points of a surveyed linear roadway 
standard of 1000 feet or more (observed and recorded manually from 
the speed sensor display).
    [sbull] Five to fifteen seconds of data from all instrument 
channels as the configured and prepared test vehicle is driven in a 
straight line on a level, uniform, solid-paved road surface at 60 
mph.

4.6 Tire Break-In Procedure

    Prior to each test series, the tires must be ``scrubbed in'' to 
wear away mold sheen and be brought up to operating temperature. 
Test vehicles are to be driven around a circle 100 feet in diameter 
at a speed that produces a lateral acceleration of approximately 0.5 
to 0.6 g. Using this circle, three clockwise laps are to be followed 
by three counterclockwise laps. Once the six laps of the circle are 
complete, the driver is to input, sinusoidal steering at a frequency 
of 1 Hz and a handwheel amplitude ([delta]ss) 
corresponding to 0.5-0.6 g for 10 cycles while maintaining a vehicle 
speed of 35 mph. A total of four passes using sinusoidal steering 
are to be used. The handwheel magnitude of the final cycle of the 
final pass is to be twice that of [delta]ss. These four 
sinusoid passes typically require an area similar in size to that 
required by the Fishhook maneuver. The steering machine should be 
programmed to execute the sinusoids. There should be only a minimal 
delay between the completion of the tire break-in and the start of a 
test series to allow for the collection of a static data file, 
steering machine and data acquisition system adjustment, and final 
driver briefing.

4.7 Static Datums

    At the completion of the tire break-in procedure and before the 
start of a test series, fifteen seconds of data are collected from 
all instrument channels with the test vehicle at rest, the engine 
running, the transmission in ``Park'' (automatic transmission) or in 
neutral with the parking brake applied (manual transmission), and 
the front of the test vehicle facing in the direction of positive 
gradient (uphill) on the test surface. The static data files are 
used in post processing to establish datums for each instrument 
channel.

4.8 Vehicle Gear Selection

    All tests are performed with automatic transmissions in 
``Drive'' or with manual transmissions in the highest gear capable 
of sustaining the desired test speed (Slowly Increasing Steer) or 
Maneuver Entrance Speed (Fishhook), with one exception:
    Slowly Increasing Steer tests may be performed with automatic 
transmissions in lower gears if 50 mph cannot be maintained in 
``Drive'' and the gear selection does not result in engine 
overspeeding. In some cases, 50 mph cannot be maintained through to 
the end of the steering schedule regardless of the gear selection 
due to low engine power or chassis responses that result in the loss 
of traction or spin out. It has been NHTSA's experience, however, 
that maximum lateral acceleration is generally achieved well before 
the maneuver's maximum handwheel angle is attained.
    Manual transmission clutches are to remain engaged during all 
maneuvers.

4.9 Outrigger Adjustment

    The initial clearance between the road surface and the bottom of 
the NHTSA outrigger skid pads is approximately 14 inches for the 
``standard'' outriggers and approximately 12 inches for the 
``short'' outriggers with the test vehicle at rest on a level 
surface. Note that the Multi-Passenger Configuration may compress 
the suspension more than the Nominal Load Configuration (reducing 
outrigger clearance). As such, outrigger height adjustment may be 
required when transitioning from one load configuration to the next.
    Outrigger height adjustment may be required during a test 
series. If an outrigger skid pad contacts the road surface during a 
test run wherein there is no two-wheel lift, the outrigger at the 
affected end of the vehicle is raised 0.75 inches and the test run 
is repeated at the same maneuver entrance speed. If both outriggers 
make contact with the test surface during a test run wherein there 
is no two-wheel lift, both outriggers are raised 0.75 inches and the 
test run is repeated at the same maneuver entrance speed.

4.10 Videotape Documentation

    It is recommended that all test runs be documented on videotape. 
NHTSA videotapes Slowly Increasing Steer tests from a viewpoint 
several hundred feet outside the circular path of the test vehicle. 
Fishhook maneuver tests are videotaped from a viewpoint that 
facilitates observation of the inboard side of the vehicle so as to 
best record instances of two-wheel lift. For both maneuvers, it is 
recommended the zoom of the camera be adjusted during each test such 
that the vehicle fills the view frame to the greatest extent 
possible.

4.11 Summary of Tests To Be Performed for Each Vehicle

    For each test vehicle, testing will be performed according to 
the following plan:
1. Installation of new tires
2. Tire break-in
3. Slowly Increasing Steer Maneuver test series in the Nominal Load 
or Multi-Passenger Configuration
4. Tire change
5. Tire break-in
6. NHTSA Fishhook maneuver test series in the Nominal Load or Multi-
Passenger Configuration with additional tire changes and break-ins 
as indicated in the maneuver protocol

4.12 Summary of Metrics Measured For Each Vehicle

1. Overall handwheel position at 0.3 g in the Nominal Load 
Configuration
2. Two-Wheel Lift in NHTSA Fishhook maneuver in Nominal Load or 
Multi-Passenger Configuration (Yes/No)
3. Rim-to-Pavement Contact or Tire Debeading in Nominal Load or 
Multi-Passenger Configuration (Yes/No)

4.13 Post Processing

    Data are filtered in post processing with a 6-Hz 12-pole, 2-
pass, phaseless digital Butterworth filter. All accelerations are 
corrected for CG displacement (see Section 2.5.1.3). Laser height 
measurements are filtered with a one-pass 200 ms running average 
technique.
    Post processing also includes roll effects correction for 
lateral acceleration as follows.

ayc = aymcos[Theta] -- 
azmsin[Theta]

where,

ayc is the corrected lateral acceleration (i.e., the 
vehicle's lateral acceleration in a plane horizontal to the test 
surface)
aym is the measured lateral acceleration in the vehicle 
reference frame
azm is the measured vertical acceleration in the vehicle 
reference frame

[[Page 59275]]

[Theta] is the vehicle s roll angle


    Note: The z-axis sign convention is positive in the downward 
direction for both the vehicle and test surface reference frames.

5.0 References

    1. Forkenbrock, G.J., Garrott, W.R., Heitz, Mark, O'Harra, Brian 
C., ``A Comprehensive Experimental Examination of Test Maneuvers 
That May Induce On-Road, Untripped Light Vehicle Rollover--Phase IV 
of NHTSA's Light Vehicle Rollover Research Program,'' NHTSA 
Technical Report, DOT HS 809 513, October 2002.
    2. Forkenbrock, G.J., O'Harra, Brian C., Elsasser, Devin, ``An 
Experimental Examination of 26 Light Vehicles Using Test Maneuvers 
That May Induce On-Road, Untripped Light Vehicle Rollover--Phase VI 
of NHTSA's Light Vehicle Rollover Research Program,'' NHTSA 
Technical Report, DOT HS 809 547, 2003.
    3. NHTSA, ``NHTSA's Experience With Outriggers Used For Testing 
Light Vehicle--A Brief Summary,'' Docket No. NHTSA-2001-9663, 
January 2003.
    4. NHTSA, ``NHTSA's Set-Up Procedures for Wheel Lift Sensors--A 
Brief Overview,'' Docket No. NHTSA-2001-9663, April 2003.
    5. SAE J266, Surface Vehicle Recommended Practice, ``Steady-
State Directional Control Test Procedures For Passenger Cars and 
Light Trucks,'' 1996.

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Appendix II. Development of a Rollover Risk Model

    In its study of our rating system for rollover resistance 
(Transportation Research Board Special Report 265), the National 
Academy of Sciences (NAS) recommended that we use logistic 
regression rather than linear regression for analysis of the 
relationship between rollover risk and SSF. We had considered a 
logistic regression model during the development of the rollover 
resistance rating system used by NCAP for 2001 to 2003 vehicles, but 
we observed that it predicted rollover rates that were 
systematically lower than actual rollover rates for vehicles with 
low SSF. Our first step was to explore the use of transformations of 
SSF to create a logistic regression model that better matched actual 
rollover rates while following the recommendation of the NAS.
    A satisfactory logistic regression model using SSF only was the 
starting point for developing a risk model that used both a 
vehicle's SSF and its performance in dynamic maneuver tests to 
predict its rollover rate. We used four binary variables to describe 
whether or not the vehicle tipped up in two dynamic maneuver tests 
each performed at two different occupant load conditions. The final 
model required the results of only the Fishhook maneuver test with 
the heavy five occupant load and the SSF of a vehicle. The predicted 
rollover rate determines the rollover resistance rating of the 
vehicle.

A. Improving the Fit of the Logistic Regression Model With SSF Only

    We had considered logistic regression during the development of 
the SSF based rating system (66 FR 3393, January 12, 2001), but 
found that it consistently under-predicted the actual rollover rate 
at the low end of the SSF range where the rollover rates are high. 
The NAS study acknowledged this situation and gave the example of 
another analysis technique (non-parametric) that made higher 
rollover rate predictions at the low end of the SSF scale. In the 
NPRM, we discussed our plan to first examine ways to improve the fit 
of the logistic regression model to the actual rollover rates in the 
simpler model with SSF as the only vehicle attribute before 
expanding the logistic regression model to predict rollover rates 
using maneuver test results and SSF as vehicle attributes. In this 
way, the addition of maneuver test results is more likely to have an 
effect that reflects the additional information they represent on 
rollover causation.
    A consultant to the Bureau of Transportation Statistics who 
lectured on logistic regression suggested that we use a 
transformation of SSF, like Log(SSF), rather than SSF alone to 
change the shape of the trend line generated by the logistic 
regression in our range of interest of SSF. This technique is 
similar to what we used to improve the fit of the linear regression 
model in the SSF rating system (Figure II.1). Linear regression 
creates a ``best fit'' straight line to predict the relationship 
between the independent variable, SSF in this case, and the 
dependent variable, rollover rate per single vehicle crash in this 
case. However, the observations of rollover rate for groups of 
vehicles with a known SSF did not appear to lie on a straight line. 
The relationship appeared to be exponential with a reduction in 
rollover rate with increase in SSF much greater at low SSFs than at 
high SSFs. We used the transformation Log(SSF) to replace SSF alone 
in the linear regression model so that it would compute a ``best 
fit'' exponential curve instead of a best fit straight line in order 
better fit the prediction line to the observations. We referred to 
Figure II.1 in notices 65 FR 34998 and 66 FR 3388 as a linear 
regression model because of the analysis technique, but the NAS 
study refers to it as the exponential model because of its curve 
shape.
    Figure II.2 plots the actual rollover rates as a function of SSF 
observed for 293,000 single vehicle crashes involving 100 vehicle 
groups in six states from 1994 to 2001 (not all state's data 
available in every year). The point designated ``actual rate'' at 
each value of SSF gives the proportion of single vehicle crashes for 
vehicles of that SSF that resulted in rollover. For example, the 
leftmost point shows that for all single vehicle crashes observed 
for vehicles with an SSF of 1.00, slightly less than 50% resulted in 
rollover. There are fewer than 100 data points because the data at 
each SSF often include the crashes of several vehicles with the same 
SSF.
    Figure II.2 also plots the rollover rates predicted for the same 
293,000 crashes by a logistic regression model operating on SSF 
without transformation as the only vehicle variable. The model was 
developed from a database that contained the driver characteristic 
and road condition variables in the state crash reports of 293,000 
crashes in six states. Data from Maryland, Florida, North Carolina, 
Missouri, Utah and Pennsylvania were used because these were the 
only states with electronic records available to NHTSA in which we 
could identify the make/model of the vehicle and could be sure 
whether or not a rollover occurred. The driver variables were 
gender, age [young (less than 25), old (70 or older), neither], and 
evidence of alcohol or drug use. The road condition variables were 
weather, speed limit, curve, hill, darkness, wet or icy surface, and 
potholes or other bad surface conditions. The SAS logistic 
regression program used these driver and road variables, the vehicle 
SSF, the State and the outcome (rollover or not) for each of 293,000 
single vehicle crashes to compute the risk model. Figure II.2 shows 
the exercise of inputting the driver, road, state and vehicle SSF 
circumstances for each individual crash of the 293,000 back into the 
risk model to test how well the model can predict the actual 
rollover outcomes.
    In similar fashion as the ``actual rate'' points on Figure II.2, 
the ``predicted rate'' points at each value of SSF give the 
proportion of single vehicle crashes for vehicles of that SSF that 
resulted in rollover. The number and circumstances (as well as can 
be described from state crash report variables) of crashes 
represented by the actual and predicted rate points are identical. 
However, in one case the rollover outcomes are the actual outcomes 
reported in the state data. But in the other case, the rollover 
outcomes are the predictions of the risk model given the driver and 
road variables and vehicle SSF for each actual the crash. The 
predicted rate points do not lie on a continuous curve when plotted 
against SSF because the distribution of driver and road variables 
are different for the single vehicle crashes experienced by each 
group of vehicles represented by its SSF value.
    Figure II.2 shows that the risk model obtained using the 
untransformed SSF computes predictions that match the actual 
rollover rates well at SSFs higher than 1.3, but its predictions are 
consistently low at the low end of the SSF range. The predictions 
also tend to be too high in the 1.15 to 1.25 SSF range. For this 
reason we described the form of the curve inherent to the logistic 
regression computation as being too flat or lacking sufficient 
curvature to represent rollover risk in our past notices.
    Figure II.2 also lists an objective measure of the goodness of 
fit of the predictions to aid in the comparisons of models with and 
without using transformations of SSF. It is the R2 value 
for linear regression between the predicted and actual rollover 
rates. Figure II.3 is a plot of predicted versus actual rollover 
rates taken from Figure II.2. It shows how the R2 value 
was obtained. A linear regression of the form ``y = mx'' computes 
the best fit line that passes through the origin. The R2 
value that describes the goodness of fit of the points to the line 
``y = 0.9673x'' is 0.752. A perfect set of predictions would cause 
an R2 value of 1.0 on the line ``y = 1.0x''.
    Figures II.4, II.5, and II.6 show the predictions of a series of 
risk models obtained in the same way as that shown in Figure II.2 
except that transformations of SSF were used as the vehicle variable 
instead of just SSF. The first transformation, shown in Figure II.4, 
was Log(SSF). This is the transformation currently used in the 
linear regression rollover risk model. It makes a very small 
improvement both to the under-predictions at the low end of the SSF 
range and the over-predictions in the 1.15 to 1.25 SSF range. The 
R2 goodness of fit indicator increased to 0.7975.
    Next we tried the transformation Log (SSF-margin). Figure II.5 
shows the predictions of a logistic regression model with a margin 
of 0.85. The subtraction of a margin from SSF makes a large 
improvement in the fit of the predicted rollover rates to the actual 
rollover rates in the SSF range of 1.0 to 1.25. The R2 
goodness of fit indicator increased to 0.8811 about the line ``y = 
1.0011x'' for the whole SSF range of data base (1.0 to 1.53). This 
transformation caused a small sacrifice in the fit of the model at 
the high end of the SSF range. However, a good fit in the 1.0 to 
1.25 SSF range is more important to a rating system because most of 
the consumer requests for rollover information involve vehicles in 
this range.
    Figure II.6 shows the fit of the model with a margin of 0.9. The 
R2 goodness of fit indicator increased slightly to 0.8948 
about the line ``y = 1.0091x'', but the sacrifice of fit at the high 
SSF end also increased. Figure II.7 is a plot of predicted versus 
actual rollover rates taken from Figure II.6. The use

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of the transformation Log(SSF-0.90) instead of SSF alone in the 
logistic regression gave us a risk model with the benefits of 
logistic regression recommended by the NAS and a goodness of fit 
with the actual rollover rate data at least equivalent to that of 
the linear regression model we have been using.
    Figure II.8 shows the best logistic regression model (margin = 
0.90) and the linear regression model we have been using. In this 
presentation, the driver and road variables of the crashes for each 
SSF were the same so that the differences in predicted rollover 
rates along each line were a purely a function of SSF differences, 
and the risk curve is continuous. The common scenario of driver and 
road variables represented the average conditions for the entire 
293,000 single vehicle crashes (only 20% of which resulted in 
rollover). The linear regression model represents the same scenario.
    The line in Figure II.8 representing the linear regression model 
is described by the equation:
[GRAPHIC] [TIFF OMITTED] TR14OC03.033

    The line in Figure II.8 representing the logistic regression 
model is described by the following equation:
[GRAPHIC] [TIFF OMITTED] TR14OC03.034

B. Adding Dynamic Maneuver Test Results to the Logistic Regression 
Model

    The dynamic maneuver test results (tip-up or no tip-up in each 
maneuver/load combination in Table 1 of the main body of the notice) 
were used as four binary variables in the logistic regression 
analysis. They were entered in addition to SSF to describe the 
vehicle. The same driver and road variables from state crash reports 
discussed above were used. The state crash report data for twenty-
four of the vehicles used in the logistic regression analysis with 
dynamic maneuver test variables was a subset of the database of 
293,000 single vehicle crashes described above. One extra vehicle 
was added for the maneuver tests that was not among the 100 vehicle 
groups we had studied previously, but state crash report data from 
the same years and states was obtained for it. However, the database 
with SSF and dynamic maneuver tests was much smaller than the 
293,000 sample size available for the logistic regression model with 
SSF only. Its sample size was 96,000 single vehicle crashes of 25 
vehicles including 20,000 rollovers.
    The risk models combining SSF and dynamic maneuver test results 
(``dynamic results'' for short) are computed in the same way as the 
logistic regression curve in Figure II.7. The logistic regression 
analysis of the database of 96,000 state reports of single vehicle 
crashes along with the dynamic results and SSF of each crashed 
vehicle provides a mathematical relationship between all of the 
vehicle, driver and road variables and a prediction of whether 
rollover will occur in a single vehicle crash described by any 
combination of the variables. Next, for the number of sets of driver 
and road variables that define the average crash scenario of the 
293,000 single vehicle crash database, predictions of rollover or no 
rollover in the crash are made at each combination of SSF and 
dynamic results. The proportion of crashes that are predicted to 
result in rollover is plotted at each SSF and dynamic result. 
Continuous curves predicting rollover rate versus SSF for each 
combination of dynamic results is the form of the model. Since all 
of the predictions were made with the same driver and road scenario, 
the changes in rollover rate along each SSF curve or between dynamic 
results are functions of vehicle attributes.
    Figure II.9 illustrates the form of the model with dynamic 
results. It shows the predicted rollover rate as a function of SSF 
and whether or not the vehicle tipped-up in the Fishhook maneuver 
with 5 occupant loading (fishhook heavy or FH). It predicts a 
rollover rate that is strongly dependant on SSF but higher for 
vehicles that tip-up in this severe maneuver than for vehicles that 
do not tip up in the test.
    The intent of using dynamic results from four tests was to 
provide tests with a range of severity to best discriminate between 
vehicles on the basis of dynamic performance. The Fishhook heavy 
maneuver was the most severe, and the J-turn light was the least 
severe. The expectation was that tip-up in the least severe maneuver 
would predict a greater rollover risk than tip-up in the most severe 
maneuver.
    Figures II.10, II.11 and II.12 show logistic regression models 
using each of the other maneuvers as a single variable for dynamic 
results. In Figure II.10, vehicles that tip-up in J-turn heavy are 
predicted to have a slightly greater rollover risk than those that 
do not tip. However, in the Fishhook light and J-turn light 
maneuvers, the logistic regression models of Figures II.11 and II.12 
predicted a greater rollover risk for vehicles that did not tip-up.
    We do not believe vehicles that tip up in the least severe 
maneuvers are actually safer than those that do not tip up. A more 
rational interpretation is that the numbers of vehicle tipping up in 
these maneuvers were too few to establish a definitive correlation. 
Only three vehicles tipped up in the J-turn light maneuver, and six 
vehicles tipped up in the Fishhook light maneuver. Only one more 
vehicle tipped up in the J-turn heavy maneuver than in the Fishhook 
light, and the prediction of the model with J-turn heavy was 
consistent with expectations that tip-up in the test predicts 
greater rollover risk. However, the extra vehicle in the J-turn 
heavy tip-up group was the Ford Ranger 2 WD with a very large sample 
size of over 8,000 single vehicle crashes (nearly 10 percent of the 
entire data base).
    Next we computed a logistic regression using both dynamic 
results variables, Fishhook heavy and J-turn heavy, that were 
observed to have a directionally correct result when entered into 
the model individually. The result was that the variable, J-turn 
heavy, was rejected by the logistic regression program as not 
statistically significant in the presence of the Fishhook heavy 
variable. In other words, the predictions based on tip-up in the 
Fishhook heavy maneuver do not change whether or not the vehicle 
also tips up in the J-turn heavy maneuver.
    Figure II.13 shows the final model that uses only Fishhook heavy 
of the dynamic results variables. The printout of the SAS logistic 
regression procedure that establishes the coefficients of the model 
has been docketed separately. This model has a risk prediction for 
vehicles that tip up in the dynamic maneuver tests based on the 
greatest number of vehicles possible in our 25 vehicle data base. 
All 11 vehicles that tipped up in any maneuver are represented on 
the tip-up curve, and the 14 vehicles without tip-up are represented 
on the other curve. The logistic regression model based on SSF only 
for 100 vehicles is included for reference. It is very similar to 
the risk model with dynamic result variables for vehicles that tip 
up in the Fishhook heavy maneuver. This result is not surprising 
because the SSF only model was optimized for best fit in the 1.00 to 
1.25 SSF range that included all vehicles tipping up in dynamic 
maneuver tests. The SSF only model was based on a vehicle sample 
that included 10 of the 11 vehicles that tipped up in the dynamic 
tests, but the sample included 90 additional vehicles. The fact that 
the prediction based on the SSF of 100 vehicles closely matches the 
prediction based on 11 vehicles that tipped up in the dynamic tests 
suggests that the small sample has produced a robust prediction 
although the predictive power of tip-up in the dynamic test may not 
be great.
    In Figure II.13, the equation of the line representing the SSF 
only model (from the 100 vehicle database) is:
[GRAPHIC] [TIFF OMITTED] TR14OC03.035

    The equations for the final model representing a combination of 
SSF with dynamic scores for each of the dynamic results (tip-up and 
no tip-up) are:
[GRAPHIC] [TIFF OMITTED] TR14OC03.036


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[FR Doc. 03-25360 Filed 10-7-03; 8:45 am]
BILLING CODE 4910-59-C