[Federal Register Volume 61, Number 16 (Wednesday, January 24, 1996)]
[Rules and Regulations]
[Pages 2004-2036]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-682]




[[Page 2003]]

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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 571



Federal Motor Vehicle Safety Standards Rear Impact Guards; Rear Impact 
Protection; Final Rule

  Federal Register / Vol. 61, No. 16 / Wednesday, January 24, 1996 / 
Rules and Regulations   

[[Page 2004]]


DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. 1-11, Notice 11]
RIN 2127-AA43


Federal Motor Vehicle Safety Standards Rear Impact Guards; Rear 
Impact Protection

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

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: This final rule establishes two Federal Motor Vehicle Safety 
Standards (FMVSS) which will operate together to reduce the number of 
injuries and fatalities resulting from the collision of passenger 
vehicles with the rear end of heavy trailers and semitrailers. The 
first standard (FMVSS No. 223, Rear Impact Guards, or the ``equipment 
standard'') specifies performance requirements that rear impact guards 
(guards) must meet before they can be installed on new trailers and 
semitrailers. It specifies strength requirements, as well as test 
procedures that NHTSA will use to determine compliance with the 
standard. The guard may be tested for compliance while mounted to a 
non-vehicle ``test fixture'' or a complete vehicle. The equipment 
standard also requires the guard manufacturer to provide instructions 
on the proper installation of the guard. The final rule also specifies 
requirements to ensure energy absorption by the guards.
    The second standard (FMVSS No. 224, Rear Impact Protection, or the 
``vehicle standard'') requires that most new trailers and semitrailers 
with a Gross Vehicle Weight Rating of 4,536 kilograms (kg) (10,000 
pounds (lbs)) or more be equipped with a rear impact guard meeting the 
equipment standard. Requirements for the location of the guard relative 
to the rear end of the trailer are also specified in the vehicle 
standard. The vehicle standard further requires that the guard be 
mounted on the trailer or semitrailer in accordance with the 
instructions of the guard manufacturer.

DATES: This rule will become effective on January 26, 1998. Petitions 
for reconsideration of this rule must be received no later than March 
11, 1996.

ADDRESSES: Petitions for reconsideration should refer to the docket 
number and notice number and be submitted in writing to: Docket 
Section, National Highway Traffic Safety Administration, Room 5109, 400 
Seventh Street, SW, Washington DC 20590. Telephone: (202) 366-5267.

FOR FURTHER INFORMATION CONTACT: Dr. Leon DeLarm, Dr. George 
Mouchahoir, or Mr. Sam Daniel, in the Office of Vehicle Safety 
Standards (Telephone: 202-366-4919), or Mr. Paul Atelsek, in the Office 
of the Chief Counsel (202-366-2992), National Highway Traffic Safety 
Administration, 400 Seventh Street, SW, Washington, DC 20590.

SUPPLEMENTARY INFORMATION:
Table of Contents

I. The Safety Problem
II. Existing Regulations
III. Past Proposals
IV. Summary of the 1981 NPRM
V. Summary of 1981 NPRM Comments
VI. Summary of the 1992 SNPRM
VII. Summary of 1992 SNPRM Comments
VIII. Recent Testing by NHTSA
IX. Overview of the Final Rule
X. Summary of Changes From the 1992 SNPRM
XI. Analysis and Response to Comments on the 1992 SNPRM
A. Separate Equipment and Vehicle Standards
B. Standard for Equipment
1. Relationship of Strength, Energy Absorption, and PCI
2. Guard Strength
3. Guard Energy Absorption
4. Vertical Cross-sectional Height of Horizontal Cross-member
5. Shape of the Horizontal Cross-member
6. Guard Attachment
7. Compliance Test Requirements and Procedures
a. Dynamic Versus Static Testing
b. Test Sites
c. Labeling and Certification
C. Standard for Vehicles
1. Configuration Issues
a. Maximum Guard Ground Clearance
b. Guard Width
c. Specification of the Rear Extremity
d. Distance Between the Guard Rear Surface and the Vehicle Rear 
Extremity
2. Exclusions
a. Single Unit (Straight Body) Trucks
b. Special Purpose Vehicles
c. Wheels Back Vehicle
D. Costs
E. Benefits
F. Lead Time
G. Miscellaneous Issues
1. Metric System Units
2. Federal Highway Administration Rulemaking on Underride Guards
XII. Rulemaking Analyses and Notices
A. Executive Order 12866 (Federal Regulation) and Regulatory 
Policies and Procedures
B. Regulatory Flexibility Act
C. Executive Order 12612 (Federalism)
D. Preemptive Effect and Judicial Review
E. Paperwork Reduction Act
I. The Safety Problem
    This rule addresses the problem of rear underride crashes, in which 
a passenger car, light truck, or multipurpose vehicle with a Gross 
Vehicle Weight Rating (GVWR) of 4,563 kg (10,000 lbs) or less (referred 
to collectively in this rule as passenger vehicles) collides with the 
rear end of a trailer or semitrailer (trailers and semitrailers are 
referred to collectively in this rule as trailers) and the front end of 
the passenger vehicle slides under (i.e., underrides) the rear end of 
the trailer. Underride occurs to some extent in most collisions in 
which a passenger vehicle crashes into the rear end of a large trailer 
because most trailer beds are higher than the hoods of passenger 
vehicles. In the worst cases, referred to as passenger compartment 
intrusion (PCI) or ``excessive underride'' crashes, the passenger 
vehicle underrides so far that the rear end of the trailer strikes and 
enters its passenger compartment. PCI collisions generally result in 
passenger vehicle occupant injuries and fatalities caused by occupant 
contact with the rear end of the trailer.
    The solution to PCI is upgrading underride guards to make them 
stronger, but this introduces another concern. Even if guards succeed 
in preventing PCI, overly rigid guards may stop the passenger vehicle 
too suddenly, resulting in excessive occupant compartment deceleration 
forces and killing or injuring passenger vehicle occupants.
    The agency estimates that about 11,551 rear-end crashes with 
trucks, trailers, and semitrailers occur annually. These crashes result 
in approximately 423 passenger vehicle occupant fatali-ties and about 
5,030 non-fatal injuries.
II. Existing Regulations
    The initial Federal regulation addressing the issue of heavy 
vehicle rear underride was issued in 1953 by the Bureau of Motor 
Carriers of the Interstate Commerce Commission (presently the Office of 
Motor Carriers of the Federal Highway Administration, DOT). This 
regulation (49 CFR 393.86), which is still in effect, requires heavy 
trucks, trailers, and semitrailers to be equipped with a rear-end 
device designed to help prevent underride. The rule requires that the 
ground clearance of the underride guard not exceed 760 mm (30 inches 
(in)) when the vehicle is empty. The rule also requires that the device 
be located not more than 610 mm (24 in) forward of the rear of the 
vehicle and that it extend laterally to within 460 mm (18 in) of each 
side. The regulation further requires that the ``[guards] shall be 
substantially constructed and firmly attached.''
    The Research and Special Programs Administration (RSPA) of DOT has
    
[[Page 2005]]

specified configuration requirements for guards on tankers that carry 
hazardous materials (49 Part 178.345-8). The bottom of the guard must 
be at least 100 mm (4 in) below the lower surface of any part of the 
rear of the vehicle, and not more than 1,520 mm (60 in) from the ground 
when the tanker is empty. The guard must be very strong. It must 
deflect 150 mm (6 in) forward when subjected to a 20 m/s\2\ (2 G) 
impact while loaded, without contacting the cargo tank. These 
requirements are designed primarily to protect the tank and piping, not 
the colliding vehicle, in the event of a rear end collision.

III. Past Proposals

    From time to time, NHTSA has assessed the requirements of the 
Federal Highway Administration's (FHWA) regulation and considered 
whether NHTSA should issue a Federal Motor Vehicle Safety Standard 
(FMVSS) requiring heavy vehicles to be equipped with rear underride 
protection. The issues of particular concern have been the requirements 
for rear end guard ground clearance, guard strength, and the injury and 
fatality benefits of such a standard. The most recent of several NHTSA 
notices was a Supplemental Notice of Proposed Rulemaking (SNPRM) issued 
in 1992 (57 FR 252; January 3, 1992). Prior to the 1992 SNPRM, the 
agency issued a Notice of Proposed Rulemaking (NPRM) in 1981 (46 FR 
2136; January 8, 1981.) The notices of proposed rulemaking issued by 
NHTSA and FHWA prior to the 1981 NPRM are cited and discussed in the 
1981 NPRM (Docket 1-11; Notice 8).

IV. Summary of the 1981 NPRM

    The 1981 NPRM proposed to adopt a FMVSS for all new trucks and 
trailers with a GVWR of 4536 kg (10,000 lbs) or more. This NPRM was 
issued after research and computer modeling studies indicated that it 
was feasible to manufacture light-weight guards that could prevent 
excessive underride and absorb crash energy. Guard energy absorption is 
important because overly rigid guards could result in passenger 
compartment forces that would increase the risk of occupant injuries 
even in the absence of underride.
    The 1981 NPRM proposed that heavy trailers, semitrailers, and 
single unit (i.e., unarticulated) trucks be equipped with an underride 
guard that met certain requirements for strength and configuration. The 
NPRM proposed exclusions from this requirement for trailers with 
chassis that are low enough to the ground to meet the configuration 
requirements for the underride guard (low chassis vehicle), trailers 
that have the rear tires set back to within 305 mm (12 in) of the rear 
(wheels back vehicle), and trailers that have work-performing equipment 
in the lower rear whose function would be impaired by a guard (special 
purpose vehicle).
    NHTSA tentatively concluded that the proposed standard was superior 
to the FHWA regulation in three major ways. First, NHTSA specified 
objective requirements for guard strength (FHWA requires that the guard 
be ``substantially constructed and firmly attached''). Second, the NPRM 
proposed a guard configuration that permitted less ground clearance 560 
mm (22 in), less longitudinal distance between the guard and the 
trailer rear extremity 305 mm (12 in), and less lateral distance 
between the guard and the vehicle side extremities 100 mm (4 in), than 
the FHWA regulation. Third, the NPRM specified detailed procedures for 
testing the guards as installed on the vehicle for which they were 
intended by applying a specific force at certain points on the guard.

V. Summary of 1981 NPRM Comments

    The agency received over 100 comments on the NPRM. Many of the 
comments were from vehicle manufacturers and operators who believed 
their vehicles should be excluded from the requirements because they 
were special purpose vehicles. Some commenters objected to the proposed 
requirements and suggested alternative means of reducing the injuries 
and deaths caused by rear underride crashes. The alternative approach 
most often cited involved reducing the incidence of underride crashes 
through improved heavy vehicle conspicuity.
    The agency agreed that conspicuity was an important issue. The 
Fatal Accident Reporting System (FARS, a database containing a census 
of all vehicle fatalities in the U.S.) statistics had indicated that 
about 65 percent of the fatalities resulting from passenger vehicle 
collisions with the rear end of heavy vehicles occurred under non-
daylight conditions. NHTSA conducted a fleet study between 1980 and 
1985 of the effectiveness of improved conspicuity. As a result of this 
study, the agency determined that conspicuity improvement could reduce 
the incidence of the accidents by about 15 percent. Consequently, the 
agency published a NPRM on improved heavy vehicle conspicuity in 
December 1991, (56 FR 63474) and a final rule on conspicuity 
improvement in December 1992 (57 FR 58406).
    The agency believes, however, that improved rear impact guards 
could mitigate some of the rear impact fatalities and serious injuries 
not addressed by the improved conspicuity rule. The rear impact guard 
is especially important in cases in which the passenger vehicle 
driver's abilities are impaired by alcohol or drowsiness. Accident data 
indicate that alcohol is a factor for passenger vehicle drivers in 
about 30-40 percent of fatal rear underride accidents.
    Commenters on the 1981 NPRM also expressed concern that the 
proposed requirements would be a substantial financial burden on some 
truck and trailer manufacturers. Several commenters argued that the 
agency's cost estimate for rear underride guards was well below the 
actual cost of equipping the wide variety of single unit trucks with 
compliant guards. As to the trailer manufacturing industry, its members 
were said to be predominantly small firms that lack the engineering 
capabilities to meet the requirements of the proposed rule. In response 
to the comments and statistical data, the agency sought to determine if 
it could revise the proposed rule to reduce the financial burden on the 
manufacturers.

VI. Summary of the 1992 SNPRM

    The 1992 SNPRM contained requirements that are similar to those in 
the 1981 NPRM in terms of the guard's strength and configuration. 
However, the SNPRM differed substantially from the NPRM in terms of its 
impact on the industry. In place of the 1981 proposal of a single 
vehicle standard specifying the testing of guards on a completed 
vehicle, the SNPRM proposed two standards: (1) An equipment standard 
providing for the testing of guards on a test fixture, and (2) a 
vehicle standard requiring installation of guards complying with the 
equipment standard.
    The equipment standard proposed strength requirements and an 
objective test for determining compliance with these requirements. The 
guard manufacturer would conduct a test involving quasi-static loading 
of the guard with the guard mounted on a rigid test fixture rather than 
installed on a completed vehicle. Guards certified as passing the test 
could then be marketed to vehicle manufacturers for installation in 
accordance with the configuration requirements of the vehicle standard. 
Testing in this manner would relieve vehicle manufacturers, especially 
small ones, of the burden associated with compliance testing.
    The other major difference from the NPRM is that the SNPRM proposed 
to exclude single unit trucks from the rulemaking. NHTSA added this 

[[Page 2006]]
exclusion to those in the NPRM because single unit trucks are far less 
likely to be involved in fatal accidents than combination trucks (i.e., 
trailers and semitrailers). FARS and GES accident statistics indicate 
that only about 27 percent of the 423 average annual rear end 
fatalities and 18 percent of the 5,030 injuries involve single unit 
trucks, even though these vehicles represent 72 percent of the 
registered heavy vehicles. Thus, single unit trucks are significantly 
under-represented in rear end crashes. On the other hand, trailers are 
highly over-represented in rear end crashes, as they represent only 28 
percent of the registered heavy vehicles, but account for 73 percent of 
the occupant fatalities and 82 percent of the injuries. Therefore, the 
agency believed that excluding single unit trucks from the proposed 
rule would result in a better rule in terms of the ratio of benefits to 
costs.

VII. Summary of 1992 SNPRM Comments

    The agency received approximately 2,250 individual comments on the 
SNPRM. Industry-related comments were generally supportive of the 
proposal, while consumer interest organizations, local and State 
governments, and private citizens were generally critical.
    Representing the industry were comments from automobile and truck 
manufacturers, trade associations, manufacturers of trailers and 
semitrailers, and manufacturers of specialized usage heavy duty 
vehicles. Most of these commenters supported Federal rulemaking in this 
area. The trade associations and manufacturers of trucks and trailers 
were generally in agreement with the proposed requirements. 
Manufacturers and operators of specialized vehicles suggested that the 
proposed rule be modified to better define the types of vehicles that 
would be excluded from the standard.
    The vast majority of the critical comments were post cards or 
letters with multiple signatures from private citizens. These post 
cards and letters, as well as more detailed submittals from consumer 
interest organizations, expressed concern that the agency's proposal 
had three deficiencies. First, the commenters recommended that the 
rulemaking apply to single unit trucks as well as trailers and 
semitrailers. Second, the commenters recommended that the proposed 
maximum ground clearance, 560 mm (22 in), be reduced to a 405 to 455 mm 
(16 to 18 in) range. Third, these commenters expressed the opinion that 
the agency should mandate ``energy absorbing'' rear impact guards for 
heavy vehicles, i.e., guards with hydraulic pistons or shock absorbers 
designed to deflect or deform in a controlled manner upon impact and 
thereby lessen the deceleration experienced by passenger vehicles 
colliding with them. Several consumer interest organizations and 
private citizens also suggested that the proposed minimum guard 
strength requirements were insufficient.
    The consumer interest organizations and some private citizens also 
expressed concern that the proposed equipment standard for the rear 
impact guard did not require guards to be tested while mounted on a 
vehicle. As a result, guards complying with the proposed strength 
requirements could be installed on vehicles in such a location or in a 
manner that the guard/vehicle combination would be ineffective. In 
addition, some of these commenters stated that the crash tests NHTSA 
relied on in formulating the SNPRM were inadequate because they were 
not conducted under representative conditions of guard height, car 
bumper height, and car speed. Specifically, they stated that car bumper 
height would be depressed if the driver were braking to avoid colliding 
with the trailer, thus increasing the likelihood that the car hood 
would underride a 560 mm (22 in) high guard without engaging any 
substantial body structure. The consumer interest organizations also 
questioned the validity of the FARS accident data that NHTSA used to 
determine the benefits of the SNPRM, contending that the agency had 
underestimated the benefits of the rule. The state and local 
governments that commented expressed concerns similar to those raised 
by private citizens and consumer interest organizations.
    A summary of comments has been prepared and is available for 
inspection in Docket No. 1-11. Significant SNPRM issues raised by the 
commenters and NHTSA's response to the comments are discussed below. In 
response to the comments, the final rule includes several modifications 
to the rule proposed in the SNPRM, including clarified definitions, 
improved compliance test procedures, and a minimum guard energy 
absorption requirement.

VIII. Recent Testing by NHTSA

    In responding to comments to the SNPRM and a congressional request 
for a report on several heavy truck underride issues, NHTSA conducted a 
research project on Heavy Truck Rear Underride Protection at the 
Vehicle Research and Testing Center (VRTC) between September 1992 and 
June 1993 to evaluate the effectiveness of an underride guard meeting 
the requirements of the SNPRM. A copy of the test report (VRTC-82-0267) 
was placed in the public docket (No. 01-11-N09-54. See also Publication 
No. DOT-HS-808-081).
    For the purposes of the evaluation, NHTSA took the conservative 
approach of modifying the most common conventional guard design and 
developed a rear impact guard that was only slightly (10 percent) 
stronger than the minimum requirements of the SNPRM when tested at the 
vertical supports, which is the most significant location along the 
width of the guard's horizontal member. NHTSA arrived at this 
``minimally complying'' design through an iterative process of 
fabrication and testing in accordance with the proposed compliance test 
procedures.
    These minimally compliant guards were then evaluated in two series 
of full scale crash tests. The guards provided the proposed maximum 
ground clearance 560 mm (22 in). For the initial series of crash tests, 
the guards were mounted to a test fixture simulating the geometry of 
the rear end of heavy trailers. The guards were mounted on a late model 
production trailer for the other series. A total of seven crash tests 
were conducted with the minimally complying guard design. The tests 
were conducted at an impact speed of 48 kph (30 miles per hour (mph)) 
with late model compact and subcompact cars with mass between 1135 and 
1590 kg (or weight between 2500-3200 lbs). In each category, vehicles 
were selected which had low hood profiles, and were therefore most 
likely to underride the 560 mm (22 in) guard height.
    Four of the seven crash tests resulted in no PCI when the minimally 
compliant guard was mounted flush with the rear extremity of the 
trailer and simulated trailer. See Tables 6, 8, and 10 of the VRTC test 
report. The hood of one passenger car was driven through the windshield 
during one of these tests (Corsica 1, VRTC test report, page 26). The 
magnitude of the passenger compartment intrusion by the hood was 
marginal, however, and the test dummies were not contacted by the hood 
during the collision. Two cases of PCI were caused by guard system 
failure, one in a simulated trailer test and one in a production 
trailer test (respectively, Saturn 1 in Table 8 and Corsica (trailer) 
in Table 10 of VRTC test report). The guard system failure in the 
simulated trailer test was due to attachment hardware failure. The 
failure in the production trailer test was the 

[[Page 2007]]
result of trailer structural failure at the guard attachment locations. 
In each case, the guard attachment hardware and the trailer structure 
were upgraded with simple, inexpensive materials for subsequent tests. 
Retests with the modified hardware and trailer frame showed adequate 
guard system performance.
    All these crash tests included Hybrid III test dummies positioned 
in the driver and outboard front passenger seating locations for each 
crash test. The procedures used for frontal barrier crash test 
preparation under FMVSS No. 208, Occupant Crash Protection, were 
followed with respect to dummy positioning, restraint usage, and dummy 
instrumentation. Dummy instrumentation indicated very low potential for 
serious or fatal injury in all seven of the crash tests with the 
minimally compliant guard, even those in which there was PCI.
    The VRTC research project also performed a crash test using a very 
strong, i.e., ``rigid,'' guard, to compare the amount of underride and 
deceleration forces generated with those generated by the minimally 
compliant guard. The 48 kph (30 mph) impact generated a peak force of 
about 415 kN (93,000 lbs) and the guard sustained an insignificant 
amount of permanent deformation. Although underride in this crash test 
was minimal, occupant compartment forces generated during the crash 
were significant, with on-board dummy readings indicating a potential 
for serious driver chest injuries (dummy chest acceleration was 61 G, 
slightly higher than the 60 G permitted in FMVSS No. 208, Occupant 
Crash Protection). A similar crash test with the minimally compliant 
guard was conducted with the same make and model passenger vehicle. The 
minimally compliant guard, with a force resistance capability of about 
200 kN (45,000 lbs), allowed more underride than the rigid guard and 
marginal PCI. However, at 48 kph (30 mph), the minimally compliant 
guard test generated occupant compartment forces low enough that they 
posed essentially no potential for life-threatening occupant injuries. 
This test further demonstrated the adequacy of the proposed guard 
ground clearance requirement of 560 millimeters (mm) (22 in).

IX. Overview of the Final Rule

    This rule establishes two Federal Motor Vehicle Safety Standards. 
The two standards are being announced in this single notice because 
they are complementary and because their substantive requirements both 
derive from a single standard proposed in an earlier NPRM (Docket No. 
1-11, notice 8). The first standard will be referred to as the 
``equipment standard'' because it sets forth requirements that a rear 
impact guard must meet as an item of motor vehicle equipment. The 
second standard will be referred to as the ``vehicle standard'' because 
it requires a new trailer or semitrailer to be equipped with a guard 
that meets the equipment standard.
    The equipment standard specifies the procedures that the agency 
will use when testing a guard. The guard is first mounted to a rigid 
test fixture or a secured trailer, in accordance with the installation 
instructions which the guard manufacturer is required to provide. The 
standard describes how to select three test locations across the width 
of the guard. At these three locations, the testing procedure provides 
that force be slowly applied until the guard has been deflected by 125 
mm (5 in). The standard specifies procedures for determining whether 
the tested guard has met the minimum requirements for strength and 
energy absorption. Guards that can pass the strength and energy 
absorption tests may be certified and labeled as complying with the 
equipment standard and sold to vehicle manufacturers if accompanied by 
the necessary attachment hardware and mounting instructions.
    The guard mounting instructions are a crucial interface between the 
equipment standard and the vehicle standard. NHTSA has modified the 
equipment standard proposed in the SNPRM to require the guard 
manufacturer's instructions to include (1) a description of the types 
of structures to which attachment must be made, and (2) the manner in 
which attachment must be made, in order for the guard to perform in its 
designed fashion.
    The vehicle standard requires that most new trailers and 
semitrailers be equipped with a rear impact guard certified to the 
equipment standard. The vehicle manufacturer can manufacture and 
certify the guards according to the equipment standard, or simply 
purchase and install certified guards from a guard manufacturer. The 
vehicle standard requires that the guards extend laterally to within 
100 mm (4 in) of the sides of the trailer, that the guard have a ground 
clearance of no more than 560 mm (22 in), and that the guard be placed 
as close to the rear of the vehicle as possible. To ensure that the 
guard will perform properly, the vehicle standard further requires that 
the guard be mounted on the trailer or semitrailer in accordance with 
installation instructions provided by the guard manufacturer.
    The vehicle standard lists and defines certain types of vehicles 
that are excluded from the requirement to have rear impact guards. 
Single unit (unarticulated) trucks, truck tractors, pole trailers, low 
chassis vehicles, special purpose vehicles, and wheels back vehicles do 
not have to have rear impact guards.

X. Summary of Changes From the 1992 SNPRM

    The greatest change from the SNPRM is the addition to the equipment 
standard of a requirement for energy absorption. The SNPRM would have 
permitted fairly rigid guards because it did not require the guard to 
yield in response to force. Rigid guards may stop the passenger vehicle 
too quickly, causing occupant deaths and injuries from sudden 
deceleration. To ensure that the guards will yield, this rule adds a 
requirement that the guards absorb a certain amount of energy during 
the strength test. The new requirement does not necessitate the use of 
any additional new test equipment or the following of any additional 
test procedures. It does require more frequent measurements of the load 
during the strength test, and a few extra calculations after the test.
    The test procedures in the equipment standard have been modified to 
allow velocity-sensitive rear impact guards. Velocity-sensitive guards 
would have failed the quasi-static strength test procedure proposed in 
the SNPRM because these guards are designed to provide resistance that 
is proportional to the displacement rate, and the test procedure 
displaces the guard very slowly. The final rule provides for modifying 
the guards to deactivate the energy absorbing components prior to the 
strength test. Because velocity sensitive guards typically have 
excellent energy absorption characteristics and because quasi-static 
testing does not test their energy absorbing capabilities, velocity-
sensitive guards do not have to be tested for energy absorption. The 
only type of velocity-sensitive guards that the agency is aware of use 
hydraulic fluid properties to deform in a controlled manner. Therefore, 
these ``hydraulic guards'' are the only ones excluded from the energy 
absorption test.
    The final rule requires greater specificity in statements regarding 
trailer structure in the installation instructions provided by the 
guard manufacturer. The SNPRM said only that the instructions had to 
specify the types of vehicles for which the guard was intended, state 
the necessity for 

[[Page 2008]]
attaching the guard to the vehicle chassis, and explain how the 
attachment hardware was to be used. The regulatory text of the final 
rule makes it clear that the installation instructions must specify all 
aspects of the trailer that are necessary to the proper functioning of 
the guard. The test procedure has been modified to indirectly test the 
adequacy of the attachment.
    NHTSA has changed some of the guard configuration requirements in 
the vehicle standard. The SNPRM proposed to require that the horizontal 
member of the guard extend to within 100 mm (4 in) of the side 
extremities of the vehicle and to within 305 mm (12 in) of the rear 
extremities. These requirements have been modified to allow rounded 
guard ends. The final rule allows an extra six inches in these 
dimensions only for the portion of a guard that is curved. Using 
rounded guard ends will diminish the hooking potential of the guards 
when the trailer is turning sharply. Guard ends that are rounded upward 
and attached to the vehicle may add strength to the horizontal member 
near the side extremity of the vehicle.
    To account for high, overhanging rear protrusions on trailers, 
NHTSA changed the definition of the vertical zone to be considered when 
determining the trailer's ``rear extremity.'' Determination of the 
``rear extremity'' is important because the location of the guard is 
based on the location of the rear extremity. The SNPRM defined ``rear 
extremity'' as the rearmost point above 560 mm (22 in) from the ground. 
Since high overhangs pose no risk to colliding passenger vehicles, 
NHTSA has set a maximum height of 1905 mm (75 in) from the ground on 
the zone. Higher protrusions will not be considered as the rear 
extremity.
    Another change in the configuration requirements is that the final 
rule requires the guard to be mounted as close to the rear extremity as 
practical within the 305 mm (12 in) zone forward of the rear extremity. 
The SNPRM did not regulate where in the zone the guard had to be 
mounted.

XI. Analysis and Response to Comments on the 1992 SNPRM

A. Separate Equipment and Vehicle Standards

    Companies such as Waltco and industry groups such as the National 
Truck Equipment Association supported the separate equipment and 
vehicle standards as a method to prevent undue testing burdens.
    One of the concerns raised by consumer interest organizations is 
that allowing the guards to be tested on a ``non-vehicle'' rigid test 
fixture posed a problem if it is done in the expectation that the 
guards would necessarily perform in a similar manner once they are 
installed on vehicles. The Institute for Injury Reduction (IIR) 
commented that neither the equipment standard nor the vehicle standard 
specifies or regulates the interface between the guard and the vehicle. 
Therefore, IIR was concerned that there are no ``real-world'' tests 
performed on the guards as installed on the vehicle and suggested that 
it is unclear whether a failure of such a test would represent 
noncompliance by the guard manufacturer, the vehicle manufacturer, 
both, or neither.
    NHTSA agrees that an underlying assumption of this regulatory 
scheme is that the guards would perform in the real world in a manner 
similar to the way they do in the tests. This assumption is supported 
by the results of the VRTC research project, which show that the 
maximum force measured in quasi-static tests is similar to the maximum 
force generated in dynamic crash tests. Moreover, this regulatory 
scheme has worked well for tires, which also have separate equipment 
(49 CFR 571.109) and vehicle (Sec. 571.110) standards.
    NHTSA disagrees with IIR's argument that separate guard and vehicle 
standards leave the guard/vehicle interface unregulated. The vehicle 
standard specifies that the guard be attached in accordance with the 
guard manufacturer's installation instructions, the same instructions 
used to attach the guard to the test fixture during agency compliance 
testing under the equipment standard.
    When writing installation instructions, the guard manufacturer must 
take into account the possibility of inadequate trailer structure to 
support the guard. Depending on the guard design, the guard 
manufacturer may want to specify in the instructions that the guard 
cannot be attached to certain structures (e.g., floorboards) and that 
it must be attached to other surfaces, for example, frame rails with a 
horizontal surface and specified wall thickness of a certain material 
(e.g., hardened steel). The guard manufacturer may have to specify 
local reinforcement if the trailer chassis is inadequate to pass the 
compliance test with the chassis surface mounted on the rigid test 
fixture.
    The installation instructions must be appropriate to the trailer 
design, so that the vehicle manufacturer knows which guard to purchase 
and does not have to deviate from the instructions to install the 
guard. To help assure this, the regulatory text has been modified to 
make it clear that the guard manufacturer must either list appropriate 
trailers or specify in the installation instructions all attributes 
that make a trailer suitable for the proper installation and 
functioning of the guard. These include the types of trailer 
structures, design types with dimensions, materials thickness and tire 
track widths that are appropriate as an installation location.
    NHTSA will install the guards during compliance testing based on 
these instructions. Therefore, it is essential that the attachment site 
and attachment method be adequately specified. This is especially 
important to avoid failure of the attachment itself during the test.
    In a VRTC test of the minimally complying guard mounted on a 
typical trailer, the trailer frame rails worked with the guard by 
bending/deforming to absorb the colliding vehicle's crash energy. 
However, the attachment site on the frame rails had to be strengthened 
with an inexpensive local reinforcement.
    IIR's argument that failure during compliance testing would leave 
the identity of the non-complying party in doubt is incorrect. The only 
testing procedures in NHTSA's rule are the compliance tests in the 
equipment standard. Therefore, the only party that can be responsible 
for a testing failure is the guard manufacturer. Noncompliance by the 
vehicle manufacturer may be established by inspecting the vehicle and 
observing improperly installed guards, such as during an FHWA heavy 
truck inspection. If the vehicle manufacturer manufactures the guard 
which it uses, as NHTSA believes will usually be the case, there will 
be no ambiguity as to the party responsible for testing failure or 
improper installation.

B. Standard for Equipment

1. Relationship of Strength, Energy Absorption, and PCI
    In specifying performance standards for rear impact guards, the 
agency must balance various performance attributes. The vast majority 
of the commenters, including virtually all of the consumer safety 
groups, asserted that underride guards should be strong, yet energy 
absorbing. NHTSA agrees that these are both desirable properties in an 
underride guard, but emphasizes that an increase in strength may result 
in a decrease in the capability of the guard to absorb energy, and vice 
versa. An impact guard strong enough to restrain a large car travelling 
at high speeds would impart high deceleration forces to a small car 
crashing into it at the 

[[Page 2009]]
same speed. Conversely, an impact guard that is optimized to restrain a 
small car without excessive deceleration forces might fail (i.e., 
deform so much that it allows PCI) if a large car crashes into it, or 
if a small car crashes into it at higher speeds.
    Energy absorption must also be balanced against PCI prevention. 
Energy absorption may be maximized by allowing the guard to yield for a 
greater distance before bringing the passenger car to a stop. However, 
the more the guard yields, the farther the colliding vehicle travels 
and the greater the likelihood of PCI. This rulemaking has focussed on 
balancing the need for PCI-prevention against minimizing crash 
injuries. FARS data show a strong correlation between PCI and 
fatalities or serious injuries. Preventing PCI demands a guard that is 
strong enough to prevent the passenger vehicle from advancing very far 
after contact with the guard.
    Compounding the difficulty of balancing the guard's performance 
attributes is the wide range of colliding passenger vehicle weight, 
speed, and size. The combination of weight and speed determines the 
level of kinetic energy to which the guard will be subjected. Passenger 
vehicle weight generally correlates with the hood height and length, 
which determines how far the vehicle can proceed after contact with the 
guard before PCI occurs. Fortunately, these factors offset one another 
for large cars (i.e., the greater weight promotes greater amounts of 
underride, while the higher hood profile results in better guard 
engagement and the longer hood allows for more underride before 
experiencing PCI).
    Small pickups and vans have relatively high profiles but a 
relatively short distance from the front of the vehicle to the occupant 
compartment. A guard would have to yield only slightly, or have high 
strength to prevent minivans and some pickups (which typically have a 
mass more than 1810 kg or weigh more than 4,000 lbs and have short 
hoods) from experiencing PCI. Because the passenger compartment is so 
close to the front of a heavy standard van, no underride guard is 
likely to be very effective in preventing PCI for these vehicles. 
Nevertheless, some reduction in fatalities and non-fatal injuries can 
be expected due to the initial energy absorption of the guard. 
Fortunately, vans have only been involved in 0.5 percent of all 
underride fatalities from 1982 to 1992. Pickups have been involved in 
about 18 percent of the fatalities during this period.
    It should be recognized, therefore, that impact guards cannot be 
optimized for all situations. The requirements in this rule should 
reduce the incidence of PCI, fatalities, and injuries for all passenger 
vehicles, but some more than others. A minimally compliant guard should 
protect all passenger vehicles from PCI and excessive deceleration 
forces up to some speed in the 40 kph (25 mph) to 56 kph (35 mph) 
range, although that speed will vary on a sliding scale depending on 
the vehicle weight and front end profile. For example, NHTSA 
analytically estimates that mid and full size cars and light trucks and 
vans with a mass greater than 1590 kg (3,500 lbs) will experience PCI 
at approximately 43 kph (27 mph), while mini-compacts of less than 1135 
kg (2,500 lbs) will be able to collide with the required guard at about 
61 kph (38 mph) without PCI. This estimate is obtained by equating the 
energy absorbed by a 48 kph (30 mph) collision of a 1590 kg (3,500 lb) 
vehicle rigid barrier crash to the energy absorbed by a different 
weight vehicle). For example, for a 907 kg (2000 lb) vehicle, the 
calculated impact speed without PCI is: (square root of (1,590 kg/907 
kg)) x 48 kph=63.5 kph, or (square root of (3,500 lb/2,000 lb)) x 30 
mph=39.7 mph.
2. Guard Strength
    Several consumer interest organizations and private citizens 
criticized the 1992 SNPRM's proposed guard strength requirements. These 
commenters' objections are either that guards meeting the requirements 
would be too weak to prevent underride or that they would be so strong 
that the passenger vehicle would be subjected to excessive deceleration 
forces. As explained above, the issues of strength and energy 
absorption are closely related. However, issues relating primarily to 
energy absorption will be addressed in the next section.
    The SNPRM, which was premised upon underride protection being 
provided by a horizontal member, proposed to require that the 
horizontal member resist a force of 50 kilonewtons (kN) (11,240 lbs) 
applied at the center (site P2) and near the outboard ends (sites P1), 
and a force of 100 kN (22,480 lbs) at an intermediate position (sites 
P3), in separate quasi-static strength tests. For these tests, guard 
resistance at the specified force level would have to occur at less 
than or equal to a 125 mm (5 in) displacement of the guard's horizontal 
member.
    Several commenters stated that overly ``rigid'' or non-yielding 
guards would be permitted by the proposed rule. They expressed concern 
that those guards would be too stiff, citing the results of full-scale, 
heavy truck rear underride crash tests conducted in the late 1970's and 
early 1980's by the Texas Transportation Institute (TTI), Dynamic 
Sciences, Inc., and the Insurance Institute for Highway Safety (IIHS). 
These crash tests indicated occupant compartment forces generated in 
collisions with rigid guards at impact speeds above 48 kph (30 mph) 
could produce potentially fatal driver and front passenger head and 
chest injuries.
    Advocates for Highway and Auto Safety (Advocates) stated that the 
proposed guard would not perform as well as the agency expects, and 
would be excessively deformed or fail in impacts not much above 40 to 
48 kph (25 to 30 mph). Advocates further stated that NHTSA directed its 
contracted researcher in 1982 to reduce the impact speed of a dynamic 
crash test on a Chevrolet Impala from 48 kph (30 mph) to 40 kph (25 
mph), specifically to ensure that excessive underride did not occur. 
The actual speed of the tested 1,840 kg (4,060 lb) Chevrolet Impala was 
38.5 kph (23.9 mph). Advocates contends that the agency admitted in a 
memorandum from Mr. Tomassoni (who worked for NHTSA at the time) that 
the test would have resulted in PCI at 48 kph (30 mph). IIHS also 
included these criticisms in its comment.
    Some commenters recommended that NHTSA require specific levels of 
strength higher than those proposed in the SNPRM. Advocates attached a 
1991 technical paper by Mr. G. Rechnitzer, of Monash University in 
Australia, which reviewed European truck underride data. The example 
with the widest application, the Economic Commission for Europe's (ECE) 
Regulation No. 58 for heavy truck rear underride guards, currently 
requires a guard force resistance of 100 kN (22,480 lbs) at the point 
on the guard corresponding with this rule's P3 test point, 50 kN 
(11,240 lbs) at the center, and up to 25 kN (5,620 lbs) at the outboard 
test position corresponding with this rule's P1 position. Mr. 
Rechnitzer recommended that the rear impact guard strength requirements 
be upgraded to 150 kN (33,370 lbs) at the P3 location and 100 kN 
(22,480 lbs) at the center and P1 locations. Mr. Byron Bloch, of Auto 
Safety Design, suggested an even stronger guard. He thought the rule 
should require that the guard resist 222 kN (50,000 lbs) at the P3 test 
location, where the SNPRM requires that the guard resist a force of 100 
kN (22,480 lbs).
    The VRTC tests indicate that the strength of the 1992 SNPRM guard 
is adequate for preventing underride with 

[[Page 2010]]
PCI in a collision with an impact speed of up to 48 kph (30 mph) for 
vehicles with a mass of about 1,450 kg (3,200 lbs). PCI resistance 
would be expected at higher impact speeds for lighter vehicles and 
lower impact speeds for heavier vehicles. The test data also indicate 
that rear impact guards having somewhat more strength than the proposed 
level of strength could resist PCI at higher impact speeds without 
generating life-threatening passenger compartment force levels. 
Although stronger guard strengths may be desirable, the agency cannot 
quantify the increased benefits that might be obtained without further 
testing.
    Based on the VRTC tests, the agency believes that the guard 
strength requirements proposed in the 1992 SNPRM are of sufficient 
magnitude to prevent PCI for most late model passenger vehicles at 
impact speeds of about 45 kph (28 mph). This rule has an additional 
requirement that guards yield enough to maintain survivable levels of 
occupant compartment deceleration when impacted by passenger vehicles. 
Therefore, the agency has decided to retain the strength requirements 
of the SNPRM in the final rule.
    The IIHS advocated a specific guard design, which it said was 
preferable for strength purposes. That organization believes a diagonal 
strut from the horizontal member of the guard to the trailer chassis 
could augment guard strength without a large increase in guard weight. 
NHTSA agrees with the IIHS that this type of design is quite efficient 
with respect to weight and strength, though not necessarily with 
respect to energy absorption. However, the agency does not believe that 
it is necessary or desirable to mandate a specific design, since 
similar crash performance may be achieved with other designs.
3. Guard Energy Absorption
    Although all non-rigid guards absorb some of the kinetic energy of 
the striking vehicle, there was considerable concern that the SNPRM did 
not require energy absorbing guards. The consumer interest 
organizations and about 2,200 private citizens urged NHTSA to mandate 
``energy absorbing'' guards. By deforming, rear impact guard structures 
absorb some of the kinetic energy of the striking vehicle. The more 
energy the guard absorbs, the less energy must be absorbed by 
deformation of the striking vehicle before it stops. Commenters were 
concerned that the SNPRM would have permitted rigid guard designs that 
would impart high levels of crash forces to the striking vehicle's 
occupants.
    As used by the consumer interest groups, the term ``energy 
absorbing guards'' generally refers to guards whose vertical support 
members are designed to pivot about their attachment braces at the 
vehicle chassis. These guards absorb energy by means such as 
cylindrical, telescoping hydraulic or plastic struts, which are also 
attached to the guard's horizontal member and the vehicle chassis. When 
impacted, these energy absorbing units respond by compressing without 
substantial deformation until the units have reached their maximum 
deflection, or ``bottomed out.'' On the other hand, the primary energy 
absorbing mechanism of a fixed guard, such as the design used in the 
VRTC tests, is the flexing and bending of the guard's vertical 
supports. Keeping this in mind, the agency uses the term ``energy 
absorbing guards'' below in the same sense as used by the commenters, 
as a shorthand way of referring to guard designs with special energy 
absorbing design features.
    Advocates recommended that guards be required to be energy 
absorbing so that 64 kph (40 mph) impacts of small cars with the rear 
of heavy vehicles are survivable through the combined energy absorption 
of the car and the guard. The National Association of Independent 
Insurers (NAII) suggested that the proposed rule be modified to require 
a more flexible, energy absorbing guard. Citizens for Reliable and Safe 
Highways (CRASH) stated that the agency fails to acknowledge the need 
for and potential benefits from improved, slightly more expensive, 
energy absorbing guards that are in use in Europe.
    To ensure that the guard will provide the combination of strength 
and energy absorption necessary to prevent underride with PCI at a 
specified impact speed, as recommended by Advocates, a full-scale 
dynamic compliance test including a passenger vehicle would be 
necessary. VRTC conducted full-scale crash tests with guards that were 
also tested in accordance with the SNPRM compliance procedures. These 
tests demonstrated that the proposed quasi-static compliance test is 
adequate for determining guard strength. The peak forces generated by 
the guard in the quasi-static compliance tests and the full-scale crash 
tests were approximately the same. Guard strength or peak force 
capability is the primary factor in underride prevention. Guard energy 
absorption characteristics determine the guard's ability to maintain 
impact forces at survivable levels in the striking vehicle, as well as 
the guard's resistance to structural failure.
    The agency has decided to retain the quasi-static compliance test 
for guard strength due to the greater complexity and cost of a dynamic 
compliance test procedure. Although the guard's ability to resist PCI 
at a specific impact speed will not be tested directly, the VRTC tests 
show that dynamic guard performance can be accurately estimated from 
the quasi-static compliance test results. Therefore, it is not 
necessary to conduct expensive full-scale dynamic tests to attain most 
of the benefits of dynamic testing.
    Advocates also stated that British researchers assess the potential 
fatality reduction effectiveness of stronger, energy absorbing guards 
at 25 to 35 percent. This is about twice the current guard 
effectiveness in Europe, according to the document cited by Advocates, 
an opinion paper by P.F. Gloyns, et al., of Vehicle Safety Consultants, 
Ltd., entitled ``Legislative Implications of Accident Experience in the 
UK of Rear Under-Run Guards.'' The Gloyns paper does not quantify the 
increase in guard strength or the magnitude of guard energy absorption 
required to achieve the estimated increase in guard effectiveness. The 
agency acknowledges that various combinations of guard strength and 
energy absorption capability could increase the effectiveness of rear 
impact guards. However, without more quantitative information, NHTSA 
cannot address the guard effectiveness claims of Gloynes, et al.
    It may be that energy absorbing rear underride guards, which were 
referred to by CRASH and which are currently in use on one to two 
percent of vehicles in Europe, are superior to a moderate strength, 
fixed guard meeting the minimum performance requirements specified in 
the rulemaking proposal. The agency notes that these European guards, 
or guards with similar energy absorbing characteristics and design 
features, would not be prohibited by NHTSA's proposed rule and will no 
doubt be considered by the industry as a possible means of compliance, 
just as they were in Europe.
    The agency has tested one guard, the Quinton-Hazel rear impact 
guard, which utilized pivoting vertical support members along with 
telescoping hydraulic struts and coil springs. The guard demonstrated 
excellent overall performance in a crash test conducted in 1979 by the 
Texas Transportation Institute. The striking crash test vehicle was a 
1,810 kg (4,000 lb) Chevrolet and the impact speed was 56 kph (35 mph). 
The collision did not result in PCI, and all measured occupant 
responses indicated that the potential for driver 

[[Page 2011]]
and front passenger serious injuries was low. It is estimated that 
similar guards would weigh about 1.33 to 3 times more and cost 3 times 
more than a fixed, moderate strength guard designed to meet the 
requirements of the SNPRM. In other words, it would cost $300-$350 and 
have a mass of 136 kg (300 lbs) to 181 kg (400 lbs). Further, hydraulic 
energy absorbing guards would be considerably more complex than fixed 
guards that comply minimally with this rulemaking, and would require 
periodic maintenance. It is NHTSA's understanding that there are 
currently no guards in production in this country or in Europe that 
utilize hydraulic or plastic energy absorbing, telescoping units. A 
letter from one of the former manufacturers, Quinton-Hazel, indicates 
that the market probably rejected them as too costly.
    Nevertheless, in response to the comments recommending energy 
absorbing guards, the agency has added a performance requirement for 
guard energy absorption to the rule. The requirement does not include 
design specifications such as pivoting vertical supports or telescoping 
energy absorbing units. The agency is requiring that each guard absorb 
a minimum amount of energy based on the forces and displacements 
specified in the 1992 SNPRM. The same quasi-static compliance test 
procedure proposed for strength testing will be used to determine 
compliance with this new specification. The test for guard energy 
absorption will be conducted only at the P3 location used for guard 
strength testing. The minimum magnitude of guard energy absorption will 
be 5,650 joules (4,170 foot-pounds), which is based on the force 
required to comply with the strength test at the P3 test location and 
the maximum displacement allowed for the guard to generate the force 
(125 mm, or 5 in). The energy absorption test will require that the 
guard's horizontal member undergo 125 mm (5 in) of displacement while 
the force generated by the guard is recorded at least ten times per 25 
mm. The magnitude of guard energy absorption at the P3 location is 
sufficient to absorb about 12 percent of the total kinetic energy of a 
48 kph (30 mph) centric collision with a 1,135 kg (2500 lb) vehicle. 
This magnitude of guard energy absorption capability is also similar to 
the amount recommended in several British research papers provided by 
Advocates.
    Several commenters, including consumer interest organizations and 
trailer manufacturers, stated that the proposed rule would permit 
overly ``rigid'' or non-yielding guards that would absorb little or no 
crash energy. The commenters expressed concern that those guards would 
be too stiff and would result in fatal driver and front vehicle 
passenger head and chest injuries.
    The agency has drafted the energy absorption requirement to address 
these concerns. NHTSA recognizes the potential trade-off between 
designs of underride guards that minimize occupant injury criteria 
responses and those that provide the most protection from PCI. The 
agency also recognizes that an increase in the level of rigidity from 
the minimally compliant guard used in the VRTC tests is desirable, but 
this should not be at the expense of energy absorption. On the other 
hand, the agency does not want to restrict or dictate guard design by 
specifying the rigidity of the guard. Therefore, to discourage overly 
rigid guards, this rule requires that a minimum amount of the energy be 
absorbed during the energy absorption test from permanent yielding, or 
plastic deformation, of the guard. After the guard has reached the full 
125 mm (5 in) of deformation, the load is reduced and any elastic 
``rebound'' of the guard is measured until the load is zero. The 
elastic component of the energy that is returned by the guard is not 
included in the calculation of total energy absorbed by the guard. This 
method gives guard designers flexibility to select guard material 
properties and frame member spatial configuration.
    Some commenters observed that the test procedures proposed in the 
SNPRM precluded the use of hydraulic energy absorbing guards. Mr. John 
Tomassoni stated that the 125 mm (5 in) displacement maximum allowed in 
the strength test would allow only passive structures such as steel 
struts designed to bend on impact. This is because active energy 
absorbing struts that are hydraulic (analogous to a vehicle shock 
absorber) are velocity sensitive. With the slow application of force 
during the quasi-static test, the hydraulic fluid units would develop 
almost no resistance. He recommended adding a ``bottoming'' provision 
to allow static testing after hydraulic systems have reached full 
stroke.
    NHTSA agrees that quasi-static test procedures are inappropriate 
for hydraulic guards, or any other type of velocity sensitive guard 
(although NHTSA is unaware of any non-hydraulic guards that are 
velocity sensitive). A dynamic test would be required to assess their 
energy-absorbing capabilities by supplying the sudden onset of force 
their energy absorbing units require to generate resistance. Because 
the agency does not want to discourage the use of these advanced guard 
designs by requiring expensive dynamic tests, and because these guards 
typically have excellent energy absorbing capabilities, the final rule 
excludes these guards from the energy absorption requirements.
    There are also problems with subjecting velocity sensitive guards 
to the strength requirement. However, complete exclusion of those 
guards from the performance requirements would be inappropriate. 
Accordingly, the agency has modified the test procedures to allow 
velocity sensitive guards to be tested for compliance with the strength 
requirement. The agency is concerned that, if the hydraulic energy 
absorbing units do not operate properly, the guard will not generate 
significant resistance and energy absorption. NHTSA wants to assure 
that the guard has enough residual strength, even without the energy 
absorbing units, to meet the same strength requirements as other 
guards. Therefore, velocity sensitive energy absorbing guards will be 
tested by slowly compressing the energy absorbing units to the full 
extent of their designed travel or 610 mm (24 in), whichever occurs 
first. This will allow the frame of the guard itself to generate 
resistance, rather than having the piston simply compress the hydraulic 
shock absorbers.
4. Vertical Cross-sectional Height of Horizontal Cross-member
    The SNPRM proposed a minimum vertical cross sectional height of 100 
mm (4 in) across the entire width of the guard's horizontal cross-
member. Advocates stated in its comment that the guard must be at least 
205 mm (8 in), and preferably 305 mm (12 in), high to better manage the 
loading impact forces and assure full engagement of the vehicle front 
end. In contrast, the Truck Trailer Manufacturers Association (TTMA) 
suggested reducing the requirement, urging that the guard be only 50 mm 
(2 in) high because that is all that is required for adequate strength. 
It asserted that requiring greater vertical cross section height just 
adds unnecessary weight and cost to the guards.
    NHTSA agrees with Advocates' position that a higher vertical cross 
section has the potential to better distribute the impact forces, but 
this does not mean that the proposed 100 mm (4 in) height is 
insufficient. The 100 mm (4 in) height would be inferior if it sheared 
or ``cut'' through the front of the striking vehicle, thus allowing 
forward vehicle motion without much energy absorption due to the low 
magnitude of 

[[Page 2012]]
force generated by the guard. A guard should cause the vehicle to 
absorb energy by crushing, rather than shearing through, frontal 
vehicle structural components. Shearing through did not occur in the 
agency's testing with a 100 mm (4 in) high guard horizontal member. 
None of the crash tests conducted pursuant to this rulemaking resulted 
in significant shearing of the passenger vehicle's frontal structure 
(above the 560 mm (22 in) high guard). The crash tests show that the 
100 mm (4 in) profile of the guard horizontal member resulted in 
adequate engagement of the car's front end and is harmonized with the 
guard specified in ECE Regulation 58. Moreover, a 205 mm (8 in) high 
profile may require heavier and more expensive guards. Finally, the 
agency notes that 100 mm (4 in) is only a minimum height, so guard 
manufacturers are free to manufacture the guards that Advocates 
recommends. Accordingly, the agency concludes that a higher vertical 
cross sectional height requirement is unnecessary.
    NHTSA also disagrees with TTMA's position that a 50 mm (2 in) 
vertical cross sectional height would be appropriate. The TTMA did not 
provide any data to support its assertion that the strength should be 
adequate. Even if the 50 mm (2 in) height were sufficient for strength 
purposes, it would have a greater tendency to shear into the front of 
the passenger vehicle instead of crushing it. This would result in a 
reduction of energy absorption by the guard and an increase of the 
striking vehicle damage in low speed crashes of 16 to 24 kph (10 to 15 
mph). Accordingly, the agency has decided to retain the 100 mm (4 in) 
cross sectional vertical height requirement in the final rule.
5. Shape of the Horizontal Cross-member
    Some commenters stated that NHTSA should require the guards to have 
blunted or rounded ends. The Florida Department of Transportation, 
based on visual evaluations of the installed guard, stated that the 
requirement that the guard extend to within 100 mm (4 in) of the side 
of the vehicle would make it a dangerous ``hook'' for adjacent 
vehicles, especially during sharp turns of the trailer. It suggested 
requiring a ``U'' shaped guard, similar to one used by some carriers 
which is attached at either end to the underside or rear of the 
vehicle. It thought that the ends on these guards could be located 
further inboard. The TTMA had a similar suggestion, proposing that 
NHTSA allow (but not require) guards with rounded corners, to lessen 
the hooking potential when the sliding tandem is positioned forward. 
The TTMA suggested that the rule be modified to allow such guards to 
begin curving at a point 255 mm (10 in) inboard of the edges of the 
vehicle, while retaining the 100 mm (4 in) requirement for straight 
guards.
    NHTSA agrees that there is some potential for hooking the guard on 
the fenders and wheel wells of adjacent passenger vehicles when the 
rear end of the trailer swings out laterally during a sharp turn. This 
phenomenon would be accentuated when the rear wheels on a sliding 
tandem are positioned forward. The rear wheels are generally positioned 
forward to give the trailer greater maneuverability, so it is likely 
that trailers in this configuration will be making sharp turns.
    On the other hand, rounded or U-shaped guards would be more 
expensive to manufacture and would weigh more. Moreover, rounded 
corners offer very limited potential added value on roadways where 
sharp turns are infrequent, such as on the interstate highways, which 
are heavily traveled by trailers. Therefore, while the agency wants to 
allow guards with rounded ends for operations where they are desired, 
NHTSA does not think it is necessary or even appropriate to require 
them.
    The commenters referred to rounded guard ends that curve upward, 
but a rounded end that curves forward could also be useful. It would 
serve the purpose of making hooking less likely because the guard end 
would sweep through a smaller arc and present a less pointed profile to 
adjacent passenger vehicles. Moreover, forward-curving guards could 
slightly enhance guard effectiveness if a passenger vehicle strikes the 
trailer in the rear corner at an angle. However, forward-curving guard 
ends might interfere with the rear wheels if a sliding tandem were 
moved to the rearmost position.
    NHTSA notes that the SNPRM would not prohibit guards with rounded 
ends, but its configuration requirements would have restricted their 
curves to a 100 mm (4 in) radius of curvature. To minimize hooking 
potential and property damage in some applications, the final rule 
adopts the TTMA's suggestion and allows a guard with rounded ends to 
begin curving 255 mm (10 in) inboard of the side extremity of the 
trailer. This will allow a radius of curvature of 150 mm (6 in), or 255 
mm (10 in) if the guard end extends all the way to the side 
extremities. To make the same allowances for forward-curving guards, 
should guard manufacturers want to produce them, NHTSA is allowing 
those guards to begin curving forward 255 mm (10 in) inboard of the 
side extremities, even if the guards are already mounted as far forward 
as possible--305 mm (12 in) forward of the rear extremity.
6. Guard Attachment
    The SNPRM did not specify a particular guard attachment method. To 
assure an adequate interface between the guard and the trailer, the 
SNPRM proposed to require that the guard be attached to the trailer 
chassis in accordance with the instructions provided by the guard 
manufacturer.
    Several commenters thought the SNPRM inadequately addressed the 
issue of guard attachment and discussed the merits of certain guard 
designs. Citing a study by Vehicle Safety Consultants (VSC) Ltd., 
Advocates stated that attaching the horizontal member of the guard to 
the vehicle with vertical members is not ideal because the guard tends 
to pivot forward and up if it is struck from the rear by a passenger 
vehicle and fails. It said that the vertical members then form an 
inverse ramp, thus aggravating any underride tendency by pushing the 
passenger vehicle down and the trailer up. To solve this problem, 
Advocates appears to recommend either guards with diagonal hydraulic 
struts or the use of hinged, pivoting energy absorbing guards that can 
fold up for rail or other intermodal transportation. IIHS also believed 
a diagonal strut would improve guard strength without adding weight and 
would make it more likely that the guard will move downward as it 
deforms, thus helping to stop the passenger vehicle.
    The agency agrees with IIHS and Advocates that designs employing 
diagonal struts are strong yet light, but believes it would be 
inappropriate to require such designs. There is no evidence that only 
designs with diagonal struts perform adequately. To the contrary, the 
design used in the VRTC tests did not have diagonal struts and 
performed acceptably. Diagonal struts may also be impracticable in some 
cases, due to trailer construction and use.
    Likewise, while the pivoting, fold-away design that Advocates 
recommended has obvious practical advantages in some circumstances, the 
agency does not believe that there is any necessity for mandating that 
all guards incorporate that design. Such designs would be unneeded by 
many trailer operators since most trailers do not travel by ship or 
train. If trailer operators need fold-away guards for intermodal 
transportation or other 

[[Page 2013]]
operational environments, they may specify such guards when ordering 
new trailers.
    NHTSA believes that specifying a particular attachment 
configuration, as suggested by Advocates and IIHS, would unnecessarily 
restrict design flexibility on the part of guard manufacturers. 
Adequate performance may be achieved by a variety of attachment 
methods. Moreover, it is impracticable for NHTSA to attempt to 
anticipate all the factors that may go into the choice of attachment 
method, given the variety of possible guard and trailer configurations. 
The agency's decision not to specify a particular attachment method 
leaves the guard manufacturers free to choose an appropriate design.
    Some commenters had conflicting impressions that the SNPRM required 
a particular attachment method. Transamerica Leasing interprets the 
SNPRM's reference to ``attachment hardware'' as meaning that the 
proposed rule contemplates only bolt-on guards. It thinks that guards 
that are welded on should also be allowed. In contrast, Advocates 
suggested that the SNPRM requires guards with vertical supports for the 
horizontal member and welded steel construction.
    No specific attachment method was proposed in the SNPRM. Nothing in 
the SNPRM nor in this final rule requires vertical supports or welded 
construction. Similarly, the agency did not intend its references to 
attachment hardware in the SNPRM to imply that only bolt-on guards are 
permitted. The agency's intent was to require that any necessary 
attachment hardware be included with the guard when a guard 
manufacturer sells the guard to a trailer manufacturer if the guard 
manufacturer's method of attachment involves attachment hardware, as in 
the case of bolt-on guards. Weld-on guards are also permitted. However, 
if the guard manufacturer's installation instructions do not adequately 
specify the welding procedures, welds of poor quality could break in 
NHTSA's compliance testing. Weld strength could probably be assured 
through incorporating by reference welding industry standard practices.
    Some commenters believed that the guard-trailer interface was 
inadequately addressed by the SNPRM. IIHS noted that the SNPRM proposed 
no minimum strength for the chassis or the attachment method, and 
concluded that the attachment may fail before the guard. It stated that 
NHTSA's static tests showed that the trailer frame rails failed without 
a doubler plate and that, even with a doubler plate, the flange welds 
failed in dynamic tests. It also believed that NHTSA should require 
installation instructions that are specific to each make and model of 
trailer. IIHS reiterated these comments in a September 16, 1994 letter 
that pointed to failures of the guard attachment hardware and trailer 
structures resulting in PCI in two of the VRTC crash tests. IIHS urged 
NHTSA to either require minimum strength levels for the guard 
attachment hardware and frame rail or require that the guard be tested 
together with the type of trailer frame rail to which it would be 
attached.
    Mr. John Tomassoni suggested that the preamble to this rule should 
encourage manufacturers to install guards with due care so that the 
attachment is as good as the guard. He said that the trailer frame is 
the ``weak link'' in crashes today, and that adding ``doubler plates'' 
to trailer frame members helps to maintain the integrity of the 
attachment in a crash.
    NHTSA's test results show the importance of considering the 
strength of the attachment point when designing a guard. The agency 
does not at this time believe that it is necessary to define strength 
requirements for the chassis or the attachment hardware because the 
necessary strength is dependent on the design of the guard. For 
example, a guard that is attached to the rear of the frame rail with 
two vertical supports (i.e., the commonly used cantilever design used 
in the VRTC tests and on most trailers) would require a stronger 
attachment site and attachment hardware than a guard with many 
attachment points or with diagonal struts. Therefore, without knowing 
the design of the guard, NHTSA cannot readily specify minimum strengths 
for the trailer frame or the attachment hardware, as suggested by IIHS.
    However, the guard manufacturer must consider frame and hardware 
strength in order to have a basis for certifying the guard for use on 
the types of vehicles specified in the installation instructions. NHTSA 
agrees with Mr. Tomassoni that, if a cantilever design is used, guard 
manufacturers should consider doubler plates or other appropriate frame 
reinforcement to prevent frame failure. NHTSA does not want to require 
such features, however, because a different attachment design or a 
sturdier trailer frame may eliminate the need for reinforcement. It is 
not a requirement of this rule that guard manufacturers specify frame 
strength or reinforcement procedures in the installation instructions. 
However, as a practical matter, to have a basis for certification, they 
must consider frame strength using testing, engineering analysis, or 
both, to be assured that the guard attachment is appropriate for the 
types of vehicles specified in those instructions.
    The VRTC test experience illustrates why guard manufacturers should 
appropriately design the strength of the attachment. In one case, 
attachment bolts which were marginally weaker than those used in the 
quasi-static test sheared under the sudden onset of force in the 
dynamic test. In another case, the proximity of the guard to the rear 
edge of the frame rail resulted in tearing of the trailer frame rail 
webbing. In each case, the guard itself was not really exercised 
because the attachment failed. In each case, simple modifications 
solved the problem. The importance of careful attachment hardware 
material selection and attachment design cannot be overemphasized.
    Although guard manufacturers are free to issue separate 
instructions for each specific make and model of trailer, as IIHS 
recommends, it is not necessary for NHTSA to require such instructions. 
An efficient way to specify trailer type would be to list specific 
make/model combinations. However, as long as the instructions are 
adequate to identify which vehicles are appropriate for the 
installation of the guard, specification of the make and model of the 
trailer may not be necessary. One reasonable alternative for a guard 
manufacturer with a very adaptable guard design is to show in its 
instructions the types of trailer, types of chassis configurations, and 
frame strengths that are necessary to the functioning of that 
particular guard. For example, the guard manufacturer might specify 
that any flatbed or van trailer with longitudinal frame rails extending 
to within 305 mm (12 in) of the rear, spaced between 760 mm and 1,270 
mm (30 and 50 in) apart, and with the bottom of the frame rails 
configured as a horizontal surface at least 100 mm (4 in) wide, 
composed of steel that is at least 6 mm (1/4 of an inch) thick, would 
be an appropriate trailer for mounting the guard.
    Some commenters believed that defining ``chassis'' as the ``load 
supporting structure of a motor vehicle'' was too restrictive or 
otherwise inadequate. NSWMA asked NHTSA to modify S5.3.2 of the vehicle 
standard to allow vehicle manufacturers with ``unique design 
considerations'' to attach the underride guard ``to a load supporting 
structure of the vehicle or body, or through other means that provide 
equivalent protection.'' It believed that this change is necessary to 
take into account body designs that do not use a conventional chassis 
frame. 

[[Page 2014]]
Mr. John Tomassoni also suggested that NHTSA further define the term 
``load supporting structure'' because the longitudinal frame members 
don't extend all the way to the rear end of some trailers.
    Although NSWMA did not provide any specifics on its vehicles, NHTSA 
agrees that there may be some trailers that do not have adequate 
chassis structure, in terms of a frame structure, to support a 
conventionally designed rear impact guard. However, no change to the 
requirements is necessary. Although the frame components are the 
obvious attachment point in the case of most trailers, attachment to 
this chassis member is not required by this rule. In certain cases, an 
unconventional guard design that is attached to other parts of the 
chassis may be necessary. In rare cases, custom-designed guards or even 
extension of the trailer chassis may be necessary to mount the guard.
    The TTMA suggested changing the installation requirements in S5.3 
to apply to ``guards that are produced or modified and installed by a 
vehicle manufacturer * * *,'' so that a trailer manufacturer can modify 
stock guards to fit its particular trailers. It assumes that the guard 
manufacturer is unlikely to provide installation instructions for the 
wide variety of trailer configurations. It reasons that, since the 
trailer manufacturer has to certify that the trailer is in compliance 
with all Federal motor vehicle safety standards anyway, why not let it 
modify the guard?
    Vehicle manufacturers are allowed to modify purchased guards to 
suit their own trailers. There may be minor modifications to widely 
available guard designs that will make them suitable for trailers for 
which they were not designed. However, if a vehicle manufacturer 
modifies the guard in a way not contemplated by the instructions 
provided by the guard manufacturer, that vehicle manufacturer becomes a 
guard manufacturer. The vehicle manufacturer may no longer rely on the 
certification of the original guard manufacturer, because the original 
manufacturer presumably did not intend its guards to be so modified. As 
a guard manufacturer, the vehicle manufacturer would have to certify 
that the guard, as modified, complies with the equipment standard. 
Also, the vehicle manufacturer would have to affix its own 
certification label and prepare modified installation procedures. The 
installation procedures are necessary both to ensure that the guards 
are modified and installed the same way each time, and to allow NHTSA 
to duplicate the modification when conducting compliance testing.
    The original guard manufacturer's installation instructions may 
provide for some flexibility in the installation. For example, they may 
specify that a certain kind of spacer may be used to achieve a proper 
fit, or that a doubler plate be installed if the thickness of the 
chassis is below a certain amount. However, NHTSA may employ any of the 
installation options provided to the vehicle manufacturer when 
subjecting a guard to compliance testing. Any test failure of a 
properly installed guard will represent noncompliance by the guard 
manufacturer.
7. Compliance Test Requirements and Procedures
    a. Dynamic Versus Static Testing. Several commenters, including 
Advocates, urged that NHTSA require that the guards be tested 
dynamically, that is, by crashing cars into the rear of trailers 
equipped with the rear impact guard. The agency agrees that dynamic 
testing more closely simulates the conditions in which underride 
crashes occur in the real world than the quasi-static testing does. 
However, dynamic testing is also far more expensive. To test one guard/
trailer combination with a dynamic test for strength and energy 
absorption would entail total test costs of approximately $30,000.
    Dynamic tests would be so expensive that specifying such testing of 
trailers could raise practicability concerns regarding those trailer 
manufacturers that are small businesses. A requirement based on such 
tests would place these small manufacturers, which are numerous, at a 
competitive disadvantage, relative to larger companies, and would 
represent a significant financial burden.
    Quasi-static tests provide similar information far more 
economically than dynamic tests. The VRTC research project demonstrated 
that quasi-static testing generates similar forces to those generated 
in an actual crash test, albeit at a slower rate. The project also 
demonstrated that guards only ten percent stronger than the minimum 
level of strength necessary to pass quasi-static test requirements 
performed adequately in dynamic tests. The quasi-static compliance test 
for a single guard at VRTC cost only about $3,500. Based on the 
foregoing and the discussion in the section above on separate equipment 
and vehicle standards, the agency believes that dynamic testing of 
underride guards is unnecessary and overly expensive. NHTSA further 
believes that quasi-static testing is adequate to ensure the 
manufacture of safe and effective rear impact guards and that it will 
do so at a far lower cost. Therefore, the quasi-static testing 
procedure has been retained in the final rule.
    Some commenters commented on the definition of ``rigid test 
fixture.'' The TTMA assumes that a trailer can be used as a rigid test 
fixture, and other commenters urged that testing be permitted on 
trailers. The Institute for Injury Reduction commented that the terms 
``sufficiently large,'' ``appropriately configured,'' and ``no 
significant amount of energy'' in the definition of rigid test fixture 
are vague, imprecise, ambiguous and in no way ``stated in objective 
terms.''
    NHTSA notes that a trailer may meet the equipment standard's 
definition of a rigid test fixture, but because of slight flexing of 
the vehicle structure, in other cases, they may not meet this 
definition. NHTSA is persuaded that the benefits of testing on trailers 
outweigh the possible effect on testing repeatability and does not want 
to discourage testing on trailers by conducting its compliance testing 
only on a rigid test fixture. The TTMA comment indicates that, although 
it is not required, some vehicle manufacturers will conduct quasi-
static guard testing on trailers or trailer portions. NHTSA sees no 
reason why this should not serve as a basis for manufacturer 
certification even if the trailer is not a rigid test fixture. The use 
of a trailer would be desirable because there is nothing more 
``appropriately configured'' for guard mounting than the actual trailer 
the guard will be installed on and because the structural integrity of 
the trailer chassis will also be tested. However, caution must be 
exercised to assure that the trailer is secured so that it does not 
move during the test. If the guard is mounted to a trailer, the trailer 
chassis will be secured so that there is no rotation or translation of 
the trailer tires during the tests for guard strength and energy 
absorption.
    When conducting compliance testing, the agency will give the guard 
manufacturer the option of designating testing on a rigid test fixture 
or on a trailer. NHTSA notes that it may test on any trailer described 
as appropriate in the guard manufacturer's installation instructions, 
even if the guard manufacturer based its certification for that trailer 
not on actual testing but on engineering analysis.
    NHTSA agrees with the Institute for Injury Reduction that the 
definition of ``rigid test fixture'' needs a slight modification. The 
reference to size has been eliminated because size is not really as 
important as rigidity. However, it is not necessary to define the 
amount 

[[Page 2015]]
of energy the fixture can absorb, because, like the ``fixed collision 
barrier'' defined in 49 CFR 571.3, the guards will be expected to pass 
the test no matter how little energy is absorbed by the fixture. Also, 
the term ``appropriately configured'' has been clarified. There is no 
way to precisely define how the test fixture will have to be configured 
because that will depend on the design of the guard being tested. There 
may be a number of appropriate configurations. As long as the guard can 
be attached to the test fixture in the same way that the guard 
manufacturer's instructions specifies the guard is to be attached to 
the vehicle, without either modifying the guard or adding adaptive 
parts to obtain a better fit between the guard and the fixture in a way 
that is inconsistent with the instructions, the test fixture is 
appropriately configured.
    The agency had modified the strength test procedures to promote 
ease of testing. Paragraph (b) of S6.5 now requires the application of 
the force to the loading device to achieve a constant deflection rate, 
rather than a constant increase in force, as proposed in the SNPRM. In 
other words, rather than increasing the force at a constant rate, the 
deflection rate is required to be held constant and the force will vary 
depending on the resistance offered by the guard. Specification of a 
deflection rate procedure is consistent with existing agency practice. 
For example, the quasi-static compliance tests in S4(d)-(e) of Standard 
No. 214, Side Impact Protection and S6.3 of Standard No. 216, Roof 
Crush Resistance utilize this technique for force application.
    b. Test Sites. Several commenters recommended changes in the 
language 'specifying the test sites to be used during the compliance 
tests. Mr. John Tomassoni recommended defining the P1 test site such 
that the ``3/8 L'' lateral dimension (see Figure 1) is defined relative 
to the side extremities of the trailer, as opposed to the center of the 
guard. He suggested that this change would account for newer 2,600 mm 
(102 in) wide trailers which have a 1,270 mm (50 in) longitudinal frame 
rail span, or for any other width trailer. This approach, however, is 
inconsistent with a separate equipment standard because the exact width 
of the trailer may not be known at the time of testing. Moreover, the 
requirement that guards extend to within 100 mm (4 in) of the side of 
the trailer should assure that the P1 site will be sufficiently 
outboard on the trailer, because wider guards will be required for 
wider trailers, and the P1 location is dependent upon guard width.
    Mr. Tomassoni also suggested that S5.2.2 and Figure 1 should be 
modified to specify that the vertical center of force should not be 
more than 560 mm (22 in) from the ground, rather than at ``the 
horizontal plane that passes through the vertical center of the 
horizontal member,'' as proposed in the SNPRM. Mr. Tomassoni indicates 
that a guard with a horizontal member of cross sectional vertical 
height greater than 100 mm (4 in) would result in higher test points. 
Higher test points would yield test results that are not indicative of 
the guard's effective impact strength near the bottom edge, where force 
is likely to be concentrated in real world crashes. Although it is not 
possible to define the test points relative to the ground because the 
guard is not required to be mounted on the vehicle during testing, 
NHTSA has modified the rule to define the test points relative to the 
bottom of the guard itself. This should assure adequate strength and 
energy absorption at the level of likely impact force.
    Mr. John Kourik pointed out that the P1 test site was defined 
incorrectly in the SNPRM, although it was correctly portrayed in Figure 
1. The text of S5.2.2(a) (redesignated S6.4(a) in this rule) read ``3/8 
of the transverse horizontal distance * * * between the * * * vertical 
centerline of the guard [and] and the outermost edge * * * of the 
guard.'' The P1 definition has been corrected to reflect that the point 
is located 3/8 of the total guard width outboard of the centerline. Mr. 
Kourik also suggested that the four asterisks showing the P3 test sites 
in Figure 1 be reduced to two asterisks. NHTSA has modified the figure 
to make it clearer that there is only one P3 test site on each side of 
the guard, but that the location of the site is within a range from the 
centerline.
    The TTMA and other commenters suggested broadening the range of 
locations of the P3 test site to allow it to be ``any point selected by 
the manufacturer * * * between 14 and 25 [rather than 20] inches 
outboard'' of the guard centerline. Most new trailers are wider than in 
the past with a frame rail span of 127 cm (50 in), and the frame rail 
is a likely chassis structure for guard attachment. TTMA wanted NHTSA 
to conduct the more demanding 100 kN (22,480 lb) P3 test near the 
attachment point of the guard's supports. This was NHTSA's general 
objective in specifying the P3 test location, and this objective is 
furthered by accommodating TTMA's request in part. The rule has been 
modified to provide that P3 is located 355 to 635 mm (14 to 25 in) from 
the guard centerline. However, NHTSA will select any point within the 
range for compliance testing, rather than permit a manufacturer to 
specify a single test site within the 355 to 635 mm (14 to 25 in) 
range.
    c. Labeling and Certification. The TTMA suggested that affixing a 
certification label is redundant in those instances in which the guard 
is manufactured by the vehicle manufacturer because the vehicle 
manufacturer has to certify compliance with all the safety standards 
anyway. Although this is true, allowing some guard manufacturers to 
omit the label would be impractical from an enforcement standpoint, 
because vehicle inspectors would not be able to tell whether the guard 
was certified by the guard/vehicle manufacturer as part of the vehicle 
or whether the vehicle manufacturer installed a guard purchased from a 
guard manufacturer who neglected to make a required certification. 
Moreover, NHTSA does not believe that affixing the label is a 
significant burden. Therefore, the final rule retains the requirement 
of a separate guard certification for all guards.
    The TTMA also recommended that the label be affixed to the roadside 
vertical supporting member of the guard, instead of the center of the 
horizontal guard member, to prevent damage and abuse. NHTSA believes 
that docking and other routine operations could damage the label if 
affixed in the proposed location. Therefore, the rule has been modified 
to require the label to be affixed in a less vulnerable location. The 
rule now requires the certification label to be placed on the 
forwardmost surface of the horizontal member of the guard at an offset 
location 305 mm (12 in) inboard of the right side end of the guard.
    The TTMA also suggested changes in the label format. Specifically, 
it recommended that the letters and numbers should be 2.5 mm (\3/32\ of 
an inch) high, which is the same as the trailer certification label, 
rather than 13 mm (\1/2\ inch) high as proposed in the SNPRM. TTMA also 
asked that NHTSA require that the label be furnished to the vehicle 
manufacturer with a protective cover that can be removed after 
painting.
    The agency believes that the smaller letters suggested by TTMA are 
sufficiently legible for inspection purposes, and has changed the rule 
to adopt this suggestion. However, market forces should determine 
whether protective covers are provided. Vehicle manufacturers will 
probably cover the labels themselves when painting to avoid having 
their guard confused with a noncomplying guard. 

[[Page 2016]]


C. Standard for Vehicles

1. Configuration Issues
    a. Maximum Guard Ground Clearance. One of the major issues 
addressed by nearly all the commenters was the maximum ground clearance 
of the horizontal member of the rear impact guard. The SNPRM proposed a 
maximum guard height of 560 mm (22 in). Consumer safety groups and 
private citizens generally favored lowering the guard to within 405 or 
460 mm (16 or 18 in) of the ground in the belief that doing so would 
provide more complete protection for low profile vehicles such as sub-
compact and mini-compact passenger cars. Since the real issue is not 
ground clearance, but guard height relative to the front structure of 
colliding passenger vehicles, some of these commenters addressed 
related issues such as the height of the engine block, hood, and cowl 
(windshield base) of those vehicles. Except for the consumer safety 
groups and a few private citizens, few provided a rationale or any data 
to support a lower guard height. The organizations and private 
companies related to the trucking industry generally supported a 560 mm 
(22 in) height, but offered a variety of reasons not to lower the guard 
further. Most of their concerns related to operational difficulties 
that would be caused by lower guard heights.
    The consumer safety groups focussed their comments on guard 
effectiveness. Advocates advanced several reasons for reducing the 
guard height in order to achieve better engagement between the guard 
and the engine block, bumper, and tires of colliding passenger 
vehicles. Advocates stated that lower engine block heights on modern 
automobiles, combined with the lowering of the passenger vehicle's 
front end due to suspension compression during severe braking, will 
result in the rear impact guard passing over the engine and engaging 
only the hood and fenders of most cars. In addition to the front end 
lowering caused by braking, Advocates claim that additional frontal 
lowering will occur on downgrades due to forward weight transfer. 
Citing a random survey it made of subcompact cars and urging NHTSA to 
conduct a more thorough survey, it said that no engine block is higher 
than 560 mm (22 in) above the ground and bumpers are in the 430 to 535 
mm (17 to 21 in) range. It stated that earlier NHTSA data using the 
average hood height above the ground was misleading because its 
``casual'' survey of subcompact hood front edges showed none higher 
than 635 mm (25 in). It interprets these data to mean that only fender 
top and hood sheet metal would be engaged, and concluded that air bag 
sensors probably will not be triggered. Advocates also maintains that, 
even if the top of the engine were engaged, the underride guard will 
cause the blocks of transversely-mounted engines used in most 
subcompacts to rotate (roll) rearward, crushing the car occupant's 
legs. Based on British research, Advocates recommends a guard height of 
no more than 405 mm (16 in), and ideally 305 mm (12 in). Both Advocates 
and Mr. Byron Bloch, of Auto Safety Design, cited the 1980 study by 
Dynamic Science which concluded that the guard height should not exceed 
510 mm (20 in). Mr. Bloch recommended a height of 405 to 460 mm (16 to 
18 in). CRASH solicited many private citizens to send in petitions, 
letters, and pre-printed cards stating that the guard height should be 
set at 405 mm (16 in), but none provided supporting technical 
information.
    The IIHS, citing the same studies as Advocates, urged NHTSA to 
adopt a maximum ground clearance of 460 mm (18 in). IIHS is primarily 
concerned that a 560 mm (22 in) high guard will override car bumpers, 
thus bypassing much of the potential front end energy absorption. Other 
concerns expressed by IIHS were late air bag activation, braking-
induced bumper depression of two to 100 mm (4 in) or more, and possible 
lifting of the rear end of the trailer as the car wedges under the 
guard. IIHS implied that a 460 mm (18 in) requirement is practical, 
noting that one U.S. freight carrier reportedly sets its guards at 495 
mm (19.5 in).
    IIHS believes NHTSA's estimate that trailers probably sit 50 to 75 
mm (2 to 3 in) lower when loaded is wrong. IIHS tests on 11 trailers 
showed the most heavily loaded trailers showed only 38 to 57 mm (1.5 to 
2.25 in) of depression with an average of 28 mm (1.1 in). Four of the 
trailers even raised in the rear, indicating that load distribution is 
probably a factor in determining rear extremity compression height. 
IIHS believes that modern air suspensions compensate for loading 
depression. Even if loaded trailers are depressed, it believes that 
passenger vehicles should be protected from partially loaded or empty 
trailers, which it says are involved in 29 percent of fatal crashes. 
Therefore, IIHS urges NHTSA to assume no depression of the trailer bed 
due to loading.
    Mr. John Tomassoni commented that a lower guard would be better 
because engine block resistance to a rigid guard doesn't start until 
460 to 610 mm (18 to 24 in) behind the bumper. However, Mr. Tomassoni 
concluded that a 560 mm (22 in) requirement is a significant 
improvement over the existing 760 mm (30 in) height, and one that can 
be implemented with little or no difficulty. He notes that trailers 16 
meters (m) (53 feet (ft)) or longer are currently being equipped with 
560 mm (22 in) high guards.
    Some municipalities sent comments in favor of lower guard heights. 
For example, the City of Durham, North Carolina sent an unsigned 
resolution that the height be set at no more than 460 mm (18 in). Its 
Transportation Advisory Committee submitted a similar comment. About 
2,300 private citizens recommended a guard height of 405 mm (16 in).
    The industry groups focussed their comments relating to guard 
height on operational restrictions that would result from the reduced 
``angle of departure'' that lower ground clearance would cause. The 
angle of departure is basically the acute angle formed by the ground 
and a line connecting the point where the rear tires meet the ground 
with the bottom of the guard. The lower the guard, and the further 
forward the rear wheels are positioned relative to the guard, the 
smaller the departure angle is, and therefore the more likely the guard 
is to scrape or ``hang'' on the ground when the trailer mounts a steep 
incline. The problem is exacerbated for the longer 16 m (53 ft) 
trailers being used today, because they have correspondingly greater 
rear overhangs, and thus smaller departure angles. Many trailers have 
their rear wheels mounted on sliding tandems, or bogeys, that can be 
moved forward or rearward on the trailer's frame, depending on the load 
and the need for maneuverability. The further forward the wheels are, 
the more maneuverable the trailer is and the more the rear end of the 
trailer ``swings out'' in turns.
    Changes in the industry since 1981 seem to have relieved the 
concerns of the rail industry that the proposed ground clearance of 560 
mm (22 in) would interfere with rail car loading and unloading 
operations, in which trailers are driven up steep ``circus ramps'' onto 
flat cars. The Association of American Railroads (AAR) and TTX Company, 
a trailer-on-flat-car operator, opposed the 1981 NPRM, but now support 
the 560 mm (22 in) requirement because there are few ``circus'' ramps 
still operating. However, they caution that a significantly lower 
height would interfere with intermodal flatcar operations. TTX asserted 
that such a reduction in guard clearance could interfere with lift-on 
and lift-off operations for one type of railroad car (TTAX ``spin 
cars'') handling 16 m (53 

[[Page 2017]]
ft) trailers. It added that there must be extra guard clearance to 
account for loading depression and bouncing. To illustrate the 
potential economic impact of lower guard clearance, TTX stated that 
there are 2,300 such cars costing $340 million, which are only 1.8 
years old on average. TTX estimates that lowering the guard clearance 
could eliminate 75 percent of the capacity for 14 railroads.
    In contrast, the 560 mm (22 in) guard height is still considered 
low by the portion of the industry that transports trailers in ships. 
Transamerica Leasing, Inc. recommends that NHTSA conduct further study 
before issuing this rule because a 560 mm (22 in) high guard would 
scrape loading ramps during roll-on/roll-off ship loading when the 
wheels are positioned forward to provide the maneuverability necessary 
in ships. The American Trucking Associations (ATA) supports the 560 mm 
(22 in) proposed ground clearance, but stated that any lower clearance 
would be unacceptable. It calculates that a loaded trailer driven onto 
a barge or vessel, which it says have departure angles as high as 15 
degrees, would drag the guard if the rear axle is 190 cm (74.5 in) or 
more forward of the guard. It said that many states have restrictions 
on trailer kingpin-to-rear- axle distances that result in a 245 to 275 
cm (96 to 108 in) rear-wheel-to-guard distance on 16 m (53 ft) 
trailers. It concludes that these trailers' guards would hang on such 
vessel loading ramps or on any 20 percent grade. It finds the 560 mm 
(22 in) clearance acceptable only because 16 m (53 ft) trailers are 
rarely used on vessels, and because 20 percent grades are rare. The 
Truck Maintenance Council of the ATA recommends a guard clearance of 
560 mm (22 in) for general freight equipment. According to Mr. Robert 
Crail, a trailer designer and manufacturer, the proposed 560 mm (22 in) 
height is acceptable because, although many trailers are still driven 
into ships rather than being crane loaded, vessel owners can adjust 
their ramps, and because it is compatible with the dimensions 
established by the trucking industry and loading dock restraint device 
manufacturers. Ford Motor Company had no specific data, but is 
concerned that 560 mm (22 in) may be inadequate ground clearance for 
loading and unloading of long trailers in trains or ships. Ford also 
noted that some single unit trucks are equipped with kneel-down air 
suspensions to facilitate loading and unloading, which Ford says are 
incompatible with a 560 mm (22 in) high guard.
    Even outside the context of intermodal loading and unloading 
operations, some commenters were concerned about the reduced departure 
angle that a 560 mm (22 in) high guard would create. The National Solid 
Waste Management Association (NSWMA) emphasized the importance of 
maneuverability for sanitation trucks in negotiating driveways and 
backing into tight places. It estimated that a 560 mm (22 in) guard 
mounted flush with the rear extremity of a sanitation truck would have 
a departure angle of only 9 degrees, which it says is typical of many 
driveway entrances. Although it appears that many of the trucks NSWMA 
is concerned with are single unit trucks that are excluded from the 
rule, NSWMA is also concerned about the guards getting hung up on the 
ground when the trailers are taken off-road onto the soft, unpaved, 
uneven roads at landfills and construction sites.
    One additional industry concern is engagement of the guard with 
``dock locks.'' When trailers back up to loading docks, these devices 
engage the underride guard to keep the trailer from moving away from 
the loading docks as forklifts repeatedly travel across the rear door 
sill. Transamerica Leasing believes that the 560 mm (22 in) high guards 
may interfere with ``dock lock'' engagement arms. Yellow Freight System 
states that thousands of dock locks have been installed according to 
the 560 mm (22 in) guard height recommended by the Maintenance Council 
of the ATA, and urges NHTSA not to change now. However, Rite Hite 
Corporation, a manufacturer of dock locks, submitted information 
indicating that dock locks can accommodate guard heights between 355 
and 760 mm (14 and 30 in).
    One industry group endorsed a lower guard height. The AFL-CIO 
Teamsters Union suggested that NHTSA could require a ground clearance 
lower than 560 mm (22 in) because auto carriers and UPS trailer fleets 
have reported no problems with lower guard heights. It also observed 
that 16 m (53 ft) trailers in many states have no problem using 560 mm 
(22 in) guards.
    The question of proper guard ground clearance involves a balancing 
of the effectiveness of the guard in providing protection against PCI 
against the cost and operational restrictions that lower guard heights 
could impose on the industry.
    The effectiveness of the guards is a primary consideration. 
Regarding Advocates' survey of bumper and hood heights on compact and 
subcompact cars, NHTSA conducted a similar survey of engine block 
height and front end profile of a sample of 40 vehicles. The results of 
this survey were summarized in the agency's Truck Underride Report to 
Congress, dated November, 1993. The NHTSA survey showed that the height 
of the top of the engine block was between 660 and 790 mm (26 and 31 
in), with an average height of 840 mm (28 in). The hood leading edge in 
NHTSA's survey averaged about 685 mm (27 in) and the lower edge of the 
windshield frame averaged about 840 mm (33 in). The agency is not aware 
of the basis upon which Advocates selected the cars for its survey, but 
NHTSA's survey was targeted preferentially at cars with the lowest 
front end profile. Since NHTSA's average heights were higher than those 
obtained by Advocates, NHTSA has no explanation for the discrepancy, 
unless the survey methodologies were different. Hood heights have been 
getting lower over the past few years, but that trend may have stopped 
in the last two years. NHTSA believes that the average hood heights in 
its survey are representative of the anticipated dimensions for new 
passenger vehicles 5 to 10 years in the future. NHTSA concludes from 
the VRTC test results that a 255 to 305 mm (10 to 12 in) overlap 
between the guard bottom and the lower edge of the windshield will 
ensure adequate structural engagement with the guard for the vast 
majority of compact and subcompact cars.
    NHTSA agrees with IIHS that a guard 560 mm (22 in) high will 
override most bumpers, but disagrees that bypassing the bumper 
sacrifices much of the potential front end energy absorption 
capability. The bumper is designed to prevent cosmetic damage in low 
speed crashes (less than 16 kph, or 10 mph) and provides only a small 
portion of the energy absorption by a car crashing at higher speeds. 
The bumper is mounted to the frontal crash energy management components 
which extend rearward and upward to the rearmost section of the engine 
compartment. These components will be adequately engaged by the rear 
impact guard during a collision. Regarding IIHS's contention that NHTSA 
should assume no loading-induced depression of the trailer bed, NHTSA 
has not made such an assumption. The final rule regulates the guard 
height only when the trailers are unloaded, and the 560 mm (22 in) 
guard height was adequate in NHTSA's VRTC tests.
    The agency conducted seven full scale crash tests with the proposed 
guard in the course of the recent research project, using two types of 
subcompact and two types of compact cars. These vehicles were 
representative of average hood and engine heights for cars in those 
size classes. The minimally compliant rear 

[[Page 2018]]
impact guard was set 560 mm (22 in) above the ground. During these 
tests, the cars had their front ends depressed to simulate the lowering 
that would be experienced during heavy braking, but the guard was not 
depressed to a level below the minimum clearance, as it might be if the 
trailer were loaded. In some sense, therefore, these tests represented 
a ``worst case scenario'' with regard to guard height. In each test, 
the air bags were fully deployed before dummy contact and the 
deceleration readings were much better than the minimum requirements in 
Standard No. 208, Occupant Crash Protection. When there was no guard 
attachment failure, they adequately engaged the structure of each car 
and prevented PCI. There was little movement of the engine and no 
contact between the engine and fire wall. The transversely mounted 
engines did not rotate substantially, and none of the dummies legs were 
crushed. Therefore, based on the docket comments, the recently 
completed crash tests, and the assessment of late model passenger 
vehicle frontal structure characteristics, NHTSA concludes that the 560 
mm (22 in) maximum guard ground clearance is adequate to engage the 
frontal crash energy management structure of most subcompact and 
compact cars.
    Although some small sectors of the industry may be affected, NHTSA 
does not believe that there will be any insurmountable problems with a 
560 mm (22 in) guard height. Several states have required 560 mm (22 
in) maximum guard ground clearances in conjunction with the passage of 
laws allowing 16 m (53 ft) trailers. NHTSA contacted several 
distributorships/dealerships that sell heavy trailers in excess of 15 m 
(50 ft) in length to the trucking industry and was unable to obtain 
information documenting substantial operational problems due to guard 
ground clearances of 560 mm (22 in) or less. The AFL-CIO Teamsters 
Union did not give NHTSA enough information about the operating 
environment of Carolina Freight Carriers Corporation, the trucking 
company that sets its guards at 495 mm (19.5 in), to determine why they 
have not experienced the problems that the other commenters expect with 
guards lower than 560 mm (22 in).
    NHTSA does not believe that the number of trailers involved in ship 
roll-on/roll-off and trailer-on-flat-car circus ramp operations is 
significant. TTMA data indicate that less than 5 percent of trailers in 
the U.S. are ever transported by ship or barge, and that between one 
and less than ten percent of new trailers are produced for trailer-on-
flat-car use. Modifications of may solve these problems. Most of the 
vehicles in the waste services fleet mentioned by NSWMA are single unit 
trucks excluded from the rule. However, in those few cases where there 
are still problems, movable or adjustable guards may be needed.
    There is adequate evidence in the comments to conclude that 
requiring a guard height lower than 560 mm (22 in) would cause an undue 
burden on the industry. Of particular concern are the comments of ATA, 
TTX, AAR, and Transamerica Leasing, indicating that any height below 
560 mm (22 in) will cause interference in intermodal operations. 
Moreover, a lower height will increase the probability that the guard 
will scrape or snag during normal vehicle operations and be damaged as 
a result. Therefore, because the 560 mm (22 in) maximum ground 
clearance proposed in the SNPRM appears to be the lowest height that 
provides adequate effectiveness without imposing an undue burden, it 
has been retained in the final rule. The agency notes that guards may 
be mounted with less than the maximum allowable ground clearance.
    b. Guard Width. The SNPRM proposed that the horizontal member of 
the guard be required to extend across the width of the trailer to 
within 100 mm (4 in) of the side extremities, but not outboard of the 
side extremities. Advocates commented that the 100 mm (4 in) allowance 
appeared arbitrary, based on the rulemaking record, but did not 
actually suggest that the guard should extend fully to the side 
extremities of the trailer. The AFL-CIO Teamsters Union indicated that 
it fully supports the SNPRM's 100 mm (4 in) allowance, while noting 
much anecdotal information from drivers about the importance of a 
``full width'' guard, especially for crashes that occur at an angle to 
the rear of the trailer.
    NHTSA notes that there is no requirement of a 100 mm (4 in) inset. 
Vehicle manufacturers are permitted to install guards extending the 
full width of the trailer. However, the 100 mm (4 in) allowance gives 
trailer and guard manufacturers some flexibility in choosing and 
providing guards, without sacrificing safety or effectiveness. From the 
perspective of guard effectiveness, it is doubtful that the extra 
lateral coverage would significantly increase the strength of the guard 
at its extremities or its ability to protect passengers in an offset 
collision.
    In fact, a 100 mm (4 in) inset would decrease the previously 
mentioned ``hooking'' potential during sharp turns of the trailer and 
provide more clearance in certain passing situations. The Florida 
Department of Transportation and the TTMA recommended allowing rounded 
guard ends to alleviate this potential problem, but NHTSA notes that a 
100 mm (4 in) inset on an unrounded guard will partially accomplish the 
same goal. As discussed above in the section on shape of the horizontal 
cross member, pursuant to the TTMA's suggestion NHTSA has modified the 
rule to allow rounded corners on guards to begin curving at a point 255 
mm (10 in) inboard of the edges of the vehicle, while retaining the 100 
mm (4 in) requirement for straight guards. Curved guards still have to 
meet the other requirements of the vehicle standard (i.e., extend to 
within 100 mm, or 4 in, of the side extremity). This modification 
merely removes for the curved portion of the guard the requirement that 
the bottom of the horizontal member be within 560 mm (22 in) of the 
ground, in the case of upward curving guards, and the requirement that 
the rear surface of the horizontal member be within 305 mm (12 in) of 
the vehicle rear extremity, in the case of forward curving guards.
    c. Specification of the Rear Extremity. Some commenters requested 
that NHTSA modify the proposed definition of ``rear extremity'' to take 
into account vehicles with high protrusions in the rear. The SNPRM 
defined the rear extremity as the rearmost point of the vehicle that is 
located 560 mm (22 in) or more above the ground. The specification of 
the rear extremity is important because the SNPRM also requires that 
the rear impact guard be located no more than 305 mm (12 in) forward of 
the rear extremity of the vehicle. Some trailers and semitrailers, such 
as hopper trailers with V-shaped bins and trailers with liftgates or 
refrigerator units in the upper rear, are shaped such that the rear 
extremity of the vehicle is located well above the road surface. These 
protrusions do not present a danger of PCI because they are located 
well above the roof line of most passenger vehicles. Yet, applying the 
rear extremity definition in the SNPRM, a rear impact guard would have 
to be mounted such that it extends rearward from the base of the 
trailer to a position within 305 mm (12 in) of the back of the high 
protrusion. Such an extended guard might pose a safety hazard as well 
as operational difficulties.
    Several manufacturers of vehicles with high rear end overhang 
recommended alternative definitions of ``rear extremity'' that excluded 
portions of the trailer rear that were high enough to clear the roofs 
of passenger vehicles. The TTMA and the ATA recommended that vehicle 
structure with a ground 

[[Page 2019]]
clearance of 1,680 mm (66 in) or more be excluded from the definition 
of rear extremity. NSWMA recommended excluding that portion of the rear 
of the vehicle located 1,520 mm (60 in) or more above the ground.
    The agency acknowledges the potential problem with the proposed 
specifications and believes that redefining the rear extremity to 
accommodate these vehicles is possible without reducing rear impact 
guard effectiveness or creating new safety hazards. NHTSA contacted 
officials from TTMA and ATA to obtain more information about the 
current number and future production plans for vehicles of this type. 
According to TTMA, these are mostly highly specialized vehicles and the 
high overhang often consists of equipment such as cranes in addition to 
``bubble door'' type container trailers. TTMA estimates that these 
vehicles constitute less than one percent of the annual trailer and 
semitrailer production and there is no trend toward increasing the 
numbers substantially. ATA also estimated that the number of vehicles 
produced annually with high rear overhanging structure represents less 
than 5 percent of the total annual production of trailers and 
semitrailers. ATA did not provide information on the future trend of 
production of these vehicles, but indicated that the number has been 
fairly constant in the recent past with new vehicles brought into 
service primarily to replace vehicles going out of service.
    The NSWMA recommended that the rule specifically state that, for 
roll-off/hoist type trailers, the containers on the hoist frame be 
considered as part of the load and not as part of the vehicle for 
purposes of rear extremity specification. It suggests that the rearmost 
part of the hoist frame should be considered the rear extremity. 
Containers extend up to 1.5 m (5 ft) rearward from the end of the hoist 
frame.
    The agency has decided to revise the SNPRM's definition of ``rear 
extremity'' to limit its ambit to the portion of the vehicle's rear 
located between a lower and upper height limit. The lower limit 
specification remains unchanged at 560 mm (22 in) (that is, guard 
ground clearance). An upper limit for the area in which the rear 
extremity is located has been specified at 1,900 mm (75 in) above the 
ground surface for purposes of the vehicle standard. The portion of the 
rear of the trailer that is located in the same horizontal planes as a 
passenger vehicle windshield is the critical area for rear underride 
protection. This is between 760 mm and 1,900 mm (30 and 75 in) above 
the ground for almost all passenger cars, vans, and light trucks.
    With regard to roll-on/hoist type trailers, the agency agrees with 
NSWMA that there would be numerous regulatory problems involved in 
considering the containers to be part of the vehicle, rather than part 
of the load. Although the containers may extend beyond the end of the 
vehicle and are capable of causing PCI just like the rear end of a 
trailer, they are not part of a new vehicle as manufactured. Further, 
the boxes, tanks, and other specialty containers are manufactured, 
maintained, and in many cases owned separately from the vehicle. NHTSA 
has no authority to regulate vehicle loads under 49 U.S.C. Chapter 301.
    While NHTSA cannot require guards on the container on roll-on/hoist 
type trailers, it can require guards on the rear of the trailer that 
carries it. If the vehicle is designed to carry containers that do not 
extend appreciably beyond the rear of the vehicles, the agency sees no 
basis for excluding it. Casual observations indicate that the 
containers do not usually extend beyond the rear of the vehicle, so 
these trailers are required to have guards. The rear extremity will be 
determined without the container.
    d. Distance between the Guard Rear Surface and the Vehicle Rear 
Extremity. Several commenters urged NHTSA to change the requirement 
proposed in the SNPRM that the guard's horizontal member be mounted not 
more than 305 mm (12 in) forward of the rear extremity of the trailer 
and not rearward of the rear extremity. The distance between the guard 
and the trailer rear extremity is significant because the sooner the 
passenger vehicle engages the underride guard, the farther its occupant 
compartment will be from the rear of the trailer when the guard is 
engaged, and the better the chance that the passenger vehicle will stop 
short of PCI.
    Some commenters thought that NHTSA should allow the guard's 
horizontal member to extend rearward of the rear extremity. Mr. John 
Tomassoni stated that he saw no good safety reason for restricting rear 
extension, since it is beneficial for preventing PCI. The TTMA also saw 
no reason why the guard should not be located rearward of the rear 
extremity. It also suggested a change in the language of S5.1.3 that 
makes it clear that, even above 560 mm (22 in) the guard cannot be more 
than 305 mm (12 in) from the rear extremity of the vehicle.
    The Rite Hite Corporation stated that, for dock locks to function, 
there must be no more than 230 mm (9 in) between the rear extremity and 
the guard. It is concerned that the 305 mm (12 in) allowance will 
render the dock locks useless.
    NHTSA notes that the 305 mm (12 in) allowance is not a minimum, but 
a maximum requirement. Casual observations by the agency indicate that 
nearly all trailers currently have their guards mounted flush with the 
rear extremity of the trailers. This practice is also specified as the 
recommended practice in the ATA Maintenance Council guidance (RP 707). 
It is also the configuration most compatible with dock locking 
mechanisms. Based upon the TTMA's comment relating to mounting rearward 
of the rear extremity, the industry appears to be in favor of mounting 
as far rearward as possible. Therefore, NHTSA believes that trailer 
manufacturers will continue to mount guards flush with the rear 
extremity of the vehicle.
    The main incentive to change the prevailing practice relates to the 
smaller departure angle that will be created by lowering the maximum 
guard ground clearance from 760 mm to 560 mm (30 to 22 in). Moving the 
guard 305 mm (12 in) forward will slightly increase the departure 
angle. However, nothing in this rule increases that existing incentive. 
Therefore, the agency does not expect that a 305 mm (12 in) allowance 
would have any effect on prevailing practice. Further, NHTSA does not 
believe the benefit of moving the guard forward would be very 
significant. Nevertheless, the agency had modified the requirement in 
section 5.1.3. for guard rear surface location, or off-set, to state 
that the guard should be mounted as close as practical to the rear 
extremity of the vehicle. This will prevent vehicle manufacturers from 
mounting the guard with up to 305 mm (12 in) of forward off-set from 
the rear extremity of the vehicle unless the off-set is necessary and 
not merely convenient. It should be noted that the requirement to mount 
the guard as close to the rear extremity as practical is identical to 
the requirements of ECE Regulation 58.
    NHTSA agrees that having the horizontal member of the guard 
positioned rearward of the rear extremity would be beneficial for 
preventing PCI in the event of a crash. Some meritorious guard designs, 
such as the Quinton-Hazel hydraulic energy absorbing guard and the Hope 
rearguard underrun device, utilize horizontal members that are hinged 
so that they are angled down and slightly rearward from the rear of the 
trailer. This rearward positioning enables the guard to engage a 
striking vehicle at a greater distance from the rear extremity and 
gives the guard a greater distance to swing 

[[Page 2020]]
forward and ``ride down'' the energy of the striking vehicle before PCI 
occurs. If vehicle manufacturers want to provide this extra measure of 
safety, this agency will not discourage it, as long as vehicle 
manufacturers consider State laws governing overall combination truck 
length. However, NHTSA does not want to require rearward positioning 
because this configuration exacerbates the previously mentioned 
potential for ``hooking'' adjacent vehicles during sharp trailer turns 
and in other situations. Therefore, NHTSA has removed the SNPRM's 
prohibition on positioning the horizontal member rearward of the rear 
extremity. The new requirement that the member be as close to the rear 
extremity as practical is limited so that it does not prohibit mounting 
rearward of the rear extremity.
    Advocates stated that NHTSA has no data to support the 305 mm (12 
in) allowance because all crash tests were done with guards positioned 
at the very rear of the trailer, thus implying that testing in the 
forward-mounted position is required to support the allowance.
    Even though the crash tests conducted by NHTSA had the rear impact 
guards mounted in the usual position, flush with the rear of the 
trailer, NHTSA has used a simple mathematical calculation to determine 
whether, and to what extent, PCI would have occurred if the guard had 
been mounted 305 mm (12 in) forward of the rear extremity (see VRTC 
report ``Heavy Truck Rear Underride Protection,'' June, 1993. DOT-HS-
808-081). The agency assumed that if the guard had been mounted 305 mm 
(12 in) farther forward, the car's occupant compartment would have come 
to a rest 305 mm (12 in) closer to the rear of the trailer after the 
crash. There is no reason to expect that the guards would have 
performed more poorly if mounted further forward in the 305 mm (12 in) 
zone at the rear of the trailer. Therefore, there is no need, as 
Advocates suggests, to mount the guards at the ``worst case'' 
forwardmost point for testing purposes. In any case, the new 
requirement to mount the guards as close to the rear extremity as 
possible minimizes the number of trailers with guards mounted forward 
of the rear extremity.
    Mr. Byron Bloch recommended that the guard should be located no 
more than 150 mm (6 in) forward of the rear extremity instead of 305 mm 
(12 in). He said that the 150 mm (6 in) gained could be used to make 
the guard more effective, by permitting the guard to absorb more energy 
by utilizing a 255 mm (10 in) stroke rather than the proposed 125 mm (5 
in) stroke. He stated that this would allow the manufacturers greater 
flexibility in choosing an energy absorbing type of guard.
    While it might be desirable to have guards that absorb an 
equivalent amount of energy over a greater distance, Mr. Bloch's 
suggestion could make PCI more likely. NHTSA does not want to reduce 
the vehicle manufacturer's flexibility to offset the guard up to 305 mm 
(12 in) forward of the rear of the trailer. If the agency permitted a 
greater stroke for guards designed to be mounted closer to the rear 
extremity, it would be difficult to control where these guards are 
actually mounted. If mounted too far forward within the permitted 
offset, they would allow excessive penetration under the trailer. NHTSA 
is also concerned that guards with a greater amount of stroke will 
pivot at the vehicle chassis, causing the horizontal member of the 
guard to rotate up until it no longer engages substantial striking 
vehicle structure of lower profile vehicles. This also would make PCI 
more likely.
2. Exclusions
    The SNPRM excluded certain categories of vehicles from the 
requirement for rear impact guards. These categories were: Single unit 
trucks (also referred to as ``straight body'' because they are 
unarticulated); truck tractors; pole trailers; low chassis trailers; 
special purpose vehicles; and wheels-back vehicles.
    Almost every comment addressed one or more of these exclusions. The 
consumer safety groups and most of the comments from the general public 
were especially opposed to the exclusion for single unit trucks. The 
consumer groups were also opposed to the exclusion for wheels back 
vehicles. There was little opposition from the consumer safety groups 
or the public to the exclusion for special purpose vehicles. Industry 
groups generally supported all the exclusions. Many industry groups and 
equipment manufacturers requested that their vehicles be explicitly 
included in the special purpose vehicle category. Industry groups also 
commented on the wheels back vehicle definition, generally requesting 
that it be expanded to cover more vehicles.
    The comments on the excluded vehicles are discussed in more detail 
below. Since there was no substantive comment on the exclusions for 
pole trailers, low chassis trailers, and truck tractors, these 
exclusions are not discussed.
    a. Single Unit (Straight body) Trucks. NHTSA expressly solicited 
comment on the issue of applicability of the proposed rule to single 
unit trucks. The majority of docket submissions, including comments 
from trade associations, safety and consumer interest groups, and 
private citizens, expressed the opinion that the proposed rule should 
apply to single unit trucks. Many of these commenters stated that the 
exclusion did not make sense because the underriding passenger vehicle 
would not be any less at risk in striking the rear end of a single unit 
truck than striking the rear of a trailer. Advocates said single unit 
trucks account for about 300,000 of the 500,000 heavy vehicles produced 
each year. IIHS and Advocates stated that medium and heavy duty single 
unit trucks account for 36 percent of all the vehicle miles traveled by 
heavy vehicles and 68 percent of all non-fatal (AIS 1-5) injuries 
associated with passenger vehicle impacts with the rear of heavy 
vehicles. CRASH's analysis indicated that the number of fatal accidents 
in which passenger vehicles collide with the rear of trailers has been 
increasing at a rate of about 6 percent per year. According to CRASH, 
rear impacts involving single unit trucks have been increasing at a 
rate of 11 percent annually in the recent past.
    Mr. Robert Crail and Transamerica Leasing opposed the exclusion 
because single unit truck manufacturers would be able to obtain guards 
from the same places as trailer manufacturers. Mr. Byron Bloch 
recommended that single-unit trucks should be excluded only by 
exemption petition from individual manufacturers, and that if petitions 
are granted, NHTSA should require a warning sign on the truck. The 
State of New York Attorney General expressed the opinion that NHTSA is 
required by the 49 U.S.C. Chapter 301 requirement that a safety 
standard must meet the need for motor vehicle safety to include single 
unit trucks in this rule, based on the ``very modest costs involved.'' 
Mr. John Kourik could find no definition anywhere in NHTSA's 
regulations for the term ``single unit truck.''
    Additional organizations recommending that the rule apply to single 
unit trucks include the International Brotherhood of Teamsters, the 
Owner-Operator Independent Drivers' Association, the Specialized 
Carriers and Rigging Association, and the American Insurance Services 
Group. About 2,200 private citizens also recommended that the rule 
apply to single unit trucks as well as trailers and semitrailers.
    Mr. John Tomassoni commented that including vehicles with a gross 
vehicle weight rating (GVWR) of greater than 14,536 kg (10,000 lbs) in 
the statistical 

[[Page 2021]]
cost benefit analysis made the trailers appear unfairly dangerous 
because most single unit trucks are in the low end of this weight 
range, yet the larger trucks can still cause underride fatalities. He 
suggested that cost effectiveness be reassessed on the basis of 
requiring guards on trucks and trailers weighing greater than 11,790 kg 
(26,000 lbs). He further recommended that even if the single unit 
exclusion were retained in the final rule, the rule should at least 
``encourage'' manufacturers of single unit trucks above 9,070 kg 
(20,000 lbs) GVWR to install ``upgraded'' guards.
    Manufacturers, owners, and operators of single unit trucks 
supported the agency proposal to exclude those vehicles from the 
rulemaking. Single unit trucks have many different configurations, 
according to Ford Motor Company (Ford), some of which would make 
installation of the rear impact protection guard impracticable. For 
example, school buses with a 3,810 mm (150 in) distance from the rear 
axle to the rear extremity of the vehicle would have their angle of 
departure severely limited by the proposed rear impact protection 
guard. Ford also indicated that there would be many questions 
concerning guard installation responsibility because many units are 
sold without bodies to secondary manufacturers.
    The National Truck Equipment Association (NTEA) supported NHTSA's 
proposal to exclude single unit trucks from the guard requirements, 
citing the low rate of rear end impacts for trucks as compared to 
trailers. NTEA also stated that single unit truck rear impact guard 
installation cost would be considerably more (up to $3,000 where 
custom-made guards are required) than the installation cost for 
trailers because of the high number of special purpose single unit 
trucks. It also said that single unit trucks are often farm vehicles, 
dump trucks, and delivery trucks that travel short distances, at lower 
speeds, generally in the daytime.
    NSWMA says the single unit truck exclusion is important because the 
safety benefits to passenger vehicles would be offset by the increased 
risk to the truck operator and waste service personnel resulting from 
the design restrictions that would be imposed by requiring guards on 
single unit trucks.
    Agency accident data indicate that approximately 27 percent of the 
striking vehicle occupant fatalities and 15.8 percent the serious 
injuries (AIS 3-5) in rear end collisions with heavy vehicles involve 
single unit trucks, while 73 percent of striking vehicle occupant 
fatalities and 84.2 percent of serious injuries involve trailers and 
semitrailers. This relatively low involvement of single unit trucks 
contrasts sharply with their contrasts sharply with their predominance 
among heavy vehicles. Single unit trucks represent 72 percent of 
registered heavy vehicles. Also, there are 1.6 times as many single 
unit trucks produced as there are trailers and semitrailers that would 
be candidates (i.e., assuming they do not qualify for some other 
exclusion) for underride protection guards. Therefore, this rule covers 
about 28 percent of the total vehicles and would achieve about 73 
percent of the fatality reduction benefits. The SNPRM estimated that 
collisions with single unit trucks account for approximately 68 percent 
of the total injuries based on 1986 NASS data. Based on a reevaluation 
of the data from the newer General Estimate System (GES) data set, 
NHTSA has revised this estimate to about 18 percent.
    According to FARS data from 1982 through 1992, fatalities resulting 
from passenger vehicle collisions with the rear of single unit trucks 
have remained fairly constant, with a slight increasing trend. This 
shows that single unit trucks are not an increasing problem, as 
suggested by CRASH.
    NHTSA has concluded that this category of vehicles should not be 
covered by the rule at this time. It may be desirable to cover at least 
some single unit trucks. However, the agency lacks sufficient 
information at this time to deal with single unit trucks as it has with 
trailers, i.e., by excluding from the larger group of single unit 
trucks those subgroups with special problems. The agency is concerned 
that the variety, complexity, and relatively low weight and chassis 
strength of many single unit trucks could require guards that are 
substantially more costly than the guards for trailers and 
semitrailers. This would prevent the industry from benefiting from the 
economies of scale that the separate equipment and vehicle standards 
were intended to promote. NHTSA is currently conducting a study of the 
single unit truck production to see if there are groups of single unit 
trucks that, like trailers, could be fitted with rear impact guards 
without excessive costs.
    The vast majority of heavy truck striking vehicle occupant 
fatalities (73 percent) and injuries (84.2 percent) involve collisions 
with the rear ends of trailers and semitrailers. Therefore, NHTSA can 
capture most of the benefits from rear underride guards by requiring 
them at the outset for trailers and semitrailers. The agency may 
supplement this action by initiating a separate rulemaking action to 
consider rear impact guards for single unit trucks after completion of 
its study.
    The agency does not see any merit in Mr. Tomassoni's suggestion. 
There would be little benefit in requiring or encouraging manufacturers 
to install guards on single unit trucks with a GVWR greater than 11,790 
kg (26,000 lbs), because only 10 percent of single unit trucks are 
between 4,536 and 11,790 kg (10,000 and 26,000 lbs).
    In response to Mr. Kourik's observation that there was no 
definition in the SNPRM or elsewhere for ``single unit truck,'' the 
regulatory text of the final rule does not use that term, thus such a 
definition is not necessary there. Single unit truck refers to trucks 
that do not have an articulated chassis.
    b. Special Purpose Vehicles. Several manufacturers and operators of 
specialty vehicles such as vehicles with rear mounted liftgates, dump 
trailers, auto transporters, farm equipment, and recreational vehicles 
recommended that their vehicles be explicitly excluded from the rule. 
They recommended that the definition of ``special purpose vehicle'' in 
the 1992 SNPRM be revised to include these vehicles.
    A number of liftgate manufacturers submitted comments. Thieman 
Tailgates, Waltco Truck Equipment Company (Waltco), and Leyman 
Manufacturing Company all recommended explicit exclusion of trailers 
equipped with liftgates. Most liftgates are installed after the trailer 
leaves the manufacturer. They also stated that it would be very 
burdensome on small businesses to design liftgates around the guard 
configuration requirements.
    Waltco estimated that several thousand new vehicles are equipped 
with liftgates annually. If required, guards for trailers equipped with 
liftgates would be more expensive than NHTSA's cost estimate, according 
to Waltco. Some guards would have to be movable and compliance testing 
would be more complicated since some configurations would necessitate 
that the guard be mounted to the liftgate itself. Waltco provided 
diagrams to show that all of its liftgate designs are incompatible 
because they must either swing through the guard area or create 
dangerous shear/pinch zones between gate and guard.
    Anthony Liftgates (Anthony) estimated that each year 3,000 new 
trailers and semitrailers are equipped with rear mounted liftgates, 500 
of the liftgates being manufactured by Anthony. Anthony stated that 
rail-type liftgates are the most commonly used and their rail-type 
models would be compatible with the proposed guard. 

[[Page 2022]]
Anthony requested that NHTSA give special consideration to vehicles 
equipped with liftgates since certain restrictions would be highly 
detrimental to the industry.
    NTEA stated that vehicles equipped with liftgates comprise the 
largest group of special purpose vehicles. NTEA estimated that 2,500 of 
the 150,000 trailers built each year are equipped with liftgates at the 
rear, comprising only 1.7 percent of the market. The NTEA assured NHTSA 
that no trailer manufacturer would use the special purpose vehicle 
exclusion to evade the guard requirement because liftgates cost 
($6,000) so much more than guards.
    The Leyman Manufacturing Company stated that positioning the guard 
as specified in the proposal would eliminate the installation of 
liftgates. Leyman also pointed out that vehicles equipped with 
liftgates were excluded from the January 8, 1981 NPRM.
    The agency concurs with the observations made by liftgate 
manufacturers regarding the complexities associated with the 
installation of rear impact protection guards on these vehicles. NHTSA 
acknowledges that vehicles equipped with liftgates were cited in the 
January 8, 1981 NPRM as vehicles that would fall within the special 
purpose vehicle exclusion. The agency also agrees that the rear impact 
protection guard would interfere with the operation of some rear 
liftgates. However, NHTSA does not think it is necessary to exclude all 
liftgate-equipped trailers explicitly. Instead, the agency has modified 
the definition of special purpose vehicle to make it clear that 
vehicles with rear mounted liftgates that operate by swinging through 
the area that is designated for the rear impact guard are excluded. 
Consequently, vehicles equipped with the rail type liftgates that 
Anthony Liftgates said would be compatible with a guard are not 
excluded, while vehicles equipped with tuckunder and other types of 
incompatible liftgates are excluded.
    The Manufactured Housing Institute (MHI) stated that manufactured 
homes are generally moved once or twice over their lifetime on an 
integral, temporary chassis under strict oversize permits. MHI 
recommended that NHTSA exclude these trailers from the proposed rule, 
stating that the standard should not apply to manufactured homes, 
modular structures, and mobile homes. According to MHI, there are about 
300,000 units transported annually in the United States, being hauled 
as trailers for an average distance of 160 to 200 kilometers (km) (100 
to 125 miles (mi)). MHI also noted that mobile homes in transport have 
305 to 560 mm (12 to 22 in) of ground clearance.
    Mobile homes are not covered by the FMVSS. NHTSA has long 
interpreted the Mobile Home Construction and Safety Standards Act of 
1974 (Pub.L. 93-383) as withdrawing NHTSA's authority to regulate 
mobile homes as motor vehicles and vesting this authority in the 
Department of Housing and Urban Development. Therefore, mobile homes 
are not covered by this rule. This conclusion does not, however, apply 
to motor homes.
    The Recreational Vehicle Industry Association (RVIA) recommended 
that recreational trailers be excluded from the proposed regulation as 
special purpose vehicles. According to RVIA, recreational vehicles are 
probably involved in a small percentage of the rear end collisions due 
primarily to low mileage and little nighttime highway exposure. RV 
trailers often require high ground clearance for off-road use, 
according to RVIA.
    The agency does not believe that recreational vehicles should be 
included in the definition of special purpose vehicle because they do 
not have work performing equipment in their lower rear extremity. 
However, NHTSA has concluded that certain recreational vehicles should 
be explicitly excluded under the applicability section of the rule. 
Most of these vehicles are believed to be low chassis vehicles, and 
even if they are not, their chassis will generally be too weak to 
support a guard. Therefore, vehicles with ``temporary living 
quarters,'' as defined in 49 CFR 523.2, are excluded from the rule.
    The Specialized Carriers and Rigging Association (SC&RA) suggested 
that two types of heavy hauler trailers be listed in the final rule as 
examples of ``special purpose vehicles''. The vehicles cited have rear 
end configurations that vary based on use. According to SC&RA, rear 
underride guards would interfere with the function of these types of 
vehicles. The SC&RA asserts that design considerations prevent 
compliance with the proposed rule.
    If SC&RA is correct in asserting that design considerations prevent 
the two vehicle types from having rear impact guards, these vehicles 
would clearly meet the special purpose vehicle definition. The 
illustrations provided indicate that they have work performing 
equipment or would qualify for the low chassis vehicle exclusion. 
Therefore, the agency sees no need to explicitly list these vehicles as 
examples of special purpose vehicles.
    NSWMA recommended that the ``special purpose vehicle'' definition 
be modified to include vehicles with special equipment mounted at the 
rear that is not directly affected in an adverse manner by the rear 
impact protection guard. NSWMA believes that this exclusion is 
necessary because of the potential impairment of function in waste 
industry specialized hauling vehicles from factors such as reduced 
departure angle and off-road use.
    NHTSA does not believe that the special purpose vehicle definition 
should be modified in response to NSWMA's recommendation. Vehicles with 
work performing equipment at the rear whose operation would not be 
adversely affected by the rear impact guard should be equipped with 
guards. All trailer users will have to deal with a reduced angle of 
departure. Further, exclusions of vehicles need to be made on the basis 
of physical attributes instead of anticipated functional restrictions. 
NSWMA has not alleged that these trailers are physically different from 
any other trailers, only that they are used in a demanding operational 
environment.
    NHTSA believes that the use of adjustable guards will alleviate 
most operational restrictions where the work performing equipment does 
not qualify the vehicle for the special purpose vehicle exclusion, such 
as trailers that travel on uneven surfaces or that have beds that raise 
and lower at their rear ends. NSWMA acknowledged that most of the 
vehicles it refers to are excluded as single unit trucks.
    The National Potato Council recommended that vehicles used 
primarily for harvesting be excluded from the rule. The Potato Council 
stated that rear-unload semitrailers have rear conveyors whose function 
would be significantly impaired if rear impact guards were required. It 
also requested that eighteen wheelers that travel no more than 240 km 
(150 mi) from their base farm should be excluded from the proposed 
rule. These vehicles are on road for very short periods, according to 
the Potato Council--one to two months in the spring to haul seeds, and 
a similar period in the fall to bring the crop to market.
    Assuming the Potato Council is correct that underride guards would 
substantially impair the function of the rear-unload semitrailers, 
these vehicles would qualify as special purpose vehicles. A specific 
mention of them in the rule is therefore unnecessary. Regarding the 
eighteen wheelers, sporadic road use and short travel distances have 
been considered in the past as factors in determining whether vehicles 
are ``motor vehicles'' that are subject to NHTSA's safety standards. 
However, the fact that the vehicles are 

[[Page 2023]]
used on the public roads only two to four months a year does not 
disqualify them as motor vehicles. The same may be true for many pickup 
trucks used on farms. Merely because a given trailer happens to be used 
on the farm most of the year does not mean it was not manufactured 
primarily for use on the public streets. Similarly, the shortness of 
the trips the vehicle takes is not dispositive, unless it is used only 
to cross from field to field or to travel between job sites. It appears 
that the trailers the Potato Council refers to are used primarily for 
transportation during the spring and fall. Therefore, the definition of 
special purpose vehicles has not been modified as recommended by the 
Potato Council.
    Mr. John Kourik suggested that the application section be expanded 
to show whether or not the rule covers the following kinds of vehicles: 
boat trailer, fire fighting vehicle (some have trailers), trailer 
converter dolly, agricultural commodity truck, auto transporter (a 
combination vehicle), container chassis trailer, pulpwood trailer, 
heavy hauler trailer, and straddle trailer. In the alternative, he 
suggests that some method for obtaining interpretations of 
configurations is needed, other than tedious petitions for exemptions.
    NHTSA is not providing interpretations for each of the vehicles 
listed by Mr. Kourik. Applicability is based on the configuration of 
the vehicle, rather than vehicle function, as Mr. Kourik's list 
suggests. The agency is unsure about the physical attributes of some of 
the listed vehicles. In the absence of more detailed information, NHTSA 
cannot give definitive interpretations for the listed vehicles. NHTSA 
believes that the rule adequately defines those vehicles that are 
included and those that are excluded. NHTSA believes further that the 
applicability will be obvious in almost all cases to persons 
sufficiently familiar with details of the physical attributes of the 
vehicles in question. Given his knowledge about these vehicles, Mr. 
Kourik should be able to determine whether they fall within the 
agency's exclusions. The agency notes that the public is not required 
to petition for an exemption to obtain an interpretation of the rule's 
applicability to a particular vehicle configuration. The Office of the 
Chief Counsel issues such interpretations in response to letters of 
inquiry which provide sufficient background information.
    FHWA initially indicated that the definition of a special purpose 
vehicle should include certain dimensions for the work performing 
equipment. The maximum ground clearance, minimum width, or maximum 
distance between any work performing equipment and the side of the 
vehicle were cited by FHWA as dimensions that should be included in the 
definition. According to FHWA, adding language to the rule that further 
defines the location of work performing equipment would provide better 
guidance to vehicle manufacturers and reduce potential enforcement 
problems for NHTSA and FHWA.
    NHTSA believes that the relationship of the work performing 
equipment to the location in which the rear impact guard would have to 
be installed, and not the mere presence of the equipment, should be the 
criterion for determining exclusion. If the equipment needs to move 
through the area that could be occupied by the horizontal member of the 
guard, as defined in S5.1.1 through 5.1.3 of the vehicle standard, the 
presence of a guard would impair or eliminate the usefulness of the 
equipment. NHTSA has decided that it would be both impracticable and an 
undue burden to require rear impact guards on such vehicles. However, 
if the equipment is detached or stows out of the guard area while in 
the vehicle is in transit, a guard would not be an impediment to the 
equipment, and a guard is required. Although it is not required, NHTSA 
encourages vehicle manufacturers to move the guard within the limits of 
S5.1.1 through S5.1.3 to accommodate the work performing equipment.
    It is neither practical nor necessary to specify location or 
dimensions for the work performing equipment. The ground clearance, 
width, and distance from the work performing equipment to the side of 
the vehicle are not relevant because the work performing equipment is 
not required to perform as a guard. NHTSA does not want to restrain 
innovation by giving direction to vehicle manufacturers on the 
configurations of their work performing equipment. Defining the 
dimensions or location of the work performing equipment is not 
necessary for an enforceable rule. All that is required to confirm the 
applicability of the exclusion is a demonstration that the work 
performing equipment, while the vehicle is in transit, resides in the 
area defined by S5.1.1 through S5.1.3 as the guard's horizontal member 
or passes through that area to perform its function. Therefore, the 
definition of special purpose vehicle in the rule has been revised to 
reflect that the foundation of the special purpose vehicle exclusion is 
the presence of work-performing equipment that resides in or, to 
perform its function, moves through the area designated for the 
underride guard while the vehicle is in transit.
    The definition of special purpose vehicle has been modified to 
explicitly recognize the piping of hazardous materials tankers as work 
performing equipment. RSPA's rule for underride guards on hazardous 
materials tankers (49 CFR 178.345-8) is generally compatible with this 
rule, and this rule applies to hazardous materials tankers. However, to 
prevent any confusion as to the relationship between RSPA's rule and 
NHTSA's rule, this rule explicitly recognizes that piping that carries 
hazardous materials while in transit needs the special protection that 
is provided by RSPA's rule. Therefore, hazardous materials tankers with 
piping in front of the guard are excluded from the requirements of this 
rule.
    c. Wheels Back Vehicle. A ``wheels back vehicle'' was defined in 
the SNPRM's vehicle standard as a vehicle which has a permanently fixed 
rear axle with tires whose rearmost surface is located not more than 
305 mm (12 in) forward of a vertical transverse plane tangent to the 
rear extremity of the vehicle. Several commenters recommended that the 
wheels back vehicle definition be changed to include vehicles with rear 
tires located as much as 610 mm (24 in) from the rear extremity of the 
vehicle. Other commenters expressed concern that impacting the rear 
tires of a trailer or semitrailer is similar to impacting a rigid 
barrier and the agency should delete this category of exclusion.
    Industry groups and some other commenters favored an expansion of 
the wheels back definition by allowing the wheels to be positioned more 
than 305 mm (12 in) forward of the rear extremity. The ATA and the TTMA 
noted that the proposed rule allowed guards to be mounted up to 305 mm 
(12 in) forward of the rear extremity while allowing an additional 125 
mm (5 in) to meet the strength requirements of the 1992 SNPRM. TTMA 
recommended, therefore, that the distance between the rear tires and 
the rear extremity of the vehicle be increased from 305 to 430 mm (12 
to 17 in). According to ATA, the spirit of the ``wheels back vehicle'' 
exclusion would not be violated by allowing the tires to be located as 
much as 560 mm (22 in) forward of the rear extremity. ATA reasons that 
guards mounted 305 mm (12 in) forward of the rear of the vehicle will 
allow some vehicles to underride more than 305 mm (12 in) prior to 
contact with the guard since the forward most area of the car may not 
be contacted.
    TTMA's recommendation to add the 125 mm (5 in) of permitted test 

[[Page 2024]]
    deflection to the 305 mm (12 in) of permitted setback, resulting in 430 
mm (17 in) of permitted setback, is not practical. It does not account 
for the fact that, in a crash, a portion of the impacting vehicle's 
initial energy and velocity will be absorbed after the guard has 
undergone 125 mm (5 in) of deflection or deformation. This is a very 
different situation from one in which the initial impact contact 
between the passenger car and the underride guard takes place 430 mm 
(17 in) forward of the trailer's rear extremity. With a 430 mm (17 in) 
setback, even if the rear impact guard were completely rigid, the 
striking vehicle would still advance closer to the rear of the trailer 
(and potential PCI) before coming to rest because the vehicle would be 
forced to absorb more energy (thus increasing the likelihood of 
occupant injury).
    While some passenger vehicles may underride the impact protection 
guard prior to contact, as stated by ATA, this non-contact underride is 
not likely to be more than a few inches. If anything, this fact 
mitigates in favor of requiring the guards to be positioned farther to 
the rear. This final rule adds the requirement that the underride guard 
be positioned as far to the rear of the vehicle as practical.
    Some commenters recommended allowing the wheels to be positioned 
even farther forward if there were a guard in between the rear wheels. 
The ATA encouraged NHTSA to allow vehicles to use the ``wheels back'' 
exclusion vehicles with tires up to 610 mm (24 in) forward of the rear 
extremity if a ``center'' guard were provided. This partial guard would 
be located no more than 305 mm (12 in) forward of the rear extremity 
and no more than 150 mm (6 in) inboard of the inside sidewalls of the 
tires. The center guard's placement between the wheels would complement 
the tires in resisting underride. Mr. Robert Crail suggested that a 
partial underride protection guard be specified for double trailers 
with the rear tires mounted between 430 and 610 mm (17 and 24 in) 
forward of the rear extremity, because the trailer wheels are as 
effective as a guard at full deflection. He said that the partial rear 
underride protection guard should extend to within 205 mm (8 in) of the 
inboard sidewalls of the rear tires.
    The agency believes that the specification of a partial rear impact 
guard would not enhance safety because it is unlikely that a passenger 
vehicle would pass between the rear tires of the trailer. The spacing 
between the inside surfaces of the rear tires on a 2,600 mm (102 in) 
wide trailer was measured by the agency as 1,310 mm (51.5 in). There 
are almost no passenger vehicles produced with widths of less than 1600 
mm (63 in). Therefore, even a centric collision between the widest 
trailers and the narrowest cars would probably result in considerable 
engagement of the tires with the frontal vehicle structure.
    Other commenters, in addition to the ATA and Mr. Crail, believe 
that the 305 mm (12 in) maximum offset makes the exclusion too 
restrictive. Yellow Freight System suggested that the wheels back 
definition be changed to allow the wheels to be 560 mm (22 in) forward 
of the rear extremity. It states that most trailers cannot position the 
wheels closer than 460 to 560 mm (18 to 22 in) from the rear extremity 
because the combined effect of shorter distances and the Federal Bridge 
formula would be to restrict the weight of the load that can be 
carried. Strick Trailers stated that operators routinely position the 
rear axle at 915 and 1,065 mm (36 and 42 in) forward of the rear 
extremity of the vehicle, which would exclude them from the wheels back 
vehicle category.
    The rationale for all these suggestions appears to be that most 
trailers with the axle in the rearmost position have the rear tire 
within a range of 405 to 610 mm (16 to 24 in) forward of the rear, and 
an expanded wheels-back definition would lower costs by allowing more 
trailers to qualify as wheels back. The agency notes that many of the 
commenters mentioned ``positioning'' of the rear wheels, which implies 
that they are referring to the vehicles that do not have fixed axles. 
Therefore, these vehicles would not be eligible for the wheels back 
exclusion anyway. NHTSA does not believe that carriers would change the 
wheel positioning of their fleets merely to avoid the small one-time 
incremental cost of installing an upgraded guard, as Yellow Freight 
suggests. Moreover, while NHTSA is concerned with the costs of the 
rule, the ultimate goal is to prevent PCI without imparting 
unacceptable deceleration forces to the impacting vehicle. Allowing 
vehicles to have their wheels farther forward would increase the 
likelihood of PCI. The agency does not believe, based on available 
information, that the definition of wheels back vehicle should be 
modified to increase the allowable distance between the rear extremity 
of the vehicle and the rear tires.
    Advocates appeared to favor eliminating the wheels back exclusion 
altogether. Advocates stated that the agency has no test data on 
``wheels back vehicles'' which support the conclusion that they should 
be excluded from the proposed rulemaking. Advocates further stated that 
the agency has contradicted the argument that impacting the rear wheels 
of trailers results in acceptable crash forces, because the Preliminary 
Regulatory Evaluation (PRE) likens a collision with the wheels to 
striking a ``rigid wall.'' Trailer tires will not provide an acceptable 
level of rear impact protection, according to Advocates. Advocates 
acknowledged that two crash tests with wheels back vehicles were 
conducted by the Texas Transportation Institute (TTI), but referenced a 
paper co-authored by John Tomassoni, a former NHTSA engineer, as 
evidence that the collision forces would be ``relatively high.'' 
Advocates also stated that the rule should define ``permanent'' 
settings for sliding bogeys by requiring that they be welded or bolted 
in place.
    Vehicles meeting the wheels back requirements should be capable of 
preventing the trailer structure from penetrating a passenger vehicle 
occupant compartment during a rear end collision. Two full-scale crash 
tests involving ``wheels back vehicles'' were conducted by the TTI in 
1979. For these wheels back vehicle tests, the rear tires were located 
about 100 to 205 mm (4 to 8 in) forward of the rear extremity of the 
trailer. In each test, in an offset crash in which a Chevrolet Impala 
struck the tires and in a centric crash in which a VW Rabbit struck the 
axle and other components between the tires, PCI was prevented at about 
56 kph (35 mph). In the test with the VW Rabbit, post-crash photos 
indicate that, when dynamic underride reached the maximum, the body of 
the trailer was 305 to 355 mm (12 to 14 in) from the A-pillar and 
windshield area of the passenger vehicle. These crash tests indicate 
that a fixed rear axle with the tires mounted within 305 mm (12 in) of 
the vehicle's rear extremity constitutes an adequate substitute for a 
rear impact protection guard from the standpoint of preventing PCI.
    The rear wheels of a trailer are adequate for managing the energy 
of an underride crash. The on-board dummy instrumentation during both 
crashes indicated a relatively low potential for serious injuries. In 
fact, the wheels back vehicle performed better in the offset crash than 
all other guards tested in the TTI research project except the Quinton-
Hazel guard. Although the maximum vehicle deceleration of a VW Rabbit 
that was driven centrically into a wheels-back trailer at 33 mph was 
similar to the deceleration of the same make/model vehicle driven into 
a rigid wall (35 mph), partial guards for the sole purpose of energy 
absorption in centric crashes are not warranted from a cost-benefit 
standpoint. 

[[Page 2025]]

    NHTSA has decided to retain the wheels back exclusion for vehicles 
with the rear wheels within 305 mm (12 in) of the rear extremity of the 
vehicle. Vehicles with wheels set farther forward than that will have 
sufficient room between the guard and the trailer rear tires for the 
guard to deflect and absorb some of the passenger vehicle's energy 
before the guard contacts the rear wheels of the trailer. Vehicles with 
rear wheels within 305 mm (12 in) of the rear extremity will not have 
sufficient room for the guard to do much good before it contacts the 
wheels.
    The wheels back vehicle exclusion is intended to apply exclusively 
to vehicles with the rear tires permanently located close to the rear 
extremity of the vehicle. The concept of ``permanent'' is clear enough 
and does not require elaboration, as Advocates suggests. The rear 
wheels must be either welded in place or designed so that they can 
occupy only one position. Vehicles with moveable bogeys cannot be 
wheels back vehicles even if their wheels are set in a wheels back 
position, as suggested by the comments of Yellow Freight and Strick 
Trailers.

D. Costs

    Many of the commenters addressed the question of cost of the guard. 
The consumer safety groups thought that the agency's estimate of the 
cost of energy absorbing guards was too high. Conversely, the industry 
commenters generally thought the agency's estimate was either low or 
about right. Most of the private citizens who commented on guard cost 
said that energy absorbing guards were worth the price, without giving 
specifics.
    Advocates stated that NHTSA had not taken into account the fact 
that economies of scale would lower the cost of hydraulic energy-
absorbing guards to nearly that of the proposed guard. It said that the 
hydraulic guards are within the price range of the proposed guard. 
Advocates also commented that NHTSA provides no guidance information to 
carriers on effectiveness, cost/benefit ratio, mounting heights, or 
crashworthiness that would allow them to choose a superior (i.e., 
energy absorbing) guard.
    The American Automobile Association (AAA), the New York Attorney 
General, and many private citizens expressed the view that the 
additional cost for energy absorbing guards (variously described by 
them as approximately $200 additional, or ``modest'') is reasonable. 
These commenters did not provide information on where such guards would 
be obtained or why a doubling to tripling of the cost represents a 
``modest'' increase.
    TTMA provided a table showing estimated costs to the customer over 
current ``bumper'' (NHTSA assumes TTMA means guard) prices for various 
kinds of vehicles. Estimated cost increases range from $130 to $200, 
except for tilt deck trailers. For those vehicles, the costs of the 
hydraulics to swivel the guard out of the way would cost $3000.
    Based on the costs incurred during the fabrication of 15 minimally 
compliant guards for the VRTC research project, NHTSA estimates the 
incremental cost of the guard hardware is between $77 and $96 per unit. 
For a complete analysis of costs, see the Final Regulatory Evaluation 
(FRE). NHTSA agrees with Advocates that the economies of scale would 
lower the cost of hydraulic guards, or any guards, if they were to 
become widely accepted. However, Advocates submitted no data to show 
that the economies of scale would lower the cost of hydraulic guards 
close to the estimated price of the minimally compliant guard. NHTSA 
sees no basis for this assertion, especially since, to the best of this 
agency's knowledge, there are currently no hydraulic guards on the U.S. 
market. NHTSA has taken the economies of scale into account in its cost 
estimates in the FRE, as an offset to dealer mark-up, but notes that 
the amount cannot be quantified. TTMA's estimated incremental costs 
that were submitted to the agency on June 8, 1992 are 30 to 100 percent 
higher than NHTSA's if their list represents incremental increases. If, 
as NHTSA assumes, TTMA is referring to total guard equipment cost 
(excluding fuel penalty, maintenance, and payload loss), then NHTSA 
agrees.
    As to Advocates' suggestion about providing information on 
hydraulic guards, the market place will sort out competing guard 
designs and technologies based on their effectiveness, cost/benefit 
ratio, mounting heights, and crashworthiness. Manufacturers of superior 
guards can be expected to provide carriers with information favorable 
to their products. If hydraulic energy absorbing guards are more 
advantageous than minimally compliant guards, vehicle manufacturers 
will undoubtedly install them. The commenters who stated that the 
benefits of energy absorbing guards were worth the modest costs will 
see this opinion tested in the marketplace.
    Another aspect of costs addressed by the commenters was the revenue 
loss to the carriers due to the added mass of approximately 25 kg (55 
lbs) of the upgraded guards displacing payload that they could 
otherwise carry. Advocates contended that NHTSA had eliminated 
hydraulic guards from consideration because of their extra weight, even 
though NHTSA's contracted researcher and agency staff had said that the 
payload displacement was exaggerated and the percentage of trailer 
fleet impacted is infinitesimal. Advocates concluded that the revenue 
loss is negligible because the majority of commercial carriers reach 
their maximum cubic cargo capacity before they reach permissible gross 
load limits. Advocates also believes that the agency based its 
conclusions on unrealistically high estimates of hydraulic guard mass 
(135 kg, or 300 lbs). Ford incorrectly asserted that NHTSA's calculated 
costs do not account for lost revenue from payload displacement. 
Transamerica Leasing stated that the 25 kg (55 lb) add-on in mass is a 
correct figure. Yellow Freight System considers the loss of 
productivity due to additional tare weight to be unquantifiable. 
However, it estimated the fuel cost penalties due to the additional 
weight of the guard at $29.53, and the maintenance of the upgraded 
guards at $13.33, over the lifetime of the trailers. Finally, Yellow 
Freight System estimated that this rule will cost it $2.2 million as 
their trailer fleet is retired and replaced.
    The agency has reviewed its cost and weight data and concluded that 
the Quinton-Hazel guard is more costly (at $300) and heavier (135 kg, 
or 300 lbs). NHTSA does not believe that the McCafferty study, 
Advocates' basis for the contention that energy absorbing guards are 
weight-efficient, adequately supports that conclusion. A September 
1980, Texas Transportation Institute report entitled ``Performance 
Upgrading of Commercial Vehicle Underride Guards'' states that the mass 
of the Quinton-Hazel energy absorbing guard ranges from about 60 to 143 
kg (133 to 315 lbs). Yellow Freight System's estimates were based on 
the PRE, but NHTSA has updated these figures in the analysis in the 
FRE. The FRE now provides estimates of the payload displacement revenue 
loss of 33 cents over the life of the trailer, and estimates of 
lifetime fuel cost of $23.05.
    Guard design and testing are other additional costs associated with 
this rule. Although some guards probably already meet the proposed 
requirements, NHTSA assumes in the FRE that all existing guards will 
need to be redesigned to meet the strength and energy absorption 
requirements. No commenters provided cost estimates for guard redesign. 
However, NHTSA notes that design and testing are one-time costs, and 
can be recovered over the 

[[Page 2026]]
lifetime of the guard design. NHTSA further notes that the TTMA's 
Recommended Practice ``Rear Impact Guard and Protection'' appears to 
have been based on the SNPRM. This Recommended Practice is designated 
RP No. 92-94, and was originally issued in April of 1994 and revised in 
November of 1994. Apparently it has been adopted as an industry 
standard, so little reengineering should be necessary.
    Testing of a guard design once it is produced is another expense 
related to this rule. IIHS commented that guard manufacturers must 
carefully consider the chassis in developing installation instructions. 
Therefore, IIHS concluded that testing with the guard attached to a 
part of the chassis (provided by the vehicle manufacturer) would result 
in little additional burden.
    NHTSA agrees that there will generally be little additional burden 
in testing on a chassis part. However, the agency does not want to 
require such testing because there may be other valid bases for 
certification, such as engineering analysis, on certain models of 
trailers. Why should the guard manufacturer test on fifty different 
chassis parts when they are all nearly identical? NHTSA has adopted 
IIHS's suggestion to some extent by allowing testing on trailers, but 
it is an option, not a requirement.
    Mr. John Kourik stated that there is no estimate given for the 
trailer manufacturer's costs for testing in situations in which the 
guard is incorporated or integrated into the chassis structure itself, 
rather than attached as a separate unit.
    There is no estimate given for integrated guard designs because the 
agency considers it highly unlikely that manufacturers will produce 
integrated guards. Replacement or repair costs on such guards would be 
prohibitive. The FRE's estimates of testing costs are based on 
conventional designs that meet the performance requirements. Vehicle 
manufacturers can be expected to factor the increased testing costs 
into their decision whether to produce such an integrated design.
    Four liftgate manufacturers commented on the responsibility for and 
burden of testing. Waltco Truck Equipment Company, Leyman Manufacturing 
Corporation, and Venco stated that not excluding vehicles with 
liftgates would put an undue burden on vehicle manufacturers of 
developing and testing guards compatible with the various liftgate 
designs. Leyman added that the SNPRM's estimated guard cost of $112 
doesn't account for its removal and reinstallation when installing 
liftgates. Anthony Liftgates, Inc. stated that liftgate manufacturers 
cannot afford testing and that testing should be the responsibility of 
the trailer manufacturer or the last party to certify the trailer for 
highway use.
    The agency recognizes the costs associated with designing, 
installing and testing underride guards. This is the reason NHTSA 
changed to separate equipment and vehicle standards. Testing is the 
responsibility of the guard manufacturer, not the trailer manufacturer. 
However, as with any piece of motor vehicle equipment required by a 
FMVSS, subsequent alterers may not render the guard inoperative. 
Moreover, trailers bearing liftgates in the lower rear have been 
excluded from the requirement to have rear impact guards.
    NHTSA has also accounted for the incremental fuel and materials 
cost increase that will be expended in complying with the upgraded 
guard requirements. NHTSA estimates that an additional 25 kg (55 lbs) 
of steel will be required in a minimally compliant guard. This means 
that approximately 2,340 metric tons (2,580 tons) of additional steel 
will be required annually by the trailer industry. NHTSA estimates a 
lifetime additional fuel cost, due to the additional weight of the 
upgraded guards, of $23.05. Based on the weighted vehicle miles 
traveled, this translates to an additional 0.00007 liters of diesel 
fuel per kilometer (0.00003 gallons per mile). Since most tractor 
trailers now get about 2.3 kilometers per liter (5.5 miles per gallon), 
this seems insignificant.

E. Benefits

    The main benefits of this rule will be the fatalities and injuries 
avoided by the upgraded guards. Commenters focussed solely on fatality 
and injury benefits. Advocates believes that the benefits of the rule 
could be much higher than NHTSA estimated. It believes that potential 
benefits are being foregone because a minority of newly manufactured 
trucks, only 15 percent of the American truck fleet, will be covered. 
Many other commenters also stated that a minority of trucks would be 
covered. Advocates says that NHTSA has not calculated the benefits lost 
through exclusion of special purpose vehicles and wheels back vehicles. 
Advocates also said that the agency's estimated benefit of 9 to 19 
lives per year does not account for deaths due to unsurvivable 
deceleration forces from overly rigid guards permitted by the proposal. 
It believes that saving only 9 to 19 out of its claim of nearly 500 
truck rear-end fatalities per year is inadequate. Advocates cannot 
reconcile the drop in the estimated number of lives saved (63 in the 
1981 NPRM versus 9-19 in the 1992 SNPRM) with the SNPRM's statement 
that single unit trucks cause a minority of PCI deaths. It asserted 
that such a low benefits figure indicates that NHTSA has not revealed 
certain assumptions that it used in its cost benefit analysis. 
Advocates asserted that the benefits of the lower death/injury rate 
from energy absorbing guards make them worth requiring.
    CRASH and IIHS asserted that the data NHTSA relied on in its 
calculations were inadequate. CRASH argued that NHTSA improperly 
arrived at a 4:1 combination/single unit ratio by using 26 ``hard 
copy'' FARS reports, while dismissing as ``unrepresentative'' other 
state, national, and international studies. It cited estimates of 28 
percent, 44 percent, and most recently 66 percent of rear end truck 
fatalities caused by underride. Using the 66 percent number and NHTSA's 
upper range (27 percent) of guard effectiveness, CRASH concluded that a 
rule including single unit trucks would save 122 lives in 1995, six 
times the highest NHTSA projection. CRASH accuses NHTSA of defining 
underride as only involving full PCI as a pretext for discarding the 
much higher figures from other studies.
    IIHS thinks that NHTSA's estimate of 72 fatalities per year is 
understated by between 46 and 96 fatalities because the crashes were 
not properly coded in the FARS. It based this conclusion on IIHS 
calculations of parked truck underrides and other underrides that were 
not so coded in the FARS, extrapolating from California data. CRASH 
also stated that parked trucks were not properly treated in the 
analysis, even though they cause 20 percent of underride deaths. IIHS 
cited studies concluding that the European standard is only saving half 
of the lives that it could because its guard, at about 560 mm (22 in), 
is set too high. IIHS also sent a September 16, 1994 letter to the 
agency detailing inconsistencies between FARS and NASS data on 
underride. The letter concluded that the FARS analysts failed 
approximately 50 percent of the time to identify whether underride was 
involved because of inadequate information on the PARs and because FARS 
analysts are not familiar with typical indicators of underride.
    CRASH also faulted NHTSA's benefit calculation methods, and says 
that the agency systematically chose the lowest possible figures to 
calculate potential benefits in the Preliminary Regulatory Evaluation 
(PRE). It thinks that NHTSA is falsely showing the underride fatality 
statistics as static by using only the 

[[Page 2027]]
FARS data on combination trucks, and only during the period from 1985 
to 1989. Its analysis of the data show that the single unit truck 
underride fatalities are growing most rapidly (80 percent between 1982 
to 1989, claiming 145 persons in 1989). Extrapolating these data to the 
rule's 1995 effective date, CRASH calculates that single unit trucks 
account for 229 out of 685 total underride fatalities, an increase of 
90 percent over NHTSA's static total.
    Regarding Advocates' comment on the limited applicability of the 
SNPRM, the benefits of requiring guards on single unit trucks are far 
less than those for requiring guards on trailers because single unit 
trucks cause a proportionally smaller number of underride fatalities. 
Also, single unit trucks come in a much wider variety of 
configurations, making it much more difficult to attach standardized 
guards. Even if it would be cost beneficial to require some subsets of 
the single unit truck fleet to use underride guards, NHTSA does not now 
have the information necessary to define those subsets that should not 
be excluded. The FRE has a more complete analysis of the benefits. For 
these reasons, NHTSA may address underride guards for single unit 
trucks in a separate rulemaking. NHTSA has determined that there will 
be essentially no benefits lost by excluding wheels-back vehicles, 
since the rear tires of the trailer represent an adequate underride 
guard from the standpoint of PCI prevention. A similar argument can be 
made for low-chassis vehicles. PCI will be avoided due to trailer 
design, but the rear of the trailer may have other impact hazards that 
reduce effectiveness as a rear impact guard. The agency does not know 
how many trailers have work performing equipment that would qualify for 
the special purpose vehicle exclusion, but believes this number to be 
very small. Any benefits lost to it would likely be partially 
compensated for by the work performing equipment, such as liftgates, 
acting as a guard.
    The energy absorption requirement in the final rule will adequately 
prevent deaths and injuries from overly rigid guards. Therefore, the 
agency believes that its estimate of the fatalities prevented by this 
rule is realistic, and will not be degraded by overly rigid guards, as 
Advocates claims. NHTSA cannot respond to Advocates comment about the 
benefits of the hydraulic energy absorbing guards because the agency 
has not been provided with sufficient information. Inquiries with the 
Quinton-Hazel Company revealed that they no longer produce the guard, 
and the basis for the study concluding that the guard was cost 
effective is unclear.
    Regarding Advocate's comment that a rule that would save only 9 to 
19 fatalities is inadequate because it should save more lives, the 
agency notes that two key factors resulted in the low benefits 
calculations: (1) The low annual underride fatality rate, and (2) guard 
effectiveness estimates. Based on 8 years of FARS data and 79 detailed 
police accident reports, NHTSA's preliminary estimate (PRE) determined 
that the national underride rate with PCI was 14-23.5 percent. This 
translates to an annual average of only 59 fatalities per year 
attributable to rear underride with PCI, or about one per state per 
year. Based on the 1979 Michigan data, NHTSA estimates that about one-
third of these fatalities occur at speeds below 40 kph (25 mph), which 
is the maximum design speed of the minimally compliant guard for most 
vehicles. The low number of potentially affected fatalities was 
reflected in the guard effectiveness range (18-27 percent) used in the 
agency's preliminary benefit calculations. This effectiveness range is 
similar to that suggested for the comparable European guard by the 
British researchers cited by Advocates.
    The drop in estimated benefits from the earlier notices is a result 
of improved calculation methods and data. The 1981 NPRM's estimate of 
63 fatalities was based on an assumed average PCI rate of 35 percent 
and an assumed guard effectiveness of 50 percent. The 9-19 fatalities 
estimated in the SNPRM were based on a PCI underride fatality rate of 
14 to 23.4 percent and a guard effectiveness of 18 to 27 percent. NHTSA 
subsequently has decided that a more appropriate methodology is to rely 
only on the FARS database, which is now well established. Therefore, 
based on better data (13 years of FARS plus inspection of 139 police 
accident reports) NHTSA now believes that the PCI rate is 11 to 17 
percent. The 10 to 25 percent guard effectiveness estimate is 
consistent with experience with the European guard, modeling studies, 
and accident investigations, which are detailed in the FRE. Based on 
these parameters, the anticipated annual benefits of this rule, 
including the effects of conspicuity, are estimated to be 4 to 15 lives 
saved by preventing PCI and 29 serious injuries (AIS 2-5) prevented. An 
unknown number of non-PCI related lives will also be saved, as well as 
145 minor injuries (AIS 1) prevented.
    Advocates' suggestion that NHTSA is using unstated assumptions in 
the calculation of benefits is baseless. The regulatory evaluations 
explicitly state all of the important factors and assumptions used in 
the benefits calculation.
    NHTSA acknowledges that the FARS data are not perfect. However, the 
agency disagrees with CRASH and IIHS that the FARS is an inadequate 
basis for making estimates of benefits and drawing conclusions for the 
purpose of this rulemaking. In fact, the FARS and NASS databases are 
the best available. The FARS represents a census of all fatal accidents 
occurring in the United States. Therefore, NHTSA considers the FARS to 
be a better basis for decisionmaking than the regional studies and 
casual surveys cited by some of the consumer safety groups. Based on 
NHTSA's survey of 113 police accident reports from across the country, 
NHTSA concludes that fatalities coded as underride are properly coded 
and that virtually all of them involve PCI. It is possible that some 
fatal accidents where some degree of underride occurred should have 
been coded as PCI in the police accident reports or the FARS, but were 
not. However, the FARS are the best data available.
    The NASS, HSRI, and VSC (IIHS-sponsored) studies are inappropriate 
indicators of the percentage of underride fatalities with PCI. The use 
of non-census data such as NASS, which is based on a sample of tow-away 
crashes, has the potential to build sampling error into the 
conclusions. Problems with using these various studies are explained in 
more detail in the FRE. The FRE also explains why it is inappropriate 
to extrapolate the underride statistics from the atypical State of 
California to the rest of the nation, as IIHS urges.
    The agency believes that CRASH's comment that a rule including 
single unit trucks would save 122 lives in 1995 is based on highly 
optimistic assumptions. Their estimate is based on unrealistic 
projections of the number of fatalities (685, compared to 423 in 1992), 
a high underride rate from a United Kingdom study which may not be 
applicable to the United States, and the 27 percent upper bound of 
guard effectiveness range estimated in the Preliminary Regulatory 
Evaluation.
    NHTSA has expanded the scope of data considered in its FRE benefits 
analysis, as suggested by CRASH and other consumer safety groups, but 
the augmented data do not support their characterization of the 
underride problem. NHTSA included the FARS data for the eleven years 
from 1982 through 1992. In response to the comments from the consumer 
safety 

[[Page 2028]]
groups, NHTSA has taken parked trailers into account in the analysis of 
benefits in the FRE. NHTSA has also expanded the number of police 
accident reports it inspected to determine the ratio of single unit 
trucks to trailers involved in parked underride accidents. NHTSA looked 
at 60 selected police accident reports over a three year period to 
determine this ratio. Figure IV-1A in the FRE demonstrates that the 
underride problem for single unit trucks is not increasing, as CRASH 
suggests, but is relatively static, as stated in the PRE. Therefore, 
NHTSA believes that CRASH's extrapolations of average annual fatalities 
to the rule's effective date are invalid. For reasons explained in the 
FRE, the agency remains unpersuaded by the estimates of underride 
percentage and the corresponding benefits suggested in CRASH's 
comments.
    Ford also questioned NHTSA's estimated level of benefits. Ford 
stated that enhanced conspicuity, seat belt usage, and the reduction in 
the number of alcohol-related crashes will also reduce the incidence of 
underride-type crashes. Therefore, Ford doubts that reductions of 
fatalities and injuries in the magnitude estimated by the agency could 
be achieved solely by this rule. Ford also said that over the last ten 
years private trailer fleets that do not depend on public docks have 
lowered designs to increase productivity through use of small diameter, 
low profile tires and low ride suspensions. Therefore, a 1,000 to 1,250 
mm (40 to 50 in) high trailer chassis may no longer be typical, and 
therefore the future benefits of rule may be inaccurate.
    NHTSA agrees that all the factors cited by Ford will contribute to 
the reduction in fatalities from underride. However, NHTSA has 
accounted for the effects of the conspicuity rule in its FRE. Moreover, 
the effectiveness of the new automatic restraint systems depends on the 
prevention of PCI, because air bags need space to deploy. There may be 
some reduction in underride crashes due to increased seat belt usage 
and alcohol awareness, but such synergistic factors cannot be separated 
out at this point because projections of seat belt and alcohol use are 
difficult. NHTSA will assess analytically the effectiveness of this 
standard in the future and will normalize these factors in the 
analysis. Although lower chassis heights may now be more common in 
private fleets, NHTSA disagrees with Ford's suggestion that the 
standard trailer heights are no longer ``typical.'' NHTSA's data 
indicate that the vast majority of trailer chassis are still set at the 
1,000 to 1,250 mm (40 to 50 in) height to provide access to public 
loading docks. The 1990/92 TTMA van trailer data indicate that 98 
percent of floor heights range from 1,219 to 1,320 mm (48 to 52 in). 
The agency considers it unlikely that loading dock heights will change 
dramatically in the near future because standardization is very 
important to the trucking industry and a large investment would be 
required to change heights.
    Volkswagen enclosed three studies of European accident statistics 
showing reductions in fatalities of between 5 and 17 percent for the 
European guards, and recommended harmonization with the European 
standards.
    NHTSA does not dispute the studies cited by Volkswagen on the 
effectiveness of the European guard. However, NHTSA is not bound to 
follow the European standard. NHTSA's rule should be about 10 to 25 
percent effective and the requirements of this rule are slightly more 
stringent than the European standard.
    Yellow Freight System conducted a review of their 1991 accidents 
and concluded that there was no safety benefit from the use of the 
guards. It does not believe that any of its fatal accidents would have 
been prevented by the upgraded guards.
    Yellow Freight System provided no evidence to show that upgraded 
guards on their trailers would not have prevented any fatalities during 
1991. Even if it had, the particular experience of a single carrier 
over a single year period would not be indicative of the extent of the 
need for underride guards in the industry generally.

F. Lead Time

    Most of the commenters supported the agency's proposal of a 24 
month lead time. No commenter said that two years was insufficient. The 
American Truck Dealers Division of the National Automobile Dealers 
Association approved of the proposed lead time, stating that it will 
minimize the impact of the rule on the industry. Mr. Robert Crail, a 
trailer designer and manufacturer, indicated that two years would be 
adequate. The TTMA also supported the two year lead time, based on the 
requirements proposed in the SNPRM.
    One commenter suggested that the proposed lead time was too long. 
Mr. John Tomassoni recommended that the lead time be lowered to 1 year, 
because only ``marginally more effort'' would be required to design, 
produce, and install the required guards. According to Mr. Tomassoni, 
this is because vehicle manufacturers are already producing and 
installing ``geometrically compliant'' guards, or guards that meet the 
configuration requirements of this rule, on 16 m (53 ft) trailers in 
order to meet State requirements. Since the basic design shown in the 
SNPRM has been available for some time, he believes that upgrading the 
current guards to meet the strength requirements should not be 
difficult.
    While this may be a valid point for those manufacturers currently 
producing geometrically compliant guards, establishing too short a lead 
time period might create a competitive disadvantage for those 
manufacturers who are not. Also, the agency wants to allow enough lead 
time to permit engineers to produce innovative, highly efficient guard 
designs, rather than forcing them to rush to market with an upgraded 
version of the current design. Further, the agency notes that an energy 
absorption requirement has been added in the final rule that Mr. 
Tomassoni did not consider in suggesting that a year would be 
sufficient lead time.
    Therefore, NHTSA does not believe that a shorter lead time than two 
years would be appropriate. Engineers will have to design guards and 
rigid test fixtures, and the guards will have to be manufactured, 
tested, and in some cases marketed. There is currently no industry in 
the business of manufacturing underride guards for third parties, 
although NHTSA anticipates that one may emerge to meet the demand 
created by this rule. Smaller trailer manufacturers wishing to acquire 
manufactured guards need time to work with the emerging guard 
designers/manufacturers regarding their frame and chassis 
configurations and appropriate attachment hardware. Because a 
relatively low level of technology is needed, NHTSA believes that two 
years will be sufficient time. Therefore, the two year lead time is 
being retained in the final rule. Compliance will be required 24 months 
from the date of publication of this rule in the Federal Register.

G. Miscellaneous Issues

1. Metric System Units
    Section 5164 of the Omnibus Trade and Competitiveness Act (Pub. L. 
100-418) and Executive Order 12770 direct Federal agencies to use the 
metric system (SI, the International System of Units) where possible in 
rulemakings. Therefore, the values that were proposed in English system 
units in the SNPRM are adopted using SI units. To facilitate cross-
reference to the preceding notices, approximate English system 
equivalent measurements follow the SI measurements in the preamble. 

[[Page 2029]]

2. Federal Highway Administration Rulemaking on Underride Guards
    Many commenters, mostly private citizens, requested that NHTSA make 
this rule apply to existing trailers, thus requiring that the owners of 
those trailers remove the FHWA-required guards and retrofit the 
trailers with improved underride guards. The law firm of Lipman and 
Katz, Mr. Byron Bloch, and many others requested that NHTSA mandate 
retrofit of existing trucks.
    NHTSA has no authority to issue such requirements. Authority to 
regulate existing trucks rests with the Federal Highway Administration. 
Some commenters realized this. The New York Attorney General said there 
is no excuse for not coordinating with FHWA and arranging for a 
parallel and simultaneous rulemaking by that agency for existing 
trucks. The American Truck Dealers Division of the National Automobile 
Dealers Association requested that NHTSA encourage FHWA to require 
retrofit.
    FHWA has worked with NHTSA to ensure that its standards are 
compatible with the Federal Motor Vehicle Safety Standards whenever 
possible. As part of this effort, FHWA will continue to adopt 
appropriate sections of NHTSA's standards into the Federal Motor 
Carrier Safety Regulations (FMCSR). FHWA is considering a rulemaking to 
amend the FMCSR at 49 CFR 393.86, Parts and Accessories Necessary for 
Safe Operation, to require vehicles which are subject to NHTSA's rear 
impact guard requirements to maintain the devices. As part of that 
rulemaking, FHWA will determine if retrofitting of existing vehicles 
with rear impact guards should be required.

XII. Rulemaking Analyses and Notices

A. Executive Order 12866 (Federal Regulation) and Regulatory Policies 
and Procedures

    This rulemaking action was reviewed under Executive Order 12866. 
The action has been determined to be ``significant'' under Executive 
Order 12866 and under the Department of Transportation regulatory 
policies and procedures because it concerns a matter in which there is 
substantial public interest. The FRE for this rule describes the 
economic and other effects of this rulemaking action in detail. A copy 
of the FRE has been placed in the docket for public inspection.
    The cost and benefit information for this rule can be summarized as 
set forth below. Rear impact guards meeting the requirements of this 
rule would cost approximately $128 to $148 per trailer or semitrailer. 
This cost includes an incremental increase (above the cost of current 
rear impact guards) of between $77 and $96 per guard to satisfy the 
rear impact guard and rear impact protection requirements. An 
additional estimated cost of $7.00 per trailer may be needed to 
reinforce the frame of the trailer, depending on guard design. To 
repair the horizontal member of the guard when damaged, NHTSA estimates 
an incremental increase in lifetime maintenance/repair costs of $16.44. 
An added lifetime present value fuel cost of approximately $23.05 is 
estimated, based on the added mass of the guard (an incremental 
increase of approximately 25 kg or 55 lbs). The added weight will also 
cause a revenue loss due to payload displacement of $0.33 over the life 
of the trailer. There will be an additional cost for compliance testing 
of the guard (excluding the cost of the test fixture), which is 
estimated to be between $1.16 and $1.46 per vehicle. The incremental 
cost increase of the guard will be less than two percent of the trailer 
retail cost. NHTSA estimates that the total consumer cost of the rule 
will be about $11.9 to 13.7 million annually.
    The agency estimates that 4 to 15 PCI fatalities will be eliminated 
annually by this rule when it is in full effect and all vehicles to 
which it is applicable are in compliance. The estimate of fatality 
reduction is based on the number of passenger vehicle occupants killed 
in PCI collisions. It is also based on an estimate that the rear impact 
guard is 10 to 25 percent effective in reducing PCI fatalities. There 
will also be non-PCI underride fatalities prevented but the agency was 
unable to quantify them. NHTSA further estimates that 29 non-minor 
injuries (AIS 2-5) and 145 minor injuries (AIS 1) would be prevented in 
both PCI and non-PCI collisions.

B. Regulatory Flexibility Act

    NHTSA has analyzed the potential impacts of this rule on small 
entities under the Regulatory Flexibility Act and certifies that this 
rule will have a significant economic impact on a substantial number of 
small entities. NHTSA has described those possible impacts in the FRE, 
which is, in part, a regulatory flexibility analysis.
    The agency seeks to reduce the severity of underride crashes by 
improving the design of the affected vehicle, the trailer or 
semitrailer. Accordingly, trailer and semitrailer manufacturers will be 
affected by the rule. Based on the 1994 AAMA Motor Vehicle Facts and 
Figures, there were approximately 327 trailer and semitrailer 
manufacturers in the U.S. in 1991, most of which are small 
manufacturers (less than 500 employees). These manufacturers will be 
required to produce each of their vehicles with a rear impact guard and 
ensure that the guard is positioned within the specified distances from 
the ground, the vehicle's sides, and the vehicle's rear extremity. If 
the vehicle manufacturers obtain a guard from a supplier, they will 
only have to install the guard in accordance with the installation 
instructions provided with the guard. If the vehicle manufacturers 
produce their own guards, they will have to ensure that the guards meet 
the rear impact requirements for guards.
    The agency has designed this rule to minimize the impact on small 
businesses by issuing separate equipment and vehicle standards. This 
issuance of two separate standards relieves small trailers 
manufacturers of the necessity for testing their completed trailers. 
Rear impact guard suppliers as well as vehicle manufacturers which 
manufacture their own guards may test mount guards on a test fixture to 
assess for compliance with the strength and energy absorption 
requirements of the equipment standard. This compliance test option 
minimizes the cost impact on small entities in a manner consistent with 
the purposes of 49 U.S.C. Chapter 301.

C. Executive Order 12612 (Federalism)

    Based on available information, the agency believes the federalism 
implications of this rulemaking are minimal. Nearly all states require 
underride protection guards for heavy trailers and semitrailers. 
Further, most states require that the guards meet certain configuration 
requirements, or that they be positioned in a certain location relative 
to the rear and sides of the vehicle. The rule will preempt State 
requirements for rear impact protection. However, the agency believes 
that federalism implications will be minor because the guards required 
by this rulemaking are not fundamentally different from those required 
by State law. Several States including Michigan, North Carolina, New 
York, and New Jersey require longer trailers 15 m (50 ft) to have 
guards with the configuration required by this rulemaking. For 
practical purposes, the only effect that this rulemaking would have in 
these States is to require the guards to be tested and certified for 
strength and energy absorption.
    The agency has determined that this rulemaking does not have 
sufficient federalism implications to warrant the preparation of a 
Federalism Assessment. NHTSA believes that effective rear 

[[Page 2030]]
impact protection measures can be implemented only at the national 
level. Only vehicle manufacturers can produce trailers and semitrailers 
with improved rear impact protection. The improvements required by this 
rulemaking will cause vehicle manufacturers and operators to incur 
costs that could affect their competitive position if compliance is 
voluntarily implemented by some, but not all manufacturers. This 
Federal rulemaking applies uniformly to all manufacturers and will 
ensure that the competitive position of the manufacturers will not be 
significantly affected by these safety improvements.

D. Preemptive Effect and Judicial Review

    This final rule does not have any retroactive effect. Under 49 
U.S.C. 30103(b), 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. 49 U.S.C. 30161 sets forth a procedure for judicial review of 
final rulemaking establishing, amending, or revoking Federal motor 
vehicle safety standards. That section does not require submission of a 
petition for reconsideration or other administrative proceeding before 
parties may file suit in court.

E. Paperwork Reduction Act

    The labeling and installation instructions requirements associated 
with this rule have been submitted to the Office of Management and 
Budget (OMB) for approval in accordance with 44 USC chapter 35.
    Administration: National Highway Traffic Safety Administration.
    Title: Labeling and Installation Instructions Requirements for Rear 
Impact Guards.
    Need for Information: Labeling--Identification of guards as meeting 
equipment standard for strength and energy absorption; Installation 
Instructions--Ensure that obtained guards are properly installed.
    Anticipated Use of information: Labeling--Routine trailer 
inspection by FHWA; Installation Instructions--Installation of obtained 
guards by vehicle manufacturers.
    Frequency: Labeling--On occasion; Installation Instructions--On 
occasion.
    Burden Estimate: Labeling--7,500 hrs.; Installation Instructions--
2,000 hrs.
    Average Burden Hours per Respondent: Labeling--25; Installation 
Instructions--10.
    For Further Information Contact: The Information Requirements 
Division, M-34, Office of the Secretary of Transportation, 400 Seventh 
St. SW, Washington DC 20590, (202) 366-4735.

List of Subjects in 49 CFR Part 571

    Imports, Motor vehicle safety, Motor vehicles, Rubber and rubber 
products, Tires.

    In consideration of the foregoing, 49 CFR Part 571 is amended as 
follows:

PART 571--FEDERAL MOTOR VEHICLE SAFETY STANDARDS

    1. The authority citation for part 571 continues to read as 
follows:

    Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166; 
delegation of authority at 49 CFR 1.50.

    2. A new Sec. 571.223 is added to read as follows:


Sec. 571.223  Standard No. 223; rear impact guards.

    S1. Scope. This standard specifies requirements for rear impact 
guards for trailers and semitrailers.
    S2. Purpose. The purpose of this standard is to reduce the number 
of deaths and serious injuries that occur when light duty vehicles 
collide with the rear end of trailers and semitrailers.
    S3. Application. This standard applies to rear impact guards for 
trailers and semitrailers subject to Federal Motor Safety Standard No. 
224, Rear Impact Protection (Sec. 571.224).
    S4. Definitions.
    In this standard, directional terms such as bottom, center, height, 
horizontal, longitudinal, transverse, and rear refer to directions 
relative to the vehicle orientation when the guard is oriented as if it 
were installed on a vehicle according to the installation instructions 
in S5.5 of this section.
    Chassis means the load supporting frame structure of a motor 
vehicle.
    Guard width means the maximum horizontal guard dimension that is 
perpendicular to the longitudinal vertical plane passing through the 
longitudinal centerline of the vehicle when the guard is installed on 
the vehicle according to the installation instructions in S5.5 of this 
section.
    Horizontal member means the structural member of the guard that 
meets the configuration requirements of S5.1.1 through 5.1.3 of 
Sec. 571.224, Rear Impact Protection, when the guard is installed on a 
vehicle according to the guard manufacturer's installation 
instructions.
    Hydraulic guard means a guard designed to use fluid properties to 
provide resistance force to deformation.
    Rear impact guard means a device installed on or near the rear of a 
vehicle so that when the vehicle is struck from the rear, the device 
limits the distance that the striking vehicle's front end slides under 
the rear end of the impacted vehicle.
    Rigid test fixture means a supporting structure on which a rear 
impact guard can be mounted in the same manner it is mounted to a 
vehicle. The rigid text fixture is designed to resist the forces 
applied to the rear impact guard without significant deformation, such 
that a performance requirement of this standard must be met no matter 
how small an amount of energy is absorbed by the rigid test fixture.
    S5. Requirements.
    S5.1 Cross-Sectional Vertical Height. The horizontal member of each 
guard shall have a cross sectional vertical height of at least 100 mm 
at any point across the guard width. See Figure 1 of this section.
    S5.2 Strength and Energy Absorption. When tested under the 
procedures of S6 of this section, each guard shall comply with the 
strength requirements of S5.2.1 of this section at each test location 
and the energy absorption requirements of S5.2.2 of this section at 
test location P3, as specified in S6.4 of this section. However, a 
particular guard (i.e., test specimen) need not be tested at more than 
one location.
    S5.2.1 Guard Strength. The guard must resist the force levels 
specified in S5.2.1 (a) through (c) of this section without deflecting 
by more than 125 mm.
    (a) A force of 50,000 N at test location P1 on either the left or 
the right side of the guard as defined in S6.4(a) of this section.
    (b) A force of 50,000 N at test location P2 as defined in S6.4(b) 
of this section.
    (c) A force of 100,000 N at test location P3 on either the left or 
the right side of the guard as defined in S6.4(c) of this section.
    S5.2.2 Guard Energy Absorption. A guard, other than a hydraulic 
guard, shall absorb by plastic deformation within the first 125 mm of 
deflection at least 5,650 J of energy at each test location P3. See 
Figure 2 of this section.
    S5.3 Labeling. Each guard shall be permanently labeled with the 
information specified in S5.3 (a) through (c) of this section. The 
information shall be in English and in letters that are at least 2.5 mm 
high. The label shall be placed on the forward-facing surface of the 
horizontal member of the guard, 305 mm inboard of the right end of the 
guard.
    (a) The guard manufacturer's name and address. 
    
[[Page 2031]]

    (b) The statement: ``Manufactured in ________'' (inserting the 
month and year of guard manufacture).
    (c) The letters ``DOT'', constituting a certification by the guard 
manufacturer that the guard conforms to all requirements of this 
standard.
    S5.4 Guard Attachment Hardware. Each guard, other than a guard that 
is to be installed on a vehicle manufactured by the manufacturer of the 
guard, shall be accompanied by all attachment hardware necessary for 
installation of the guard on the chassis of the motor vehicle for which 
it is intended.
    S5.5 Installation Instructions. The manufacturer of rear impact 
guards for sale to vehicle manufacturers shall include with each guard 
printed instructions in English for installing the guard, as well as a 
diagram or schematic depicting proper guard installation. The 
manufacturer of a rear impact guard for one of its own vehicles shall 
prepare and keep a copy of installation procedures applicable to each 
vehicle/guard combination for a period of one year from the date of 
vehicle manufacture and provide them to NHTSA on request. The 
instructions or procedures shall specify:
    (a) Vehicles on which the guard can be installed. Vehicles may be 
designated by listing the make and model of the vehicles for which the 
guard is suitable, or by specifying the design elements that would make 
any vehicle an appropriate host for the particular guard (e.g., 
vehicles with frame rails of certain spacing and gauge of steel).
    (b) A description of the chassis surface to which the guard will be 
attached, including frame design types with dimensions, material 
thickness, and tire track width. This description shall be detailed 
enough to permit the agency to locate and duplicate the chassis surface 
during compliance testing.
    (c) An explanation of the method of attaching the guard to the 
chassis of each vehicle make and model listed or to the design elements 
specified in the instructions or procedures. The principal aspects of 
vehicle chassis configuration that are necessary to the proper 
functioning of the guard shall be specified. If the chassis strength is 
inadequate for the guard design, the instructions or procedures shall 
specify methods for adequately reinforcing the vehicle chassis. 
Procedures for properly installing any guard attachment hardware shall 
be provided.
    S6. Guard Test Procedures. The procedures for determining 
compliance with S5.2 of this section are specified in S6.1 through S6.6 
of this section.
    S6.1 Preparation of Hydraulic Guards. For hydraulic guards, the 
horizontal member of the guard is deflected in a forward direction 
until the hydraulic unit(s) have reached the full extent of their 
designed travel or 610 mm, whichever occurs first. The hydraulic units 
are compressed before the application of force to the guard in 
accordance with S6.6 of this section and maintained in this condition 
throughout the testing under S6.6 of this section.
    S6.2 Guard Installation for Strength and Energy Absorption Tests.
    (a) The rear impact guard is attached to a test device.
    (b) The test device for the compliance test will be whichever of 
the following devices, if either was used, the manufacturer used as a 
basis for its certification of the guard in S5.3(c) of this section. If 
the manufacturer did not use one of these devices or does not specify a 
device when asked by the agency, the agency may choose either of the 
following devices--
    (1) A rigid test fixture. In the case of testing on a rigid test 
fixture NHTSA will consult the installation instructions or procedures 
to determine the surface or structure that the guard is supposed to be 
mounted to and mount it to the rigid test fixture in the same way.
    (2) A complete trailer for which installation of the guard is 
suitable, as provided in the manufacturer's installation instructions 
or procedures required by S5.5 of this section. The trailer chassis is 
secured so that it behaves essentially as a fixed object during the 
test, such that the test must be passed no matter how little it moves 
during the test.
    (c) The guard is attached in accordance with the instructions or 
procedures for guard attachment provided by the guard manufacturer for 
that guard as required by S5.5 of this section.
    S6.3 Force Application Device. The force application device 
employed in S6.6 of this section consists of a rectangular solid made 
of rigid steel. The steel solid is 203 mm in height, 203 mm in width, 
and 25 mm in thickness. The 203 mm by 203 mm face of the block is used 
as the contact surface for application of the forces specified in 
S5.2.1 (a) through (c) of this section. Each edge of the contact 
surface of the block has a radius of curvature of 5 mm plus or minus 1 
mm.
    S6.4 Test Locations. With the guard mounted to the rigid test 
fixture or to a complete trailer, determine the test locations P1, P2, 
and P3 in accordance with the procedure set forth in S6.4 (a) through 
(c) of this section. See Figure 1 of this section.
    (a) Test location P1 is the point on the rearmost surface of the 
horizontal member of the guard that:
    (1) Is located at a distance of \3/8\ of the guard width from the 
vertical longitudinal plane passing through center of the guard;
    (2) Lies on either side of the center of the guard's horizontal 
member; and
    (3) Is 50 mm above the bottom of the guard.
    (b) Test location P2 is the point on the rearmost surface of the 
horizontal member of the guard that:
    (1) Lies in the longitudinal vertical plane passing through the 
center of the guard's horizontal member; and
    (2) Is 50 mm above the bottom of the guard.
    (c) Test location P3 is any point on the rearmost surface of the 
horizontal member of the guard that:
    (1) Is not less than 355 mm and not more than 635 mm from the 
vertical longitudinal plane passing through center of the guard;
    (2) Lies on either the right or left side of the horizontal member 
of the guard; and
    (3) Is 50 mm above the bottom of the guard.
    S6.5 Positioning of Force Application Device. Before applying any 
force to the guard, locate the force application device such that:
    (a) The center point of the contact surface of the force 
application device is aligned with and touching the guard test 
location, as defined by the specifications of S6.4 of this section.
    (b) The longitudinal axis of the force application device passes 
through the test location and is perpendicular to the transverse 
vertical plane that is tangent to the rearmost surface of the guard's 
horizontal member.
    S6.6 Force Application. After the force application device has been 
positioned according to S6.5 of this section, apply the loads specified 
in S5.2.1 of this section. Load application procedures are specified in 
the S6.6 (a) through (d) of this section.
    (a) Using the force application device, apply force to the guard in 
a forward direction such that the displacement rate of the force 
application device is constant and not less than 1 mm and not more than 
1.5 mm per second.
    (b) If conducting a strength test to satisfy the requirement of 
S5.2.1 of this section, the force is applied until the forces specified 
in S5.2.1 of this section have been exceeded, or until the displacement 
of the force application device has reached at least 125 mm, whichever 
occurs first.
    (c) If conducting a test to be used for the calculation of energy 
absorption 

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levels to satisfy the requirement of S5.2.2 of this section, apply the 
force to the guard until displacement of the force application device 
has reached 125 mm. For calculation of guard energy absorption, the 
value of force is recorded at least ten times per 25 mm of displacement 
of the contact surface of the loading device. Reduce the force until 
the guard no longer offers resistance to the force application device. 
Produce a force vs. deflection diagram of the type shown in Figure 2 of 
this section using this information. Determine the energy absorbed by 
the guard by calculating the shaded area bounded by the curve in the 
force vs. deflection diagram and the abscissa (X-axis).
    (d) During each force application, the force application device is 
guided so that it does not rotate. At all times during the application 
of force, the location of the longitudinal axis of the force 
application device remains constant.

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    3. A new Sec. 571.224 is added to read as follows:


Sec. 571.224  Standard No. 224; rear impact protection.

    S1. Scope. This standard establishes requirements for the 
installation of rear impact guards on trailers and semitrailers with a 
gross vehicle weight rating (GVWR) of 4,536 kg or more.
    S2. Purpose. The purpose of this standard is to reduce the number 
of deaths and serious injuries occurring when light duty vehicles 
impact the rear of trailers and semitrailers with a GVWR of 4,536 kg or 
more.
    S3. Application. This standard applies to trailers and semitrailers 
with a GVWR of 4,536 kg or more. The standard does not apply to pole 
trailers, low chassis vehicles, special purpose vehicles, wheels back 
vehicles, or temporary living quarters as defined in 49 CFR 529.2
    S4. Definitions.
    Chassis means the load supporting frame structure of a motor 
vehicle.
    Horizontal member means the structural member of the guard that 
meets the configuration requirements of S5.1 of this section when the 
guard is installed on the vehicle according to the installation 
instructions or procedures required by S5.5 of Sec. 571.223, Rear 
Impact Guards.
    Low chassis vehicle means a trailer or semitrailer having a chassis 
that extends behind the rearmost point of the rearmost tires and a 
lower rear surface that meets the configuration requirements of S5.1.1 
through 5.1.3 of this section.
    Outer or Outboard means away from the trailer centerline and toward 
the side extremities of the trailer.
    Rear extremity means the rearmost point on a vehicle that is above 
a horizontal plane located 560 mm above the ground and below a 
horizontal plane located 1,900 mm above the ground when the vehicle is 
configured as specified in S5.1 of this section and when the vehicle's 
cargo doors, tailgate, or other permanent structures are positioned as 
they normally are when the vehicle is in motion. Nonstructural 
protrusions such as taillights, rubber bumpers, hinges and latches are 
excluded from the determination of the rearmost point.
    Rounded corner means a guard's outermost end that curves upward or 
forward toward the front of the vehicle, or both.
    Side extremity means the outermost point on a vehicle's side that 
is located above a horizontal plane 560 mm above the ground, below a 
horizontal plane located 190 cm above the ground, and between a 
transverse vertical plane tangent to the rear extremity of the vehicle 
and a transverse vertical plane located 305 mm forward of that plane 
when the vehicle is configured as specified in S5.1 of this section. 
Non-structural protrusions such as taillights, hinges, rubber bumpers, 
and latches are excluded from the determination of the outermost point.
    Special purpose vehicle means a trailer or semitrailer having work-
performing equipment (including any pipe equipment that would hold 
hazardous materials in transit and require rear-end protection under 49 
CFR 178.345-8(d)) that, while the vehicle is in transit, resides in or 
moves through the area that could be occupied by the horizontal member 
of the rear underride guard, as defined by S5.1.1 through S5.1.3 of 
this section.
    Wheels back vehicle means a trailer or semitrailer whose rearmost 
axle is permanently fixed and is located such that the rearmost surface 
of tires of the size recommended by the vehicle manufacturer for the 
vehicle on that axle is not more than 305 mm forward of the transverse 
vertical plane tangent to the rear extremity of the vehicle.
    S5. Requirements.
    S5.1 Installation; vehicle configuration. Each vehicle shall be 
equipped with a rear impact guard certified as meeting Federal Motor 
Vehicle Safety Standard No. 223, Rear Impact Guards (Sec. 571.223). 
When the vehicle to which the guard is attached is resting on level 
ground, unloaded, with its full capacity of fuel, and with its tires 
inflated and air suspension, if so equipped, pressurized in accordance 
with the manufacturer's recommendations, the guard shall comply with 
the requirements of S5.1.1 through S5.1.3 of this section. See Figure 1 
of this section.
    S5.1.1 Guard width. The outermost surfaces of the horizontal member 
of the guard shall extend outboard to within 100 mm of the longitudinal 
vertical planes that are tangent to the side extremities of the 
vehicle, but shall not extend outboard of those planes. See Figure 1 of 
this section.
    S5.1.2 Guard height. The vertical distance between the bottom edge 
of the horizontal member of the guard and the ground shall not exceed 
560 mm at any point across the full width of the member. 
Notwithstanding this requirement, guards with rounded corners may curve 
upward within 255 mm of the longitudinal vertical planes that are 
tangent to the side extremities of the vehicle. See Figure 1 of this 
section.
    S5.1.3 Guard rear surface. At any height 560 mm or more above the 
ground, the rearmost surface of the horizontal member of the guard 
shall be located as close as practical to a transverse vertical plane 
tangent to the rear extremity of the vehicle, but no more than 305 mm 
forward of that plane. Notwithstanding this requirement, the horizontal 
member may extend rearward of the plane, and guards with rounded 
corners may curve forward within 255 mm of the longitudinal vertical 
planes that are tangent to the side extremities of the vehicle.
    S5.2 Installation Requirements. Guards shall be attached to the 
vehicle's chassis by the vehicle manufacturer in accordance with the 
installation instructions or procedures provided pursuant to S5.5 of 
Standard No. 223, Rear Impact Guards (Sec. 571.223). The vehicle must 
be of a type identified in the installation instructions as appropriate 
for the guard.

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    Issued on January 16, 1996.
Ricardo Martinez,
Administrator.
[FR Doc. 96-682 Filed 1-17-96; 4:42 pm]
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