[Federal Register Volume 61, Number 109 (Wednesday, June 5, 1996)]
[Proposed Rules]
[Pages 28550-28560]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-14145]



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DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration

49 CFR Part 571
[Docket No. 91-68; Notice 5]
RIN 2127-AC64


Federal Motor Vehicle Safety Standards; Rollover Prevention

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

ACTION: Denial of petitions for reconsideration.

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SUMMARY: This notice announces the denial of petitions for 
reconsideration of the agency's decision to terminate rulemaking to 
develop a vehicle rollover stability standard.

FOR FURTHER INFORMATION CONTACT: The following persons at the National 
Highway Traffic Safety Administration, 400 Seventh Street, S.W., 
Washington, D.C. 20590:
    For non-legal issues: Gayle Dalrymple, Office of Crash Avoidance 
Standards, telephone (202) 366-5559, facsimile (202) 366-4329.
    For legal issues: Steve Wood, Office of the Chief Counsel, NCC-20, 
telephone (202) 366-2992, facsimile (202) 366-3820.

SUPPLEMENTARY INFORMATION:

I. 1994 Notice Terminating Rulemaking on a Vehicle Rollover 
Stability Standard

    On June 28, 1994, NHTSA published a notice in the Federal Register 
announcing two agency actions: (1) the termination of rulemaking to 
develop a Federal Motor Vehicle Safety Standard on vehicle rollover 
stability; and (2) the proposal of a consumer regulation for labeling 
vehicles with rollover stability information. (59 FR 33254)
    In the portion of the 1994 notice terminating rulemaking, the 
agency examined the suitability of using a variety of vehicle stability 
metrics <SUP>1 as a basis for a rollover standard. NHTSA concluded that 
two such metrics, tilt table angle (TTA) <SUP>2 and critical sliding 
velocity (CSV),<SUP>3 can each separately account for approximately 
half of the variability in rollover risk in single vehicle accidents 
remaining after considering driver, roadway, and environmental factors. 
NHTSA stated:

     <SUP>1  A vehicle stability metric is a measured vehicle 
characteristic that is analyzed to determine whether it is related 
to a vehicle's likelihood of rollover involvement.
     <SUP>2  The tilt table test involves placing the vehicle on a 
platform which is then tilted about an axis parallel to the 
vehicle's longitudinal axis. TTA is the angle at which the last tire 
on the upper side of the platform loses contact with the platform 
and the vehicle begins to fall off the platform. This metric is 
influenced by changes in a vehicle's mass, center of gravity height, 
track width, and suspension movement, all of which are physically 
related to rollover stability.
     <SUP>3  Critical sliding velocity includes the roll moment of 
inertia as well as the various static factors included in tilt table 
angle. CSV is calculated from an equation which can be found in the 
June 28, 1994 notice, as corrected on July 26, 1994 (59 FR 38038).
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    The suitability of a vehicle safety standard based on rollover 
stability depends on the importance of rollover stability, as 
represented by a vehicle metric, relative to other rollover 
influences, such as vehicle handling properties, vehicle condition, 
the nature of the roadway and shoulder terrain, and driver behavior. 
The agency sought to determine whether vehicle stability metrics are 
significant variables in a statistical model of the risk of 
rollover. If they are, then a standard regulating stability might be 
justified, depending on the results of a comparison of benefits and 
costs for such a standard.
    After analyzing a number of static and dynamic rollover metrics, 
the agency concluded that two vehicle metrics, tilt table angle and 
critical sliding velocity, can account for about 50 percent of the 
variability in rollover risk in single vehicle accidents, after 
considering driver, roadway, and environmental factors. (Rollover 
risk is the number of single vehicle rollovers involving a 
particular make/model divided by the number of single vehicle 
crashes of all types involving the same make/model.) This 
statistical analysis was conducted on all light duty vehicles 
treated as a group. However, analysis of accident data indicated 
that certain subgroups of light duty vehicles are more likely to 
roll over than other subgroups. For example, sport utility vehicles 
and compact pickup trucks tend to be the most likely vehicles to 
roll over. Large passenger cars tend to be the least likely to roll 
over.

59 FR 33254, at 33258.
    While NHTSA concluded that the two vehicle stability metrics were 
of some value in estimating the likelihood that a single vehicle 
accident involving a particular model of vehicle would result

[[Page 28551]]

in a rollover, the agency emphasized that analyses also ``show that 
other factors in addition to those analyzed are affecting rollover 
risk.'' (Id., at 33260) As the agency noted, ``[t]he suitability of a 
vehicle safety standard based on rollover stability depends on the 
importance of rollover stability, as represented by a vehicle metric, 
relative to other rollover influences, such as vehicle handling 
properties, vehicle condition, the nature of the roadway and shoulder 
terrain, and driver behavior.'' (Id., at 33258) In other words, the 
issue was not simply whether there is a statistical relationship, but 
also whether that relationship is strong enough, considering other 
influences, so that improvements in the stability metrics, especially 
relatively small improvements, would generate benefits commensurate 
with the costs. If the relationship is not sufficiently strong, even 
significant changes in the stability metrics may be overwhelmed by the 
other influences and thus fail to cause a significant change in 
rollover experience.
    The agency concluded that while each of the stability metrics has 
some causal relationship to the potential for rollover and a 
statistical relationship to real-world rollover frequency, a standard 
based on either of the metrics would yield measurable benefits only if 
it required that the metrics be increased to an extent that would 
impose excessive costs and necessitate radically redesigning one or 
more types of light trucks.<SUP>4 The agency reached this conclusion 
after examining the merits of establishing a single rollover standard 
for all light duty vehicles (i.e., passenger cars and light trucks).
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    \4\ The term ``light trucks'' includes sport utility vehicles, 
vans, and pickup trucks with a gross vehicle weight rating of 4,536 
kilograms (10,000 pounds) or less.
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    With respect to a single standard, the agency stated:

    The agency also determined that, considering the costs and 
benefits involved, proposing a safety standard specifying a single 
minimum stability value for both cars and light trucks could not be 
justified. While light trucks have lower stability measurements than 
cars do, the greatest number of rollover-related deaths and injuries 
occur in passenger cars because of their larger population size. 
Therefore, if the agency wished to set a stability minimum high 
enough to realize significant reductions in the number of fatalities 
in all light duty vehicles, it would have to set the minimum above 
the stability number of most light trucks. The costs of such a 
standard, in terms of the cost of vehicle redesign and the loss of 
consumer-desired attributes, were determined to be very high, as 
entire classes of light trucks would probably need to be 
substantially redesigned to meet such a standard. This redesign 
could result in the elimination of some vehicle types, e.g., sport 
utility vehicles, as they are known today.

Id., at 33258.

    To avoid such drastic consequences for light trucks, the agency 
considered whether it would be appropriate to set one standard for cars 
and separate standards for various classes of light trucks.<SUP>5 NHTSA 
concluded that it was not appropriate. Since its analysis of the 
ability of the two vehicle stability metrics to account for the 
variability in rollover risk in single vehicle accidents was conducted 
on all light duty vehicles as a group, the agency examined the ability 
of the metrics to account for variability within individual subgroups 
of those vehicles. Regarding the results of that examination, NHTSA 
stated:

    \5\ Id., at 33258.
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    [I]t was necessary to determine whether either of the stability 
metrics exhibited sufficiently high levels of correlation to assure 
the agency that a requirement applying to only one class of vehicle 
would be expected to reduce the incidence of rollovers for vehicles 
in that class. * * * [T]he agency found that the statistical 
correlations of the metrics with rollover accident data within a 
class of vehicles was not so consistent as for all vehicles grouped 
together. This weakening of the predictive ability of the metric is, 
to some extent, the result of the smaller range of the metric within 
any class of vehicles together with the inherent variability in the 
data. Based on this analysis, and the general analysis of costs and 
benefits discussed later, the agency determined that proposing a 
standard specifying one minimum stability value for cars and others 
for various classes of light trucks could not be justified.

Id., at 33528.

II. Petitions for Reconsideration of Decision To Terminate 
Rulemaking

    In July 1994, the agency received two petitions for reconsideration 
of its decision to terminate rulemaking on a rollover stability 
standard. One petition was submitted by Advocates for Highway and Auto 
Safety and the Insurance Institute for Highway Safety (Advocates/IIHS) 
and the other by Randall and Sandy Vance, Doug White, and Robert and 
Glenda Cammack (Vance, et al.). Both petitions asked NHTSA to 
reconsider its decision to terminate rulemaking to establish a minimum 
standard for vehicle rollover stability. The Vance et al. petition 
expressed general disagreement with that decision, while the Advocates/
IIHS petition identified detailed points of disagreement. For this 
reason, unless otherwise specified, references below to ``the 
petition'' or ``the petitioners'' are references to the Advocates/IIHS 
petition.
    While the petitioners made numerous contentions, they focused on 
four general areas: the character of a reasonable rollover standard, 
the agency's statistical analysis of how a standard could be selected, 
the agency's benefit calculations, and the agency's statements 
concerning cost burden to the manufacturing industry. The following is 
a summary of the more important contentions addressed in this notice 
and the appendix to this notice:
    <bullet> NHTSA should have more thoroughly considered establishing 
separate standards for separate classes of vehicles.
    <bullet> To achieve a better relationship between costs and 
benefits, NHTSA should have considered the alternative of setting a 
standard for the most rollover-prone vehicles within one or more of the 
following groups: sport utility vehicles (SUVs), vans, and pickup 
trucks.
    <bullet> Compact SUVs <SUP>6 are the most rollover prone group of 
light duty vehicles.
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    \6\ The vehicles considered compact SUVs in NHTSA's analysis 
were: Ford Explorer, Chevy S10 Blazer, Jeep Cherokee, Jeep Wrangler, 
Toyota 4-Runner, Nissan Pathfinder, Geo Tracker, GMC S-15 Jimmy 
(essentially a twin of the Blazer), Isuzu Trooper, Isuzu Rodeo, 
Suzuki Sidekick (essentially a twin of the Tracker), Mazda Navaho 
(essentially a twin of the 4WD Explorer), Mitsubishi Montero, Isuzu 
Amigo, and Suzuki Samurai.
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    <bullet> Minor vehicle changes (e.g., suspension changes) could be 
used to achieve stability improvements at reasonable cost.
    <bullet> NHTSA did not provide any factual support for its 
assertion that there are serious safety problems associated with 
improving vehicle stability metrics through suspension changes.
    <bullet> NHTSA did not explain the nature and extent of the major 
design changes that it said were necessary to meet any stability 
metric, nor how much such changes would cost.
    <bullet> The level of projected benefits of a rollover standard was 
understated by the agency because it:
    <bullet> used average class values in lieu of model specific 
rollover accident data for the rollover experience of some vehicle 
models;
    <bullet> used inappropriate statistical measures; and
    <bullet> viewed rollover prevention as accident mitigation instead 
of accident prevention.
    <bullet> Although Congress did not mandate the issuance of a 
rollover stability standard, it expected that such a standard would be 
issued.
    <bullet> Contrary to NHTSA's position, the statute governing the 
agency's vehicle

[[Page 28552]]

safety rulemaking readily permits the elimination of a class of 
vehicles widely accepted in the marketplace.
    <bullet> The agency may not consider the policy concerns underlying 
the Regulatory Flexibility Act without preparing a regulatory 
flexibility analysis.

III. Response To Petitions for Reconsideration

    In response to the petitions, the agency has reconsidered its 
decision to terminate rulemaking on a rollover stability standard. As 
explained below, the agency is, on reconsideration, reaffirming that 
decision.
    The petitions raise several points that are not disputed by NHTSA; 
however, they do not compel the conclusion that NHTSA should establish 
a rollover standard based on vehicle stability metrics. For example, 
the agency agrees that single vehicle rollover is a significant safety 
problem. NHTSA also agrees that the two vehicle stability metrics are 
useful in estimating the likelihood that a single vehicle accident 
involving a particular model of vehicle will result in a rollover.
    Finally, the agency agrees that it is appropriate in determining 
the desirability of a rollover standard to consider a rollover standard 
regulating vehicles in the most rollover-prone groups. While the 1994 
notice focused primarily on the approach of a single standard for all 
light duty vehicles, the agency did analyze separate standards for 
separate classes of vehicles. The notice explained that the predictive 
ability of the vehicle stability metrics decreased as the vehicle 
population was divided into smaller groups. As noted above, the agency 
concluded that ``a standard specifying one minimum stability value for 
cars and others for various classes of light trucks could not be 
justified.'' (Id., at 33257). Since the petitioners suggest issuing a 
rollover standard regulating the most rollover-prone vehicles, NHTSA 
has focused on such an approach in responding to the petitions for 
reconsideration. The agency agrees with the petitioners that, in 
theory, the comparatively high rollover rate of compact SUVs makes a 
standard regulating that group of vehicles appear more likely to 
generate benefits commensurate with its costs than would a standard 
regulating any other group of vehicles.
    These areas of agreement are insufficient, however, to lead the 
agency to the conclusion reached by petitioners. To the contrary, the 
agency's detailed analysis below of a rollover stability standard based 
on TTA or CSV demonstrates that the costs and other impacts of such a 
standard manifestly outweigh the estimated but uncertain benefits.
    A general response to the petitioners' arguments appears below. 
Certain issues are covered in greater detail in the Appendix to this 
notice.

IV. Rationale for Reaffirming Decision To Terminate

A. Summary

    Following its examination of the arguments raised by the 
petitioners, the agency has revisited and, in some respects expanded, 
its rationale for terminating rulemaking on a vehicle stability 
standard. The agency again concludes that it is not appropriate to 
establish a vehicle rollover stability standard based on a vehicle 
stability metric.
    If a stability standard were set at a level that would require only 
minor vehicle changes in order for the affected models to achieve 
compliance, the standard would not produce any safety benefits. Minor 
vehicle changes, which consist predominately of suspension changes, 
would not produce significant improvements in the vehicle stability 
metrics and would not be likely to result in any reductions in 
fatalities and injuries.\7\ Moreover, there is reason to conclude that 
such suspension changes would, in fact, produce negative safety side 
effects.
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    \7\ As noted above, the agency stated in the 1994 notice that a 
standard limited in its application to a vehicle subgroup (e.g., 
sport utility vehicles) is particularly unlikely to reduce 
fatalities and injuries given the weaker statistical relationships 
between the stability metrics and the rollover involvement for 
vehicle subgroups. (Id., at 33528)
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    If a stability standard were set high enough to require significant 
improvements in the vehicle stability metrics, it would necessitate 
full vehicle redesigns and major vehicle changes. However, the safety 
benefits of such changes would nevertheless be relatively modest. 
Moreover, the overall costs and loss of consumer choice resulting from 
full vehicle redesigns involving major vehicle changes would be 
substantial and excessive. On balance, the potential for improved 
vehicle safety associated with such improvements in the vehicle 
stability metrics is not sufficiently large to justify such redesigns.

B. Vehicle Changes To Increase Vehicle Stability Metrics

    There are two general categories of vehicle changes that would 
increase the vehicle stability metrics (TTA and CSV). One consists of 
relatively minor vehicle changes (i.e., suspension changes); the other, 
of major vehicle changes (i.e., widening the vehicle track and lowering 
the center of gravity) that could only be achieved through full 
redesign of the vehicle. The petitioners appear to believe that a 
vehicle can be redesigned so it will be significantly less likely to 
roll over, that the means for accomplishing this will be ``invisible'' 
to the consumer, and that the vehicle will look and function as it did 
before the redesign. As discussed below, redesigning a vehicle to 
significantly reduce its likelihood of rolling over necessarily 
involves making fundamental changes in the vehicle's dimensions (making 
it wider, longer, lower, heavier) and compromising its utility to 
consumers (e.g., by reducing its fuel efficiency, ground clearance, 
load-carrying capacity, off-road capability, or driveability on snowy 
roads).
1. Minor Vehicle Changes To Increase Vehicle Stability Metrics
    Minor vehicle changes have very little effect on the vehicle 
stability metrics. Moreover, they do not result in net safety 
improvements.
    As the petitioners correctly point out, the Preliminary Regulatory 
Evaluation (PRE) for the 1992 Advance Notice of Proposed Rulemaking 
(ANPRM) suggested that there were grounds for optimism about the 
ability of minor vehicle changes, such as suspension tuning, to affect 
stability metrics and improve rollover stability. (57 FR 242; January 
3, 1992) However, after reviewing the comments on the 1992 ANPRM, the 
agency concluded in the 1994 notice that minor vehicle changes could 
not, in fact, significantly affect the vehicle stability metrics. 
Comments from Advocates itself,\8\ as well as Ford and General Motors, 
on the ANPRM indicate that suspension changes result in very little 
improvement in rollover stability.
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    \8\ In commenting on the ANPRM, Advocates indicated that it did 
not share the agency's optimism at that time about the desirability 
of relying on suspension changes to improve rollover stability 
metrics. Advocates commented that the selection of TTR as the 
parameter to be regulated would ``permit a manufacturer to attempt 
manipulation of other stability-related elements of the vehicle's 
design, such as its suspension, in order to secure a barely passing 
tilt- table score.'' It also expressed concern that the agency ``may 
be already tending towards selection of TTRs [see footnote 12] that 
will not move the industry towards safer overall vehicle designs, 
particularly with regard to wheelbase, width, length, and center of 
gravity height, but rather will encourage the perpetuation of the 
status quo designs especially with regard to very small cars, small 
pickups, and SUVs that will continue to show high rollover 
propensities.''
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    Moreover, vehicle rollover stability is not the same as vehicle 
handling and control. Some measures that improve

[[Page 28553]]

TTA or CSV do not necessarily result in improved directional control 
and stability. Available information suggests that directional control 
and stability would be adversely affected as a result of relying upon 
suspension changes to make small increases in the vehicle stability 
metrics. This information was supplied in comments from Advocates, 
Ford, and General Motors on the ANPRM expressing concern with the side 
effects of suspension changes to improve TTA.
    For example, Ford used a computer simulation of a compact pickup 
truck to evaluate the effect of a series of suspension changes on 
directional stability and side-to-side load transfer in cornering. 
(Docket 91-68-N01-21) Ford evaluated substantial suspension changes, 
including a 30 percent increase in spring rates, removal of stabilizer 
bars, and a change in the front suspension roll center by 1.5 inches. 
It also examined a ride height change that would lower the center of 
gravity by 0.5 inch. Ford noted that, in general, tuning a suspension 
system such that both the front and rear tires lift from the tilt table 
simultaneously would maximize the TTA. However, this optimization 
requires either decreasing the front roll stiffness (by removing the 
front stabilizer bar), or increasing the rear roll stiffness (by using 
a 30 percent greater rear spring rate). The simulation showed that, 
among the suspension changes examined by Ford, these two changes made 
the greatest improvements in TTA (an increase of 0.62 and 0.55 degrees, 
respectively). However, these changes were also shown to alter 
directional stability toward oversteer (i.e., these changes tend to 
make a vehicle turn more sharply than a driver intends). Ford's 
simulation showed that other suspension changes, such as an increase in 
front spring rate or a decrease in front roll center height, could 
increase TTA (to a lesser degree than those mentioned above), while 
altering directional stability toward understeer (i.e., these changes 
tend to make a vehicle turn less sharply that a driver intends). The 
only minor change mentioned by Ford in its comment which improved TTA 
without influencing directional stability was lowering the vehicle c.g. 
height by 0.5 inch, resulting in only a 0.17 degree increase in TTA.
    Based on its consideration of such comments, the agency concludes 
that suspension changes would not produce significant improvements in 
rollover stability and would have the potential to cause undesirable 
changes in directional stability and handling, which in turn could lead 
to an increase in crashes. In view of this conclusion, the agency has 
not examined whether those changes could be made at a reasonable cost, 
since they are unlikely to yield net safety benefits.
2. Major Vehicle Changes To Increase Vehicle Stability Metrics
    Thus, significant improvements to the vehicle stability metrics 
could be achieved only through making major changes to the vehicle 
chassis and body to increase the track width and/or lower the center of 
gravity. These major changes would require full vehicle redesigns that 
substantially change the parameters affecting vehicle stability 
metrics. The necessary extent of such redesigns is illustrated in the 
following example. Given that the center of gravity height for a 
typical compact SUV <SUP>9 is 27 inches, to raise its TTA (42.9 
degrees) to that of the typical full- size SUV (46.4 degrees), it would 
be necessary to increase the track width (i.e., the distance between 
the left and right tires on an axle) more than 6 inches. Further, such 
a track width increase would require a corresponding wheelbase (i.e., 
the distance between the front and rear axles) lengthening of 10 inches 
to retain the braking stability of the smaller SUV. As noted later in 
the sections regarding cost and impact on consumer choice, such 
modifications would eliminate most of the compact SUVs as they 
currently exist, converting the typical compact SUV into a full-size 
SUV.
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    \9\ A ``typical compact SUV'' and a ``typical full-size SUV'' 
are hypothetical vehicles with the average TTA and dimensions of all 
the vehicles in their class.
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    Citing the example of the GMC Jimmy, which was redesigned for 1995, 
petitioners argued that vehicle manufacturers can gradually redesign 
their compact SUVs so as to increase their vehicle stability. The 
petitioners presented an article from Automotive News stating that the 
new Jimmy is longer, lower, and wider than its predecessor.<SUP>10 The 
petitioners further attributed to the new Jimmy ``a chassis 
modification that can result in better stability metrics and in lower 
rollover crash rates.'' <SUP>11
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    \10\  Advocates/IIHS petition, attachment 2.
     <SUP>11  Advocates/IIHS petition, page 18.
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    NHTSA draws a very different lesson than do petitioners from the 
example of the Jimmy. In the agency's view, the petitioners 
underestimate the extent to which the parameters affecting a vehicle's 
stability metrics must be changed to significantly improve those 
metrics. As explained below, the overall lessons of the new Jimmy are 
that even a significant partial redesign of a vehicle will change its 
vehicle stability metrics little in the absence of major changes to the 
vehicle's c.g. height and track width, and that even minor changes in 
those parameters may come at the cost of adversely affecting other 
attributes desired by consumers. For example, the new Jimmy is heavier 
and more costly than the prior model.
    The agency agrees that the vehicle stability metrics of the new 
Jimmy are likely to be somewhat better than those of the old Jimmy. 
Although the agency has no TTA or CSV data on the new design, its lower 
body height and wider track suggest that it has a slightly better TTA 
than its predecessor and its longer, wider, and heavier body suggests 
that it may have a greater roll moment of inertia and, therefore, a 
slightly greater CSV.
    However, the increases in the Jimmy's vehicle stability metrics are 
likely to be very small. The reason is that the changes made to the 
parameters affecting those metrics were relatively minor. Although the 
changes increased the size and weight of the Jimmy, the magnitude of 
those changes fell short of the levels needed to make a significant 
improvement in its TTA or CSV. The body height of the 2WD model was 
reduced by 1.6 inches, but the associated reduction in center of 
gravity height is likely to be much less, since the location of the 
engine, drive train, suspension, and passenger accommodation component 
masses remained unchanged. The height reduction of the 4WD model was 
only 0.8 inches. Likewise, the body width was increased by 2.4 inches, 
but the front and rear track widths of the 4WD model were increased 
less: 1.6 and 1.0 inches, respectively. The 2WD model track width 
increases were even less: 0.9 inch at the front and 0.5 inch at the 
rear.
    Taken together, these changes to the Jimmy's parameters affecting 
the rollover stability metrics are very minor compared to the ones 
described above as being necessary for a typical compact SUV to achieve 
a TTA of 46.4 degrees. Thus, these changes predict at best a very small 
improvement in TTA or CSV.
    The impact of such small improvements in vehicle stability metrics 
on rollover risk is unknown. Since this is a new model for 1995, 
neither NHTSA nor the petitioners have data on the rollover experience 
of the new Jimmy. There is no way to know at this time if the changes 
will actually lead to a reduced risk of rollover.

C. Benefits of Improvements in Vehicle Stability Metrics

    NHTSA's 1994 notice estimated that the benefits of a rollover 
standard requiring a TTA of 46.4 degrees for all light duty vehicles 
included a modest

[[Page 28554]]

amount of benefits for compact SUVs. The agency's estimate that 63 
fatalities and 61 serious injuries might be prevented for all light 
duty vehicles included the prevention of 31 fatalities and 22 serious 
injuries for compact SUVs. The potential compact SUV benefits were 
predominately attributable to those particular compact SUV models that 
would require significant changes in track width and/or center of 
gravity height to achieve the required TTA.
    As part of its review of the petitions, the agency recomputed its 
estimate of the benefits of making significant design changes in order 
to raise the TTR <SUP>12 of compact SUVs to 1.05,<SUP>13 using data 
that were not available for some makes and models when the analysis was 
done for the 1994 notice.<SUP>14 The agency estimates that, using the 
more current data and certain optimistic assumptions (discussed below), 
22 serious injuries and 32 fatalities might be prevented annually if 
all new compact SUVs were redesigned to the extent necessary so that 
each vehicle in that class had a TTR of 1.05 and if all existing 
compact SUVs with a lower TTR were retired from the vehicles-in-use 
fleet. The potential benefits for a rollover stability standard are 
computed by considering:
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     <SUP>12  TTR is the tangent of TTA. In its analysis prior to 
the 1994 notice, the agency used TTR. Because TTA is an easier 
concept to depict on labels for the general public, the agency 
proposed the use of TTA rather than TTR for the vehicle label under 
a consumer information regulation that was proposed in the 1994 
notice. NHTSA used TTA throughout the 1994 notice for that reason. 
However, NHTSA has not converted the TTR values to TTA values when 
discussing its statistical and benefits analyses in this document.
     <SUP>13  A TTR of 1.05 is the equivalent of a TTA of 46.4 
degrees. On page 33261 of the 1994 notice, the agency explained 
that, if the agency were to adopt a rollover stability standard 
applicable to all vehicles, a TTA of 46.4 degrees was the highest 
practicable standard. The agency explained that a TTA of 46.4 
degrees is representative of the average full-size SUV. Since the 
design changes to increase TTA to that level would cause a compact 
SUV to approach the size of full-size SUVs, establishing any higher 
standard, whether for all vehicles or for compact SUVs alone, would 
lead to the virtual elimination of compact SUVs as that class 
currently exists.
     <SUP>14  The recomputation was performed using the same 
procedures used for the 1994 estimates and explained in detail in 
the document ``Potential Reductions in Fatalities and Injuries in 
Single Vehicle Rollover Crashes as a Result of a Minimum Rollover 
Stability Standard.'' That document is in Docket 91-68; Notice 3. 
However, while the procedures were the same, an expanded set of data 
(the number of rollover accidents and single vehicle accidents) were 
used in the recomputation to increase its accuracy. The use of the 
new data adequately addresses the petitioners' concerns about the 
agency's use in the 1994 notice of weighted averages for models for 
which there was insufficient data to determine the actual rollover 
rate.
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    (1) The reduction of rollovers per single vehicle accident (RO/SVA) 
predicted for increases in TTR;
    (2) The number of single vehicle accidents experienced by vehicles 
that would need to be altered in order to comply with the standard; and
    (3) The degree of harm mitigation (in the number of fatalities and 
serious injuries) as a result of rollover prevention given that a 
single vehicle accident has occurred.
    The following table, corresponding to Table 1 of the document 
``Potential Reductions in Fatalities and Injuries in Single Vehicle 
Rollover Crashes as a Result of a Minimum Rollover Stability 
Standard,'' contains the results of this latest computation. For an 
explanation of the headings and entries in the table, see that 
document.

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                                                                                                                                 Est %                          Projected     AIS3 +    Fatality
                                                                                MY 1991                  1986-88 5    1986-90      of    Est AIS3      Est       RO/SVA @   reduction  reduction
            Compact SUV make model                         Drive              production      TTR      state SVA/RV   Michigan  compact      +     fatalities    min TTR    @ min TTR  @ min TTR
                                                                                                                       RO/SVA   SUV ROs  injuries                  1.05        1.05       1.05  
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Vehicle A....................................  2 WD*\15\                          65,515        0.88   **\16\0.0068    **0.359        6        39         28         0.270        9.6        6.9
                                               4 WD                              184,554        0.88      **0.0068     **0.359       16       110         79         0.270       27.2       19.5
Vehicle B....................................  2 WD                               29,480        0.95        0.0103       0.342        4        25         18         0.280        4.6        3.3
                                               4 WD                               93,866        0.99      **0.0102        0.27        9        63         45         0.244        6.1        4.4
Vehicle C....................................  2 WD*                              19,920        1.08        0.0091       0.317        2        14         10   ...........  .........  .........
                                               4 WD                              101,541        1.08        0.0091       0.317       11        71         51   ...........  .........  .........
Vehicle D....................................  2 WD                                    0  ...........  ............  .........  .......  ........  ..........  ...........  .........  .........
                                               4 WD                               46,478        1.03        0.0163       0.273        8        50         36         0.263        1.8        1.3
Vehicle E....................................  2 WD*                               4,892        1.01        0.0211       0.362        1         9          7         0.338        0.6        0.4
                                               4 WD                               39,989        1.01        0.0211       0.362       11        74         53         0.338        4.9        3.5
Vehicle F....................................  2 WD*                               3,555        0.93      **0.0215     **0.315        1         6          4         0.258        1.1        0.8
                                               4 WD                               35,945        0.93      **0.0215     **0.315        9        59         42         0.258       10.8        7.7
Vehicle G....................................  2 WD                                    0  ...........  ............  .........  .......  ........  ..........  ...........  .........  .........
                                               4 WD                               30,702        0.978  ............      0.394        5        31         22         0.348        3.6        2.6
Vehicle H....................................  2 WD                                6,479        0.95        0.0114       0.259        1         5          3         0.219        0.7        0.5
                                               4 WD                               23,515        0.99      **0.0123       0.252        3        18         13         0.228        1.7        1.2
Vehicle I....................................  2 WD                                    0  ...........  ............  .........  .......  ........  ..........  ...........  .........  .........
                                               4 WD                               26,776        0.98   ............    **0.481        5        33         24         0.427        3.7        2.7
Vehicle J....................................  2 WD*                                 740        0.947  ............  .........        0         1          0         0.281        0.1        0.1
                                               4 WD                               23,870        0.947  ............  .........        3        20         15         0.281        3.3        2.1
Vehicle K....................................  2 WD*                               1,257        0.978  ............      0.407        0         2          1         0.360        0.2        0.1
                                               4 WD                               10,492        0.978  ............      0.407        2        13         10         0.360        1.6        1.1
Vehicle L....................................  2 WD                                    0  ...........  ............  .........  .......  ........  ..........  ...........  .........  .........
                                               4 WD                               11,404        0.88      **0.0068     **0.359        1         7          5         0.270        1.7        1.2
Vehicle M....................................  2 WD                                    0  ...........  ............  .........  .......  ........  ..........  ...........  .........  .........
                                               4 WD                               10,616        0.93   ............  .........        1         9          7         0.274        1.7        1.2
Vehicle N....................................  2 WD*                               5,011        1.016  ............  .........        1         4          3         0.315        0.2        0.2
                                               4 WD                                2,818        1.016  ............  .........        0         2          2         0.315        0.1        0.1
Vehicle O....................................  2 WD*                                 832        1.04   ............  .........        0         1          1         0.329        0.0        0.0
                                               4 WD                                3,546        1.04   ............  .........        0         3          2         0.329        0.1        0.0

[[Page 28555]]

                                                                                                                                                                                                
Weighted Averge..............................  .............................  ..........  ...........       0.01049      0.335  .......  ........  ..........  ...........  .........  .........
                                                                                                                                                                                                
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
      Total \17\.............................  .............................     783,783  ...........  ............  .........      100       669        480   ...........       85.0       61.0
      Total \18\.............................  .............................  ..........  ...........  ............  .........  .......  ........  ..........  ...........       22.0       32  
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\15\ An ``*'' in this column indicates that the agency lacked sufficient data for the 2WD version of the model. For these models, the agency assumed that the 2WD version had the same TTR and  
  the same rollover rate as the 4WD version.                                                                                                                                                    
\16\ An ``**'' in this column and in the next one indicates that 1988-91 Michigan accident data were used instead of the data indicated by the column heading.                                  
\17\ The serious injury and fatality reduction figures in this row are the benefits that might result if the standard prevented not only a rollover, but also an accident of any type.          
\18\ The serious injury and fatality reduction figures in this row are the benefits that might result if the standard prevented a rollover, but still allowed an injury-causing accident of some
  type to occur after the vehicle left the road. The injury and fatality figures in this row were derived by multiplying the figures in the row immediately above by a mitigation factor of 26  
  percent for injuries and 52 percent for fatalities. For further details on these factors, see section 3 of the Appendix to this notice.                                                       


    There are two optimistic assumptions incorporated in the 
computation process for both the original and new estimates: \19\
---------------------------------------------------------------------------

    \19\ The agency made these assumptions because limitations in 
available data made it impossible to use more precise values. When 
making these assumptions, the agency took an optimistic approach so 
as to present the prospects of a vehicle stability standard in the 
best possible light.
---------------------------------------------------------------------------

    <bullet> The number of rollover injuries and fatalities prevented 
will be proportional to the number of rollovers prevented; and
    <bullet> The fatality and injury rates of the late 1980's will be 
representative of future rates.
    The effect of these optimistic assumptions is that these new 
estimates, like the 1994 estimates based on the same assumptions, may 
in fact overstate the actual benefits, i.e., the number of fatalities 
and injuries likely to be prevented by improving the TTR of compact 
SUVs to 1.05.
    The first assumption assumes that the rollover accidents that would 
be prevented as a result of requiring an increase in TTR would have the 
same fatality and injury rates as rollover accidents in general. There 
is reason to believe that this would not be the case. The likelihood of 
fatalities and serious injuries in rollover accidents is heavily skewed 
toward crashes involving more than one quarter turn. Data show that 
light truck rollover crashes involving only a single quarter turn have 
about one-third the fatality rate of the average rollover. This 
difference in likelihood of harm is significant if moderately improving 
TTR would not be equally likely to prevent a multiple quarter-turn 
rollover as a single quarter-turn rollover. NHTSA believes that it is 
more likely that the prevented rollovers would tend to be the lowest 
energy rollovers, i.e., the single quarter-turn rollovers. At best, 
improving TTR would only slightly mitigate the more severe rollovers. 
Thus, by assuming that rollovers prevented by an improvement in TTR 
would be average rollovers instead of the least severe rollovers, the 
agency is overstating the benefits obtainable from such an improvement. 
Had the agency based its benefit estimates on the fatality rate of 
rollovers involving a single quarter turn, the estimated number of 
prevented fatalities would have been about 11 instead of 32.
    The second assumption, that the fatality and injury rate in 
rollovers will remain constant, is likely to overstate the benefits of 
a vehicle stability standard since, if recent trends continue, future 
increases in safety belt use, as a result of Federal, state, and local 
efforts, can reasonably be expected to reduce the overall harm from 
rollover accidents. As belt use increases, rollover casualties 
decrease, even if the number of rollover crashes remains constant.
    Consequently, even with liberal assumptions and using the most 
current and complete database available, NHTSA estimates that a 
rollover stability standard requiring compact SUVs to achieve the same 
TTR (1.05) as the typical full-size SUV would prevent 22 serious 
injuries and 32 fatalities annually. While precise quantification is 
impossible, the agency believes, for the reasons stated above, that the 
actual level of safety benefits would be significantly lower.

D. Costs of Improvements in Vehicle Stability Metrics

    The substantial vehicle redesigns necessary to enable many existing 
compact SUVs to achieve a TTR of 1.05 and produce the estimated 
reductions in fatalities and injuries discussed above would have 
substantial negative impacts, both in terms of reduced consumer choice 
and unmet preferences and in terms of increases in manufacturer and 
consumer costs.\20\ As noted above, the only way to achieve significant 
increases in TTR is to increase the track width and/or lower the center 
of gravity. Increasing track width or lowering the center of gravity, 
using conventional, commonly used designs and production methods, would 
necessarily, and significantly, increase vehicle size and weight. For 
NHTSA, in effect, to require compact SUVs to approach the size and 
weight of full-size SUVs would run counter to consumer preferences that 
have led to the existing fleet of compact SUVs. The strength of those 
preferences is demonstrated by the fact that compact SUVs outsold full-
size SUVs by a margin of six to one in 1994, the latest year for which 
the agency has sales data.\21\ The Ford Explorer, the compact SUV model 
with the lowest TTR and therefore the compact SUV which would be most 
affected by any minimum standard, is the best-selling SUV and is the 
ninth most popular make/model of all car and truck models combined.
---------------------------------------------------------------------------

    \20\ As explained in the Appendix, NHTSA made two cost 
estimates. The first was based on the assumption that compact SUVs 
needing a TTR increase of more than 0.06 would require a full 
vehicle redesign. The second was based on the assumption that only 
compact SUVs needing a TTR increase of more than 0.04 would require 
such a redesign.
    \21\ Model year 1994 sales data from Automotive News 1995 Market 
Data Book, Crain Communications, Detroit, Michigan, May 24, 1995.
    All light trucks--6,097,787 vehicles.
    Compact SUVs--21.9% of light trucks, or 1,335,415 vehicles.
    Full-size SUVs--3.6% of light trucks, or 219,520 vehicles.
---------------------------------------------------------------------------

    Upsizing compact SUVs so as to eliminate much of the size and 
weight difference between those vehicles and full-size SUVs also might 
have a significant adverse affect on the

[[Page 28556]]

production and sales of SUVs. The body of the average full-size SUV is 
currently about 10 inches wider than that of the average compact SUV, 
and the track width is about 9 inches greater. The 6-inch increase in 
track width necessary to bring the TTR of compact SUVs up to that of 
full-size SUVs (assuming no increase in c.g. height) would remove much 
of those differences between compact SUVs and full-size SUVs. Given the 
admonition in the legislative history of the National Traffic and Motor 
Vehicle Safety Act against eliminating vehicle types (see the 
discussion in section D of the Appendix to this notice), such a 
dramatic potential impact on the design of compact SUVs and on the 
market for those vehicles must be carefully weighed.
    In addition to impacts on consumer choice and sales, there are 
substantial monetary costs associated with redesigning those compact 
SUVs that would need significant increases in TTR to meet a standard of 
1.05.\22\ The agency estimated those costs using confidential cost data 
submitted by domestic automobile manufacturers during the course of 
several agency rulemaking proceedings to establish light truck 
Corporate Average Fuel Economy (CAFE) standards. The estimated consumer 
cost of bringing all such new compact SUVs into compliance with such a 
standard is between $310 million and $335 million, depending on which 
of two assumptions is made about the vehicles that would require a full 
vehicle redesign. A detailed discussion of the method used to estimate 
these costs is included in the Appendix to this notice.
---------------------------------------------------------------------------

    \22\ As demonstrated by Table 1, the vast majority of the 
measurable benefits from such a standard would come from 
improvements to these fully redesigned vehicles, instead of those 
vehicles that would need only lesser changes to comply with the 
standard.
---------------------------------------------------------------------------

    The agency believes that the foregoing estimate of the costs of a 
rollover standard requiring compact SUVs to achieve a minimum TTR of 
1.05 is understated. Those estimates do not include the incremental 
costs of material and labor involved in the manufacture of a larger 
vehicle. In addition, the estimates do not include any costs for 
vehicles that would only need minor changes, instead of a full vehicle 
redesign, to comply with the standard. NHTSA has not attempted to 
calculate those costs because the benefits of the standard are already 
outweighed by the initial cost estimate.
    The agency recognizes that providing a lengthy leadtime period 
would reduce the costs of compliance to the extent that manufacturers 
were able to make their compliance efforts coincide with their normal 
model changeover timetable. However, providing additional leadtime 
would do nothing to reduce the adverse impacts on consumer preferences. 
Further, an extended lead time would not affect the costs of additional 
labor or materials.

VI. Conclusion

    The discussion above and in the Appendix demonstrates that even a 
standard applicable only to compact SUVs, the vehicle type that the 
petitioners characterize as one of the two ``most rollover-prone 
vehicle types,'' <SUP>23 would generate substantial adverse impacts on 
manufacturers and consumers, both in terms of monetary costs and in 
loss of consumer choice, that would outweigh the benefits of such a 
standard. There is no reason to believe that a standard that would 
mandate significant increases in TTR/TTA or CSV for any other vehicle 
type or group of vehicle types would be any more cost beneficial.
---------------------------------------------------------------------------

     <SUP>23  Advocates/IIHS petition, page 12.
---------------------------------------------------------------------------

    Accordingly, NHTSA reaffirms its decision to terminate this 
rulemaking without proposing a rollover stability performance standard.

    Issued on May 31, 1996.
Barry Felrice,
Associate Administrator for Safety Performance Standards.

Appendix

    The Advocates/IIHS petition contained many detailed technical 
arguments. Responses to the more significant ones are provided in 
this appendix.

A. The Benefits Estimate

1. Replacing Weighted Averages With Actual Rollover Data Now Available 
Makes No Appreciable Change in the Estimate

    The petitioners criticized the benefit estimates made by the 
agency in connection with the 1994 notice because, for those vehicle 
models for which the agency lacked sufficient rollover accident 
data, it used the average of the rollover per single vehicle 
accident rate (RO/SVA) of the class of vehicles to which that make 
and model belonged, weighted by the 1991 production of each make and 
model for which the agency had RO/SVA. The benefits were calculated 
using the TTRs of 1991 makes and models and the accident records of 
1991 makes and models (and identical vehicles from prior model 
years) to represent a hypothetical future fleet.<SUP>1
---------------------------------------------------------------------------

     1  A detailed discussion of the method can be found in 
``Potential Reductions in Fatalities and Injuries in Single Vehicle 
Rollover Crashes as a Result of a Minimum Rollover Stability 
Standard'' in Docket 91-68, Notice 3.
---------------------------------------------------------------------------

    The petitioners pointed out that the average TTR for vehicles 
for which the agency did not have adequate RO/SVA data was lower 
than the average TTR of vehicles for which it had RO/SVA data, and 
therefore claimed that use of weighted averages was inappropriate. 
The petitioners' criticism concerning the use of weighted averages 
as substitutes for missing data was focused particularly on the use 
of those averages for the large number of vehicles in the 
hypothetical future fleet that were represented by the Ford 
Explorer. The agency had no RO/SVA or single vehicle accident 
involvement rate (SVA/RV) data for the Ford Explorer and certain 
other vehicles at the time of the notice because they were either 
recently introduced or comparatively low production volume models. 
The petitioners argued that a higher rollover rate should have been 
used for vehicles like the Explorer which have a lower TTA than the 
vehicles from which the weighted average was derived.
    It is not appropriate to assume that a higher than average 
rollover rate is appropriate for the Explorer or the other vehicles 
simply based on their having a lower than average TTA. The data 
demonstrate that the order of vehicle models ranked according to TTA 
is not the same as the order of models ranked according to rollover 
rate. See Table 1 in the accompanying notice of denial of petitions 
for reconsideration. Thus, although two different vehicle models may 
have the same TTA, they may not necessarily have the same rollover 
rate. Likewise, a vehicle model with a TTA lower than that of 
another model may nevertheless have a lower rollover rate, and vice 
versa.
    Accordingly, the agency has not assumed a higher rollover rate 
for those models for which sufficient rollover data are lacking. 
However, the agency has responded to the petitioners' concern about 
the use of weighted averages in connection with the 1994 notice by 
replacing those averages, where possible, with rates based on actual 
rollover accident data that became available after that notice was 
prepared.
    Where sufficient, the 1988--1991 Michigan accident data were 
used to calculate the rollover rate figures for models for which 
data were previously missing. Following the practice of previous 
analyses, the agency used the accident data to calculate rollover 
rates only for makes and models which had at least 25 single vehicle 
accidents. Actual rollover rates (RO/SVA) from Michigan were added 
for the 4WD Ford Explorer, Nissan Pathfinder, and Isuzu Trooper, and 
actual single vehicle accident rates (SVA/RV) were added for the 4WD 
Ford Explorer, the 4WD S10 Blazer, the Nissan Pathfinder, and the 
4WD GMC S15 Jimmy. The 4WD Explorer data were used for the nearly 
identical, but low production volume, Mazda Navajo.
    There were still some models for which the agency lacked 
sufficient actual make and model accident data. For most of these 
models, while the agency lacked sufficient data for the 2WD versions 
of those models, it had sufficient data for the more numerous 4WD 
versions. In these instances, the agency assumed that the rates for 
the 2WD versions were identical to the rates for the 4WD versions of 
the same make and model, instead of calculating rates based on 
weighted averages. New weighted averages

[[Page 28557]]

were computed on the basis of the expanded data and were used only 
where sufficient specific data remained unavailable for a particular 
model. The instances in which the agency computed new weighted 
averages were limited. Weighted averages of RO/SVA and SVA/RV were 
used for less than 10 percent and 19 percent, respectively, of the 
example population of compact SUVs. See Table 1.
    Using actual rollover data wherever available, the agency 
recomputed the benefit estimates for compact SUVs. Substitution of 
the new rollover rates produced very little change in the estimate 
of the numbers of fatalities and serious injuries that might be 
prevented if a rollover stability standard were adopted for compact 
SUVs. Replacing the weighted averages used in the 1994 notice with 
rates based on accident data for particular makes and models changed 
the result of the analysis very little, i.e., by less than four 
percent. This may be seen by comparing the estimates of the benefits 
that would be obtained if preventing a rollover meant preventing an 
accident altogether. Those benefits were estimated to be 83 serious 
injuries and 59 fatalities in the 1994 notice. They have been 
recomputed to be 85 serious injuries and 61 fatalities, based on the 
new accident data and less reliance on weighted averages. See Table 
1.

2. Accident Mitigation, Not Accident Prevention, Is the Proper Measure 
of Benefits

    Since an accident would still occur in the vast majority of 
instances in which a rollover is prevented, the agency reduced those 
figures accordingly using an accident mitigation factor. The 
resulting new benefit estimate is 22 serious injuries and 32 
fatalities.
    The petitioners criticized the agency for making the same 
adjustment to the benefits in the 1994 notice. Then, as now, NHTSA 
assumed that the benefits would come from accident mitigation 
instead of accident prevention. It was appropriate for the agency to 
assume that the benefits would be in terms of accident mitigation 
since over 90 percent of all single vehicle rollovers are off-road, 
tripped rollovers, i.e., rollovers that occur when a vehicle leaves 
the roadway sideways, encounters a tripping mechanism, and rolls. 
Since a vehicle is running off the road in a tripped rollover 
situation, such a vehicle will still likely crash into some off-road 
object even if the vehicle is prevented from rolling over after it 
leaves the road. If a rollover can be prevented in that situation, 
then the resulting accident will most likely be one of lower 
severity than if a rollover had occurred because rollovers tend to 
be more severe than non-rollover accidents. The primary benefits 
from a rollover stability standard would result from preventing the 
more severe form of off-road accident.

3. A Single Accident Mitigation Factor, Not Separate Factors for 
Individual Vehicle Types, Is the Proper Basis for Measuring Benefits

    The petitioners also criticized the agency for using a single 
accident mitigation factor (52 percent) for fatalities across the 
board instead of computing separate factors for different types of 
vehicles. In support of their argument for the use of different 
factors, they noted that rollover accidents account for 80 percent 
of the fatalities of the occupants of compact SUVs in single vehicle 
accidents. Based on this, the petitioners concluded that rollovers 
in compact SUVs are four times as deadly as non-rollover accidents, 
and therefore the agency should have used a mitigation factor of 75 
percent for compact SUVs.
    The agency rejects the petitioners' argument. A mitigation 
factor based on ratios of absolute numbers of fatalities, instead of 
on fatality rates, is incorrect unless the same number of occupants 
were exposed to rollover accidents and non-rollover accidents. If 
the exposure is not the same, then it is impossible to determine the 
extent to which the ratio reflects the difference in accident 
exposure versus a difference in accident severity. Further, the 
issue of a difference in accident severity is not just a matter of 
the difference in severity of a rollover accident and a non-rollover 
accident at the same speed. It is also a matter of possible 
differences in speed. For example, it is necessary to determine 
whether the consequences of 60 mph rollovers are being compared to 
those of 30 mph non-rollover accidents. Finally, it is also 
necessary to examine whether apparent differences between vehicle 
groups are a result of differences in crashworthiness, or just a 
consequence of smaller sample sizes.
    The agency's use of a single mitigation factor for fatalities 
takes these considerations into account. NHTSA considered the number 
of occupants exposed to rollover and non-rollover single vehicle 
accidents as well as the number of fatalities for each accident 
type. It also considered the speed limit of the road as a rough 
indication of the severity of the accident.
    As a first step in determining the mitigation factor, NHTSA 
compared the overall fatality rate of rollover accidents to the 
overall fatality rate of non-rollover accidents, based on single 
vehicle accidents of all cars and light trucks without consideration 
of accident severity. The fatality rate of rollover accidents was 
slightly more than twice that of non-rollovers, suggesting a 52 
percent mitigation factor.
    Next, the agency computed a series of relative fatality rates 
(with and without rollover), comparing only accidents occurring on 
roads with the same range of posted speed limits (25 mph or less; 
30-35 mph; 40-50 mph; 55-65 mph). While the accident data do not 
indicate the actual accident speed, grouping by speed limit acts as 
a rough control on accident severity, because it restricts accident 
groups to the same kinds of roads, even though the actual range of 
crash speeds may significantly exceed the range of posted speed 
limits for a particular group of accidents. The relative fatality 
rate for each road speed limit group were added and then averaged. 
The result was the same 52 percent mitigation factor for fatalities. 
Using the same process led to a mitigation factor of 26 percent for 
serious injuries.
    In addition, even if the agency were to use different mitigation 
factors for different vehicle types, their use would not result in 
dramatic changes in benefit estimates. For compact SUVs, the 75 
percent mitigation factor suggested by the petitioners would result 
in a fatality reduction of 46 rather than the 32 calculated by the 
agency. This difference is 0.15 percent of the 9,000 annual rollover 
fatalities. Using the estimates prepared for the 1994 notice, for 
the entire light duty vehicle fleet, the use of different mitigation 
factors resulted in predicting 71, instead of the agency's 63, lives 
saved from requiring a TTR of 1.05. This is a difference of 0.089 
percent.

B. The Cost Estimate

    The petitioners criticized the agency for failing to provide any 
costs for the vehicle changes that would be necessary to meet a 
minimum rollover stability standard. The agency concluded in the 
1994 notice that a large number of vehicles would require 
fundamental full redesigns to meet a minimum stability standard. 
Because the agency was aware of the magnitude of costs involved in 
vehicle redesigns, it was apparent that the costs and other impacts 
would substantially exceed the benefits. NHTSA did not, however, 
provide a quantification of those costs and other impacts.
    To demonstrate the validity of its conclusion about the costs 
and other impacts, the agency has conducted a rough cost analysis 
for this notice as set forth below.<SUP>2 To estimate the compliance 
costs for those vehicles which would have to be fully redesigned to 
make the substantial changes necessary to comply with a minimum 
stability standard, the agency used confidential cost data submitted 
by domestic automobile manufacturers during the course of several 
agency rulemaking proceedings for light truck Corporate Average Fuel 
Economy (CAFE) standards. These data are manufacturer estimates of 
the costs of full redesigns of compact SUVs that would have been 
necessary if the CAFE standards had been set at certain levels. 
These submissions include estimates of investment costs for a 
redesigned vehicle model, but do not include material and labor 
costs for the manufacture of the vehicle. NHTSA believes a full 
vehicle redesign for rollover stability purposes would necessitate 
similar investment costs. Accordingly, it is appropriate to use the 
investment cost figures from the CAFE program to estimate the 
investment costs for vehicles which would require a full redesign to 
comply with a rollover stability standard.
---------------------------------------------------------------------------

    \2\ As explained below, the agency did not calculate all costs 
of a standard because it determined that one category of those 
costs, the investment costs for vehicles requiring major changes, 
would by itself exceed the benefits of a standard.
---------------------------------------------------------------------------

    The CAFE submissions include investment cost data for five 
models of compact SUVs. Since the specific raw data are 
confidential, they cannot be set forth here or otherwise publicly 
released. To convert those data into a form in which the original 
data can not be determined, the agency divided the per model data by 
the applicable manufacturer's estimated average annual production 
capacity and then divided by the number of

[[Page 28558]]

years of the vehicle's design cycle life.<SUP>3 The per-vehicle cost 
estimates for these five vehicle design cycle lives were then 
averaged to arrive at the estimate used in this analysis. The 
individual per-vehicle cost estimates range from $317.37 to $532.37 
and the average is $416.77. Since these costs are costs to the 
manufacturer, they were adjusted to represent costs to the consumer 
by dividing them by 0.75, a standard factor used by the agency in 
its vehicle rulemaking in estimating consumer costs from 
manufacturer's wholesale costs. The resulting estimated average 
consumer cost per vehicle resulting from the redesign of a compact 
SUV is $555.69.
---------------------------------------------------------------------------

     <SUP>3  Since the submissions were made in 1986, 1989, 1993, 
and 1994, submissions for years prior to 1994 were adjusted to 1994 
dollars using the implicit gross domestic product deflator as 
calculated by the Bureau of Economic Analysis.
---------------------------------------------------------------------------

    The agency then determined the number of vehicles that would 
need vehicle redesigns to comply with a vehicle rollover stability 
standard requiring a minimum TTR of 1.05. Based on available data, 
the agency believes at least some models would have to be fully 
redesigned to achieve TTR increases of more than 0.04, and that 
almost all models would have to be fully redesigned to achieve at 
TTR increase of 0.06. The agency determined next that 558,756 
vehicles would need to be fully redesigned if the threshold for 
having to make a full redesign were 0.06 and 603,637 vehicles would 
need to be fully redesigned if the threshold were 0.04. Multiplying 
these numbers of vehicles by the $555.69 per vehicle investment cost 
estimate, the agency estimated that the total investment costs of a 
standard requiring a TTR of 1.05 would be $310,495,121 to 
$335,435,044.
    The agency believes that this range of estimated costs of a 
rollover standard requiring compact SUVs to achieve a minimum TTR of 
1.05 is understated. As noted earlier, these cost estimates do not 
include estimates of the incremental costs of material and labor 
involved in the manufacture of the vehicle. Since vehicles would 
need significant increases in track width, and attendant increases 
in wheelbase, they would be generally larger and heavier. As a 
result, the agency concludes that there would be significant 
increases in the costs of material and labor involved in the 
manufacture of such vehicles. In addition, these cost estimates do 
not include any costs for vehicles which could comply with the 
standard by changes that are less than a full vehicle redesign.

C. Objections to the Statistical Tools Used by the Agency in 
Reaching Its Decision

    The petitioners asserted that the agency did not use the 
``typical'' statistical measure, the deviance statistic, to judge 
the adequacy of the logistic regression models used by the agency in 
its analyses of the relationship of TTA to RO/SVA, and the 
importance of the vehicle stability metrics. The petitioners also 
objected to the agency's use of two statistical measures, R<SUP>2 
and the C-statistic. Finally, the petitioners questioned the 
agency's reliance on data from the State of Michigan.
    Although the agency did not use the deviance statistic to judge 
the adequacy of the logistic regression models, the agency did use a 
mathematically equivalent measure, the likelihood statistic (-
2*ln(likelihood)). Using that measure permitted the agency to 
compare the effect of adding variables (specifically the vehicle 
stability metrics) to the hypothesized models. Detailed discussions 
of the agency's analyses are found in the Technical Assessment Paper 
(TAP) (Docket 91-68-N01-03) and the Addendum to the Technical 
Assessment Paper (Docket 91-68-N03-02) which were placed in NHTSA's 
docket. The TAP and the Addendum present analyses using five 
measures: the C-statistic, R<SUP>2, the percentage change in 
R<SUP>2, the likelihood statistic, and the variables' chi-square. It 
is true that the deviance statistic was not reported because the 
computer software the agency used to conduct this analysis, SAS 
Institute's PROC LOGIST, does not include the deviance statistic as 
one of the model diagnostics. However, the agency does not believe 
that this affects the general conclusions regarding the importance 
of the vehicle stability metrics.
    NHTSA believes that it may help to explain this issue in non-
statistical terms. The petitioners' argument amounts to a complaint 
that the agency described various glasses of water in terms of how 
much water is in the glass, instead of in terms of how much water 
could be added to the glass. In either case, the capacity of the 
glass is the same. If the capacity is known, and if either the 
amount of water or the amount of unused capacity is known, the other 
amount can be derived.
    Similarly, the deviance statistic preferred by the petitioners 
describes how much of the variability <SUP>4 in the regression model 
is left to be explained. The likelihood statistic, which the agency 
used, describes how much of the variability in the model is 
explained. In either case, the total variability to be explained is 
the same. If, as the agency's analysis showed, the addition of TTR 
to the model decreased the value of the likelihood statistic, the 
deviance statistic would have increased by the same amount. Using 
either measure would lead to the same conclusion about the value of 
TTR.
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     <SUP>4  Variability is the difference between what the 
statistical model predicts and actual accident records.
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    The petitioners also assert that the use of R<SUP>2 was 
inappropriate because it is not weighted, i.e., it does not reflect 
the number of single vehicle accidents for each vehicle make and 
model. The petitioners also state that R<SUP>2 is sensitive to 
extreme values. The agency's use of R<SUP>2 was described fully on 
page 5-66 of the TAP. The agency agrees, as explained in the TAP, 
that there are limitations to the use of R<SUP>2. As also explained 
in the TAP, R<SUP>2 was used as an approach to providing the types 
of descriptive statistics of model fit with which more people are 
familiar, and not to provide a mathematically rigorous assessment of 
model fit. The agency's use of R<SUP>2 was an attempt to make the 
explanation of the analysis understandable to a wider audience, and 
was not the sole basis of the agency's decision.
    The petitioners' assertions of problems with the use of the C-
statistic are not applicable to the C-statistic as used by the 
agency. In an attempt to support their assertions, the petitioners 
pointed to an example of how the C-statistic can ``misbehave'' 
presented on page 146 of Hosmer and Lemeshow.<SUP>5 The agency's use 
of the C-statistic is not the same as that in Hosmer and Lemeshow's 
example. That example simply uses a classification table with an 
arbitrary cut point to determine, e.g., whether an actual rollover 
was predicted to be a rollover. The C-statistic employed by NHTSA 
measured the concordance between all possible pairs of observations, 
taking one from the actual rollover population and one from the 
actual non-rollover population. The C-statistic represents the 
percentage of those pairs (which number literally in the millions) 
for which the actual rollover had a higher predicted probability 
than the actual non-rollover's predicted probability (of rolling 
over), minus one-half the number of ties. There is no arbitrary 
cutoff point. In addition, the agency's decision was not based on a 
single statistical measure. The agency analyzed the data with a 
number of statistical measures, all of which pointed to the same 
conclusions. Accordingly, the agency remains confident in its 
results.
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     <SUP>5  D.W. Hosmer and S. Lemeshow, Applied Logistic 
Regression, Wiley Interscience, New York, 1989.
---------------------------------------------------------------------------

    Finally, the petitioners' objection to the agency's reliance on 
Michigan data for performing the statistical regressions instead of 
using the data from the other four states was based on their concern 
that the agency did not examine the extent to which the state is 
anomalous because of its generally flat topography. The petitioners 
stated that this could lead to a lower proportion of rollovers per 
single vehicle accident than the other states in the data base. The 
agency relied on Michigan data because they included a large number 
of available observations, and were based on a low reporting 
threshold and more refined accident reporting variables. The agency 
did examine whether the rollover rate in this state was anomalous, 
and as stated on page 13 of the Addendum, discovered that ``(t)he 
rollover rate in Michigan is near the midpoint of the range for all 
five states studied.'' The examination of the relative rollover 
rates of the five different states was fully explained in the TAP on 
pages 59-65.

D. Legal Arguments

    The petitioners also addressed the implications of the 
Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) 
(P.L. 102-240), the National Traffic and Motor Vehicle Safety Act of 
1966 (the Safety Act) (P.L. 89-563),<SUP>6 and the Regulatory 
Flexibility Act (P.L. 96-354) for rulemaking concerning a vehicle 
stability standard. The petitioners also argue that the decision not 
to issue a rollover standard is judicially reviewable.<SUP>7
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     6  After the publication of the termination notice, the Safety 
Act was codified in volume 49 of the United States Code. Any cites 
to provisions of the Safety Act have been updated to reflect the 
codification.
     <SUP>7  The agency agrees with the petitioners that this 
termination is ``final agency action'' for the purposes of judicial 
review.

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[[Page 28559]]

    The petitioners begin by citing the provision in ISTEA that 
required NHTSA to initiate rulemaking concerning a rollover 
standard. The petitioners acknowledge that Congress did not mandate 
the issuance of a final rule in this area.
    Although the petitioners make this concession, it bears 
emphasizing how clearly ISTEA and its legislative history 
demonstrate that in each instance in which Congress mandated that 
the agency initiate vehicle safety rulemaking, it clearly specified 
whether the agency had the discretion to decide not to issue a final 
rule. In sections 2502-3 of ISTEA, Congress specified that the 
agency was to initiate rulemaking regarding five different areas of 
vehicle safety performance. With respect to one area, upper interior 
head impact protection, Congress specified that rulemaking would be 
considered completed only when a final rule was issued. However, 
with respect to the other four areas, including rollover, Congress 
did not mandate the issuance of a final rule. It expressly provided 
that rulemaking on rollover and the other three areas would be 
considered completed either when the agency issued a final rule or 
when the agency decided, after considering public comments, not to 
issue a final rule. The Conference Report on ISTEA emphasized the 
discretion which it had reserved to the agency. The conferees said, 
with reference to the mandated rulemaking on rollover, ``the 
conferees do not predetermine the outcome of [this rulemaking]. The 
[NHTSA] is free to conclude the rulemaking in any manner consistent 
with the APA and the 1966 Act'' (H. Conf. Rep. 404, 102d Cong., 1st 
Sess., at 397 (1991)). Thus, Congress made no judgment in ISTEA 
about the ultimate merits of issuing a final rule on rollover. 
Instead, Congress provided NHTSA with the latitude to decide that a 
rollover standard should not be issued if, in the agency's judgment, 
the facts did not warrant such issuance. The agency's conclusion 
that such a regulation would not have sufficient benefits to justify 
its cost is an ample and proper basis for a decision not to issue a 
final rule.
    Although the petitioners concede that Congress did not require 
the agency to issue a final rule on rollover, they assert that 
Congress ``expected the agency to set some form of stability-
enhancing regulation.'' <SUP>8 As authority for that assertion, they 
cite the legislative history of the Department of Transportation and 
Related Agencies Appropriations Act of 1995. (P.L. 104-59) The 
Senate committee report on that Act contended that NHTSA had 
``effectively abandoned efforts at developing a performance standard 
for improved rollover protection.''
---------------------------------------------------------------------------

    \8\ Advocates/IIHS petition, page 41.
---------------------------------------------------------------------------

    The 1995 Appropriation Act legislative history is inapposite 
here and lacks any possible binding effect. Since that history 
pertains to a different statute, it carries no weight in the 
interpretation of NHTSA's duties under ISTEA. NHTSA notes further 
that the language cited by the petitioners is part of a discussion 
expressing concern about the agency's delay in publishing some of 
the ISTEA rulemakings. The discussion does not express any 
expectation about the substantive outcome of agency rulemaking on 
rollover, but does express an expectation that NHTSA will complete 
the remaining ISTEA rulemakings expeditiously. Finally, even if the 
Senate committee had specifically expressed an expectation 
concerning the outcome of the rollover rulemaking, that expectation 
would not impose a binding obligation on NHTSA unless Congress 
coupled that expectation with a mandate to issue a final rule on 
rollover and enacted that mandate into law. See Center for Auto 
Safety v. Peck, 751 F.2d 1336, at 1351 (D.C. Cir. 1985). Congress 
did not do so. Instead, it expressly decided not to mandate the 
issuance of a final rule on that subject.
    The petitioners argued that neither the Safety Act nor the 
Regulatory Flexibility Act provide any legal grounds for terminating 
rulemaking on a vehicle stability standard. The petitioners quoted 
statements in the 1994 notice that 49 U.S.C. Sec. 30111(b)(3) would 
preclude NHTSA from mandating any stability requirement that is 
``incompatible with certain types of vehicles,'' and that a 
stability requirement ``could raise concerns'' under the Regulatory 
Flexibility Act. (59 FR 33254, 33263) They interpreted these 
statements as implying that the agency believed it was prohibited 
from issuing any standard that might require ``the radical redesign 
of the characteristics [of] many, and in some cases all, vehicles of 
certain classes * * * and possibly even the elimination of certain 
classes of vehicles as they are known today.'' The petitioners 
countered with alternative propositions, arguing that NHTSA has 
authority to eliminate whole classes of vehicles, and that, even if 
NHTSA does not have such authority, it failed to consider a less 
demanding regulatory approach such as setting different standards 
for separate vehicle types which would not require all vehicles in a 
class to be altered. The petitioners argued also that NHTSA cannot 
rely on the Regulatory Flexibility Act when the agency did not 
prepare any analysis of the impacts of a standard on small entities.
    The primary bases for the agency's decision to terminate 
rulemaking on a vehicle stability standard are the limited safety 
benefits, and the excessive costs and market disruption of such a 
standard, regardless of whether that standard applies to all light 
duty vehicles or to particular class such as compact SUVs. The 1994 
notice discussed the high costs of a standard that specifies a 
single performance level which was applicable to all light duty 
vehicles and was high enough to require the full redesign of at 
least some passenger cars. As explained previously, the agency 
concluded that such a standard would have costs and other impacts 
which outweighed its benefits. NHTSA similarly concludes that the 
costs and other impacts of a standard applicable to compact SUVs 
would far outweigh its benefits. Logically, if a standard for the 
most rollover-prone light duty vehicles would fail this basis test, 
it follows that a standard for other groups of light duty vehicles 
would not be justified.
    It should be noted that neither 49 U.S.C. 30111(b)(3) nor the 
Regulatory Flexibility Act impose an absolute legal bar to a minimum 
stability standard. The agency is not foreclosing any possibility of 
further rulemaking. As stated above, NHTSA might reinitiate 
rulemaking in this area if information becomes available 
demonstrating the cost effectiveness of a minimum stability 
standard.
    However, the Safety Act does place limits on the agency's 
rulemaking authority. The agency lacks authority to eliminate entire 
classes of vehicles. This interpretation reflects the language of 49 
U.S.C. 30111(b)(3) and its legislative history. 49 U.S.C. 
30111(b)(3) states:

    When prescribing a motor vehicle safety standard under this 
chapter, the Secretary shall * * * consider whether a proposed 
standard is reasonable, practicable, and appropriate for the 
particular type of motor vehicle or item of motor vehicle equipment 
for which it is prescribed.

    The Senate Report accompanying the 1966 Safety Act explained 
this provision as follows:

    In determining whether any proposed standard is ``appropriate'' 
for the particular type of motor vehicle or item of motor vehicle 
equipment for which it is prescribed, the committee intends that the 
[NHTSA] will consider the desirability of affording consumers 
continued wide range of choices in the selection of motor vehicles. 
Thus it is not intended that standards will be set which will 
eliminate or necessarily be the same for small cars or such widely 
accepted models as convertibles and sports cars, so long as all 
motor vehicles meet basic minimum standards.

(S. Rep. 1301, 89th Cong., 2d Sess., at 6 (1966))

    Given this legislative history, NHTSA cannot mandate a stability 
requirement so incompatible with the most fundamental 
characteristics which define a class of vehicles that implementing 
the requirement would cause the elimination of that class. As an 
example, the agency noted in the 1994 notice that sport utility 
vehicles have features (high ground clearance and narrow track 
width) to facilitate off-road use and use on snowy roads. The agency 
would not have the authority to set a performance level so stringent 
that no vehicles could have these features. This is neither a 
radical, nor a new interpretation of the agency's authority. NHTSA 
is not suggesting, as the petitioners suggest, that the agency lacks 
any authority to issue a standard that requires significant change 
to all vehicles in a class. In fact, there are many examples of the 
agency using its authority to require changes to all vehicles in a 
particular class. Those changes did not, however, eliminate as a 
practical matter any recognized classes of vehicles.
    Petitioners incorrectly suggested that the agency had a duty 
under the Regulatory Flexibility Act to prepare a regulatory 
flexibility analysis in connection with either the 1994 notice or 
the ANPRM which preceded it. NHTSA did not ``fail'' to prepare any 
required report. That Act mandates the preparation of analyses in 
connection with notices of proposed rulemaking and final rules only.
    NHTSA believes that the Regulatory Flexibility Act was a 
relevant concern in

[[Page 28560]]

considering the possibility of proposing a stability standard 
applicable to all light duty vehicles because multistage 
manufacturers, especially van converters, which are often small 
business entities, could be affected by such a standard. NHTSA is 
not suggesting that that Act would prevent the issuance of such a 
standard or that the concerns about impacts on small manufacturers 
were insurmountable regardless of what approach is taken by the 
agency in setting the standard. In fact, a standard limited to 
compact SUVs would essentially eliminate those impacts because few, 
if any, of those vehicles are produced by multistage or other small 
manufacturers.

F. NHTSA's Alleged Lack of a Comprehensive Rollover Program

    The petitioners characterized NHTSA's identification of seven 
separate measures as part of a comprehensive agency plan to address 
rollovers as simply ``a chronicle of ongoing or prospective crash 
reduction programs that are not aimed uniquely at mitigating 
rollover losses.'' The petition went on to complain that some of the 
measures ``may never come to fruition,'' and that others have not 
been specifically tailored by the agency to address the rollover 
problem. The petitioners concluded by stating their belief that 
NHTSA's comprehensive program for rollover is really an attempt to 
try to persuade the public that the agency is taking action on 
rollover safety, notwithstanding the termination of the vehicle 
stability rulemaking.
    The agency believes that the question of whether the activities 
comprising its comprehensive rollover program uniquely address 
rollover safety is irrelevant if those activities effectively 
address that issue. If NHTSA can take actions, such as issuing a 
standard, that significantly reduces the deaths and injuries that 
occur in rollover crashes, it should make no difference whether that 
reduction is achieved by means that also reduce deaths and injuries 
in other types of crashes. The agency agrees that there is a 
possibility that some of the regulatory initiatives announced by the 
agency as part of its rollover program involve proposals that may 
never become final rules. However, this possibility exists with any 
regulatory initiative. The agency cannot foretell the nature of the 
public comments that it will receive or prejudge the outcome of its 
analyses of comments and other information obtained during the 
rulemaking process. NHTSA included those initiatives in its rollover 
program because preliminary evaluations of those initiatives 
indicate that they are promising avenues for addressing rollovers. 
The agency will pursue these initiatives expeditiously and 
conscientiously. For example, since the 1994 notice was published, 
NHTSA has published a final rule to extend the current requirements 
for side door latches to rear door latches. (60 FR 50124) This rule 
is an attempt to reduce the number of ejections from the rear door 
of vehicles, thus reducing injuries and fatalities. Based on data 
for years 1988-1992, NHTSA estimates that 147 occupants were fatally 
ejected from the rear door of vehicles. Forty two percent of those 
fatalities occurred in rollover accidents.
    One of the specific initiatives singled out for criticism by 
petitioners was the upgrade of Standard 201 to reduce head impact 
injuries. The petitioners objected to its inclusion in NHTSA's 
comprehensive rollover plan because the proposed compliance impact 
speeds ``are often less than those [speeds] responsible for the very 
high rate of severe head trauma that is suffered by occupants in 
rollover crashes.'' The final rule upgrading Standard No. 201 was 
published on August 16, 1995. (60 FR 43031) Even if the petitioners 
were correct, the essential fact remains that the final rule will 
make substantial reductions in rollover fatalities and injuries. The 
agency estimated that 244-334 fatalities and 189-273 serious 
injuries would be averted in rollovers as a result of that rule.

    Authority: 49 U.S.C. 322, 30111, 30115, 30117 and 30166; 
delegation of authority at 49 CFR 1.50 and 501.8.

[FR Doc. 96-14145 Filed 5-31-96; 4:38 pm]
BILLING CODE 4910-59-P