build smaller and lighter vehicles in order to achieve compliance,
which fare worse in head-on collisions than larger, heavier vehicles.
AISI, in contrast to U.S. Steel, stated that in its research with the
Auto/Steel Partnership and in programs supported by DOE, it had found
that the use of new Advanced HSS steel grades could enable mass of
critical crash structures, such as front rails and bumper systems, to
be reduced by 25 percent without degrading performance in standard
NHTSA frontal or IIHS offset

instrumented crash tests compared to their ``heavier counterparts.''
---------------------------------------------------------------------------

    \123\ The Aluminum Association (NHTSA-2009-0059-0067.3) stated
that its research on vehicle safety compatibility between an SUV and
a mid-sized car, done jointly with DRI, shows that reducing the
weight of a heavier SUV by 20% (a realistic value for an aluminum-
intensive vehicle) could reduce the combined injury rate for both
vehicles by 28% in moderately severe crashes. The commenter stated
that it would keep NHTSA apprised of its results as its research
progressed. Based on the information presented, NHTSA believes that
this research appears to agree with NHTSA's latest analysis, which
finds that a reduction in weight for the heaviest vehicles may
improve overall fleet safety.
---------------------------------------------------------------------------

    Agencies' response: NHTSA, in consultation with EPA and DOE, plans
to begin updating the MYs 1991-1999 database on which NHTSA's safety
analyses in the NPRM and final rule are based in the next several
months in order to analyze the differences in safety effects against
vehicles built in more recent model years. As this task will take at
least a year to complete, beginning it immediately after the NPRM would
not have enabled the agency to complete it and then conduct a new
analysis during the period between the NPRM and the final rule.
    For purposes of this final rule, however, we believe that using the
same MYs 1991-1999 database as that used in the 2003 Kahane study
provides a reasonable basis for attempting to estimate safety effects
due to reductions in mass. While commenters often stated that updating
the database would help to reveal the effect of recently-introduced
lightweight vehicles with extensive material substitution, there have
in fact not yet been a significant number of vehicles with substantial
mass reduction/material substitution to analyze, and they must also
show up in the crash databases for NHTSA to be able to add them to its
analysis. Based on NHTSA's research, specifically, on three statistical
analyses over a 12-year period (1991-2003) covering a range of 22 model
years (1978-1999), NHTSA believes that the relationships between mass,
size, and safety has only changed slowly over time, although we
recognize that they may change somewhat more rapidly in the
future.\124\ As the on-road fleet gains increasing numbers of vehicles
with increasing amounts of different methods of mass reduction applied
to them, we may begin to discern changes in the crash databases due to
the presence of these vehicles, but any such changes are likely to be
slow and evolutionary, particularly in the context of MYs 2000-2009
vehicles. The agencies do expect that further analysis of historical
data files will continue to provide a robust and practicable basis for
estimating the potential safety effects that might occur with future
reductions in vehicle mass. However, we recognize that estimates
derived from analysis of historical data, like estimates from any other
type of analysis (including simulation-based analysis, which cannot
feasibly cover all relevant scenarios), will be uncertain in terms of
predicting actual future outcomes with respect to a vehicle fleet,
driving population, and operating environment that does not yet exist.
---------------------------------------------------------------------------

    \124\ NHTSA notes the CAS' comments regarding changes in the
vehicle fleets since the introduction of CAFE standards in the late
1970s, but believes they apply more to the differences between late
1970s through 1980s vehicles and 2010s vehicles than to the
differences between 1990s and 2010s vehicles. NHTSA believes that
the CAS comments regarding the phase-out of 1970s vehicles and their
replacement with safer, better fuel-economy-achieving 1980s vehicles
paint with rather too large a brush to be relevant to the main
discussion of whether the 2003 Kahane report database can reasonably
be used to estimate safety effects of mass reduction for the MYs
2012-2016 fleet.
---------------------------------------------------------------------------

    The agencies also recognize that more recent vehicles have more
safety features than 1990s vehicles, which are likely to make them
safer overall. To account for this, NHTSA did adjust the results of
both its NPRM and final rule analysis to include known safety
improvements, like ESC and increases in seat belt use, that have
occurred since MYs 1991-1999.\125\ However, simply because newer
vehicles have more safety countermeasures, does not mean that the
weight/safety relationship necessarily changes. More likely, it would
change the target population (the number of fatalities) to which one
would apply the weight/safety relationship. Thus, we still believe that
some mass reduction techniques for both passenger cars and light trucks
can make them less safe, in certain crashes as discussed in NHTSA's
FRIA, than if mass had not been reduced.\126\
---------------------------------------------------------------------------

    \125\ See NHTSA FRIA Chapter IX.
    \126\ If one has a vehicle (vehicle A), and both reduces the
vehicle's mass and adds new safety equipment to it, thus creating a
variant (vehicle A1), the variant might conceivably have
a level of overall safety for its occupants equal to that of the
original vehicle (vehicle A). However, vehicle A1 might
not be as safe as second variant (vehicle A2) of vehicle
A, one that is produced by adding to vehicle A the same new safety
equipment added to the first variant, but this time without any mass
reduction.
---------------------------------------------------------------------------

    As for NHTSA's assumptions about mass reduction, in its analysis,
NHTSA generally assumed that lighter vehicles could be reduced in
weight by 5 percent while heavier light trucks could be reduced in
weight by 10 percent. NHTSA recognizes that manufacturers might choose
a different mass reduction scheme than this, and that its
quantification of the estimated effect on safety would be different if
they did. We emphasize that our estimates are based on the assumptions
we have employed and are intended to help the agency consider the
potential effect of the final standards on vehicle safety. Thus, based
on the 2010 Kahane analysis, reductions in weight for the heavier light
trucks would have positive overall safety effects,\127\ while mass
reductions for passenger cars and smaller light trucks would have
negative overall safety effects.
---------------------------------------------------------------------------

    \127\ This is due to the beneficial effect on the occupants of
vehicles struck by the downweighted larger vehicles.

NHTSA's estimates are inaccurate because they do not account for the
fact that lighter vehicles are safer than heavier cars in terms of
---------------------------------------------------------------------------
crash-avoidance, because they handle and brake better

    ICCT stated that lighter vehicles are better able to avoid crashes
because they ``handle and brake slightly better,'' arguing that size-
based standards encourage lighter-weight car-based SUVs with
``significantly better handling and crash protection'' than 1996-1999
mid-size SUVs, which will reduce both fatalities and fuel consumption.
ICCT stated that NHTSA did not include these safety benefits in its
analysis. DRI also stated that its 2005 report found that crash
avoidance improves with reduction in curb weight and/or with increases
in wheelbase and track, because ``Crash avoidance can depend, amongst
other factors, on the vehicle directional control and rollover
characteristics.'' DRI argued that, therefore, ``These results indicate
that vehicle weight reduction tends to decrease fatalities, but vehicle
wheelbase and track reduction tends to increase fatalities.''
    Agencies' response: In fact, NHTSA's regression analysis of crash
fatalities per million registration years measures the effects of crash
avoidance, if there are any, as well as crashworthiness. Given that the
historical empirical data for passenger cars show a trend of higher
crash rates for lighter cars, it is unclear whether lighter cars have,
in the net, superior crash avoidance, although the agencies recognize
that they may have advantages in certain individual situations. EPA
presents a discussion of improved accident avoidance as vehicle mass is
reduced in Chapter 7.6 of its final RIA. The important point to
emphasize is that it depends on the situation--it would oversimplify
drastically to point to one situation in which extra mass helps or
hurts and then extrapolate effects for crash avoidance across the board
based on only that.
    For example, the relationship of vehicle mass to rollover and
directional stability is more complex than commenters imply. For
rollover, it is true that if heavy pickups were always more top-heavy
than lighter pickups of the same footprint, their higher center of
gravity could make them more rollover-prone, yet some mass can be
placed so as to lower a vehicle's center of gravity and make it less
rollover-prone. For mass reduction to be beneficial in rollover
crashes, then, it must take

center of gravity height into account along with other factors such as
passenger compartment design and structure, suspension, the presence of
various safety equipment, and so forth.
    Similarly, for directional stability, it is true that having more
mass increases the ``understeer gradient'' of cars--i.e., it reinforces
their tendency to proceed in a straight line and slows their response
to steering input, which would be harmful where prompt steering
response is essential, such as in a double-lane-change maneuver to
avoid an obstacle. Yet more mass and a higher understeer gradient could
help when it is better to remain on a straight path, such as on a
straight road with icy patches where wheel slip might impair
directional stability. Thus, while less vehicle mass can sometimes
improve crash avoidance capability, there can also be situations when
more vehicle mass can help in other kinds of crash avoidance.
    Further, NHTSA's research suggests that additional vehicle mass may
be even more helpful, as discussed in Chapter IX of NHTSA's FRIA, when
the average driver's response to a vehicle's maneuverability is taken
into account. Lighter cars have historically (1976-2009) had higher
collision-involvement rates than heavier cars--even in multi-vehicle
crashes where directional and rollover stability is not particularly an
issue.\128\ Based on our analyses using nationally-collected FARS and
GES data, drivers of lighter cars are more likely to be the culpable
party in a 2-vehicle collision, even after controlling for footprint,
the driver's age, gender, urbanization, and region of the country.
---------------------------------------------------------------------------

    \128\ See, e.g., NHTSA (2000). Traffic Safety Facts 1999. Report
No. DOT HS 809 100. Washington, DC: National Highway Traffic Safety
Administration, p. 71; Najm, W.G., Sen, B., Smith, J.D., and
Campbell, B.N. (2003). Analysis of Light Vehicle Crashes and Pre-
Crash Scenarios Based on the 2000 General Estimates System, Report
No. DOT HS 809 573. Washington, DC: National Highway Traffic Safety
Administration, p. 48.
---------------------------------------------------------------------------

    Thus, based on this data, it appears that lighter cars may not be
driven as well as heavier cars, although it is unknown why this is so.
If poor drivers intrinsically chose light cars (self-selection), it
might be evidenced by an increase in antisocial driving behavior (such
as DWI, drug involvement, speeding, or driving without a license) as
car weight decreases, after controlling for driver age and gender--in
addition to the increases in merely culpable driver behavior (such as
failure to yield the right of way). But analyses in NHTSA's 2003 report
did not show an increase in antisocial driver behavior in the lighter
cars paralleling their increase in culpable involvements.
    NHTSA also hypothesizes that certain aspects of lightness and/or
smallness in a car may give a driver a perception of greater
maneuverability that ultimately results in driving with less of a
``safety margin,'' e.g., encouraging them to weave in traffic. That may
appear paradoxical at first glance, as maneuverability is, in the
abstract, a safety plus. Yet the situation is not unlike powerful
engines that could theoretically enable a driver to escape some
hazards, but in reality have long been associated with high crash and
fatality rates.\129\
---------------------------------------------------------------------------

    \129\ Robertson, L.S. (1991), ``How to Save Fuel and Reduce
Injuries in Automobiles,'' The Journal of Trauma, Vol. 31, pp. 107-
109; Kahane, C.J. (1994). Correlation of NCAP Performance with
Fatality Risk in Actual Head-On Collisions, NHTSA Technical Report
No. DOT HS 808 061. Washington, DC: National Highway Traffic Safety
Administration, http://www-nrd.nhtsa.dot.gov/Pubs/808061.PDF, pp. 4-
7.

NHTSA's estimates are inaccurate because fatalities are linked more to
---------------------------------------------------------------------------
other factors than mass

    Tom Wenzel stated that the safety record of recent model year
crossover SUVs indicates that weight reduction in this class of
vehicles (small to mid-size SUVs) resulted in a reduction in fatality
risk. Wenzel argued that NHTSA should acknowledge that other vehicle
attributes may be as important, if not more important, than vehicle
weight or footprint in terms of occupant safety, such as unibody
construction as compared to ladder-frame, lower bumpers, and less rigid
frontal structures, all of which make crossover SUVs more compatible
with cars than truck-based SUVs.
    Marc Ross commented that fatalities are linked more strongly to
intrusion than to mass, and stated that research by safety experts in
Japan and Europe suggests the main cause of serious injuries and deaths
is intrusion due to the failure of load-bearing elements to properly
protect occupants in a severe crash. Ross argued that the results from
this project have ``overturned the original views about
compatibility,'' which thought that mass and the mass ratio were the
dominant factors. Since footprint-based standards will encourage the
reduction of vehicle weight through materials substitution while
maintaining size, Ross stated, they will help to reduce intrusion and
consequently fatalities, as the lower weight reduces crash forces while
maintaining size preserves crush space. Ross argued that this factor
was not considered by NHTSA in its discussion of safety. ICCT agreed
with Ross' comments on this issue.
    In previous comments on NHTSA rulemakings and in several studies,
Wenzel and Ross have argued generally that vehicle design and
``quality'' is a much more important determinant of vehicle safety than
mass. In comments on the NPRM, CARB, NRDC, Sierra Club, and UCS echoed
this theme.
    ICCT commented as well that fatality rates in the EU are much lower
than rates in the U.S., even though the vehicles in the EU fleet tend
to be smaller and lighter than those in the U.S. fleet. Thus, ICCT
argued, ``This strongly supports the idea that vehicle and highway
design are far more important factors than size or weight in vehicle
safety.'' ICCT added that ``It also suggests that the rise in SUVs in
the U.S. has not helped reduce fatalities.'' CAS also commented that
Germany's vehicle fleet is both smaller and lighter than the American
fleet, and has lower fatality rates.
    Agencies' response: NHTSA and EPA agree that there are many
features that affect safety. While crossover SUVs have lower fatality
rates than truck-based SUVs, there are no analyses that attribute the
improved safety to mass alone, and not to other factors such as the
lower center of gravity or the unibody construction of these vehicles.
While a number of improvements in safety can be made, they do not
negate the potential that another 100 lbs. could make a passenger car
or crossover vehicle safer for its occupants, because of the effects of
mass per se as discussed in NHTSA's FRIA, albeit similar mass
reductions could make heavier LTVs safer to other vehicles without
necessarily harming their own drivers and occupants. Moreover, in the
2004 response to docket comments, NHTSA explained that the significant
relationship between mass and fatality risk persisted even after
controlling for vehicle price or nameplate, suggesting that vehicle
``quality'' as cited by Wenzel and Ross is not necessarily more
important than vehicle mass.
    As for reductions in intrusions due to material substitution, the
agencies agree generally that the use of new and innovative materials
may have the potential to reduce crash fatalities, but such vehicles
have not been introduced in large numbers into the vehicle fleet. The
agencies will continue to monitor the situation, but ultimately the
effects of different methods of mass reduction on overall safety in the
real world (not just in simulations) will need to be analyzed when
vehicles with these types of mass reduction are on the road in
sufficient quantities to provide statistically significant results. For
example, a vehicle that is designed to be

much stiffer to reduce intrusion is likely to have a more severe crash
pulse and thus impose greater forces on the occupants during a crash,
and might not necessarily be good for elderly and child occupant safety
in certain types of crashes. Such trade-offs make it difficult to
estimate overall results accurately without real world data. The
agencies will continue to evaluate and analyze such real world data as
it becomes available, and will keep the public informed as to our
progress.
    ICCT's comment illustrates the fact that different vehicle fleets
in different countries can face different challenges. NHTSA does not
believe that the fact that the EU vehicle fleet is generally lighter
than the U.S. fleet is the exclusive reason, or even the primary
factor, for the EU's lower fatality rates. The data ICCT cites do not
account for significant differences between the U.S. and EU such as in
belt usage, drunk driving, rural/urban roads, driving culture, etc.

The structure of the standards reduces/contributes to potential safety
risks from mass reduction

    Since switching in 2006 to setting attribute-based light truck CAFE
standards, NHTSA has emphasized that one of the benefits of a
footprint-based standard is that it discourages manufacturers from
building smaller, less safe vehicles to achieve CAFE compliance by
``balancing out'' their larger vehicles, and thus avoids a negative
safety consequence of increasing CAFE stringency.\130\ Some commenters
on the NPRM (Daimler, IIHS, NADA, NRDC, Sierra Club et al.) agreed that
footprint-based standards would protect against downsizing and help to
mitigate safety risks, while others stated that there would still be
safety risks even with footprint-based standards--CEI, for example,
argued that mass reduction inherently creates safety risks, while IIHS
and Porsche expressed concern about footprint-based standards
encouraging manufacturers to manipulate wheelbase, which could reduce
crush space and worsen vehicle handling. U.S. Steel and AISI both
commented that the ``aggressive schedule'' for the proposed increases
in stringency could encourage manufacturers to build smaller, lighter
vehicles in order to comply.
---------------------------------------------------------------------------

    \130\ We note that commenters were divided on whether they
believed there was a clear correlation between vehicle size/weight
and safety (CEI, Congress of Racial Equality, Heritage Foundation,
IIHS, Spurgeon, University of PA Environmental Law Project) or
whether they believed that the correlation was less clear, for
example, because they believed that vehicle design was more
important than vehicle mass (CARB, Public Citizen).
---------------------------------------------------------------------------

    Some commenters also focused on the shape and stringency of the
target curves and their potential effect on vehicle safety. IIHS agreed
with the agencies' tentative decision to cut off the target curves at
the small-footprint end. Regarding the safety effect of the curves
requiring less stringent targets for larger vehicles, while IIHS stated
that increasing footprint is good for safety, CAS, Wenzel, and the UCSB
students stated that decreasing footprint may be better for safety in
terms of risk to occupants of other vehicles. Daimler, Wenzel, and the
University of PA Environmental Law Project commented generally that
more similar passenger car and light truck targets at identical
footprints (as Wenzel put it, a single target curve) would improve
fleet compatibility and thus, safety, by encouraging manufacturers to
build more passenger cars instead of light trucks.
    Agencies' response: The agencies continue to believe that
footprint-based standards help to mitigate potential safety risks from
downsizing if the target curves maintain sufficient slope, because,
based on NHTSA's analysis, larger-footprint vehicles are safer than
smaller-footprint vehicles.\131\ The structure of the footprint-based
curves will also discourage the upsizing of vehicles. Nevertheless, we
recognize that footprint-based standards are not a panacea--NHTSA's
analysis continues to show that there was a historical relationship
between lower vehicle mass and increased safety risk in passenger cars
even if footprint is maintained, and there are ways that manufacturers
may increase footprint that either improve or reduce vehicle safety, as
indicated by IIHS and Porsche.
---------------------------------------------------------------------------

    \131\ See Chapter IX of NHTSA's FRIA.
---------------------------------------------------------------------------

    With regard to whether the agencies should set separate curves or a
single one, NHTSA also notes in Section II.C that EPCA requires NHTSA
to establish standards separately for passenger cars and light trucks,
and thus concludes that the standards for each fleet should be based on
the characteristics of vehicles in each fleet. In other words, the
passenger car curve should be based on the characteristics of passenger
cars, and the light truck curve should be based on the characteristics
of light trucks--thus to the extent that those characteristics are
different, an artificially-forced convergence would not accurately
reflect those differences. However, such convergence could be
appropriate depending on future trends in the light vehicle market,
specifically further reduction in the differences between passenger car
and light truck characteristics. While that trend was more apparent
when car-like 2WD SUVs were classified as light trucks, it seems likely
to diminish for the model year vehicles subject to these rules as the
truck fleet will be more purely ``truck-like'' than has been the case
in recent years.

NHTSA's estimates are inaccurate because NHTSA could mitigate
additional safety risks from mass reduction, if there are any, by
simply regulating safety more

    Since NHTSA began considering the potential safety risks from mass
reduction in response to increased CAFE standards, some commenters have
suggested that NHTSA could mitigate those safety risks, if any, by
simply regulating more.\132\ In response to the safety analysis
presented in the NPRM, several commenters stated that NHTSA should
develop additional safety regulations to require vehicles to be
designed more safely, whether to improve compatibility (Adcock, NY DEC,
Public Citizen, UCS), to require seat belt use (CAS, UCS), to improve
rollover and roof crush resistance (UCS), or to improve crashworthiness
generally by strengthening NCAP and the star rating system (Adcock).
Wenzel commented further that ``Improvements in safety regulations will
have a greater effect on occupant safety than FE standards that are
structured to maintain, but may actually increase, vehicle size.''
---------------------------------------------------------------------------

    \132\ See, e.g., MY 2011 CAFE final rule, 74 FR 14403-05 (Mar.
30, 2009).
---------------------------------------------------------------------------

    Agencies' response: NHTSA appreciates the commenters' suggestions
and notes that the agency is continually striving to improve motor
vehicle safety consistent with its mission. As noted above, improving
safety in other areas affects the target population that the mass/
footprint relationship could affect, but it does not necessarily change
the relationship.
    The 2010 Kahane analysis discussed in this final rule evaluates the
relative safety risk when vehicles are made lighter than they might
otherwise be absent the final MYs 2012-2016 standards. It does consider
the effect of known safety regulations as they are projected to affect
the target population.

Casualty risks range widely for vehicles of the same weight or
footprint, which skews regression analysis and makes computer
simulation a better predictor of the safety effects of mass reduction

    Wenzel commented that he had found, in his most recent work, after
accounting for drivers and crash location, that there is a wide range
in casualty risk for vehicles with the same weight or footprint. Wenzel
stated that for drivers, casualty risk does generally decrease as
weight or footprint increases, especially for passenger cars, but the
degree of variation in the data for vehicles (particularly light
trucks) at a given weight or footprint makes it difficult to say that a
decrease in weight or footprint will necessarily result in increased
casualty risk. In terms of risk imposed on the drivers of other
vehicles, Wenzel stated that risk increases as light truck weight or
footprint increases.
    Wenzel further stated that because a regression analysis can only
consider the average trend in the relationship between vehicle weight/
size and risk, it must ``ignore'' vehicles that do not follow that
trend. Wenzel therefore recommended that the agency employ computer
crash simulations for analyzing the effect of vehicle weight reduction
on safety, because they can ``pinpoint the effect of specific vehicle
designs on safety,'' and can model future vehicles which do not yet
exist and are not bound to analyzing historical data. Wenzel cited, as
an example, a DRI simulation study commissioned by the Aluminum
Association (Kebschull 2004), which used a computer model to simulate
the effect of changing SUV mass or footprint (without changing other
attributes of the vehicle) on crash outcomes, and showed a 15 percent
net decrease in injuries, while increasing wheelbase by 4.5 inches
while maintaining weight showed a 26 percent net decrease in serious
injuries.
    Agencies' response: The agencies have reviewed Mr. Wenzel's draft
report for DOE to which he referred in his comments, but based on
NHTSA's work do not find such a wide range of safety risk for vehicles
with the same weight, although we agree there is a range of risk for a
given footprint. Wenzel found that for drivers, casualty risk does
generally decrease as weight or footprint increases, especially for
passenger cars, and that in terms of risk imposed on the drivers of
other vehicles, risk increases as light truck weight or footprint
increases, but concluded that the variation in the data precluded the
possibility of drawing any conclusions. In the 2010 Kahane study
presented in the FRIA, NHTSA undertook a similar analysis in which it
correlated weight to fatality risk for vehicles of essentially the same
footprint.\133\ The ``decile analysis,'' provided as a check on the
trend/direction of NHTSA's regression analysis, shows that societal
fatality risk generally increases and rarely decreases for lighter
relative to heavier cars of the same footprint. Thus, while Mr. Wenzel
was reluctant to draw a conclusion, NHTSA believes that both our
research and Mr. Wenzel's appear to point to the same conclusion. We
agree that there is a wide range in casualty risk among cars of the
same footprint, but we find that that casualty risk is correlated with
weight. The correlation shows that heavier cars have lower overall
societal fatality rates than lighter cars of very similar footprint.
---------------------------------------------------------------------------

    \133\ Subsections 2.4 and 3.3 of new report.
---------------------------------------------------------------------------

    The agencies agree that simulation can be beneficial in certain
circumstances. NHTSA cautions, however, that it is difficult for a
simulation analysis to capture the full range of variations in crash
situations in the way that a statistical regression analysis does.
Vehicle crash dynamics are complex, and small changes in initial crash
conditions (such as impact angle or closing speed) can have large
effects on injury outcome. This condition is a consequence of
variations in the deformation mode of individual components (e.g.,
buckling, bending, crushing, material failure, etc.) and how those
variations affect the creation and destruction of load paths between
the impacting object and the occupant compartment during the crash
event. It is therefore difficult to predict and assess structural
interactions using computational methods when one does not have a
detailed, as-built geometric and material model. Even when a complete
model is available, prudent engineering assessments require extensive
physical testing to verify crash behavior and safety. Despite all this,
the agencies recognize that detailed crash simulations can be useful in
estimating the relative structural effects of design changes over a
limited range of crash conditions, and will continue to evaluate the
appropriate use of this tool in the future.
    Simplified crash simulations can also be valuable tools, but only
when employed as part of a comprehensive analytical program. They are
especially valuable in evaluating the relative effect and associated
confidence intervals of feasible design alternatives. For example, the
method employed by Nusholtz et al.\134\ could be used by a vehicle
designer to estimate the benefit of incremental changes in mass or
wheelbase as well as the tradeoffs that might be made between them once
that designer has settled on a preliminary design. A key difference
between the research by Nusholtz and the research by Kebschull that Mr.
Wenzel cited \135\ is in their suggested applications. The former is
useful in evaluating proposed alternatives early in the design
process--Nusholtz specifically warns that the model provides only
``general insights into the overall risk * * * and cannot be used to
obtain specific response characteristics.'' Mr. Wenzel implies the
latter can ``isolate the effect of specific design changes, such as
weight reduction'' and thus quantify the fleet-wide effect of
substantial vehicle redesigns. Yet while Kebschull reports injury
reductions to three significant digits, there is no validation that
vehicle structures of the proposed weight and stiffness are even
feasible with current technology. Thus, while the agencies agree that
computer simulations can be useful tools, we also recognize the value
of statistical regression analysis for determining fleet-wide effects,
because it inherently incorporates real-world factors in historical
safety assessments.
---------------------------------------------------------------------------

    \134\ Nusholtz, G.S., G. Rabbiolo, and Y. Shi, ``Estimation of
the Effects of Vehicle Size and Mass on Crash-Injury Outcome Through
Parameterized Probability Manifolds,'' Society of Automotive
Engineers (2003), Document No. 2003-01-0905. Available at http://
www.sae.org/technical/papers/2003-01-0905 (last accessed Feb. 15,
2010).
    \135\ Mr. Wenzel cites the report by Kebschull et al. [2004,
DRI-TR-04-04-02] as an example of what he regards as the effective
use of computer crash simulation. NHTSA does not concur that this
analysis represents a viable analytical method for evaluating the
fleet-wide tradeoffs between vehicle mass and societal safety. The
simulation method employed was not a full finite element
representation of each major structural component in the vehicles in
question. Instead, an Articulated Total Body (ATB) representation
was constructed for each of two representative vehicles. In the ATB
model, large structural subsystems were represented by a single
ellipsoid. Consolidated load-deflection properties of these
subsystems and the joints that tie them together were ``calibrated''
for an ATB vehicle model by requiring that it reproduce the
acceleration pulse of a physical NHTSA crash test. NHTSA notes that
vehicle simulation models that are calibrated to a single crash test
configuration (e.g., a longitudinal NCAP test into a rigid wall) are
often ill-equipped to analyze alternative crash scenarios (e.g.,
vehicle-to-vehicle crashes at arbitrary angles and lateral offsets).

DRI's analysis shows that lighter vehicles will save lives, and NHTSA
---------------------------------------------------------------------------
reaches the opposite conclusion without disproving DRI's analysis

    The difference between NHTSA's results and DRI's results for the
relationship between vehicle mass and vehicle safety has been at the
crux of this issue for several years. While NHTSA offered some theories
in the NPRM as to why DRI might have found a safety benefit for mass
reduction, NHTSA's work since then has enabled it to identify what we
believe is the most likely reason for DRI's findings.

The potential near multicollinearity of the variables of curb weight,
track width, and wheelbase creates some degree of concern that any
regression models with those variables could inaccurately calibrate
their effects. However, based on its own experience with statistical
analysis, NHTSA believes that the specific two-step regression model
used by DRI increases this concern, because it weakens relationships
between curb weight and dependent variables by splitting the effect of
curb weight across the two regression steps.
    The comments below are in response to NHTSA's theories in the NPRM
about the source of the differences between NHTSA's and DRI's results.
The majority of them are answered more fully in the 2010 Kahane report
included in NHTSA's FRIA, but we respond to them in this document as
well for purposes of completeness.

NHTSA and DRI may have reached different conclusions because NHTSA's
study does not distinguish between reductions in size and reductions in
weight like DRI's

    Several commenters (CARB, CBD, EDF, ICCT, NRDC, and UCS) stated
that DRI had been able to separate the effect of size and weight in its
analysis, and in so doing proved that there was a safety benefit to
reducing weight without reducing size. The commenters suggested that if
NHTSA properly distinguished between reductions in size and reductions
in weight, it would find the same result as DRI.
    Agencies' response: In the 2010 Kahane analysis presented in the
FRIA, NHTSA did attempt to separate the effects of vehicle size and
weight by performing regression analyses with footprint (or
alternatively track width and wheelbase) and curb weight as separate
independent variables. For passenger cars, NHTSA found that the
regressions attribute the fatality increase due to downsizing about
equally to mass and footprint--that is, the effect of reducing mass
alone is about half the effect of reducing mass and reducing footprint.
Unlike DRI's results, NHTSA's regressions for passenger cars and for
lighter LTVs did not find a safety benefit to reducing weight without
reducing size; while NHTSA did find a safety benefit for reducing
weight in the heaviest LTVs, the magnitude of the benefit as compared
to DRI's was significantly smaller. NHTSA believes that these
differences in results may be an artifact of DRI's two-step regression
model, as explained above.

NHTSA and DRI may have reached different conclusions because NHTSA's
study does not include two-door cars like DRI's

    One of NHTSA's primary theories in the NPRM as to why NHTSA and
DRI's results differed related to DRI's inclusion in its analysis of 2-
door cars. NHTSA had excluded those vehicles from its analysis on the
grounds that 2-door cars had a disproportionate crash rate (perhaps due
to their inclusion of muscle and sports cars) which appeared likely to
skew the regression. Several commenters argued that NHTSA should have
included 2-door cars in its analysis. DRI and James Adcock stated that
2-door cars should not be excluded because they represent a significant
portion of the light-duty fleet, while CARB and ICCT stated that
because DRI found safety benefits whether 2-door cars were included or
not, NHTSA should include 2-door cars in its analysis. Wenzel also
commented that NHTSA should include 2-door cars in subsequent analyses,
stating that while his analysis of MY 2000-2004 crash data from 5
states indicates that, in general, 4-door cars tend to have lower
fatality risk than 2-door cars, the risk is even lower when he accounts
for driver age/gender and crash location. Wenzel suggested that the
increased fatality risk in the 2-door car population seemed primarily
attributable to the sports cars, and that that was not sufficient
grounds to exclude all 2-door cars from NHTSA's analysis.
    Agencies' response: The agencies agree that 2-door cars can be
included in the analysis, and NHTSA retracts previous statements that
DRI's inclusion of them was incorrect. In its 2010 analysis, NHTSA
finds that it makes little difference to the results whether 2-door
cars are included, partially included, or excluded from the analysis.
Thus, analyses of 2-door and 4-door cars combined, as well as other
combinations, have been included in the analysis. That said, no
combination of 2-door and 4-door cars resulted in NHTSA's finding a
safety benefit for passenger cars due to mass reduction.

NHTSA and DRI may have reached different conclusions due to different
assumptions

    DRI commented that the differences found between its study and
NHTSA's may be due to the different assumptions about the linearity of
the curb weight effect and control variable for driver age, vehicle
age, road conditions, and other factors. NHTSA's analysis was based on
a two-piece linear model for curb weight with two different weight
groups (less than 2,950 lbs., and greater than or equal to 2.950 lbs).
The DRI analysis assumed a linear model for curb weight with a single
weight group. Additionally, DRI stated that NHTSA's use of eight
control variables (rather than three control variables like DRI used)
for driver age introduces additional degrees of freedom into the
regressions, which it suggested may be correlated with the curb weight,
wheelbase, and track width, and/or other control variables. DRI
suggested that this may also affect the results and cause or contribute
to the differences in outcomes between NHTSA and DRI.
    Agencies' response: NHTSA's FRIA documents that NHTSA analyzed its
database using both a single parameter for weight (a linear model) and
two parameters for weight (a two-piece linear model). In both cases,
the logistic regression responded identically, allocating the same way
between weight, wheelbase, track width, or footprint.\136\ Thus, NHTSA
does not believe that the differences between its results and DRI's
results are due to whether the studies used a single weight group or
two weight groups.
---------------------------------------------------------------------------

    \136\ Subsections 2.2 and 2.3 of new report.
---------------------------------------------------------------------------

    The FRIA also documents that NHTSA examined NHTSA's use of eight
control variables for driver age (ages 14-30, 30-50, 50-70, 70+ for
males and females separately, versus DRI's use of three control
variables for age (FEMALE = 1 for females, 0 for males, YOUNGDRV = 35-
AGE for drivers under 35, 0 for all others, OLDMAN = AGE-50 for males
over 50, 0 for all others; OLDWOMAN = AGE-45 for females over 45, 0 for
all others) to see if that affected the results. NHTSA ran its analysis
using the eight control variables and again using three control
variables for age, and obtained similar results each time.\137\ Thus,
NHTSA does not believe that the differences between its results and
DRI's results are due to the number of control variables used for
driver age.
---------------------------------------------------------------------------

    \137\ Id.

NHTSA's and DRI's conclusions may be similar if confidence intervals
---------------------------------------------------------------------------
are taken into account

    DRI commented that NHTSA has not reported confidence intervals,
while DRI has reported them in its studies. Thus, DRI argued, it is not
possible to determine whether the confidence intervals overlap and
whether the differences between NHTSA's and DRI's analyses are
statistically significant.
    Agencies' response: NHTSA has included confidence intervals for the
main results of the 2010 Kahane analysis, as shown in Chapter IX of
NHTSA's FRIA. For passenger cars, the NHTSA results are a statistically

significant increase in fatalities with a 100 pound reduction while
maintaining track width and wheelbase (or footprint); the DRI results
are a statistically significant decrease in fatalities with a 100 pound
reduction while maintaining track width and wheelbase. The DRI results
are thus outside the confidence bounds of the NHTSA results and do not
overlap.

NHTSA should include a ``best-case'' estimate in its study

    Several commenters (Center for Auto Safety, NRDC, Public Citizen,
Sierra Club et al., and Wenzel) urged NHTSA to include a ``best-case''
estimate in the final rule, showing scenarios in which lives were saved
rather than lost. Public Citizen stated that there would be safety
benefits to reducing the weight of the heaviest vehicles while leaving
the weight of the lighter vehicles unchanged, and that increasing the
number of smaller vehicles would provide safety benefits to
pedestrians, bicyclists, and motorcyclists. Sierra Club et al. stated
that new materials, smart design, and lighter, more advanced engines
can all improve fuel economy while maintaining or increasing vehicle
safety. Both Center for Auto Safety and Sierra Club argued that the
agency should have presented a ``best-case'' scenario to balance out
the ``worst-case'' scenario presented in the NPRM, especially if NHTSA
itself believed that the worst-case scenario was not inevitable. NRDC
requested that NHTSA present both a ``best-case'' and a ``most likely''
scenario. Wenzel simply stated that NHTSA did not present a ``best-
case'' scenario, despite DRI's finding in 2005 that fatalities would be
reduced if track width was held constant.
    Agencies' response: NHTSA has included an ``upper estimate'' and a
``lower estimate'' in the new 2010 Kahane analysis. The lower estimate
assumes that mass reduction will be accomplished entirely by material
substitution or other techniques that do not perceptibly change a
vehicle's shape, structural strength, or ride quality. The lower
estimate examines specific crash modes and is meant to reflect the
increase in fatalities for the specific crash modes in which a
reduction in mass per se in the case vehicle would result in a
reduction in safety: namely, collisions with larger vehicles not
covered by the regulations (e.g., trucks with a GVWR over 10,000 lbs),
collisions with partially-movable objects (e.g., some trees, poles,
parked cars, etc.), and collisions of cars or light LTVs with heavier
LTVs--as well as the specific crash modes where a reduction in mass per
se in the case vehicle would benefit safety: namely, collisions of
heavy LTVs with cars or lighter LTVs. NHTSA believes that this is the
effect of mass per se, i.e., the effects of reduced mass will generally
persist in these crashes regardless of how the mass is reduced. The
lower estimate attempts to quantify that scenario, although any such
estimate is hypothetical and subject to considerable uncertainty. NHTSA
believes that a ``most likely'' scenario cannot be determined with any
certainty, and would depend entirely upon agency assumptions about how
manufacturers intend to reduce mass in their vehicles. While we can
speculate upon the potential effects of different methods of mass
reduction, we cannot predict with certainty what manufacturers will
ultimately do.

NHTSA should not include a ``worst-case'' estimate in its study

    NRDC, Public Citizen and Sierra Club et al. commented that NHTSA
should remove the ``worst-case scenario'' estimate from the rulemaking,
generally because it was based on an analysis that evaluated historical
vehicles, and future vehicles would be sufficiently different to render
the ``worst-case scenario'' inapplicable.
    Agencies' response: NHTSA stated in the NPRM that the ``worst-case
scenario'' addressed the effect of a kind of downsizing (i.e., mass
reduction accompanied by footprint reduction) that was not likely to be
a consequence of attribute-based CAFE standards, and that the agency
would refine its analysis of such a scenario for the final rule. NHTSA
has not used the ``worst-case scenario'' in the final rule. Instead, we
present three scenarios: the first is an estimate based directly on the
regression coefficients of weight reduction while maintaining footprint
in the statistical analyses of historical data. As discussed above,
presenting this scenario is possible because NHTSA attempted to
separate the effects of weight and footprint reduction in the new
analysis. However, even the new analysis of LTVs produced some
coefficients that NHTSA did not consider entirely plausible. NHTSA also
presents an ``upper estimate'' in which those coefficients for the LTVs
were adjusted based on additional analyses and expert opinion as a
safety agency and a ``lower estimate,'' which estimates the effect if
mass reduction is accomplished entirely by safety-conscious
technologies such as material substitution.
3. How has NHTSA refined its analysis for purposes of estimating the
potential safety effects of this Final Rule?
    During the past months, NHTSA has extensively reviewed the
literature on vehicle mass, size, and fatality risk. NHTSA now agrees
with DRI and other commenters that it is essential to analyze the
effect of mass independently from the effects of size parameters such
as wheelbase, track width, or footprint--and that the NPRM's ``worst-
case'' scenario based on downsizing (in which weight, wheelbase, and
track width could all be changed) is not useful for that purpose. The
agency should instead provide estimates that better reflect the more
likely effect of the regulation--estimating the effect of mass
reduction that maintains footprint.
    Yet it is more difficult to analyze multiple, independent
parameters than a single parameter (e.g., curb weight), because there
is a potential concern that the near multicollinearity of the
parameters--the strong, natural and historical correlation of mass and
size--can lead to inaccurate statistical estimates of their
effects.\138\ NHTSA has performed new statistical analyses of its
historical database of passenger cars, light trucks, and vans (LTVs)
from its 2003 report (now including also 2-door cars), assessing
relationships between fatality risk, mass, and footprint. They are
described in Subsections 2.2 (cars) and 3.2 (LTVs) of the 2010 Kahane
report presented in Chapter IX of the FRIA. While the potential
concerns associated with near multicollinearity are inherent in
regression analyses with multiple size/mass parameters, NHTSA believes
that the analysis approach in the 2010 Kahane report, namely a single-
step regression analysis, generally reduces those concerns \139\ and
models the trends in the historical data. The results differ
substantially from DRI's, based on a two-step regression analysis.
Subsections 2.3 and 2.4 of the 2010

Kahane report attempt to account for the differences primarily by
applying selected techniques from DRI's analyses to NHTSA's database.
---------------------------------------------------------------------------

    \138\ Greene, W. H. (1993). Econometric Analysis, Second
Edition. New York: Macmillan Publishing Company, pp. 266-268;
Allison, P.D. (1999), Logistic Regression Using the SAS System.
Cary, NC: SAS Institute Inc., pp. 48-51. The report shows variance
inflation factor (VIF) scores in the 5-7 range for curb weight,
wheelbase, and track width (or, alternatively, curb weight and
footprint) in NHTSA's database, exceeding the 2.5 level where near
multicollinearity begins to become a concern in logistic regression
analyses.
    \139\ NHTSA believes that, given the near multicollinearity of
the independent variables, the two-step regression augments the
possibility of estimating inaccurate coefficients for curb weight,
because it weakens relationships between curb weight and dependent
variables by splitting the effect of curb weight across the two
regression steps as discussed further in Subsection 2.3 of NHTSA's
report.
---------------------------------------------------------------------------

    The statistical analyses--logistic regressions--of trends in MYs
1991-1999 vehicles generate one set of estimates of the possible
effects of reducing mass by 100 pounds while maintaining footprint.
While these effects might conceivably carry over to future mass
reductions, there are two reasons that future safety effects of mass
reduction could differ from projections from historical data:
     The statistical analyses are ``cross-sectional'' analyses
that estimate the increase in fatality rates for vehicles weighing n-
100 pounds relative to vehicles weighing n pounds, across the spectrum
of vehicles on the road, from the lightest to the heaviest. They do not
directly compare the fatality rates for a specific make and model
before and after a 100-pound reduction from that model. Instead, they
use the differences across makes and models as a surrogate for the
effects of actual reductions within a specific model; those cross-
sectional differences could include trends that are statistically, but
not causally related to mass.
     The manner in which mass changed across MY 1991-1999
vehicles might not be consistent with future mass reductions, due to
the availability of newer materials and design methods.

Therefore, Subsections 2.5 and 3.4 of the 2010 Kahane report supplement
those estimates with one or more scenarios in which some of the
logistic regression coefficients are replaced by numbers based on
additional analyses and NHTSA's judgment of the likely effect of mass
per se (the ability to transfer momentum to other vehicles or objects
in a collision) and of what trends in the historical data could be
avoided by current mass-reduction technologies such as materials
substitution. The various scenarios may be viewed as a plausible range
of point estimates for the effects of mass reduction while maintaining
footprint, but they should not be construed as upper and lower bounds.
Furthermore, being point estimates, they are themselves subject to
uncertainties, such as, for example, the sampling errors associated
with statistical analyses.
    The principal findings and conclusions of the 2010 Kahane report
are as follows:
    Passenger cars: This database with the one-step regression method
of the 2003 Kahane report estimates an increase of 700-800 fatalities
when curb weight is reduced by 100 pounds and footprint is reduced by
0.65 square feet (the historic average footprint reduction per 100-
pound mass reduction in cars). The regression attributes the fatality
increase about equally to curb weight and to footprint. The results are
approximately the same whether 2-door cars are fully included or
partially included in the analysis or whether only 4-door cars are
included (as in the 2003 report). Regressions by curb weight, track
width and wheelbase produce findings quite similar to the regressions
by curb weight and footprint, but the results with the single ``size''
variable, footprint, rather than the two variables, track width and
wheelbase vary even less with the inclusion or exclusion of 2-door
cars.
    In Subsection 2.3 of the new report, a two-step regression method
that resembles (without exactly replicating) the approach by DRI, when
applied to the same (NHTSA's) crash and registration data, estimates a
large benefit when mass is reduced, offset by even larger fatality
increases when track width and wheelbase (or footprint) are reduced.
NHTSA believes that the benefit estimated by this method is inaccurate,
due to the potential concerns with the near multicollinearity of the
parameters (curb weight, track width, and wheelbase) \140\ even though
the analysis is theoretically unbiased.\141\ Almost any analysis
incorporating those parameters has a possibility of inaccurate
coefficients due to near multicollinearity; however, based on our own
experience with other regression analyses of crash data, NHTSA believes
a DRI-type two-step method augments the possibility of estimating
inaccurate coefficients for curb weight, because it weakens
relationships between curb weight and dependent variables by splitting
the effect of curb weight across the two regression steps.
---------------------------------------------------------------------------

    \140\ As evidenced by VIF scores in the 5-7 range, exceeding the
2.5 level where near multicollinearity begins to become a concern in
logistic regression analyses.
    \141\ Subsection 2.3 of the 2010 Kahane report attempts to
explain why the two-step method, when applied to NHTSA's 2003
database, produces results a lot like DRI's, but it does not claim
that DRI obtained its results from its own database for exactly
those reasons. NHTSA did not analyze DRI's database. The two-step
method is ``theoretically unbiased'' in the sense that it seeks to
estimate the same parameters as the one-step analysis.
---------------------------------------------------------------------------

    In Subsection 2.4 of the new report, as a check on the results from
the regression methods, NHTSA also performed what we refer to as
``decile'' analyses: Simpler, tabular data analysis that compares
fatality rates of cars of different mass but similar footprint. Decile
analysis is not a precise tool because it does not control for
confounding factors such as driver age/gender or the specific type of
car, but it may be helpful in identifying the general directional trend
in the data when footprint is held constant and curb weight varies. The
decile analyses show that fatality risk in MY 1991-1999 cars generally
increased and rarely decreased for lighter relative to heavier cars of
the same footprint. They suggest that the historical, cross-sectional
trend was generally in the lighter [harr] more fatalities direction and
not in the opposite direction, as might be suggested by the regression
coefficients from the method that resembles DRI's approach.
    The regression coefficients from NHTSA's one-step method suggest
that mass and footprint each accounted for about half the fatality
increase associated with downsizing in a cross-sectional analysis of
1991-1999 cars. They estimate the historical difference in societal
fatality rates (i.e., including fatalities to occupants of all the
vehicles involved in the collisions, plus any pedestrians) of cars of
different curb weights but the same footprint. They may be considered
an ``upper-estimate scenario'' of the effect of future mass reduction--
if it were accomplished in a manner that resembled the historical
cross-sectional trend--i.e., without any particular regard for safety
(other than not to reduce footprint).
    However, NHTSA believes that future vehicle design is likely to
take advantage of safety-conscious technologies such as materials
substitution that can reduce mass without perceptibly changing a car's
shape or ride and maintain its structural strength. This could avoid
much of the risk associated with lighter and smaller vehicles in the
historical analyses, especially the historical trend toward higher
crash-involvement rates for lighter and smaller vehicles.\142\ It could
thereby shrink the added risk close to just the effects of mass per se
(the ability to transfer momentum to other vehicles or objects in a
collision). Subsection 2.5 of the 2010 Kahane report attempts to
quantify a ``lower-estimate scenario'' for the potential effect of mass
reduction achieved by safety-conscious technologies; the estimated
effects are substantially smaller than in the upper-

estimate scenario based directly on the regression results.
---------------------------------------------------------------------------

    \142\ This is discussed in greater depth in Subsections 2.1 and
2.5 of the 2010 Kahane report. The historic trend toward higher
crash-involvement rates for lighter and smaller vehicles is
documented in IIHS Advisory No. 5, July 1988, http://www.iihs.org/
research/advisories/iihs_advisory_5.pdf; IIHS News Release,
February 24, 1998, http://www.iihs.org/news/1998/iihs_news_
022498.pdf; Auto Insurance Loss Facts, September 2009, http://
www.iihs.org/research/hldi/fact_sheets/CollisionLoss_0909.pdf.
---------------------------------------------------------------------------

    We note, again, that the preceding paragraph is conditional.
Nothing in the CAFE standard requires manufacturers to use material
substitution or, more generally, take a safety-conscious approach to
mass reduction.\143\ Federal Motor Vehicle Safety Standards include
performance tests that verify historical improvements in structural
strength and crashworthiness, but few FMVSS provide test information
that sheds light about how a vehicle rides or otherwise helps explain
the trend toward higher crash-involvement rates for lighter and smaller
vehicles. It is possible that using material substitution and other
current mass reduction methods could avoid the historical trend in this
area, but that remains to be studied as manufacturers introduce more of
these vehicles into the on-road fleet in coming years. A detailed
discussion of methods currently used for reducing the mass of passenger
cars and light trucks is included in Chapter 3 of the Technical Support
Document.
---------------------------------------------------------------------------

    \143\ Footprint-based standards do not specify how or where to
remove mass while maintaining footprint, nor do they categorically
forbid footprint reductions, even if they discourage them.
---------------------------------------------------------------------------

    LTVs: The principal difference between LTVs and passenger cars is
that mass reduction in the heavier LTVs is estimated to have
significant societal benefits, in that it reduces the fatality risk for
the occupants of cars and light LTVs that collide with the heavier
LTVs. By contrast, footprint (size) reduction in LTVs has a harmful
effect (for the LTVs' own occupants), as in cars. The regression method
of the 2003 Kahane report applied to the database of that report
estimates a societal increase of 231 fatalities when curb weight is
reduced by 100 pounds and footprint is reduced by 0.975 square feet
(the historic average footprint reduction per 100-pound mass reduction
in LTVs). But the regressions attribute an overall reduction of 266
fatalities to the 100-pound mass reduction and an increase of 497
fatalities to the .975-square-foot footprint reduction. The regression
results constitute one of the scenarios for the possible societal
effects of future mass reduction in LTVs.
    However, NHTSA cautions that some of the regression coefficients,
even by NHTSA's preferred method, might not accurately model the
historical trend in the data, possibly due to near multicollinearity of
curb weight and footprint or because of the interaction of both of
these variables with LTV type.\144\ Based on supplementary analyses and
discussion in Subsections 3.3 and 3.4, the new report defines an
additional upper-estimate scenario that NHTSA believes may more
accurately reflect the historical trend in the data and a lower-
estimate scenario that may come closer to the effects of mass per se.
All three scenarios, however, attribute a societal fatality reduction
to mass reduction in the heavier LTVs.
---------------------------------------------------------------------------

    \144\ For example, mid-size SUVs of the 1990s typically had high
mass relative to their short wheelbase and footprint (and
exceptionally high rates of fatal rollovers); minivans typically
have low mass relative to their footprint (and low fatality rates);
heavy-duty pickup trucks used extensively for work tend to have more
mass, for the same footprint, as basic full-sized pickup trucks that
are more often used for personal transportation.
---------------------------------------------------------------------------

    Overall effects of mass reduction while maintaining footprint in
cars and LTVs: The immediate purpose of the new report's analyses of
relationships between fatality risk, mass, and footprint is to develop
the four parameters that the Volpe model needs in order to predict the
safety effects, if any, of the modeled mass reductions in MYs 2012-2016
cars and LTVs over the lifetime of those vehicles. The four numbers are
the overall percentage increases or decreases, per 100-pound mass
reduction while holding footprint constant, in crash fatalities
involving: (1) Cars < 2,950 pounds (which was the median curb weight of
cars in MY 1991-1999), (2) cars >= 2,950 pounds, (3) LTVs < 3,870
pounds (which was the median curb weight of LTVs in those model years),
and (4) LTVs >= 3,870 pounds. Here are the percentage effects for each
of the three alternative scenarios, again, the ``upper-estimate
scenario'' and the ``lower-estimate scenario'' have been developed
based on NHTSA's expert opinion as a vehicle safety agency:

                               Fatality Increase per 100-Pound Reduction (%) \145\
----------------------------------------------------------------------------------------------------------------
                                                                               NHTSA expert
                                                         Actual regression    opinion upper-      NHTSA expert
                                                          result scenario   estimate scenario    opinion lower-
                                                                                \146\        estimate scenario
----------------------------------------------------------------------------------------------------------------
Cars < 2,950 pounds....................................               2.21               2.21               1.02
Cars >= 2,950 pounds...................................               0.90               0.90               0.44
LTVs < 3,870 pounds....................................               0.17               0.55               0.41
LTVs >= 3,870 pounds...................................              -1.90              -0.62              -0.73
----------------------------------------------------------------------------------------------------------------

    In all three scenarios, the estimated effects of a 100-pound mass
reduction while maintaining footprint are an increase in fatalities in
cars < 2,950 pounds, substantially smaller increases in cars >= 2,950
pounds and LTVs < 3,870 pounds, and a societal benefit for LTVs >=
3,870 pounds (because it reduces fatality risk to occupants of cars and
lighter LTVs they collide with). These are the estimated effects of
reducing each vehicle by exactly 100 pounds. However, the actual mass
reduction will vary by make, model, and year. The aggregate effect on
fatalities can only be estimated by attempting to forecast, as NHTSA
has using inputs to the Volpe model, the mass reductions by make and
model. It should be noted, however, that a 100-pound reduction would be
5 percent of the mass of a 2000-pound car but only 2 percent of a 5000-
pound LTV. Thus, a forecast that mass will decrease by an equal or
greater percentage in the heavier vehicles than in the lightest cars
would be proportionately more influenced by the benefit for mass
reduction in the heavy LTVs than by the fatality increases in the other
groups; it is likely to result in an estimated net benefit under one or
more of the scenarios. It should also be noted, again, that the

three scenarios are point estimates and are subject to uncertainties,
such as the sampling errors associated with the regression results. In
the scenario based on actual regression results, the 1.96-sigma
sampling errors in the above estimates are  0.91 percentage
points for cars < 2,950 pounds and also for cars >= 2,950 pounds,
 0.82 percentage points for LTVs < 3,870 pounds, and  1.18 percentage points for LTVs >= 3,870 pounds. In other words,
the fatality increase in the cars < 2,950 pounds and the societal
fatality reduction attributed to mass reduction in the LTVs >= 3,870
pounds are statistically significant. The sampling errors associated
with the scenario based on actual regression results perhaps also
indicate the general level of statistical noise in the other two
scenarios.
---------------------------------------------------------------------------

    \145\ Reducing mass by 100 pounds in these vehicles is estimated
to have the listed percentage effect on fatalities in crashes
involving these vehicles. For example, if these vehicles are
involved in crashes that result in 10,000 fatalities, 2.21 means
that if mass is reduced by 100 pounds, fatalities will increase to
10,221 and -0.73 means fatalities will decrease to 9,927. In the
scenario based on actual regression results, the 1.96-sigma sampling
errors in the above estimates are 0.91 percentage points
for cars < 2,950 pounds and also for cars >= 2,950 pounds, 0.82 percentage points for LTVs < 3,870 pounds, and 1.18 percentage points for LTVs >= 3,870 pounds. In other
words, the fatality increase in the cars < 2,950 pounds and the
societal fatality reduction attributed to mass reduction in the LTVs
>= 3,870 pounds are statistically significant. The sampling errors
associated with the scenario based on actual regression results
perhaps also indicate the general level of statistical noise in the
other two scenarios.
    \146\ For passenger cars, the upper-estimate scenario is the
actual-regression-result scenario.
---------------------------------------------------------------------------

4. What are the estimated safety effects of this Final Rule?
    The table below shows the estimated safety effects of the modeled
reduction in vehicle mass provided in the NPRM and in this final rule
in order to meet the MYs 2012-2016 standards, based on the analysis
described briefly above and in much more detail in Chapter IX of the
FRIA. These are combined results for passenger cars and light trucks. A
positive number is an estimated increase in fatalities and a negative
number (shown in parentheses) is an estimated reduction in fatalities
over the lifetime of the model year vehicles compared to the MY 2011
baseline fleet.

----------------------------------------------------------------------------------------------------------------
                                   MY 2012         MY 2013         MY 2014          MY 2015          MY 2016
----------------------------------------------------------------------------------------------------------------
NPRM ``Worst Case''..........              34              54             194              313              493
NHTSA Expert Opinion Final                  9              14              26               24               22
 Rule Upper Estimate.........
NHTSA Expert Opinion Final                  2               4             (17)             (53)             (80)
 Rule Lower Estimate.........
Actual Regression Result                    0               2             (94)            (206)            (301)
 Scenario....................
----------------------------------------------------------------------------------------------------------------

    NHTSA emphasizes that the table above is based on the NHTSA's
assumptions about how manufacturers might choose to reduce the mass of
their vehicles in response to the final rule, which are very similar to
EPA's assumptions. In general, as discussed above, the agencies assume
that mass will be reduced by as much as 10 percent in the heaviest LTVs
but only by as much as 5 percent in other vehicles and that substantial
mass reductions will take place only in the year that models are
redesigned. The actual mass reduction that is likely to occur in
response to the standards will of course vary by make and model,
depending on each manufacturer's particular approach, with likely more
opportunity for the largest LTVs that still use separate frame
construction.
    The ``upper estimate'' presented above, as discussed in the FRIA,
assumes only that manufacturers will reduce vehicle mass without
reducing footprint. Thus, under such a scenario, safety effects could
be somewhat adverse if, for example, manufacturers chose to reduce
crush space associated with vehicle overhang as a way of reducing mass
without changing footprint. The ``lower estimate,'' in turn, is based
on the assumption that manufacturers will reduce vehicle mass solely
through methods like material substitution, which (under these
assumptions) fully maintain not only footprint but also all structural
integrity, and other aspects of vehicle safety. Under these scenarios,
safety effects could be worse if mass reduction was not undertaken
thoughtfully to maintain existing safety levels, but could also be
better if it was undertaken with a thorough and extensive vehicle
redesign to maximize both mass reduction and safety.
    And finally, while NHTSA does not believe that the ``worst-case''
scenario presented in the NPRM is likely to occur during the MYs 2012-
2016 timeframe, we cannot guarantee that manufacturers will never
choose to reduce vehicle footprint, particularly if market forces lead
to increased sales of small vehicles in response to sharp increases in
the price of petroleum, though this situation would not be in direct
response to the CAFE/GHG standards. Thus, we cannot completely reject
the worst-case scenario for all vehicles, although we can and do
recognize that the footprint-based standards will significantly limit
the likelihood of its occurrence within the context of this rulemaking.
    In summary, the agencies recognize the balancing inherent in
achieving higher levels of fuel economy and lower levels of
CO2 emissions through reduction of vehicle mass. Based on
the 2010 Kahane analysis that attempts to separate the effects of mass
reductions and footprint reductions, and to account better for the
possibility that mass reduction will be accomplished entirely through
methods that preserves structural strength and vehicle safety, the
agencies now believe that the likely deleterious safety effects of the
MYs 2012-2016 standards may be much lower than originally estimated.
They may be close to zero, or possibly beneficial if mass reduction is
carefully undertaken in the future and if the mass reduction in the
heavier LTVs is greater (in absolute terms) than in passenger cars. In
light of these findings, we believe that the balancing is reasonable.
5. How do the agencies plan to address this issue going forward?
    NHTSA and EPA believe that it is important for the agencies to
conduct further study and research into the interaction of mass, size
and safety to assist future rulemakings. The agencies intend to begin
working collaboratively and to explore with DOE, CARB, and perhaps
other stakeholders an interagency/intergovernmental working group to
evaluate all aspects of mass, size and safety. It would also be the
goal of this team to coordinate government supported studies and
independent research, to the extent possible, to help ensure the work
is complementary to previous and ongoing research and to guide further
research in this area. DOE's EERE office has long funded extensive
research into component advanced vehicle materials and vehicle mass
reduction. Other agencies may have additional expertise that will be
helpful in establishing a coordinated work plan. The agencies are
interested in looking at the weight-safety relationship in a more
holistic (complete vehicle) way, and thanks to this CAFE rulemaking
NHTSA has begun to bring together parts of the agency--crashworthiness,
and crash avoidance rulemaking offices and the agency's Research &
Development office--in an interdisciplinary way to better leverage the
expertise of the agency. Extending this effort to other agencies will
help to ensure that all aspects of the weight-safety relationship are
considered completely and carefully with our future research. The
agencies also intend to carefully consider comments received in
response to the NPRM in developing plans for future studies and
research and to solicit input from stakeholders.
    The agencies also plan to watch for safety effects as the U.S.
light-duty vehicle fleet evolves in response both to the CAFE/GHG
standards and to consumer preferences over the next several years.
Additionally, as new and

advanced materials and component smart designs are developed and
commercialized, and as manufacturers implement them in more vehicles,
it will be useful for the agencies to learn more about them and to try
to track these vehicles in the fleet to understand the relationship
between vehicle design and injury/fatality data. Specifically, the
agencies intend to follow up with study and research of the following:
    First, NHTSA is in the process of contracting with an independent
institution to review the statistical methods that NHTSA and DRI have
used to analyze historical data related to mass, size and safety, and
to provide recommendation on whether the existing methods or other
methods should be used for future statistical analysis of historical
data. This study will include a consideration of potential near
multicollinearity in the historical data and how best to address it in
a regression analysis. This study is being initiated because, in
response to the NPRM, NHTSA received a number of comments related to
the methodology NHTSA used for the NPRM to determine the relationship
between mass and safety, as discussed in detail above.
    Second, NHTSA and EPA, in consultation with DOE, intend to begin
updating the MYs 1991-1999 database on which the safety analyses in the
NPRM and final rule are based with newer vehicle data in the next
several months. This task will take at least a year to complete. This
study is being initiated in response to the NPRM comments related to
the use of data from MYs 1991-1999 in the NHTSA analysis, as discussed
in detail above.
    Third, in order to assess if the design of recent model year
vehicles that incorporate various mass reduction methods affect the
relationships among vehicle mass, size and safety, NHTSA and EPA intend
to conduct collaborative statistical analysis, beginning in the next
several months. The agencies intend to work with DOE to identify
vehicles that are using material substitution and smart design. After
these vehicles are identified, the agencies intend to assess if there
are sufficient data for statistical analysis. If there are sufficient
data, statistical analysis would be conducted to compare the
relationship among mass, size and safety of these smart design vehicles
to vehicles of similar size and mass with more traditional designs.
This study is being initiated because, in response to the NPRM, NHTSA
received comments related to the use of data from MYs 1991-1999 in the
NHTSA analysis that did not include new designs that might change the
relationship among mass, size and safety, as discussed in detail above.
    NHTSA may initiate a two-year study of the safety of the fleet
through an analysis of the trends in structural stiffness and whether
any trends identified impact occupant injury response in crashes.
Vehicle manufacturers may employ stiffer light weight materials to
limit occupant compartment intrusion while controlling for mass that
may expose the occupants to higher accelerations resulting in a greater
chance of injury in real-world crashes. This study would provide
information that would increase the understanding of the effects on
safety of newer vehicle designs.
    In addition, NHTSA and EPA, possibly in collaboration with DOE, may
conduct a longer-term computer modeling-based design and analysis study
to help determine the maximum potential for mass reduction in the MYs
2017-2021 timeframe, through direct material substitution and smart
design while meeting safety regulations and guidelines, and maintaining
vehicle size and functionality. This study may build upon prior
research completed on vehicle mass reduction. This study would further
explore the comprehensive vehicle effects, including dissimilar
material joining technologies, manufacturer feasibility of both
supplier and OEM, tooling costs, and crash simulation and perhaps
eventual crash testing.

III. EPA Greenhouse Gas Vehicle Standards

A. Executive Overview of EPA Rule

1. Introduction
    The Environmental Protection Agency (EPA) is establishing GHG
emissions standards for the largest sources of transportation GHGs--
light-duty vehicles, light-duty trucks, and medium-duty passenger
vehicles (hereafter light vehicles). These vehicle categories, which
include cars, sport utility vehicles, minivans, and pickup trucks used
for personal transportation, are responsible for almost 60% of all U.S.
transportation related emissions of the six gases discussed above
(Section I.A). This action represents the first-ever EPA rule to
regulate vehicle GHG emissions under the Clean Air Act (CAA) and will
establish standards for model years 2012-2016 and later light vehicles
sold in the United States.
    EPA is adopting three separate standards. The first and most
important is a set of fleet-wide average carbon dioxide
(CO2) emission standards for cars and trucks. These
standards are CO2 emissions-footprint curves, where each
vehicle has a different CO2 emissions compliance target
depending on its footprint value. Vehicle CO2 emissions will
be measured over the EPA city and highway tests. The rule allows for
credits based on demonstrated improvements in vehicle air conditioner
systems, including both efficiency and refrigerant leakage improvement,
which are not captured by the EPA tests. The EPA projects that the
average light vehicle tailpipe CO2 level in model year 2011
will be 325 grams per mile while the average vehicle fleetwide average
CO2 emissions compliance level for the model year 2016
standard will be 250 grams per mile, an average reduction of 23 percent
from today's CO2 levels.
    EPA is also finalizing standards that will cap tailpipe nitrous
oxide (N2O) and methane (CH4) emissions at 0.010
and 0.030 grams per mile, respectively. Even after adjusting for the
higher relative global warming potencies of these two compounds,
nitrous oxide and methane emissions represent less than one percent of
overall vehicle greenhouse gas emissions from new vehicles.
Accordingly, the goal of these two standards is to limit any potential
increases of tailpipe emissions of these compounds in the future but
not to force reductions relative to today's low levels.
    This final rule responds to the Supreme Court's 2007 decision in
Massachusetts v. EPA \147\ which found that greenhouse gases fit within
the definition of air pollutant in the Clean Air Act. The Court held
that the Administrator must determine whether or not emissions from new
motor vehicles cause or contribute to air pollution which may
reasonably be anticipated to endanger public health or welfare, or
whether the science is too uncertain to make a reasoned decision. The
Court further ruled that, in making these decisions, the EPA
Administrator is required to follow the language of section 202(a) of
the CAA. The case was remanded back to the Agency for reconsideration
in light of the court's decision.
---------------------------------------------------------------------------

    \147\ 549 U.S.C. 497 (2007). For further information on
Massachusetts v. EPA see the Endangerment and Cause or Contribute
Findings for Greenhouse Gases under Section 202(a) the Clean Air
Act, published in the Federal Register on December 15, 2009 (74 FR
66496). There is a comprehensive discussion of the litigation's
history, the Supreme Court's findings, and subsequent actions
undertaken by the Bush Administration and the EPA from 2007-2008 in
response to the Supreme Court remand. This information is also
available at: http://www.epa.gov/climatechange/endangerment.html.
---------------------------------------------------------------------------

    The Administrator has responded to the remand by issuing two
findings under section 202(a) of the Clean Air

Act.\148\ First, the Administrator found that the science supports a
positive endangerment finding that the mix of six greenhouse gases
(carbon dioxide (CO2), methane (CH4), nitrous
oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons
(PFCs), and sulfur hexafluoride (SF6)) in the atmosphere
endangers the public health and welfare of current and future
generations. This is referred to as the endangerment finding. Second,
the Administrator found that the combined emissions of the same six
gases from new motor vehicles and new motor vehicle engines contribute
to the atmospheric concentrations of these key greenhouse gases and
hence to the threat of climate change. This is referred to as the cause
and contribute finding. Motor vehicles and new motor vehicle engines
emit carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons.
EPA provides more details below on the legal and scientific bases for
this final rule.
---------------------------------------------------------------------------

    \148\ See 74 FR 66496 (Dec. 15, 2009), ``Endangerment and Cause
or Contribute Findings for Greenhouse Gases Under Section 202(a) of
the Clean Air Act''.
---------------------------------------------------------------------------

    As discussed in Section I, this GHG rule is part of a joint
National Program such that a large majority of the projected benefits
are achieved jointly with NHTSA's CAFE rule which is described in
detail in Section IV of this preamble. EPA projects total
CO2 equivalent emissions savings of approximately 960
million metric tons as a result of the rule, and oil savings of 1.8
billion barrels over the lifetimes of the MY 2012-2016 vehicles subject
to the rule. EPA projects that over the lifetimes of the MY 2012-2016
vehicles, the rule will cost $52 billion but will result in benefits of
$240 billion at a 3 percent discount rate, or $192 billion at a 7
percent discount rate (both values assume the average SCC value at 3%,
i.e., the $21/ton SCC value in 2010). Accordingly, these light vehicle
greenhouse gas emissions standards represent an important contribution
under the Clean Air Act toward meeting long-term greenhouse gas
emissions and import oil reduction goals, while providing important
economic benefits as well. The results of our analysis of 2012-2016 MY
vehicles, which we refer to as our ``model year analysis,'' are
summarized in Tables III.H.10-4 to III.H.10-7.
    We have also looked beyond the lifetimes of 2012-2016 MY vehicles
at annual costs and benefits of the program for the 2012 through 2050
timeframe. We refer to this as our ``calendar year'' analysis (as
opposed to the costs and benefits mentioned above which we refer to as
our ``model year analysis''). In our calendar year analysis, the new
2016 MY standards are assumed to apply to all vehicles sold in model
years 2017 and later. The net present values of annual costs for the
2012 through 2050 timeframe are $346 billion for new vehicle technology
which will provide $1.5 billion in fuel savings, both values at a 3
percent discount rate. At a 7 percent discount rate over the same
period, the technology costs are estimated at $192 billion which will
provide $673 billion in fuel savings. The social benefits during the
2012 through 2050 timeframe are estimated at $454 billion and $305
billion at a 3 and 7 percent discount rate, respectively. Both of these
benefit estimates assume the average SCC value at 3% (i.e., the $21/ton
SCC value in 2010). The net benefits during this time period are then
$1.7 billion and $785 million at a 3 and 7 percent discount rate,
respectively. The results of our ``calendar year'' analysis are
summarized in Tables III.H 10-1 to III.H.10-3.
2. Why is EPA establishing this Rule?
    This rule addresses only light vehicles. EPA is addressing light
vehicles as a first step in control of greenhouse gas emissions under
the Clean Air Act for four reasons. First, light vehicles are
responsible for almost 60% of all mobile source GHG emissions, a share
three times larger than any other mobile source subsector, and
represent about one-sixth of all U.S. greenhouse gas emissions. Second,
technology exists that can be readily and cost-effectively applied to
these vehicles to reduce their greenhouse gas emissions in the near
term. Third, EPA already has an existing testing and compliance program
for these vehicles, refined since the mid-1970s for emissions
compliance and fuel economy determinations, which would require only
minor modifications to accommodate greenhouse gas emissions
regulations. Finally, this rule is an important step in responding to
the Supreme Court's ruling in Massachusetts v. EPA, which applies to
other emissions sources in addition to light-duty vehicles. In fact,
EPA is currently evaluating controls for motor vehicles other than
those covered by this rule, and is also reviewing seven motor vehicle
related petitions submitted by various states and organizations
requesting that EPA use its Clean Air Act authorities to take action to
reduce greenhouse gas emissions from aircraft (under Sec.  231(a)(2)),
ocean-going vessels (under Sec.  213(a)(4)), and other nonroad engines
and vehicle sources (also under Sec.  213(a)(4)).
a. Light Vehicle Emissions Contribute to Greenhouse Gases and the
Threat of Climate Change
    Greenhouse gases are gases in the atmosphere that effectively trap
some of the Earth's heat that would otherwise escape to space.
Greenhouse gases are both naturally occurring and anthropogenic. The
primary greenhouse gases of concern that are directly emitted by human
activities include carbon dioxide, methane, nitrous oxide,
hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride.
    These gases, once emitted, remain in the atmosphere for decades to
centuries. Thus, they become well mixed globally in the atmosphere and
their concentrations accumulate when emissions exceed the rate at which
natural processes remove greenhouse gases from the atmosphere. The
heating effect caused by the human-induced buildup of greenhouse gases
in the atmosphere is very likely the cause of most of the observed
global warming over the last 50 years.\149\ The key effects of climate
change observed to date and projected to occur in the future include,
but are not limited to, more frequent and intense heat waves, more
severe wildfires, degraded air quality, heavier and more frequent
downpours and flooding, increased drought, greater sea level rise, more
intense storms, harm to water resources, continued ocean acidification,
harm to agriculture, and harm to wildlife and ecosystems. A detailed
explanation of observed and projected changes in greenhouse gases and
climate change and its impact on health, society, and the environment
is included in EPA's technical support document for the recently
promulgated Endangerment and Cause or Contribute Findings for
Greenhouse Gases Under Section 202(a) of the Clean Air Act.\150\
---------------------------------------------------------------------------

    \149\ ``Technical Support Document for Endangerment and Cause or
Contribute Findings for Greenhouse Gases Under Section 202(a) of the
Clean Air Act'' Docket: EPA-HQ-OAR-2009-0472-11292.
    \150\ 74 FR 66496 (Dec. 15, 2009). Both the Federal Register
Notice and the Technical Support Document for Endangerment and Cause
or Contribute Findings are found in the public docket No. EPA-OAR-
2009-0171, in the public docket established for this rulemaking, and
at http://epa.gov/climatechange/endangerment.html.
---------------------------------------------------------------------------

    Mobile sources represent a large and growing share of United States
greenhouse gases and include light-duty vehicles, light-duty trucks,
medium-duty passenger vehicles, heavy duty trucks, airplanes,
railroads, marine vessels and a variety of other sources. In 2007, all
mobile sources emitted 31% of

all U.S. GHGs, and were the fastest-growing source of U.S. GHGs in the
U.S. since 1990. Transportation sources, which do not include certain
off-highway sources such as farm and construction equipment, account
for 28% of U.S. GHG emissions, and Section 202(a) sources, which
include light-duty vehicles, light-duty trucks, medium-duty passenger
vehicles, heavy-duty trucks, buses, and motorcycles account for 23% of
total U.S. GHGs.\151\
---------------------------------------------------------------------------

    \151\ Inventory of U.S. Greenhouse Gases and Sinks: 1990-2007.
---------------------------------------------------------------------------

    Light vehicles emit carbon dioxide, methane, nitrous oxide and
hydrofluorocarbons. Carbon dioxide (CO2) is the end product
of fossil fuel combustion. During combustion, the carbon stored in the
fuels is oxidized and emitted as CO2 and smaller amounts of
other carbon compounds.\152\ Methane (CH4) emissions are a
function of the methane content of the motor fuel, the amount of
hydrocarbons passing uncombusted through the engine, and any post-
combustion control of hydrocarbon emissions (such as catalytic
converters).\153\ Nitrous oxide (N2O) (and nitrogen oxide
(NOX)) emissions from vehicles and their engines are closely
related to air-fuel ratios, combustion temperatures, and the use of
pollution control equipment. For example, some types of catalytic
converters installed to reduce motor vehicle NOX, carbon
monoxide (CO) and hydrocarbon emissions can promote the formation of
N2O.\154\ Hydrofluorocarbons (HFC) emissions are
progressively replacing chlorofluorocarbons (CFC) and
hydrochlorofluorocarbons (HCFC) in these vehicles' cooling and
refrigeration systems as CFCs and HCFCs are being phased out under the
Montreal Protocol and Title VI of the CAA. There are multiple emissions
pathways for HFCs with emissions occurring during charging of cooling
and refrigeration systems, during operations, and during
decommissioning and disposal.\155\
---------------------------------------------------------------------------

    \152\ Mobile source carbon dioxide emissions in 2006 equaled 26
percent of total U.S. CO2 emissions.
    \153\ In 2006, methane emissions equaled 0.32 percent of total
U.S. methane emissions. Nitrous oxide is a product of the reaction
that occurs between nitrogen and oxygen during fuel combustion.
    \154\ In 2006, nitrous oxide emissions for these sources
accounted for 8 percent of total U.S. nitrous oxide emissions.
    \155\ In 2006, HFC from these source categories equaled 56
percent of total U.S. HFC emissions, making it the single largest
source category of U.S. HFC emissions.
---------------------------------------------------------------------------

b. Basis for Action Under the Clean Air Act
    Section 202(a)(1) of the Clean Air Act (CAA) states that ``the
Administrator shall by regulation prescribe (and from time to time
revise) * * * standards applicable to the emission of any air pollutant
from any class or classes of new motor vehicles * * *, which in his
judgment cause, or contribute to, air pollution which may reasonably be
anticipated to endanger public health or welfare.'' As noted above, the
Administrator has found that the elevated concentrations of greenhouse
gases in the atmosphere may reasonably be anticipated to endanger
public health and welfare.\156\ The Administrator defined the ``air
pollution'' referred to in CAA section 202(a) to be the combined mix of
six long-lived and directly emitted GHGs: Carbon dioxide
(CO2), methane (CH4), nitrous oxide
(N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs),
and sulfur hexafluoride (SF6). The Administrator has further
found under CAA section 202(a) that emissions of the single air
pollutant defined as the aggregate group of these same six greenhouse
gases from new motor vehicles and new motor vehicle engines contribute
to air pollution. As a result of these findings, section 202(a)
requires EPA to issue standards applicable to emissions of that air
pollutant. New motor vehicles and engines emit CO2, methane,
N2O and HFC. This preamble describes the provisions that
control emissions of CO2, HFCs, nitrous oxide, and methane.
For further discussion of EPA's authority under section 202(a), see
Section I.C.2 of the preamble to the proposed rule (74 FR at 49464-66).
---------------------------------------------------------------------------

    \156\ 74 FR 66496 (Dec. 15, 2009).
---------------------------------------------------------------------------

    There are a variety of other CAA Title II provisions that are
relevant to standards established under section 202(a). The standards
are applicable to motor vehicles for their useful life. EPA has the
discretion in determining what standard applies over the vehicles'
useful life and has exercised that discretion in this rule. See Section
III.E.4 below.
    The standards established under CAA section 202(a) are implemented
and enforced through various mechanisms. Manufacturers are required to
obtain an EPA certificate of conformity before they may sell or
introduce their new motor vehicle into commerce, according to CAA
section 206(a). The introduction into commerce of vehicles without a
certificate of conformity is a prohibited act under CAA section 203
that may subject a manufacturer to civil penalties and injunctive
actions (see CAA sections 204 and 205). Under CAA section 206(b), EPA
may conduct testing of new production vehicles to determine compliance
with the standards. For in-use vehicles, if EPA determines that a
substantial number of vehicles do not conform to the applicable
regulations then the manufacturer must submit and implement a remedial
plan to address the problem (see CAA section 207(c)). There are also
emissions-based warranties that the manufacturer must implement under
CAA section 207(a). Section III.E describes the rule's certification,
compliance, and enforcement mechanisms.
c. EPA's Endangerment and Cause or Contribute Findings for Greenhouse
Gases Under Section 202(a) of the Clean Air Act
    On December 7, 2009 EPA's Administrator signed an action with two
distinct findings regarding greenhouse gases under section 202(a) of
the Clean Air Act. On December 15, 2009, the final findings were
published in the Federal Register. This action is called the
Endangerment and Cause or Contribute Findings for Greenhouse Gases
under Section 202(a) of the Clean Air Act (Endangerment Finding).\157\
Below are the two distinct findings:
---------------------------------------------------------------------------

    \157\ 74 FR 66496 (Dec. 15, 2009)
---------------------------------------------------------------------------

     Endangerment Finding: The Administrator finds that the
current and projected concentrations of the six key well-mixed
greenhouse gases--carbon dioxide (CO2), methane
(CH4), nitrous oxide (N2O), hydrofluorocarbons
(HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride
(SF6)--in the atmosphere threaten the public health and
welfare of current and future generations.
     Cause or Contribute Finding: The Administrator finds that
the combined emissions of these well-mixed greenhouse gases from new
motor vehicles and new motor vehicle engines contribute to the
greenhouse gas pollution which threatens public health and welfare.
    Specifically, the Administrator found, after a thorough examination
of the scientific evidence on the causes and impact of current and
future climate change, and careful review of public comments, that the
science compellingly supports a positive finding that atmospheric
concentrations of these greenhouse gases result in air pollution which
may reasonably be anticipated to endanger both public health and
welfare. In her finding, the Administrator relied heavily upon the
major findings and conclusions from the

recent assessments of the U.S. Climate Change Science Program and the
U.N. Intergovernmental Panel on Climate Change.\158\ The Administrator
made a positive endangerment finding after considering both observed
and projected future effects of climate change, key uncertainties, and
the full range of risks and impacts to public health and welfare
occurring within the United States. In addition, the finding focused on
impacts within the U.S. but noted that the evidence concerning risks
and impacts occurring outside the U.S. provided further support for the
finding.
---------------------------------------------------------------------------

    \158\ The U.S. Climate Change Science Program (CCSP) is now
called the U.S. Global Change Research Program (GCRP).
---------------------------------------------------------------------------

    The key scientific findings supporting the endangerment finding are
that:

-- Concentrations of greenhouse gases are at unprecedented levels
compared to recent and distant past. These high concentrations are the
unambiguous result of anthropogenic emissions and are very likely the
cause of the observed increase in average temperatures and other
climatic changes.
-- The effects of climate change observed to date and projected to
occur in the future include more frequent and intense heat waves, more
severe wildfires, degraded air quality, heavier downpours and flooding,
increasing drought, greater sea level rise, more intense storms, harm
to water resources, harm to agriculture, and harm to wildlife and
ecosystems. These impacts are effects on public health and welfare
within the meaning of the Clean Air Act.

    The Administrator found that emissions of the single air pollutant
defined as the aggregate group of these same six greenhouse gases from
new motor vehicles and new motor vehicle engines contribute to the air
pollution and hence to the threat of climate change. Key facts
supporting this cause and contribute finding for on-highway vehicles
regulated under section 202(a) of the Clean Air Act are that these
sources are responsible for 24% of total U.S. greenhouse gas emissions,
and more than 4% of total global greenhouse gas emissions.\159\ As
noted above, these findings require EPA to issue standards under
section 202(a) ``applicable to emission'' of the air pollutant that EPA
found causes or contributes to the air pollution that endangers public
health and welfare. The final emissions standards satisfy this
requirement for greenhouse gases from light-duty vehicles. Under
section 202(a) the Administrator has significant discretion in how to
structure the standards that apply to the emission of the air pollutant
at issue here, the aggregate group of six greenhouse gases. EPA has the
discretion under section 202(a) to adopt separate standards for each
gas, a single composite standard covering various gases, or any
combination of these. In this rulemaking EPA is finalizing separate
standards for nitrous oxide and methane, and a CO2 standard
that provides for credits based on reductions of HFCs, as the
appropriate way to issue standards applicable to emission of the single
air pollutant, the aggregate group of six greenhouse gases. EPA is not
setting any standards for perfluorocarbons (PFCs) or sulfur
hexafluoride (SF6) as they are not emitted by motor
vehicles.
---------------------------------------------------------------------------

    \159\ This figure includes the greenhouse gas contributions of
light vehicles, heavy duty vehicles, and remaining on-highway mobile
sources. Light-duty vehicles are responsible for over 70 percent of
Section 202(a) mobile source GHGs, or about 17% of total U.S.
greenhouse gas emissions. U.S. EPA.2009 Technical Support Document
for Endangerment and Cause or Contribute Findings for Greenhouse
Gases under Section 202(a) of the Clean Air Act. Washington, DC. pp.
180-194. Available at http://epa.gov/climatechange/endangerment/
downloads/Endangerment%20TSD.pdf.
---------------------------------------------------------------------------

3. What is EPA adopting?
a. Light-Duty Vehicle, Light-Duty Truck, and Medium-Duty Passenger
Vehicle Greenhouse Gas Emission Standards and Projected Compliance
Levels
    The following section provides an overview of EPA's final rule. The
key public comments are not discussed here, but are discussed in the
sections that follow which provide the details of the program. Comments
are also discussed in the Response to Comments document.
    The CO2 emissions standards are by far the most
important of the three standards and are the primary focus of this
summary. As proposed, EPA is adopting an attribute-based approach for
the CO2 fleet-wide standard (one for cars and one for
trucks), using vehicle footprint as the attribute. These curves
establish different CO2 emissions targets for each unique
car and truck footprint. Generally, the larger the vehicle footprint,
the higher the corresponding vehicle CO2 emissions target.
Table III.A.3-1 shows the greenhouse gas standards for light vehicles
that EPA is finalizing for model years (MY) 2012 and later:

                        Table III.A.3-1--Industry-Wide Greenhouse Gas Emissions Standards
----------------------------------------------------------------------------------------------------------------
   Standard/covered compounds      Form of standard    Level of standard        Credits           Test cycles
----------------------------------------------------------------------------------------------------------------
CO2 Standard: \160\ Tailpipe CO2  Fleetwide average   Projected           CO2-e credits\161\  EPA 2-cycle (FTP
                                   footprint CO2-      Fleetwide CO2                           and HFET test
                                   curves for cars     level of 250 g/mi                       cycles).\162\
                                   and trucks.         (See footprint
                                                       curves in Sec.
                                                       III.B.2).
N2O Standard: Tailpipe N2O......  Cap per vehicle...  0.010 g/mi........  None *............  EPA FTP test.
CH4 Standard: Tailpipe CH4......  Cap per vehicle...  0.030 g/mi........  None *............  EPA FTP test.
----------------------------------------------------------------------------------------------------------------
* For N2O and CH4, manufacturers may optionally demonstrate compliance with a CO2-equivalent standard equal to
  its footprint-based CO2 target level, using the FTP and HFET tests.

    One important flexibility associated with the CO2
standard is the option for

manufacturers to obtain credits associated with improvements in their
air conditioning systems. EPA is adopting the air conditioning
provisions with minor modifications. As will be discussed in greater
detail in later sections, EPA is establishing test procedures and
design criteria by which manufacturers can demonstrate improvements in
both air conditioner efficiency (which reduces vehicle tailpipe
CO2 by reducing the load on the engine) and air conditioner
refrigerants (using lower global warming potency refrigerants and/or
improving system design to reduce GHG emissions associated with leaks).
Neither of these strategies to reduce GHG emissions from air
conditioners will be reflected in the EPA FTP or HFET tests. These
improvements will be translated to a g/mi CO2-equivalent
credit that can be subtracted from the manufacturer's tailpipe
CO2 compliance value. EPA expects a high percentage of
manufacturers to use this flexibility to earn air conditioning-related
credits for MY 2012-2016 vehicles such that the average credit earned
is about 11 grams per mile CO2-equivalent in 2016.
---------------------------------------------------------------------------

    \160\ While over 99 percent of the carbon in automotive fuels is
converted to CO2 in a properly functioning engine,
compliance with the CO2 standard will also account for
the very small levels of carbon associated with vehicle tailpipe
hydrocarbon (HC) and carbon monoxide (CO) emissions, converted to
CO2 on a mass basis, as discussed further in Section
III.B.
    \161\ CO2-e refers to CO2-equivalent, and
is a metric that allows non-CO2 greenhouse gases (such as
hydrofluorocarbons used as automotive air conditioning refrigerants)
to be expressed as an equivalent mass (i.e., corrected for relative
global warming potency) of CO2 emissions.
    \162\ FTP is the Federal Test Procedure which uses what is
commonly referred to as the ``city'' driving schedule, and HFET is
the Highway Fuel Economy Test which uses the ``highway'' driving
schedule. Compliance with the CO2 standard will be based
on the same 2-cycle values that are currently used for CAFE
standards compliance; EPA projects that fleet-wide in-use or real
world CO2 emissions are approximately 25 percent higher,
on average, than 2-cycle CO2 values. Separate mechanisms
apply for A/C credits.
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    A second flexibility, being finalized essentially as proposed, is
CO2 credits for flexible and dual fuel vehicles, similar to
the CAFE credits for such vehicles which allow manufacturers to gain up
to 1.2 mpg in their overall CAFE ratings. The Energy Independence and
Security Act of 2007 (EISA) mandated a phase-out of these flexible fuel
vehicle CAFE credits beginning in 2015, and ending after 2019. EPA is
allowing comparable CO2 credits for flexible fuel vehicles
through MY 2015, but for MY 2016 and beyond, the GHG rule treats
flexible and dual fuel vehicles on a CO2-performance basis,
calculating the overall CO2 emissions for flexible and dual
fuel vehicles based on a fuel use-weighted average of the
CO2 levels on gasoline and on the alternative fuel, and on a
manufacturer's demonstration of actual usage of the alternative fuel in
its vehicle fleet.
    Table III.A.3-2 summarizes EPA projections of industry-wide 2-cycle
CO2 emissions and fuel economy levels that will be achieved
by manufacturer compliance with the GHG standards for MY 2012-2016.
    For MY 2011, Table III.A.3-2 uses the NHTSA projections of the
average fuel economy level that will be achieved by the MY 2011 fleet
of 30.8 mpg for cars and 23.3 mpg for trucks, converted to an
equivalent combined car and truck CO2 level of 326 grams per
mile.\163\ EPA believes this is a reasonable estimate with which to
compare the MY 2012-2016 CO2 emission standards. Identifying
the proper MY 2011 estimate is complicated for many reasons, among them
being the turmoil in the current automotive market for consumers and
manufacturers, uncertain and volatile oil and gasoline prices, the
ability of manufacturers to use flexible fuel vehicle credits to meet
MY 2011 CAFE standards, and the fact that most manufacturers have been
surpassing CAFE standards (particularly the car standard) in recent
years. Taking all of these considerations into account, EPA believes
that the MY 2011 projected CAFE achieved values, converted to
CO2 emissions levels, represent a reasonable estimate.
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    \163\ As discussed in Section IV of this preamble.
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    Table III.A.3-2 shows projected industry-wide average
CO2 emissions values. The Projected CO2 Emissions
for the Footprint-Based Standard column shows the CO2 g/mi
level corresponding with the footprint standard that must be met. It is
based on the promulgated CO2-footprint curves and projected
footprint values, and will decrease each year to 250 grams per mile (g/
mi) in MY 2016. For MY 2012-2016, the emissions impact of the projected
utilization of flexible fuel vehicle (FFV) credits and the temporary
lead-time allowance alternative standard (TLAAS, discussed below) are
shown in the next two columns. The Projected CO2 Emissions
column gives the CO2 emissions levels projected to be
achieved given use of the flexible fuel credits and temporary lead-time
allowance program. This column shows that, relative to the MY 2011
estimate, EPA projects that MY 2016 CO2 emissions will be
reduced by 23 percent over five years. The Projected A/C Credit column
represents the industry wide average air conditioner credit
manufacturers are expected to earn on an equivalent CO2 gram
per mile basis in a given model year. In MY 2016, the projected A/C
credit of 10.6 g/mi represents 14 percent of the 76 g/mi CO2
emissions reductions associated with the final standards. The Projected
2-cycle CO2 Emissions column shows the projected
CO2 emissions as measured over the EPA 2-cycle tests, which
will allow compliance with the standard assuming projected utilization
of the FFV, TLAAS, and A/C credits.

                                                Table III.A.3-2--Projected Fleetwide CO2 Emissions Values
                                                                    [Grams per mile]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                          Projected CO2
                                                          emissions for                                                                   Projected  2-
                       Model year                        the footprint-   Projected FFV     Projected     Projected CO2   Projected A/C     cycle CO2
                                                              based          credit       TLAAS credit      emissions        credit         emissions
                                                            standard
--------------------------------------------------------------------------------------------------------------------------------------------------------
2011...................................................  ..............  ..............  ..............           (326)  ..............            (326)
2012...................................................             295             6.5             1.2             303             3.5             307
2013...................................................             286             5.8             0.9             293             5.0             298
2014...................................................             276             5.0             0.6             282             7.5             290
2015...................................................             263             3.7             0.3             267            10.0             277
2016...................................................             250             0.0             0.1             250            10.6             261
--------------------------------------------------------------------------------------------------------------------------------------------------------

    EPA is also finalizing a series of flexibilities for compliance
with the CO2 standard which are not expected to
significantly affect the projected compliance and achieved values shown
above, but which should reduce the costs of achieving those reductions.
These flexibilities include the ability to earn: Annual credits for a
manufacturer's over-compliance with its unique fleet-wide average
standard, early credits from MY 2009-2011, credit for ``off-cycle''
CO2 reductions from new and innovative technologies that are
not reflected in CO2/fuel economy tests, as

well as the carry-forward and carry-backward of credits, and the
ability to transfer credits between a manufacturer's car and truck
fleets. These flexibilities are being adopted with only very minor
changes from the proposal, as discussed in Section III.C.
    EPA is finalizing an incentive to encourage the commercialization
of advanced GHG/fuel economy control technologies, including electric
vehicles (EVs), plug-in hybrid electric vehicles (PHEVs), and fuel cell
vehicles (FCVs), for model years 2012-2016. EPA's proposal included an
emissions compliance value of zero grams/mile for EVs and FCVs, and the
electric portion of PHEVs, and a multiplier in the range of 1.2 to 2.0,
so that each advanced technology vehicle would count as greater than
one vehicle in a manufacturer's fleet-wide compliance calculation.
Several commenters were very concerned about these credits and upon
considering the public comments on this issue, EPA is finalizing an
advanced technology vehicle incentive program to assign a zero gram/
mile emissions compliance value for EVs and FCVs, and the electric
portion of PHEVs, for up to the first 200,000 EV/PHEV/FCV vehicles
produced by a given manufacturer during MY 2012-2016. For any
production greater than this amount, the compliance value for the
vehicle will be greater than zero gram/mile, set at a level that
reflects the vehicle's average net increase in upstream greenhouse gas
emissions in comparison to the gasoline or diesel vehicle it replaces.
EPA is not finalizing a multiplier based on the concerns potentially
excessive credits using that incentive. EPA agrees that the multiplier,
in combination with the zero grams/mile compliance value, would be
excessive. EPA will also allow this early advanced technology incentive
program beginning in MYs 2009 through 2011. Further discussion on the
advanced technology vehicle incentives, including more detail on the
public comments and EPA's response, is found in Section III.C.
    EPA is also finalizing a temporary lead-time allowance (TLAAS) for
manufacturers that sell vehicles in the U.S. in MY 2009 and for which
U.S. vehicle sales in that model year are below 400,000 vehicles. This
allowance will be available only during the MY 2012-2015 phase-in years
of the program. A manufacturer that satisfies the threshold criteria
will be able to treat a limited number of vehicles as a separate
averaging fleet, which will be subject to a less stringent GHG
standard.\164\ Specifically, a standard of 125 percent of the vehicle's
otherwise applicable foot-print target level will apply to up to
100,000 vehicles total, spread over the four-year period of MY 2012
through 2015. Thus, the number of vehicles to which the flexibility
could apply is limited. EPA also is setting appropriate restrictions on
credit use for these vehicles, as discussed further in Section III. By
MY 2016, these allowance vehicles must be averaged into the
manufacturer's full fleet (i.e., they will no longer be eligible for a
different standard). EPA discusses this in more detail in Section III.B
of the preamble.
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    \164\ EPCA does not permit such an allowance. Consequently,
manufacturers who may be able to take advantage of a lead-time
allowance under the GHG standards would be required to comply with
the applicable CAFE standard or be subject to penalties for non-
compliance.
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    EPA received comments from several smaller manufacturers that the
TLAAS program was insufficient to allow manufacturers with very limited
product lines to comply. These manufacturers commented that they need
additional lead-time to meet the standards, because their
CO2 baselines are significantly higher and their vehicle
product lines are even more limited, reducing their ability to average
across their fleets compared even to other TLAAS manufacturers. EPA
fully summarizes the public comments on the TLAAS program, including
comments not supporting the program, in Section III.B. In summary, in
response to the lead time issues raised by manufacturers, EPA is
modifying the TLAAS program that applies to manufacturers with between
5,000 and 50,000 U.S. vehicle sales in MY 2009. These manufactures
would have an increased allotment of vehicles, a total of 250,000,
compared to 100,000 vehicles for other TLAAS-eligible manufacturers. In
addition, the TLAAS program for these manufacturers would be extended
by one year, through MY 2016 for these vehicles, for a total of five
years of eligibility. The other provisions of the TLAAS program would
continue to apply, such as the restrictions on credit trading and the
level of the standard. Additional restrictions would also apply to
these vehicles, as discussed in Section III.B.5. In addition, for the
smallest volume manufacturers, those with U.S. sales of below 5,000
vehicles, EPA is not setting standards at this time but is instead
deferring standards until a future rulemaking. This is the same
approach we are using for small businesses. The unique issues involved
with these manufacturers will be addressed in that future rulemaking.
Further discussion of the public comment on these issues and details on
these changes from the proposed program are included in Section
III.B.6. The agency received comments on its compliance with the
Regulatory Flexibility Act. As stated in Section III.I.3, small
entities are not significantly impacted by this rulemaking.
    EPA is also adopting caps on the tailpipe emissions of nitrous
oxide (N2O) and methane (CH4)--0.010 g/mi for
N2O and 0.030 g/mi for CH4--over the EPA FTP
test. While N2O and CH4 can be potent greenhouse
gases on a relative mass basis, their emission levels from modern
vehicle designs are extremely low and represent only about 1% of total
late model light vehicle GHG emissions. These cap standards are
designed to ensure that N2O and CH4 emissions
levels do not rise in the future, rather than to force reductions in
the already low emissions levels. Accordingly, these standards are not
designed to require automakers to make any changes in current vehicle
designs, and thus EPA is not projecting any environmental or economic
costs or benefits associated with these standards.
    EPA has attempted to build on existing practice wherever possible
in designing a compliance program for the GHG standards. In particular,
the program structure will streamline the compliance process for both
manufacturers and EPA by enabling manufacturers to use a single data
set to satisfy both the new GHG and CAFE testing and reporting
requirements. Timing of certification, model-level testing, and other
compliance activities also follow current practices established under
the Tier 2 emissions and CAFE programs.
    EPA received numerous comments on issues related to the impacts on
stationary sources, due to the Clean Air Act's provisions for
permitting requirements related to the issuance of the proposed GHG
standards for new motor vehicles. Some comments suggested that EPA had
underestimated the number of stationary sources that may be subject to
GHG permitting requirements; other comments suggested that EPA did not
adequately consider the permitting impact on small business sources.
Other comments related to EPA's interpretation of the CAA's provisions
for subjecting stationary sources to permit regulation after GHG
standards are set. EPA's response to these comments is contained in the
Response to Comments document; however, many of these comments pertain
to issues that EPA is addressing in its consideration of the final
Greenhouse Gas Permit Tailoring

Rule, Prevention of Significant Deterioration and Title V Greenhouse
Gas Tailoring Rule; Proposed Rule, 74 FR 55292 (October 27, 2009) and
will thus be fully addressed in that rulemaking.
    Some of the comments relating to the stationary source permitting
issues suggested that EPA should defer setting GHG standards for new
motor vehicles to avoid such stationary source permitting impacts. EPA
is issuing these final GHG standards for light-duty vehicles as part of
its efforts to expeditiously respond to the Supreme Court's nearly
three year old ruling in Massachusetts v. EPA, 549 U.S. 497 (2007). In
that case, the Court held that greenhouse gases fit within the
definition of air pollutant in the Clean Air Act, and that EPA is
therefore compelled to respond to the rulemaking petition under section
202(a) by determining whether or not emissions from new motor vehicles
cause or contribute to air pollution which may reasonably be
anticipated to endanger public health or welfare, or whether the
science is too uncertain to make a reasoned decision. The Court further
ruled that, in making these decisions, the EPA Administrator is
required to follow the language of section 202(a) of the CAA. The Court
stated that under section 202(a), ``[i]f EPA makes [the endangerment
and cause or contribute findings], the Clean Air Act requires the
agency to regulate emissions of the deleterious pollutant.'' 549 U.S.
at 534. As discussed above, EPA has made the two findings on
contribution and endangerment. 74 FR 66496 (December 15, 2009). Thus,
EPA is required to issue standards applicable to emissions of this air
pollutant from new motor vehicles.
    The Court properly noted that EPA retained ``significant latitude''
as to the ``timing * * * and coordination of its regulations with those
of other agencies'' (id.). However it has now been nearly three years
since the Court issued its opinion, and the time for delay has passed.
In the absence of these final standards, there would be three separate
Federal and State regimes independently regulating light-duty vehicles
to increase fuel economy and reduce GHG emissions: NHTSA's CAFE
standards, EPA's GHG standards, and the GHG standards applicable in
California and other states adopting the California standards. This
joint EPA-NHTSA program will allow automakers to meet all of these
requirements with a single national fleet because California has
indicated that it will accept compliance with EPA's GHG standards as
compliance with California's GHG standards. 74 FR at 49460. California
has not indicated that it would accept NHTSA's CAFE standards by
themselves. Without EPA's vehicle GHG standards, the states will not
offer the Federal program as an alternative compliance option to
automakers and the benefits of a harmonized national program will be
lost. California and several other states have expressed strong concern
that, without comparable Federal vehicle GHG standards, the states will
not offer the Federal program as an alternative compliance option to
automakers. Letter dated February 23, 2010 from Commissioners of
California, Maine, New Mexico, Oregon and Washington to Senators Harry
Reid and Mitch McConnell (Docket EPA-HQ-OAR-2009-0472-11400). The
automobile industry also strongly supports issuance of these rules to
allow implementation of the national program and avoid ``a myriad of
problems for the auto industry in terms of product planning, vehicle
distribution, adverse economic impacts and, most importantly, adverse
consequences for their dealers and customers.'' Letter dated March 17,
2010 from Alliance of Automobile Manufacturers to Senators Harry Reid
and Mitch McConnell, and Representatives Nancy Pelosi and John Boehner
(Docket EPA-HQ-OAR-2009-0472-11368). Thus, without EPA's GHG standards
as part of a Federal harmonized program, important GHG reductions as
well as benefits to the automakers and to consumers would be lost.\165\
In addition, delaying the rule would impose significant burdens and
uncertainty on automakers, who are already well into planning for
production of MY 2012 vehicles, relying on the ability to produce a
single national fleet. Delaying the issuance of this final rule would
very seriously disrupt the industry's plans.
---------------------------------------------------------------------------

    \165\ As discussed elsewhere, EPA's GHG standards achieve
greater overall reductions in GHGs than NHTSA's CAFE standards.
---------------------------------------------------------------------------

    Instead of delaying the LDV rule and losing the benefits of this
rule and the harmonized national program, EPA is directly addressing
concerns about stationary source permitting in other actions that EPA
is taking with regard to such permitting. That is the proper approach
to address the issue of stationary source permitting, as compared to