protocols for conducting assessments in individual cases'' (the ``Type
B'' rules).\33\ The court upheld the challenged provisions, which were
a part of a set of rules establishing a step-by-step procedure to
evaluate options based on certain criteria, and to make a decision and
document the results.
---------------------------------------------------------------------------

    \33\ State of Ohio v. U.S. Dept. of Interior, 880 F.2d 432, 439
(DC Cir. 1989).
---------------------------------------------------------------------------

    Taking the considerations above into account, including Congress'
instructions to adopt and implement compliance and enforcement
protocols, and the Secretary's authority to formulate policy and make
rules to fill gaps left, implicitly or explicitly, by Congress, the
agency interprets ``protocol'' in the context of EISA as authorizing
the agency to determine both whether manufacturers have complied with
the standards, and to establish the enforcement mechanisms and decision
criteria for non-compliance. NHTSA seeks comment on its interpretation
of this statutory requirement.

G. Future HD GHG and Fuel Consumption Rulemakings

    This proposal represents a first regulatory step by NHTSA and EPA
to address the multi-faceted challenges of reducing fuel use and
greenhouse gas emissions from these vehicles. By focusing on existing
technologies and well-developed regulatory tools, the agencies are able
to propose rules that we believe will produce real and important
reductions in GHG emissions and fuel consumption within only a few
years. Within the context of this regulatory timeframe, our proposal is
very aggressive--with limited lead time compared to historic heavy-duty
regulations--but pragmatic in the context of technologies that are
available.
    While we are now only proposing this first step, it is worthwhile
to consider how future regulations that may follow this step may be
constructed. Technologies such as hybrid drivetrains, advanced
bottoming cycle engines, and full electric vehicles are promoted in
this first step through incentive concepts as discussed in Section IV,
but we believe that these advanced technologies would not be necessary
to meet the proposed standards, which are premised on the use of
existing technologies. When we begin our future work to develop a
possible next set of regulatory standards, the agencies expect these
advanced technologies to be an important part of the regulatory program
and will consider them in setting the stringency of any standards
beyond the 2018 model year.
    We will not only consider the progress of technology in our future
regulatory efforts, but the agencies are also committed to fully
considering a range of regulatory approaches. To more completely
capture the complex interactions of the total vehicle and the potential
to reduce fuel consumption and GHG emissions through the optimization
of those interactions may require a more sophisticated approach to
vehicle testing than we are proposing for the largest heavy-duty
vehicles. In future regulations, the agencies expect to fully evaluate
the potential to expand the use of vehicle compliance models to reflect
engine and drivetrain performance. Similarly, we intend to consider the
potential for complete vehicle testing using a chassis dynamometer, not
only as a means for compliance, but also as a complementary tool for
the development of more complex vehicle modeling approaches. In
considering these more comprehensive regulatory approaches, the
agencies will also reevaluate whether separate regulation of trucks and
engines remains necessary.
    In addition to technology and test procedures, vehicle and engine
drive cycles are an important part of the overall approach to
evaluating and improving vehicle performance. EPA, working through the
WP.29 Global Technical Regulation process, has actively participated in
the development of a new World Harmonized Duty Cycle for heavy-duty
engines. EPA is committed to bringing forward these new procedures as
part of our overall comprehensive approach for controlling criteria and
GHG emissions. However, we believe the important issues and technical
work related to setting new criteria emissions standards appropriate
for the World Harmonized Duty Cycle are significant and beyond the
scope of this rulemaking. Therefore, the agencies are not proposing to
adopt these test procedures in this proposal, but we are ready to work
with interested stakeholders to adopt these procedures in a future
action.
    As with this proposal, our future efforts will be based on
collaborative outreach with the stakeholder community and will be
focused on a program that delivers on our energy security and
environmental goals without restricting the industry's ability to
produce a very diverse range of vehicles serving a wide range of needs.

II. Proposed GHG and Fuel Consumption Standards for Heavy-Duty Engines
and Vehicles

    This section describes the standards and implementation dates that
the agencies are proposing for the three categories of heavy-duty
vehicles. The agencies have performed a technology analysis to
determine the level of standards that we believe would be appropriate,
cost-effective, and feasible during the rulemaking timeframe. This
analysis, described in Section III and in more detail in the draft RIA
Chapter 2, considered:
     The level of technology that is incorporated in current
new trucks,
     The available data on corresponding CO2
emissions and fuel consumption for these vehicles,
     Technologies that would reduce CO2 emissions
and fuel consumption and that are judged to be feasible and appropriate
for these vehicles through 2018 model year,
     The effectiveness and cost of these technologies,
     Projections of future U.S. sales for trucks, and
     Forecasts of manufacturers' product redesign schedules.

A. What vehicles would be affected?

    EPA and NHTSA are proposing standards for heavy-duty engines and
also for what we refer to generally as ``heavy-duty trucks.'' As noted
in Section I, for purposes of this preamble, the term ``heavy-duty'' or
``HD'' is used to apply to all highway vehicles and engines that are
not regulated by the light-duty vehicle, light-duty truck and medium-
duty passenger vehicle greenhouse gas and CAFE standards issued for MYs
2012-2016. Thus, in this notice, unless specified otherwise, the heavy-
duty category incorporates all vehicles rated with GVWR greater than
8,500 pounds, and the engines that power these vehicles, except for
MDPVs. The CAA defines heavy-duty vehicles as trucks, buses or other
motor vehicles with GVWR exceeding 6,000 pounds. See CAA section
202(b)(3). In the context of the CAA, the term HD as used in these
proposed rules thus refers to a subset of these vehicles and engines.
EISA section 103(a)(3) defines a `commercial medium- and heavy-duty on-
highway vehicle' as an on-highway vehicle with GVWR of 10,000 pounds or
more.\34\ EISA section 103(a)(6) defines a `work truck' as a vehicle
that is rated at between 8,500 and 10,000 pounds gross vehicle weight
and is not a medium-duty passenger vehicle.\35\ Therefore, the term
``heavy-duty trucks'' in this proposal refers to both work trucks and
commercial medium- and heavy-duty on-highway vehicles as defined by
EISA. Heavy-duty engines affected by the proposed standards are those
that are installed in commercial medium- and heavy-duty trucks, except
for the engines installed in vehicles certified to a complete vehicle
emissions standard based on a chassis test, which would be addressed as
a part of those complete vehicles, and except for engines used
exclusively for stationary power when the vehicle is parked. The
agencies' scope is the same with the exception of recreational vehicles
(or motor homes), as discussed above. EPA is proposing to include
recreational on-highway vehicles within their rulemaking, while NHTSA
is limiting their scope to commercial trucks which would not include
these vehicles.
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    \34\ Codified at 49 U.S.C. 32901(a)(7).
    \35\ EISA Section 103(a)(6) is codified at 49 U.S.C.
32901(a)(19). EPA defines medium-duty passenger vehicles as any
complete vehicle between 8,500 and 10,000 pounds GVWR designed
primarily for the transportation of persons which meet the criteria
outlined in 40 CFR 86.1803-01. The definition specifically excludes
any vehicle that (1) Has a capacity of more than 12 persons total
or, (2) is designed to accommodate more than 9 persons in seating
rearward of the driver's seat or, (3) has a cargo box (e.g., pick-up
box or bed) of six feet or more in interior length. (See the Tier 2
final rulemaking, 65 FR 6698, February 10, 2000.)
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    EPA and NHTSA are proposing standards for each of the following
categories, which together comprise all heavy-duty vehicles and all
engines used in such vehicles.\36\ In order to most appropriately
regulate the broad range of heavy-duty vehicles, the agencies are
proposing to set separate engine and vehicle standards for the
combination tractors and the Class 2b through 8 vocational vehicles and
the engines installed in them. The engine standards and test procedures
for engines installed in the tractors and vocational vehicles are
discussed within the applicable vehicle sections.
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    \36\ Both agencies have authority to develop separate standards
for vehicle and engine categories, as appropriate. See CAA section
202(a)(1) (authority to establish standards for ``any class or
classes of new motor vehicles or engines'' and 49 U.S.C 32902(k)(2)
(authority to establish standards for HD vehicles that are
``appropriate, cost-effective, and technologically feasible'' that
are designed to achieve the ``maximum feasible improvement'' in fuel
efficiency; authority to establish ``separate standards for
different classes of vehicles under this subsection.'' NHTSA
interprets 49 U.S.C. 32902(k)(2) to include a grant of authority to
establish engines standards pursuant to the broader statement of
authority to establish standards that achieve the maximum feasible
improvement in fuel efficiency.
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     Class 7 and 8 Combination Tractors.
     Heavy-Duty Pickup Trucks and Vans.
     Class 2b through 8 Vocational Vehicles.
    As discussed in Section IX, the agencies are not proposing GHG
emission and fuel consumption standards for trailers at this time. In
addition, the agencies are proposing to not set standards at this time
for engine, chassis, and vehicle manufacturers which are small
businesses (as defined). More detailed discussion of each regulatory
category is included in the subsequent sections below.

B. Class 7 and 8 Combination Tractors

    EPA is proposing CO2 standards and NHTSA is proposing
fuel consumption standards for new Class 7 and 8 combination tractors.
The standards are for the tractor cab, with a separate standard for the
engines that are installed in the tractor. Together these standards
would achieve reductions up to 20 percent from tractors. As discussed
below, EPA is proposing to adopt the existing useful life definitions
for heavy-duty engines for the Class 7 and 8 tractors. NHTSA is
proposing fuel consumption standards for tractors, and engine standards
for heavy-duty engines for Class 7 and 8 tractors. The agencies'
analyses, as discussed briefly below and in more detail later in this
preamble and in the draft RIA Chapter 2, show that these standards are
appropriate and feasible under each agency's respective statutory
authorities.
    EPA is also proposing standards to control N2O,
CH4, and HFC emissions from Class 7 and 8 combination
tractors. The proposed heavy-duty engine standards for both
N2O and CH4 and details of the standard are
included in the discussion in Section II. The proposed air conditioning
leakage standards applying to tractor manufacturers to address HFC
emissions are included in Section II.
    The agencies are proposing CO2 emissions and fuel
consumption standards for the combination tractors that will focus on
reductions that can be achieved through improvements in the tractor
(such as aerodynamics), tires, and other vehicle systems. The agencies
are also proposing heavy-duty engine standards for CO2
emissions and fuel consumption that would focus on potential
technological improvements in fuel combustion and overall engine
efficiency.
    The agencies have analyzed the feasibility of achieving the
CO2 and fuel consumption standards, based on projections of
what actions manufacturers are expected to take to reduce emissions and
fuel consumption. EPA and NHTSA also present the estimated costs and
benefits of the

standards in Section III. In developing the proposed rules, the
agencies have evaluated the kinds of technologies that could be
utilized by engine and tractor manufacturers, as well as the associated
costs for the industry and fuel savings for the consumer and the
magnitude of the CO2 and fuel savings that may be achieved.
    EPA and NHTSA are proposing attribute-based standards for the Class
7 and 8 combination tractors, or, put another way, we are proposing to
set different standards for different subcategories of these tractors
with the basis for subcategorization being particular tractor
attributes. Attribute-based standards in general recognize the variety
of functions performed by vehicles and engines, which in turn can
affect the kind of technology that is available to control emissions
and reduce fuel consumption, or its effectiveness. Attributes that
characterize differences in the design of vehicles, as well as
differences in how the vehicles will be employed in-use, can be key
factors in evaluating technological improvements for reducing
CO2 emissions and fuel consumption. Developing an
appropriate attribute-based standard can also avoid interfering with
the ability of the market to offer a variety of products to meet
consumer demand. There are several examples of where the agencies have
utilized an attribute-based standard. In addition to the example of the
recent light-duty vehicle fuel economy and GHG rule, in which the
standards are based on the attribute of vehicle ``footprint,'' the
existing heavy-duty highway engine criteria pollutant emission
standards for many years have been based on a vehicle weight attribute
(Light Heavy, Medium Heavy, Heavy Heavy) with different useful life
periods, which is the same approach proposed for the engine GHG and
fuel consumption standards discussed below.
    Heavy-duty combination tractors are built to move freight. The
ability of a truck to meet a customer's freight transportation
requirements depends on three major characteristics of the tractor: The
gross vehicle weight rating (which along with gross combined weight
rating (GCWR) establishes the maximum carrying capacity of the tractor
and trailer), cab type (sleeper cabs provide overnight accommodations
for drivers), and the tractor roof height (to mate tractors to trailers
for the most fuel-efficient configuration). Each of these attributes
impacts the baseline fuel consumption and GHG emissions, as well as the
effectiveness of possible technologies, like aerodynamics, and is
discussed in more detail below.
    The first tractor characteristic to consider is payload which is
determined by a tractor's GVWR and GCWR relative to the weight of the
tractor, trailer, fuel, driver, and equipment. Class 7 trucks, which
have a GVWR of 26,001-33,000 pounds and a typical GCWR of 65,000
pounds, have a lesser payload capacity than Class 8 trucks. Class 8
trucks have a GVWR of greater than 33,000 pounds and a typical 80,000
pound GCWR. Consistent with the recommendation in the National Academy
of Sciences 2010 Report to NHTSA,\37\ the agencies are proposing a
load-specific fuel consumption metric (g/ton-mile and gal/1,000 ton-
mile) where the ``ton'' represents the amount of payload. Generally,
higher payload capacity trucks have better specific fuel consumption
and GHG emissions than lower payload capacity trucks. Therefore, since
the amount of payload that a Class 7 truck can carry is less than the
Class 8 truck's payload capacity, the baseline fuel consumption and GHG
emissions performance per ton-mile differs between the categories. It
is consequently reasonable to distinguish between these two vehicle
categories, so that the agencies are proposing separate standards for
Class 7 and Class 8 tractors.
---------------------------------------------------------------------------

    \37\ See 2010 NAS Report, Note 19, Recommendation 2-1.
---------------------------------------------------------------------------

    The agencies are not proposing to set a single standard for both
Class 7 and 8 tractors based on the payload carrying capabilities and
assumed typical payload levels of Class 8 tractors alone, as that would
quite likely have the perverse impact of increasing fuel consumption
and greenhouse gas emissions. Such a single standard would penalize
Class 7 vehicles in favor of Class 8 vehicles. However, the greater
capabilities of Class 8 tractors and their related greater efficiency
when measured on a per ton-mile basis is only relevant in the context
of operations where that greater capacity is needed. For many
applications such as regional distribution, the trailer payloads
dictated by the goods being carried are lower than the average Class 8
tractor payload. In those situations, Class 7 tractors are more
efficient than Class 8 tractors when measured by ton-mile of actual
freight carried. This is because the extra capabilities of Class 8
tractors add additional weight to vehicle that is only beneficial in
the context of its higher capabilities. The existing market already
selects for vehicle performance based on the projected payloads. By
setting separate standards the agencies do not advantage or
disadvantage Class 7 or 8 tractors relative to one another and continue
to allow trucking fleets to purchase the vehicle most appropriate to
their business practices.
    The second characteristic that affects fuel consumption and GHG
emissions is the relationship between the tractor cab roof height and
the type of trailer used to carry the freight. The primary trailer
types are box, flat bed, tanker, bulk carrier, chassis, and low boys.
Tractor manufacturers sell tractors in three roof heights--low, mid,
and high. The manufacturers do this to obtain the best aerodynamic
performance of a tractor-trailer combination, resulting in reductions
of GHG emissions and fuel consumption, because it allows the frontal
area of the tractor to be similar in size to the frontal area of the
trailer. In other words, high roof tractors are designed to be paired
with a (relatively tall) box trailer while a low roof tractor is
designed to pull a (relatively low) flat bed trailer. The baseline
performance of a high roof, mid roof, and low roof tractor differs due
to the variation in frontal area which determines the aerodynamic drag.
For example, the frontal area of a low roof tractor is approximately 6
square meters, while a high roof tractor has a frontal area of
approximately 9.8 square meters. Therefore, as explained below, the
agencies are proposing that the roof height of the tractor determine
the trailer type required to be used to demonstrate compliance of a
truck with the fuel consumption and CO2 emissions standards.
As with vehicle weight classes, setting separate standards for each
tractor roof height helps ensure that all tractors are regulated to
achieve appropriate improvements, without inadvertently leading to
increased emissions and fuel consumption by shifting the mix of vehicle
roof heights offered in the market away from a level customarily tied
to the actual trailers vehicles will haul in-use.
    Tractor cabs typically can be divided into two configurations--day
cabs and sleeper cabs. Line haul operations typically require overnight
accommodations due to Federal Motor Carrier Safety Administration hours
of operation requirements.\38\ Therefore,

some truck buyers purchase tractor cabs with sleeping accommodations,
also known as sleeper cabs, because they do not return to their home
base nightly. Sleeper cabs tend to have a greater empty curb weight
than day cabs due to the larger cab volume and accommodations, which
lead to a higher baseline fuel consumption for sleeper cabs when
compared to day cabs. In addition, there are specific technologies,
such as extended idle reduction technologies, which are appropriate
only for tractors which hotel--such as sleeper cabs. To respect these
differences, the agencies are proposing to create separate standards
for sleeper cabs and day cabs.
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    \38\ The Federal Motor Carrier Safety Administration's Hours-of-
Service regulations put limits in place for when and how long
commercial motor vehicle drivers may drive. They are based on an
exhaustive scientific review and are designed to ensure truck
drivers get the necessary rest to perform safe operations. See 49
CFR part 395, and see also http://www.fmcsa.dot.gov/rules-
regulations/topics/hos/index.htm (last accessed August 8, 2010).
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    To account for the relevant combinations of these attributes, the
agencies therefore propose to segment combination tractors into the
following nine regulatory subcategories:

 Class 7 Day Cab with Low Roof
 Class 7 Day Cab with Mid Roof
 Class 7 Day Cab with High Roof
 Class 8 Day Cab with Low Roof
 Class 8 Day Cab with Mid Roof
 Class 8 Day Cab with High Roof
 Class 8 Sleeper Cab with Low Roof
 Class 8 Sleeper Cab with Mid Roof
 Class 8 Sleeper Cab with High Roof

    The agencies have not identified any Class 7 or Class 8 day cabs
with mid roof heights in the market today but welcome comments with
regard to this market characterization.
    Adjustable roof fairings are used today on what the agencies
consider to be low roof tractors. The adjustable fairings allow the
operator to change the fairing height to better match the type of
trailer that is being pulled which can reduce fuel consumption and GHG
emissions during operation. The agencies propose to treat tractors with
adjustable roof fairings as low roof tractors and test with the fairing
down. The agencies welcome comments on this approach and data to
support whether to allow additional credits for their use.
    The agencies are proposing to classify all vehicles with sleeper
cabs as tractors. The proposed rules would not allow vehicles with
sleeper cabs to be classified as vocational vehicles. This provision is
intended prevent the initial manufacture of straight truck vocational
vehicles with sleeper cabs that, soon after introduction into commerce,
would be converted to combination tractors, as a means to circumvent
the Class 8 sleeper cab regulations. The agencies welcome comments on
the likelihood of manufacturers using such an approach to circumvent
the regulations and the appropriate regulatory provisions the agencies
should consider to prevent such actions.
(1) What are the proposed Class 7 and 8 tractor and engine
CO2 emissions and fuel consumption standards and their
timing?
    In developing the proposed tractor and engine standards, the
agencies have evaluated the current levels of emissions and fuel
consumption, the kinds of technologies that could be utilized by truck
and engine manufacturers to reduce emissions and fuel consumption from
tractors and engines, the associated lead time, the associated costs
for the industry, fuel savings for the consumer, and the magnitude of
the CO2 and fuel savings that may be achieved. The
technologies that the agencies considered while setting the proposed
tractor standards include improvements in aerodynamic design, lower
rolling resistance tires, extended idle reduction technologies, and
vehicle empty weight reduction. The technologies that the agencies
considered while setting the engine standards include engine friction
reduction, aftertreatment optimization, and turbocompounding, among
others. The agencies' evaluation indicates that these technologies are
available today, but have very low application rates in the market. The
agencies have analyzed the technical feasibility of achieving the
proposed CO2 and fuel consumption standards for tractors and
engines, based on projections of what actions manufacturers would be
expected to take to reduce emissions and fuel consumption to achieve
the standards. EPA and NHTSA also present the estimated costs and
benefits of the Class 7 and 8 combination tractor and engine standards
in Section III and in draft RIA Chapter 2.
(a) Tractor Standards
    The agencies are proposing the following standards for Class 7 and
8 combination tractors in Table II-1, using the subcategorization
approach just explained. As noted, the agencies are not aware of any
mid roof day cab tractors at this time, but are proposing that any
Class 7 and 8 day cabs with a mid roof would meet the respective low
roof standards, based on the similarity in baseline performance and
similarity in expected improvement of mid roof sleeper cabs relative to
low roof sleeper cabs.
    As explained below in Section III, EPA has determined that there is
sufficient lead time to introduce various tractor and engine
technologies into the fleet starting in the 2014 model year, and is
proposing standards starting for that model year predicated on
performance of those technologies. EPA is proposing more stringent
tractor standards for the 2017 model year which reflect the
CO2 emissions reductions required through the 2017 model
year engine standards. (As explained in Section II.B.(2)(h)(v) below,
engine performance is one of the inputs into the proposed compliance
model, and that input will change in 2017 to reflect the 2017 MY engine
standards.) The 2017 MY vehicle standards are not premised on tractor
manufacturers installing additional vehicle technologies. EPA's
proposed standards apply throughout the useful life period as described
in Section V. Similar to EPA's non-GHG standards approach,
manufacturers may generate and use credits from Class 7 and 8
combination tractors to show compliance with the standards.
    NHTSA is proposing Class 7 and 8 tractor fuel consumption standards
that are voluntary standards in the 2014 and 2015 model years and
become mandatory beginning in the 2016 model year, as required by the
lead time and stability requirement within EISA. NHTSA is also
proposing new standards for the 2017 model year which reflect
additional improvements in only the heavy-duty engines. While NHTSA
proposes to use useful life considerations for establishing fuel
consumption performance for initial compliance and for ABT, NHTSA does
not intend to implement an in-use compliance program for fuel
consumption because it is not currently anticipated there will be
notable deterioration of fuel consumption over the useful life. NHTSA
believes that the vehicle and engine standards proposed for combination
tractors are appropriate, cost-effective, and technologically feasible
in the rulemaking timeframe based on our analysis detailed below in
Section III and in the Chapter 2 of the draft RIA.
    EPA and NHTSA are not proposing to make the 2017 vehicle standards
more stringent based on the application of additional truck
technologies because projected application rates of truck technologies
used in setting the 2014 model year truck standard already reflect the
maximum application rates we believe appropriate for these vehicles
given their specific use patterns as described in Section III. We
considered setting more stringent standards for Class 7 and 8 tractors
based on the application of more advanced aerodynamic systems, such as
self-compensating side extenders or other advanced aerodynamic
technologies, but concluded that those

technologies would not be fully developed in the necessary lead time.
We request comment on this decision, supported by data as appropriate.
[GRAPHIC] [TIFF OMITTED] TP30NO10.012

    Based on our analysis, the 2017 model year standards represent up
to a 20 percent reduction in CO2 emissions and fuel
consumption over a 2010 model year baseline, as detailed in Section
III.A.2.
---------------------------------------------------------------------------

    \39\ Manufacturers may voluntarily opt-in to the NHTSA fuel
consumption program in 2014 or 2015. If a manufacturer opts-in, the
program becomes mandatory. See Section [add cross reference] below
for more information about NHTSA's voluntary opt-in program for MYs
2014 and 2015.
---------------------------------------------------------------------------

(i) Off-Road Tractor Standards
    In developing the proposal EPA and NHTSA received comment from
manufacturers and owners that tractors sometimes have very limited on-
road usage. These trucks are defined to be motor vehicles under 40 CFR
85.1703, but they will spend the majority of their operations off-road.
Tractors, such as those used in oil fields, will experience little
benefit from improved aerodynamics and low rolling resistance tires.
The agencies are therefore proposing to allow a narrow range of these
de facto off-road trucks to be excluded from the proposed tractor
standards because the trucks do not travel at speeds high enough to
realize aerodynamic improvements and require special off-road tires
such as lug tires. The trucks must still use a certified engine, which
will provide fuel consumption and CO2 emission reductions to
the truck in all applications. To ensure the limited use of these
trucks, the agencies are proposing requirements that the vehicles have
off-road tires, have limited high speed operation, and are designed for
specific off-road applications.\40\ The agencies are proposing that a
truck must meet the following requirements to qualify for an exemption
from the vehicle standards for Class 7 and 8 tractors:
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    \40\ For purposes of compliance with NHTSA's safety regulations,
such as FMVSS Nos. 119 and 121, a manufacturer wishing for their
vehicle to classify as ``off-road'' would still need to work with
the relevant NHTSA office to declare its vehicle as ``off-road'' if
it uses public roads at any point in its service.
---------------------------------------------------------------------------

     Installed tires which are lug tires or contain a speed
rating of less than or equal to 60 mph; and
     Include a vehicle speed limiter governed to 55 mph, and
     Contain Power Take-Off controls, or have axle
configurations other than 4x2, 6x2, or 6x4 and has GVWR greater than
57,000 pounds; and
     Has a frame Resisting Bending Moment greater than
2,000,000 lb-in.\41\
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    \41\ The agencies have found based on standard truck
specifications, that vehicles designed for significant off-road
applications, such as concrete pumper and logging trucks have
resisting bending moment greater than 2,100,000 lb-in. (ranging up
to 3,580,000 lb-in.). The typical on highway tractors have resisting
bending moment of 1,390,000 lb-in.
---------------------------------------------------------------------------

    EPA and NHTSA have concluded that the onroad performance losses and
additional costs to develop a truck which meets these specifications
will limit the exemption to trucks built for

the desired purposes.\42\ The agencies welcome comment on the proposed
requirements and exemptions.
---------------------------------------------------------------------------

    \42\ The estimated cost for a lift axle is approximately
$10,000. Axles with weight ratings greater than a typical on-road
axle cost an additional $3,000.
---------------------------------------------------------------------------

(b) Engine Standards
    EPA is proposing GHG standards and NHTSA is proposing fuel
consumption standards for new heavy-duty engines. The standards will
vary depending on the type of vehicle in which they are used, as well
as whether the engines are diesel or gasoline powered. This section
discusses the standards for engines used in Class 7 and 8 combination
tractors and also provides some overall background information. More
information is also provided in the discussion of the standards for
engines used in vocational vehicles.
    EPA's existing criteria pollutant emissions regulations for heavy-
duty highway engines establish four regulatory categories that
represent the engine's intended and primary truck application.\43\ The
Light Heavy-Duty (LHD) diesel engines are intended for application in
Class 2b through Class 5 trucks (8,501 through 19,500 pounds GVWR). The
Medium Heavy-Duty (MHD) diesel engines are intended for Class 6 and
Class 7 trucks (19,501 through 33,000 pounds GVWR). The Heavy Heavy-
Duty (HDD) diesel engines are primarily used in Class 8 trucks (33,001
pounds and greater GVWR). Lastly, spark ignition engines (primarily
gasoline-powered engines) installed in incomplete vehicles less than
14,000 pounds GVWR and spark ignition engines that are installed in all
vehicles (complete or incomplete) greater than 14,000 pounds GVWR are
grouped into a single engine regulatory subcategory. The engines in
these four regulatory subcategories range in size between approximately
five liters and sixteen liters. The agencies welcome comments on
updating the definitions of each subcategory, such as the typical
horsepower levels, as described in 40 CFR 1036.140.
---------------------------------------------------------------------------

    \43\ See 40 CFR 1036.140.
---------------------------------------------------------------------------

    For the purposes of the GHG engine emissions and engine fuel
consumption standards that EPA and NHTSA are proposing, the agencies
intend to maintain these same four regulatory subcategories. This class
structure would enable the agencies to set standards that appropriately
reflect the technology available for engines for use in each type of
vehicle, and that are therefore technologically feasible for these
engines. This section discusses the MHD and HHD diesel engines used in
Class 7 and 8 combination tractors. Additional details regarding the
other heavy-duty engine standards are included in Section II.D.1.b.
    EPA's proposed heavy-duty CO2 emission standards for
diesel engines installed in combination tractors are presented in Table
II-2. We should note that this does not cover gasoline or LHDD engines
as they are not used in Class 7 and 8 combination tractors. Similar to
EPA's non-GHG standards approach, manufacturers may generate and use
credits to show compliance with the standards. EPA is proposing to
adopt the existing useful life definitions for heavy-duty engines. The
EPA standards would become effective in the 2014 model year, with more
stringent standards becoming effective in model year 2017. Recently,
EPA's heavy-duty highway engine program for criteria pollutants
provided new emissions standards for the industry in three year
increments. Largely, the heavy-duty engine and truck manufacturer
product plans have fallen into three year cycles to reflect this
regulatory environment. The proposed two-step CO2 emission
standards recognize the opportunity for technology improvements over
this timeframe while reflecting the typical diesel truck manufacturers'
product plan cycles.
    With respect to the lead time and cost of incorporating technology
improvements that reduce GHG emissions and fuel consumption, EPA and
NHTSA place important weight on the fact that during MYs 2014-2017
engine manufacturers are expected to redesign and upgrade their
products. Over these four model years there will be an opportunity for
manufacturers to evaluate almost every one of their engine models and
add technology in a cost-effective way, consistent with existing
redesign schedules, to control GHG emissions and reduce fuel
consumption. The time-frame and levels for the standards, as well as
the ability to average, bank and trade credits and carry a deficit
forward for a limited time, are expected to provide manufacturers the
time needed to incorporate technology that will achieve the proposed
GHG and fuel consumption reductions, and to do this as part of the
normal engine redesign process. This is an important aspect of the
proposed rules, as it will avoid the much higher costs that would occur
if manufacturers needed to add or change technology at times other than
these scheduled redesigns. This time period will also provide
manufacturers the opportunity to plan for compliance using a multi-year
time frame, again in accord with their normal business practice.
Further details on lead time, redesigns and technical feasibility can
be found in Section III.
    NHTSA's fuel consumption standards, also presented in Table II-2,
would contain voluntary engine standards starting in 2014 model year,
with mandatory engine standards starting in 2017 model year, harmonized
with EPA's 2017 model year standards. A manufacturer may opt-in to
NHTSA's voluntary standards in 2014, 2015 or 2016. Once a manufacturer
opts-in, the standards become mandatory for the opt-in and subsequent
model years, and the manufacturer may not reverse its decision. To opt
into the program, a manufacturer must declare its intent to opt in to
the program at the same time it submits the Pre-Certification
Compliance Report. See 49 CFR 535.8 for information related to the Pre-
Certification Compliance Report. A manufacturer opting into the program
would begin tracking credits and debits beginning in the model year in
which they opt into the program.

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    Combination tractors spend the majority of their operation at
steady state conditions, and will obtain in-use benefit of technologies
such as turbocompounding and other waste heat recovery technologies
during this kind of typical engine operation. Therefore, the engines
installed in tractors would be required to meet the standard based on
the steady-state SET test cycle, as discussed further in Section
II.B(2)(i).
    The baseline HHD diesel engine performance in 2010 model year on
the SET is 490 g CO2/bhp-hr (4.81 gal/100 bhp-hr), as
determined from confidential data provided by manufacturers and data
submitted for the non-GHG emissions certification process. Similarly,
the baseline MHD diesel engine performance on the SET cycle is 518 g
CO2/bhp-hr (5.09 gallon/100-bhp-hr) in the 2010 model year.
Further discussion of the derivation of the baseline can be found in
Section III The diesel engine standards that EPA is proposing and the
voluntary standards being proposed by NHTSA for the 2014 model year
would require diesel engine manufacturers to achieve on average a three
percent reduction in fuel consumption and CO2 emissions over
the baseline 2010 model year performance for the engines. The agencies'
assessment of the findings of the 2010 NAS Report and other literature
sources indicates that there are technologies available to reduce fuel
consumption by this level in the proposed timeframe. These technologies
include improved turbochargers, aftertreatment optimization, low
temperature exhaust gas recirculation, and engine friction reductions.
Additional discussion on technical feasibility is included in Section
III below and in draft RIA Chapter 2.
    Furthermore, the agencies are proposing that diesel engines further
reduce fuel consumption and CO2 emissions from the 2010
model year baseline in 2017 model year. The proposed reductions
represent on average a six percent reduction for MHD and HHD diesel
engines required to use the SET-based standard. The additional
reductions could likely be achieved through the increased refinement of
the technologies projected to be implemented for 2014, plus the
addition of turbocompounding or other waste heat recovery systems. The
agencies' analysis indicates that this type of advanced engine
technology would require a longer development time than the 2014 model
year, and we therefore are proposing to provide additional lead time to
allow for its introduction.
    The agencies are aware that some truck and engine manufacturers
would prefer to align their product development plans for these engine
standards with their current plans to meet Onboard Diagnostic
regulations for EPA and California in 2013 and 2016. We believe our
proposed averaging, banking and trading provisions already provide
these manufacturers with considerable flexibility to manage their GHG
compliance plans consistent with the 2013 model year. Nevertheless, we
are requesting comment on whether EPA and NHTSA should provide
additional defined phase-in schedules that would more explicitly
accommodate this request. For example, we request comment on a phase-in
schedule with a standard of 485 g/bhp-hr for the model years 2013-2015
followed by a standard of 460 g/bhp-hr for 2016-18 model years with the
associated fuel consumption values for the NHTSA program. This phase-in
schedule is just one of many potential schedules that would provide
identical fuel savings and emissions reductions for the period from
2013-2018. If commenters wish to discuss a different phase-in schedule
than the one proposed by the agencies, we request that commenters
include a description of their preferred phase-in schedule, including
an analysis showing that it would be at least as effective (or more) as
the primary program for the period through the 2018 model year. We also
request comment on whether similar provisions should be made for the
vocational engine standards discussed later in this section.
    In proposing this standard for heavy-duty diesel engines used in
Class 7 and 8 combination tractors, the agencies have examined the
current performance levels of the engines across the fleet. EPA and
NHTSA found that a large majority of the engines were generally
relatively close to the average baseline, with some above and some
below. We recognize, however, that when regulating a category of
engines for the first time, there will be individual products that may
deviate significantly from this baseline level of performance. For the
current fleet there is a relatively small group of engines that are
significantly worse than the average baseline for other engines. In
proposing the standards, the agencies have looked primarily at the
typical performance levels of the majority of the engines in the fleet,
and the increased performance that would be achieved through increased
spread of technology. The agencies also recognize that for the smaller
group of products, the same reduction from the industry baseline may
experience significant issues of available lead-time and cost because
these products may require a total redesign in order to meet the
standards. These are limited instances where certain engine families
have high atypically high baseline CO2 levels and limited
line of engines across which to average performance. See 75 FR 25414-
25419, which adopts temporary lead time allowance alternative standards
to

deal with a similar issue for a subset of light-duty vehicles. To
accommodate these situations, the agencies are proposing a regulatory
alternative whereby a manufacturer, for a limited period, would have
the option to comply with a unique standard based on a three percent
reduction from an individual engine's own 2011 model year baseline
level, rather than meeting the otherwise-applicable standard level. Our
assessment is that this three percent reduction is appropriate given
the potential for manufacturers to apply similar technology packages
with similar cost to what we have estimated for the primary program. We
do not believe this alternative needs to continue past the 2016 model
year since manufacturers will have had ample opportunity to benchmark
competitive products during redesign cycles and to make appropriate
changes to bring their product performance into line with the rest of
the industry. This alternative would not be available unless and until
a manufacturer had exhausted all available credits and credit
opportunities, and engines under the alternative standard could not
generate credits. We are proposing that manufacturers can select engine
families for this alternative standard without agency approval, but are
proposing to require that manufacturers notify the agency of their
choice and to include in that notification a demonstration that it has
exhausted all available credits and credit opportunities.
    The agencies are also requesting comment on the potential to extend
this regulatory alternative for one additional year for a single engine
family with performance measured in that year as six percent beyond the
engine's own 2011 baseline level. We also request comment on the level
of reduction beyond the baseline that is appropriate in this
alternative. The three percent level reflects the aggregate improvement
beyond the baseline we are requiring of the entire industry. As this
provision is intended to address potential issues for legacy products
that we would expect to be replaced or significantly improved at the
manufacturer's next product redesign, we request comment if a two
percent reduction would be more appropriate. We would consider two
percent rather than three percent if we were convinced that making all
of the changes we have outlined in our assessment of the technical
feasibility of the standards was not possible for some engines due to
legacy design issues that will change in the future. We are proposing
that manufacturers making use of these provisions would need to exhaust
all credits within this subcategory prior to using this flexibility and
would not be able to generate emissions credits from other engines in
the same regulatory subcategory as the engines complying using this
alternate approach.
    EPA and NHTSA considered setting even more stringent engine
standards for the 2017 model year based on the use of more
sophisticated waste heat recovery technologies such as bottoming cycle
engine designs. We are not proposing more stringent standards because
we do not believe this technology can be broadly available by 2017
model year. We request comment on the technological feasibility and
cost-effectiveness of more stringent standards in the timeframe of the
proposed standards.
(c) In-Use Standards
    Section 202(a)(1) of the CAA specifies that EPA is to adopt
emissions standards that are applicable for the useful life of the
vehicle. The in-use standards that EPA is proposing would apply to
individual vehicles and engines. NHTSA is not proposing to adopt in-
use.
    EPA is proposing that the in-use standards for heavy-duty engines
installed in tractors be established by adding an adjustment factor to
the full useful life emissions and fuel consumption results projected
in the EPA certification process. EPA is proposing a 2 percent
adjustment factor for the in-use standard to provide a reasonable
margin for production and test-to-test variability that could result in
differences between the initial emission test results and emission
results obtained during subsequent in-use testing. Details on the
development of the adjustment factor are included in draft RIA Chapter
3.
    EPA is also proposing that the useful life for these engine and
vehicles with respect to GHG emissions be set equal to the respective
useful life periods for criteria pollutants. EPA proposes that the
existing engine useful life periods, as included in Table II-3:, be
broadened to include CO2 emissions and fuel consumption for
both engines and tractors (see 40 CFR 86.004-2).
[GRAPHIC] [TIFF OMITTED] TP30NO10.014

    EPA and NHTSA request comments on the magnitude and need for an in-
use adjustment factor for the engine standard and the compliance model
(GEM) based tractor standard.
(2) Test Procedures and Related Issues
    The agencies are proposing a complete set of test procedures to
evaluate fuel consumption and CO2 emissions from Class 7 and
8 tractors and the engines installed in them. The test procedures
related to the tractors are all new, while the engine test procedures
build substantially on EPA's current non-GHG emissions test procedures,
except as noted. This section discusses the proposed simulation model
developed for demonstrating compliance with the tractor standard and
the proposed engine test procedures.
(a) Truck Simulation Model
    We are proposing to set separate engine and vehicle-based emission
standards to achieve the goal of reducing emissions and fuel
consumption for both trucks and engines. For the Class 7 and 8
tractors, engine manufacturers would be subject to the engine
standards, and Class 7 and 8 tractor manufacturers would be required to
install engines in their tractors certified for use in the tractor. The
tractor manufacturer would be subject to a separate vehicle-based
standard that would use a proposed truck simulation model to evaluate
the

impact of the tractor cab design to determine compliance with the
tractor standard.
    A simulation model, in general, uses various inputs to characterize
a vehicle's properties (such as weight, aerodynamics, and rolling
resistance) and predicts how the vehicle would behave on the road when
it follows a driving cycle (vehicle speed versus time). On a second-by-
second basis, the model determines how much engine power needs to be
generated for the vehicle to follow the driving cycle as closely as
possible. The engine power is then transmitted to the wheels through
transmission, driveline, and axles to move the vehicle according to the
driving cycle. The second-by-second fuel consumption of the vehicle,
which corresponds to the engine power demand to move the vehicle, is
then calculated according to a fuel consumption map in the model.
Similar to a chassis dynamometer test, the second-by-second fuel
consumption is aggregated over the complete drive cycle to determine
the fuel consumption of the vehicle.
    NHTSA and EPA are proposing to evaluate fuel consumption and
CO2 emissions respectively through a simulation of whole-
vehicle operation, consistent with the NAS recommendation to use a
truck model to evaluate truck performance. The agencies developed the
Greenhouse gas Emissions Model (GEM) for the specific purpose of this
proposal to evaluate truck performance. The GEM is similar in concept
to a number of vehicle simulation tools developed by commercial and
government entities. The model developed by the agencies and proposed
here was designed for the express purpose of vehicle compliance
demonstration and is therefore simpler and less configurable than
similar commercial products. This approach gives a compact and quicker
tool for vehicle compliance without the overhead and costs of a more
sophisticated model. Details of the model are included in Chapter 4 of
the draft RIA. The agencies are aware of several other simulation tools
developed by universities and private companies. Tools such as Argonne
National Laboratory's Autonomie, Gamma Technologies' GT-Drive, AVL's
CRUISE, Ricardo's VSIM, Dassault's DYMOLA, and University of Michigan's
HE-VESIM codes are publicly available. In addition, manufacturers of
engines, vehicles, and trucks often have their own in-house simulation
tools. The agencies welcome comments on other simulation tools which
could be used by the agencies. The use criteria for this model are that
it must be able to be managed by the agencies for compliance purposes,
has no cost to the end-user, is freely available and distributable as
an executable file, contains open source code to provide transparency
in the model's operation yet contains features which cannot be changed
by the user, and is easy to use by any user with minimal or no prior
experience.
    GEM is designed to focus on the inputs most closely associated with
fuel consumption and CO2 emissions--i.e., on those which
have the largest impacts such as aerodynamics, rolling resistance,
weight, and others.
    EPA has validated GEM based on the chassis test results from a
SmartWay certified tractor tested at Southwest Research Institute. The
validation work conducted on these three vehicles is representative of
the other Class 7 and 8 tractors. Many aspects of one tractor
configuration (such as the engine, transmission, axle configuration,
tire sizes, and control systems) are similar to those used on the
manufacturer's sister models. For example, the powertrain configuration
of a sleeper cab with any roof height is similar to the one used on a
day cab with any roof height. Overall, the GEM predicted the fuel
consumption and CO2 emissions within 4 percent of the
chassis test procedure results for three test cycles--the California
ARB Transient cycle, 65 mph cruise cycle, and 55 mph cruise cycle.
These cycles are the ones the agencies are proposing to utilize in
compliance testing. Test to test variation for heavy-duty vehicle
chassis testing can be higher than 4 percent based on driver variation.
The proposed simulation model is described in greater detail in Chapter
4 of the draft RIA and is available for download by interested parties
at (http://www.epa.gov/otaq/climate/regulations.htm). We request
comment on all aspects of this approach to compliance determination in
general and to the use of the GEM in particular.
    The agencies are proposing that for demonstrating compliance, a
Class 7 and 8 tractor manufacturer would measure the performance of
specified tractor systems (such as aerodynamics and tire rolling
resistance), input the values into GEM, and compare the model's output
to the standard. The agencies propose that a tractor manufacturer would
provide the inputs for each of following factors for each of the
tractors it wished to certify under CO2 standards and for
establishing fuel consumption values: Coefficient of Drag, Tire Rolling
Resistance Coefficient, Weight Reduction, Vehicle Speed Limiter, and
Extended Idle Reduction Technology. These are the technologies on which
the agencies' own feasibility analysis for these vehicles is
predicated. An example of the GEM input screen is included in Figure
II-3.
    The input values for the simulation model would be derived by the
manufacturer from test procedures proposed by the agencies in this
proposal. The agencies are proposing several testing alternatives for
aerodynamic assessment, a single procedure for tire rolling resistance
coefficient determination, and a prescribed method to determine tractor
weight reduction. The agencies are proposing defined model inputs for
determining vehicle speed limiter and extended idle reduction
technology benefits. The other aspects of vehicle performance are fixed
within the model as defined by the agencies and are not varied for the
purpose of compliance.
(b) Metric
    Test metrics which are quantifiable and meaningful are critical for
a regulatory program. The CO2 and fuel consumption metric
should reflect what we wish to control (CO2 or fuel
consumption) relative to the clearest value of its use: In this case,
carrying freight. It should encourage efficiency improvements that will
lead to reductions in emissions and fuel consumption during real world
operation. The agencies are proposing standards for Class 7 and 8
combination tractors that would be expressed in terms of moving a ton
(2000 pounds) of freight over one mile. Thus, NHTSA's proposed fuel
consumption standards for these trucks would be represented as gallons
of fuel used to move one ton of freight 1,000 miles, or gal/1,000 ton-
mile. EPA's proposed CO2 vehicle standards would be
represented as grams of CO2 per ton-mile.
    Similarly, the NAS panel concluded, in their report, that a load-
specific fuel consumption metric is appropriate for HD trucks. The
panel spent considerable time explaining the advantages of and
recommending a load-specific fuel consumption approach to regulating
the fuel efficiency of heavy-duty trucks. See NAS Report pages 20
through 28. The panel first points out that the nonlinear relationship
between fuel economy and fuel consumption has led consumers of light-
duty vehicles to have difficulty in judging the benefits of replacing
the most inefficient vehicles. The panel describes an example where a
light-duty vehicle can save the same 107 gallons per year (assuming
12,000 miles travelled per year) by improving one vehicle's fuel
efficiency from 14 to 16 mpg or improving another vehicle's fuel
efficiency from 35 to 50.8 mpg. The use

of miles per gallon leads consumers to undervalue the importance of
small mpg improvements in vehicles with lower fuel economy. Therefore,
the NAS panel recommends the use of a fuel consumption metric over a
fuel economy metric. The panel also describes the primary purpose of
most heavy-duty vehicles as moving freight or passengers (the payload).
Therefore, they concluded that the most appropriate way to represent an
attribute-based fuel consumption metric is to normalize the fuel
consumption to the payload.
    With the approach to compliance NHTSA and EPA are proposing, a
default payload is specified for each of the tractor categories
suggesting that a gram per mile metric with a specified payload and a
gram per ton-mile metric would be effectively equivalent. The primary
difference between the metrics and approaches relates to our treatment
of mass reductions as a means to reduce fuel consumption and greenhouse
gas emissions. In the case of a gram per mile metric, mass reductions
are reflected only in the calculation of the work necessary to move the
vehicle mass through the drive cycle. As such it directly reduces the
gram emissions in the numerator since a vehicle with less mass will
require less energy to move through the drive cycle leading to lower
CO2 emissions. In the case of Class 7 and 8 tractors and our
proposed gram/ton-mile metric, reductions in mass are reflected both in
less mass moved through the drive cycle (the numerator) and greater
payload (the denominator). We adjust the payload based on vehicle mass
reductions because we estimate that approximately one third of the time
the amount of freight loaded in a trailer is limited not by volume in
the trailer but by the total gross vehicle weight rating of the
tractor. By reducing the mass of the tractor the mass of the freight
loaded in the tractor can go up. Based on this general approach, it can
be estimated that for every 1,200 pounds in mass reduction total truck
vehicle miles traveled and therefore trucks on the road could be
reduced by one percent. Without the use of a per ton-mile metric it
would not be clear or straightforward for the agencies to reflect the
benefits of mass reduction from large freight carrying vehicles that
are often limited in the freight they carry by the gross vehicle weight
rating of the truck. The agencies seek comment on the use of a per ton-
mile metric and also whether other metrics such as per cube-mile should
be considered instead.
(c) Truck Aerodynamic Assessment
    The aerodynamic drag of a vehicle is determined by the vehicle's
coefficient of drag (Cd), frontal area, air density and speed. The
agencies are proposing to establish and use pre-defined values for the
input parameters to GEM which represent the frontal area and air
density, while the speed of the vehicle would be determined in GEM
through the proposed drive cycles. The agencies are proposing that the
manufacturer would determine a truck's Cd, a dimensionless measure of a
vehicle's aerodynamics, for input into the model through a combination
of vehicle testing and vehicle design characteristics. Quantifying
truck aerodynamics as an input to the GEM presents technical challenges
because of the proliferation of truck configurations, the lack of a
clearly preferable standardized test method, and subtle variations in
measured Cd values among various test procedures. Class 7 and 8 tractor
aerodynamics are currently developed by manufacturers using a range of
techniques, including vehicle coastdown testing, wind tunnel testing,
computational fluid dynamics, and constant speed tests as further
discussed below. Reflecting that each of these approaches has
limitations and no one approach appears to be superior to others, the
agencies are proposing to allow all three aerodynamic evaluation
methods to be used in demonstrating a vehicle's aerodynamic
performance. The agencies welcome comments on each of these methods.
    The agencies are proposing that the coefficient of drag assessment
be a product of test data and vehicle characteristics using good
engineering judgment. The primary tool the agencies expect to use in
our own evaluation of aerodynamic performance is the coastdown
procedure described in SAE Recommended Practice J2263. Allowing
manufacturers to use multiple test procedures and modeling coupled with
good engineering judgment to determine aerodynamic performance is
consistent with the current approach used in determining representative
road load forces for light-duty vehicle testing (40 CFR 86.129-
00(e)(1)). The agencies anticipate that as we and the industry gain
experience with assessing aerodynamic performance of HD vehicles for
purposes of compliance a test-only approach may have advantages.
    We believe this broad approach allowing manufacturers to use
multiple different test procedures to demonstrate aerodynamic
performance is appropriate given that no single test procedure is
superior in all aspects to other approaches. However, we also recognize
the need for consistency and a level playing field in evaluating
aerodynamic performance. To accomplish this, the agencies propose to
use a two-part approach that evaluates aerodynamic performance not only
through testing but through the application of good engineering
judgment and a technical description of the vehicles aerodynamic
characteristics. The first part of the proposed evaluation approach
uses a bin structure characterizing the expected aerodynamic
performance of tractors based on definable vehicle attributes. This bin
approach is described further below. The second proposed evaluation
element uses aerodynamic testing to measure the vehicle's aerodynamic
performance under standardized conditions. The agencies expect that the
SAE J2263 coastdown procedures will be the primary aerodynamic testing
tool but are interested in working with the regulated industry and
other interested stakeholders to develop a primary test approach.
Additionally, the agencies propose to have a process that would allow
manufacturers to demonstrate that another aerodynamic test procedure
should also be allowed for purposes of generating inputs used in
assessing a truck's performance. We are requesting comment on methods
that should form the primary aerodynamic testing tool, methods that may
be appropriate as alternatives, and the mechanism (including standards,
practices, and unique criteria) for the agencies to consider allowing
alternative aerodynamic test methods.
    NHTSA and EPA are proposing that manufacturers use a two part
screening approach for determining the aerodynamic inputs to the GEM.
The first part would require the manufacturers to assign each vehicle
aerodynamic configuration to one of five aerodynamics bins created by
EPA and NHTSA as described below. The assignment by bin reflects the
aerodynamic characteristics of the vehicle. For each bin, EPA and NHTSA
have already defined a nominal Cd that will be used in the GEM and a
range of Cd values that would be expected from testing of vehicles
meeting this bin description. The second part would require the
manufacturer to then compare its own test results of aerodynamic
performance (as conducted in accordance with the agencies'
requirements) for the vehicle to confirm the actual aerodynamic
performance was consistent with the agencies' expectations for vehicles
within this

bin. If the predicted performance and actual observed performance
match, the Cd value as an input for the GEM is the nominal Cd value
defined for the bin. If, however, a manufacturer's test data
demonstrates performance that is better than projected for the assigned
bin a manufacturer may use the test data and good engineering judgment
to demonstrate to the agencies that this particular vehicle's
performance is in keeping with the performance level of a more
aerodynamic bin and with the agencies' permission may use the Cd value
of the more aerodynamic bin. Conversely, if the test data demonstrates
that the performance is worse than the projected bin, then the
manufacturer would use the Cd value from the less aerodynamic bin.
Using this approach, the bin structure can be seen as the agencies'
first effort to create a common measure of aerodynamic performance to
benchmark the various test methods manufacturers may use to demonstrate
aerodynamic performance. For example, if a manufacturer's test methods
consistently produce Cd values that are better than projected by the
agencies, EPA and NHTSA can use this information to further scrutinize
the manufacturer's test procedure, helping to ensure that all
manufacturers are competing on a level playing field.
    The agencies are proposing aerodynamic technology bins which divide
the wide spectrum of tractor aerodynamics into five bins (i.e.,
categories). The first category, ``Classic,'' represents tractor bodies
which prioritize appearance or special duty capabilities over
aerodynamics. The Classic trucks incorporate few, if any, aerodynamic
features and may have several features which detract from aerodynamics,
such as bug deflectors, custom sunshades, B-pillar exhaust stacks, and
others. The second category for aerodynamics is the ``Conventional''
tractor body. The agencies consider Conventional tractors to be the
average new tractor today which capitalizes on a generally aerodynamic
shape and avoids classic features which increase drag. Tractors within
the ``SmartWay'' category build on Conventional tractors with added
components to reduce drag in the most significant areas on the tractor,
such as fully enclosed roof fairings, side extending gap reducers, fuel
tank fairings, and streamlined grill/hood/mirrors/bumpers. The
``Advanced SmartWay'' aerodynamic category builds upon the SmartWay
tractor body with additional aerodynamic treatments such as underbody
airflow treatment, down exhaust, and lowered ride height, among other
technologies. And finally, ``Advanced SmartWay II'' tractors
incorporate advanced technologies which are currently in the prototype
stage of development, such as advanced gap reduction, rearview cameras
to replace mirrors, wheel system streamlining, and advanced body
designs. The agencies recognize that these proposed aerodynamic bins
are static and referential and that there may be other technologies
that may provide similar aerodynamic benefit. In addition, it is
expected that aerodynamic equipment will advance over time and the
agencies may find it appropriate and necessary to revise the bin
descriptions.
    Under this proposal, the manufacturer would then input into GEM the
Cd value specified for each bin as also defined in Table II-4. For
example, if a manufacturer tests a Class 8 sleeper cab high roof
tractor with features which are similar to a SmartWay tractor and the
test produces a Cd value of 0.59, then the manufacturer would assign
this tractor to the Class 8 Sleeper Cab High Roof SmartWay bin. The
manufacturer would then use the Cd value of 0.60 as the input to GEM.
[GRAPHIC] [TIFF OMITTED] TP30NO10.015

    Coefficient of drag and frontal area of the tractor-trailer
combination go hand-in-hand to determine the force required to overcome
aerodynamic drag. As explained above, the agencies are proposing that
the Cd value is one of the GEM inputs which will be derived by the
manufacturer. However, the agencies are proposing to specify the
truck's frontal area for each regulatory category (i.e., each of the
seven subcategories which are proposed and listed in Table II-4 under
the Aerodynamic Input to GEM). The frontal area of a high roof tractor
pulling a box trailer will be determined primarily by the box trailer's
dimensions and the ground clearance of the tractor. The frontal area of
low and mid roof tractors will be determined by the tractor itself. An
alternate approach to the proposed frontal area specification is to
create the aerodynamic input table (as shown in Table II-4) with values
that represent the Cd multiplied by the frontal area. This approach
will provide the same aerodynamic load, but it will not allow the
comparison of aerodynamic efficiency across regulatory categories that
can be done with the Cd values alone. The agencies are interested in
comments regarding the frontal area of trucks, specifically whether the
specified frontal areas are appropriate and whether the use of standard
frontal areas may have unanticipated consequences.
    EPA and NHTSA recognize that wind conditions, most notably wind
direction, have a greater impact on real world CO2 emissions
and fuel consumption of heavy-duty trucks than of light-duty vehicles.
As noted in the NAS report,\44\ the wind average drag coefficient is
about 15 percent higher than the zero degree coefficient of drag. The
agencies considered proposing the use of a wind averaged drag
coefficient in this regulatory program, but ultimately decided to
propose using coefficient of drag values which represent zero yaw
(i.e., representing wind from directly in front of the vehicle, not
from the side) instead. We are taking this approach recognizing that
wind tunnels are currently the only tool to accurately assess the
influence of wind speed and direction on a truck's aerodynamic
performance. The agencies recognize, as NAS did, that the results of
using the zero yaw approach may result in fuel consumption predictions
that are offset slightly from real world performance levels, not unlike
the offset we see today between fuel economy test results in the CAFE
program and actual fuel economy performance observed in-use. We believe
this approach will not impact technology effectiveness or change the
kinds of technology decisions made by the tractor manufacturers in
developing equipment to meet our proposed standards. However, the
agencies are interested in receiving comment on approaches to develop
wind averaged coefficient of drag values using computational fluid
dynamics, coastdown, and constant speed test procedures.
---------------------------------------------------------------------------

    \44\ See 2010 NAS Report, Note 19, Finding 2-4 on page 39.
---------------------------------------------------------------------------

    The methodologies the agencies are considering for aerodynamic
assessment include coastdown testing, wind tunnel testing,
computational fluid dynamics, and constant speed testing. The agencies
welcome information on a constant speed test procedure and how it could
be applied to determine aerodynamic drag. In addition, the agencies
seek comment on allowing multiple aerodynamic assessment methodologies
and the need for comparison of aerodynamic assessment methods to
determine method precision and accuracy.
(i) Coastdown Testing
    The coastdown test procedure has been used extensively in the
light-duty industry to capture the road load force by coasting a
vehicle along a flat straightaway under a set of prescribed conditions.
Coast down testing has been used less extensively to obtain road load
forces for medium- and heavy-duty vehicles. EPA has conducted a
significant amount of test work to demonstrate that coastdown testing
per SAE J2263 produces reasonably repeatable test results for Class 7
and 8 tractor/trailer pairings, as described in draft RIA Chapter 3.
The agencies propose that a manufacturer which chooses this method
would determine a tractor's Cd value through analysis of the road load
force equation derived from SAE J2263 Revised 2008-12 test results, as
proposed in 40 CFR 1066.210.
(ii) Wind Tunnel Testing
    A wind tunnel provides a stable environment yielding a more
repeatable test than coastdown. This allows the manufacturer to run
multiple baseline vehicle tests and explore configuration modifications
for nearly the same effort (e.g., time and cost) as conducting the
coastdown procedure. In addition, wind tunnels provide testers with the
ability to yaw the vehicle at positive and negative angles relative to
the original centerline of the vehicle to accurately capture the
influence of non-uniform wind direction on the Cd (e.g., wind averaged
Cd).
    The agencies propose to allow the use of existing wind tunnel
procedures adopted by SAE International with some minor modifications
as discussed in Section V of this proposal. The agencies seek comments
on the appropriateness of using the existing SAE wind tunnel
procedures, and the modifications to these procedures, for this
regulatory purpose.
(iii) Computational Fluid Dynamics
    Computational fluid dynamics, or CFD, capitalizes on today's
computing power by modeling a full size vehicle and simulating the
flows around this model to examine the fluid dynamic properties, in a
virtual environment. CFD tools are used to solve either the Navier-
Stokes equations that relate the physical law of conservation of
momentum to the flow relationship around a body in motion or a static
body with fluid in motion around it, or the Boltzman equation that
examines fluid mechanics and determines the characteristics of
discreet, individual particles within a fluid and relates this behavior
to the overall dynamics and behavior of the fluid. CFD analysis
involves several steps: Defining the model structure or geometry based
on provided specifications to define the basic model shape; applying a
closed surface around the structure to define the external model shape
(wrapping or surface meshing); dividing the control volume, including
the model and the surrounding environment, up into smaller, discreet
shapes (gridding); defining the flow conditions in and out of the
control volume and the flow relationships within the grid (including
eddies and turbulence); and solving the flow equations based on the
prescribed flow conditions and relationships.
    This approach can be beneficial to manufacturers since they can
rapidly prototype (e.g., design, research, and model) an entire vehicle
without investing in material costs; they can modify and investigate
changes easily; and the data files can be re-used and shared within the
company or with corporate partners.
    The accuracy of the outputs from CFD analysis is highly dependent
on the inputs. The CFD modeler decides what method to use for wrapping,
how fine the mesh cell and grid size should be, and the physical and
flow relationships within the environment. A balance must be achieved
between the number of cells, which defines how fine the mesh is, and
the computational times for a result (i.e., solution-time-efficiency).
All of these decisions affect the results of the CFD aerodynamic
assessment.

    Because CFD modeling is dependent on the quality of the data input
and the design of the model, the agencies propose and seek comment on a
minimum set of criteria applicable to using CFD for aerodynamic
assessment in Section V.
(d) Tire Rolling Resistance Assessment
    NHTSA and EPA are proposing that the tractor's tire rolling
resistance input to the GEM be determined by either the tire
manufacturer or tractor manufacturer using the test method adopted by
the International Organization for Standardization, ISO 28580:2009.\45\
The agencies believe the ISO test procedure is appropriate to propose
for this program because the procedure is the same one used by NHTSA in
its fuel efficiency tire labeling program \46\ and is consistent with
the direction being taken by the tire industry both in the United
States and Europe. The rolling resistance from this test would be used
to specify the rolling resistance of each tire on the steer and drive
axle of the vehicle. The results would be expressed as a rolling
resistance coefficient and measured as kilogram per metric ton (kg/
metric ton). The agencies are proposing that three tire samples within
each tire model be tested three times each to account for some of the
production variability and the average of the nine tests would be the
rolling resistance coefficient for the tire. The GEM would use a
combined tire rolling resistance, where 15 percent of the gross weight
of the truck and trailer would be distributed to the steer axle, 42.5
percent to the drive axles, and 42.5 percent to the trailer axles.\47\
The trailer tires' rolling resistance would be prescribed by the
agencies as part of the standardized trailer used for demonstrating
compliance at 6 kg/metric ton, which was the average trailer tire
rolling resistance measured during the SmartWay tire testing.\48\
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    \45\ ISO, 2009, Passenger Car, Truck, and Bus Tyres--Methods of
Measuring Rolling Resistance--Single Point Test and Correlation of
Measurement Results: ISO 28580:2009(E), First Edition, 2009-07-01.
    \46\ NHTSA, 2009. ``NHTSA Tire Fuel Efficiency Consumer
Information Program Development: Phase 1--Evaluation of Laboratory
Test Protocols.'' DOT HS 811 119. June. (http://www.regulations.gov,
Docket ID: NHTSA-2008-0121-0019).
    \47\ This distribution is equivalent to the Federal over-axle
weight limits for an 80,000 GVWR 5-axle tractor-trailer: 12,000
Pounds over the steer axle, 34,000 pounds over the tandem drive
axles (17,000 pounds per axle) and 34,000 pounds over the tandem
trailer axles (17,000 pounds per axle).
    \48\ U.S. Environmental Protection Agency. SmartWay Transport
Partnership July 2010 e-update accessed July 16, 2010, from http://
www.epa.gov/smartwaylogistics/newsroom/documents/e-update-july-
10.pdf.
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    We acknowledge that the useful life of original equipment tires
used on tractors is shorter than the tractor's useful life. In this
proposal, we are treating the tires as if the owner replaces the tire
with tires that match the original equipment. Some owners opt for the
original tires under the assumption that this is the best product.
However, tractor tires are often retreaded or replaced. Steer tires on
a highway tractor might need replacement after 75,000 to 150,000 miles.
Drive tires might need retreading or replacement after 150,000 to
300,000 miles. Of course, tire removal miles can be much higher or
lower, depending upon a number of factors that affect tire removal
miles. These include the original tread depth; desired tread depth at
removal to maintain casing integrity; tire material and construction;
typical load; tire ``scrub'' due to urban driving and set back axles;
and, tire under-inflation. Since it is common for both medium- and
heavy-duty truck tires to be replaced and retreaded, we welcome
comments in this area. We are specifically seeking data for the rolling
resistance of retread and replacement heavy-duty tires and the typical
useful life of tractor tires.
(e) Weight Reduction Assessment
    EPA and NHTSA are seeking to account for the emissions and fuel
consumption benefits of weight reduction as a control technology in
heavy-duty trucks. Weight reduction impacts the emissions and fuel
consumption performance of tractors in different ways depending on the
truck's operation. For trucks that cube-out, the weight reduction will
show a small reduction in grams of CO2 emitted or fuel
consumed per mile travelled. The benefit is small because the weight
reduction is minor compared to the overall weight of the combination
tractor and payload. However, a weight reduction in tractors which
operate at maximum gross vehicle weight rating would result in an
increase in payload capacity. Increased vehicle payload without
increased GVWR significantly reduces fuel consumption and
CO2 emissions per ton mile of freight delivered. It also
leads to fewer vehicle miles driven with a proportional reduction in
traffic accidents.
    The empty curb weight of tractors varies significantly today. Items
as common as fuel tanks can vary between 50 and 300 gallons each for a
given truck model. Information provided by truck manufacturers
indicates that there may be as much as a 5,000 to 17,000 pound
difference in curb weight between the lightest and heaviest tractors
within a regulatory subcategory (such as Class 8 sleeper cab with a
high roof). Because there is such a large variation in the baseline
weight among trucks that perform roughly similar functions with roughly
similar configurations, there is not an effective way to quantify the
exact CO2 and fuel consumption benefit of mass reduction
using GEM because of the difficulty in establishing a baseline.
However, if the weight reduction is limited to tires and wheels, then
both the baseline and weight differentials for these are readily
quantifiable and well-understood. Therefore, the agencies are proposing
that the mass reduction that would be simulated be limited only to
reductions in wheel and tire weight. In the context of this heavy-duty
vehicle program with only changes to tires and wheels, the agencies do
not foresee any related impact on safety.\49\ The agencies welcome
comments regarding this approach and detailed data to further improve
the robustness of the agencies' assumed baseline truck tare/curb
weights for each regulatory category used within the model, as outlined
in draft RIA Chapter 3.5.
---------------------------------------------------------------------------

    \49\ For more information on the estimated safety effects of
this proposed rule, see Chapter 9 of the draft RIA.
---------------------------------------------------------------------------

    EPA and NHTSA are proposing to specify the baseline vehicle weight
for each regulatory category (including the tires and wheels), but
allow manufacturers to quantify weight reductions based on the wheel
material selection and single wide versus dual tires per Table II-5.
The agencies assume the baseline wheel and tire configuration contains
dual tires with steel wheels because these represent the vast majority
of new vehicle configurations today. The proposed weight reduction due
to the wheels and tires would be reflected in the payload tons by
increasing the specified payload by the weight reduction amount
discounted by two thirds to recognize that approximately one third of
the truck miles are travelled at maximum payload, as discussed below in
the payload discussion.

[GRAPHIC] [TIFF OMITTED] TP30NO10.016

(f) Extended Idle Reduction Technology Assessment
    Extended idling from Class 8 heavy-duty long haul combination
tractors contributes to significant CO2 emissions and fuel
consumption in the United States. The Federal Motor Carrier Safety
Administration regulations require a certain amount of driver rest for
a corresponding period of driving hours.\50\ Extended idle occurs when
Class 8 long haul drivers rest in the sleeper cab compartment during
rest periods as drivers find it both convenient and less expensive to
rest in the truck cab itself than to pull off the road and find
accommodations. During this rest period a driver will idle the truck in
order to provide heating or cooling or run on-board appliances. In some
cases the engine can idle in excess of 10 hours. During this period,
the truck will consume approximately 0.8 gallons of fuel and emit over
8,000 grams of CO2 per hour. An average truck can consume 8
gallons of fuel and emit over 80,000 grams of CO2 during
overnight idling in such a case.
---------------------------------------------------------------------------

    \50\ Federal Motor Carrier Safety Administration. Hours of
Service Regulations. Last accessed on August 2, 2010 at http://
www.fmcsa.dot.gov/rules-regulations/topics/hos/.
---------------------------------------------------------------------------

    Idling reduction technologies are available to allow for driver
comfort while reducing fuel consumptions and CO2 emissions.
Auxiliary power units, fuel operated heaters, battery supplied air
conditioning, and thermal storage systems are among the technologies
available today. The agencies are proposing to include extended idle
reduction technology as an input to the GEM for Class 8 sleeper cabs.
The manufacturer would input the value based on the idle reduction
technology installed on the truck. As discussed further in Section III,
if a manufacturer chooses to use idle reduction technology to meet the
standard, then it would require an automatic main engine shutoff after
5 minutes to help ensure the idle reductions are realized in-use. As
with all of the technology inputs discussed in this section, the
agencies are not mandating the use of idle reductions or idle shutdown,
but rather allowing their use as one part of a suite of technologies
feasible for reducing fuel consumption and meeting the proposed
standards. The proposed value (5 g CO2/ton-mile or 0.5 gal/
1,000 ton-mile) for the idle reduction technologies was determined
using an assumption of 1,800 idling hours per year, 125,000 miles
travelled, and a baseline idle fuel consumption of 0.8 gallons per
hour. Additional detail on the emission and fuel consumption reduction
values are included in draft RIA Chapter 2.
(g) Vehicle Speed Limiters
    Fuel consumption and CO2 emissions increase proportional
to the square of vehicle speed.\51\ Therefore, lowering vehicle speeds
can significantly reduce fuel consumption and GHG emissions. A vehicle
speed limiter (VSL), which limits the vehicle's maximum speed, is a
simple technology that is utilized today. The feature is electronically
programmed and controlled. Manufacturers today sell trucks with vehicle
speed limiters and allow the customers to set the limit. However, as
proposed the GEM will not provide a fuel consumption reduction for a
limiter that can be overridden. In order to obtain a benefit for the
program, the manufacturer must preset the limiter in such a way that
the setting will not be capable of being easily overridden by the fleet
or the owner. As with other engine calibration aspects of emission
controls, tampering with a calibration would be considered unlawful by
EPA. If the manufacturer installs a vehicle speed limiter into a truck
that is not easily overridden, then the manufacturer would input the
vehicle speed limit setpoint into GEM.
---------------------------------------------------------------------------

    \51\ See 2010 NAS Report, Note 19, Page 28. Road Load Force
Equation defines the aerodynamic portion of the road load as \1/2\ *
Coefficient of Drag * Frontal Area * air density * vehicle speed
squared.
---------------------------------------------------------------------------

(h) Defined Vehicle Configurations in the GEM
    As discussed above, the agencies are proposing methodologies that
manufacturers would use to quantify the values to be input into the GEM
for these factors affecting truck efficiency: Coefficient of Drag, Tire
Rolling Resistance Coefficient, Weight Reduction, Vehicle Speed
Limiter, and Extended Idle Reduction Technology. The other aspects of
vehicle performance are fixed within the model and are not varied for
the purpose of compliance. The defined inputs being proposed include
the drive cycle, tractor-trailer combination curb weight, payload,
engine characteristics, and drivetrain for each vehicle type, and
others. We are seeking comments accompanied with data on the defined
model inputs as described in draft RIA Chapter 4.
(i) Vehicle Drive Cycles
    As noted by the 2010 NAS Report,\52\ the choice of a drive cycle
used in compliance testing has significant consequences on the
technology that will be employed to achieve a standard as well as the
ability of the technology to achieve real world reductions in emissions
and improvements in fuel consumption. Manufacturers naturally will
design vehicles to ensure they satisfy regulatory standards. If the
agencies propose an ill-suited drive cycle for a regulatory category,
it may encourage GHG emissions and fuel consumption technologies which
satisfy the test but do not achieve the same benefits in use. For
example, requiring all trucks to use a constant speed highway drive
cycle will drive significant aerodynamic improvements. However, in the
real world a combination tractor used for local

delivery may spend little time on the highway, reducing the benefits
that would be achieved by this technology. In addition, the extra
weight of the aerodynamic fairings will actually penalize the GHG and
fuel consumption performance in urban driving and may reduce the
freight carrying capability. The unique nature of the kinds of
CO2 emissions control and fuel consumption technology means
that the same technology can be of benefit during some operation but
cause a reduced benefit under other operation.\53\ To maximize the GHG
emissions and fuel consumption benefits and avoid unintended reductions
in benefits, the drive cycle should focus on promoting technology that
produces benefits during the primary operation modes of the
application. Consequently, drive cycles used in GHG emissions and fuel
consumption compliance testing should reasonably represent the primary
actual use, notwithstanding that every truck has a different drive
cycle in-use.
---------------------------------------------------------------------------

    \52\ See 2010 NAS Report, Note 19, Chapters 4 and 8.
    \53\ This situation does not typically occur for heavy-duty
emission control technology designed to control criteria pollutants
such as PM and NOX.
---------------------------------------------------------------------------

    The agencies are proposing a modified version of the California ARB
Heavy Heavy-duty Truck 5 Mode Cycle,\54\ using the basis of three of
the cycles which best mirror Class 7 and 8 combination tractor driving
patterns, based on information from EPA's MOVES model.\55\ The key
advantage of the California ARB 5 mode cycle is that it provides the
flexibility to use several different modes and weight the modes to fit
specific truck application usage patterns. EPA analyzed the five cycles
and found that some modifications to the modes appear to be needed to
allow sufficient flexibility in weightings. The agencies are proposing
the use of the Transient mode, as defined by California ARB, because it
broadly covers urban driving. The agencies are also proposing altered
versions of the High Speed Cruise and Low Speed Cruise modes which
would reflect only constant speed cycles at 65 mph and 55 mph
respectively. EPA and NHTSA relied on the EPA MOVES analysis of Federal
Highway Administration data to develop the proposed mode weightings to
characterize typical operations of heavy-duty trucks, per Table II-6
below.\56\ A detailed discussion of drive cycles is included in draft
RIA Chapter 3.\57\
---------------------------------------------------------------------------

    \54\ California Air Resources Board. Heavy Heavy-duty Diesel
Truck chassis dynamometer schedule, Transient Mode. Last accessed on
August 2, 2010 at http://www.dieselnet.com/standards/cycles/
hhddt.html.
    \55\ EPA's MOVES (Motor Vehicle Emission Simulator). See http://
www.epa.gov/otaq/models/moves/index.htm for additional information.
    \56\ The Environmental Protection Agency. Draft MOVES2009
Highway Vehicle Population and Activity Data. EPA-420-P-09-001,
August 2009 http://www.epa.gov/otaq/models/moves/techdocs/
420p09001.pdf.
    \57\ In the light-duty vehicle rule, EPA and NHTSA based
compliance with tailpipe standards on use of the FTP and HFET, and
declined to use alternative tests. See 75 FR 25407. NHTSA is
mandated to use the FTP and HFET tests for CAFE standards, and all
relevant data was obtained by FTP and HFET testing in any case. Id.
Neither of these constraints exists for Class 7-8 tractors. The
little data which exist on current performance are principally
measured by the ARB Heavy Heavy-duty Truck 5 Mode Cycle testing, and
NHTSA is not mandated to use the FTP to establish heavy-duty fuel
economy standards. See 49 U.S.C. 32902(k)(2) authorizing NHTSA,
among other things, to adopt and implement appropriate ``test
methods, measurement metrics, * * * and compliance protocols''.
[GRAPHIC] [TIFF OMITTED] TP30NO10.017

(ii) Empty Weight and Payload
    The total weight of the tractor-trailer combination is the sum of
the tractor curb weight, the trailer curb weight, and the payload. The
total weight of a truck is important because it in part determines the
impact of technologies, such as rolling resistance, on GHG emissions
and fuel consumption. The agencies are proposing to specify each of
these aspects of the vehicle.
    The agencies developed the proposed tractor curb weight inputs from
actual tractor weights measured in two of EPA's test programs and based
on information from the manufacturers. The proposed trailer curb weight
inputs were derived from actual trailer weight measurements conducted
by EPA and weight data provided to ICF International by the trailer
manufacturers.\58\ Details of the individual weight inputs by
regulatory category are included in draft RIA Chapter 3.
---------------------------------------------------------------------------

    \58\ ICF International. Investigation of Costs for Strategies to
Reduce Greenhouse Gas Emissions for Heavy-Duty On-road Vehicles.
July 2010. Pages 4-15. Docket Number EPA-HQ-OAR-2010-0162-0044.
---------------------------------------------------------------------------

    There are several methods that the agencies have considered for
evaluating the GHG emissions and fuel consumption of tractors used to
carry freight. A key factor in these methods is the weight of the truck
that is assumed for purposes of the evaluation. In use, trucks operate
at different weights at different times during their operations. The
greatest freight transport efficiency (the amount of fuel required to
move a ton of payload) would be achieved by operating trucks at the
maximum load for which they are designed all of the time. However,
logistics such as delivery demands which require that trucks travel
without full loads, the density of payload, and the availability of
full loads of freight limit the ability of trucks to operate at their
highest efficiency all the time. M.J. Bradley analyzed the Truck
Inventory and Use Survey and found that approximately 9 percent of
combination tractor miles travelled empty, 61 percent are ``cubed-out''
(the trailer is full before the weight limit is reached), and 30
percent are ``weighed out'' (operating weight equal 80,000 pounds which
is the gross vehicle weight limit on the Federal Interstate Highway
System or greater than 80,000 pounds for vehicles traveling on roads
outside of the interstate system).\59\
---------------------------------------------------------------------------

    \59\ M.J. Bradley & Associates. Setting the Stage for Regulation
of Heavy-Duty Vehicle Fuel Economy and GHG Emissions: Issues and
Opportunities. February 2009. Page 35. Analysis based on 1992 Truck
Inventory and Use Survey data, where the survey data allowed
developing the distribution of loads instead of merely the average
loads.
---------------------------------------------------------------------------

    As described above, the amount of payload that a tractor can carry
depends on the category (or GVWR) of the vehicle. For example, a
typical Class 7 tractor can carry less payload than a Class 8 tractor.
The Federal Highway Administration developed Truck Payload Equivalent
Factors to inform the development of highway system strategies using
Vehicle Inventory and Use Survey (VIUS) and Vehicle Travel Information
System data. Their results

found that the average payload of a Class 8 truck ranged from 36,247 to
40,089 pounds, depending on the average distance travelled per day.\60\
The same results found that Class 7 trucks carried between 18,674 and
34,210 pounds of payload also depending on average distance travelled
per day. Based on this data, the agencies are proposing to prescribe a
fixed payload of 25,000 pounds for Class 7 tractors and 38,000 pounds
for Class 8 tractors for their respective test procedures. The agencies
are proposing a common payload for Class 8 day cabs and sleeper cabs
because the data available does not distinguish based on type of Class
8 tractor. These payload values represent a heavily loaded trailer, but
not maximum GVWR, since as described above the majority of tractors
``cube-out'' rather than ``weigh-out.'' Additional details on proposed
payloads are included in draft RIA Chapter 3.
---------------------------------------------------------------------------

    \60\ The U.S. Federal Highway Administration. Development of
Truck Payload Equivalent Factor. Table 11. Last viewed on March 9,
2010 at http://ops.fhwa.dot.gov/freight/freight_analysis/faf/faf2_
reports/reports9/s510_11_12_tables.htm.
---------------------------------------------------------------------------

(iii) Standardized Trailers
    NHTSA and EPA are proposing that the tractor performance in the GEM
would be judged by assuming it is pulling a standardized trailer. The
agencies believe that an assessment of the tractor aerodynamics should
be conducted using a tractor-trailer combination to reflect the impact
of aerodynamic technologies in actual use, where tractors are designed
and used with a trailer. Assessing the tractor aerodynamics using only
the tractor would not be a reasonable way to assess in-use impacts. For
example, the in-use aerodynamic drag while pulling a trailer is
different than without the trailer and the full impact of an
aerodynamic technology on reducing emissions and fuel consumption would
not be reflected if the assessment is performed on a tractor without a
trailer.
    In addition to assessing the tractor with a trailer, it is
appropriate to adopt a standardized trailer used for testing, and to
vary the standardized trailer by the regulatory category. This is
similar to the standardization of payload discussed above, as a way to
reasonably reflect in-use operating conditions. High roof tractors are
optimally designed to pull box trailers. The roof fairing on a tractor
is the feature designed to minimize the height differential between the
tractor and typical trailer to reduce the air flow disruption. Low roof
tractors are designed to carry flat bed or low-boy trailers. Mid roof
tractors are designed to carry tanker and bulk carrier trailers. The
agencies conducted a survey of tractor-trailer pairing in-use to
evaluate the representativeness of this premise. The survey of over
3,000 tractor-trailer combinations found that in 95 percent of the
combination tractors the tractor's roof height was paired appropriately
for the type of trailer that it was pulling.\61\ The agencies also have
evaluated the impact of pairing a low roof tractor with a box trailer
in coastdown testing and found that the aerodynamic force increases by
20 percent over a high roof tractor pulling the same box trailer.\62\
Therefore, drivers have a large incentive to use the appropriate
matching to reduce their fuel costs. However, the agencies recognize
that in operation tractors sometimes pull trailers other than the type
that it was designed to carry. The agencies are proposing the matching
of trailers to roof height for the test procedure. To do otherwise
would necessarily result in a standard reflecting substandard
aerodynamic performance, and thereby result in standards which are less
stringent than would be appropriate based on the reasonable assumption
that tractors will generally pair with trailer of appropriate roof
height. The other aspects of the test procedure such as empty trailer
weight, location of payload, and tractor-trailer gap are being proposed
for each regulatory category to provide consistent test procedures.
---------------------------------------------------------------------------

    \61\ U.S. EPA. Truck and Trailer Roof Height Match Analysis
Memorandum from Amy Kopin to the Docket, August 9, 2010. Docket
Identification Number EPA-HQ-OAR-2010-0162-0045.
    \62\ See the draft RIA Chapter 2 for additional detail.
---------------------------------------------------------------------------

(iv) Standardized Drivetrain
    The agencies' assessment of the current vehicle configuration
process at the truck dealer's level is that the truck companies provide
tools to specify the proper drivetrain matched to the buyer's specific
circumstances. These dealer tools allow a significant amount of
customization for drive cycle and payload to provide the best
specification for the customer. The agencies are not seeking to disrupt
this process. Optimal drivetrain selection is dependent on the engine,
drive cycle (including vehicle speed and road grade), and payload. Each
combination of engine, drive cycle, and payload has a single optimal
transmission and final drive ratio. The agencies are proposing to
specify the engine's fuel consumption map, drive cycle, and payload;
therefore, it makes sense to also specify the drivetrain that matches.
(v) Engine Input to GEM
    As the agencies are proposing separate engine and tractor
standards, the GEM will be used to assess the compliance of the tractor
with the tractor standard. To maintain the separate assessments, the
agencies are proposing to define the engine characteristics used in
GEM, including the fuel consumption map which provides the fuel
consumption at hundreds of engine speed and torque points. If the
agencies did not standardize the fuel map, then a tractor that uses an
engine with emissions and fuel consumption better than the standards
would require fewer vehicle reductions than those technically feasible
reductions being proposed. The agencies are proposing two distinct fuel
consumption maps for use in GEM. EPA proposes the first fuel
consumption map would be used in GEM for the 2014 through 2016 model
years and represents an average engine which meets the 2014 model year
engine CO2 emissions standards being proposed. NHTSA
proposes to use the same fuel map for its voluntary standards in the
2014 and 2015 model years, as well as its mandatory program in the 2016
model year. A second fuel consumption map would be used beginning in
2017 model year and represents an engine which meets the 2017 model
year CO2 emissions and fuel consumption standards and
accounts for the increased stringency in the proposed MY 2017 standard.
Effectively there is no change in stringency of the tractor vehicle
(not including the engine) and there is stability in the tractor
vehicle (not including engine) standards for the full rulemaking
period.\63\ These inputs are appropriate given the separate proposed
regulatory requirement that Class 7 and 8 combination tractor
manufacturers use only certified engines.
---------------------------------------------------------------------------

    \63\ As noted earlier, use of the 2017 model year fuel
consumption map as a GEM input results in numerically more stringent
proposed vehicle standards for MY 2017.
---------------------------------------------------------------------------

(i) Engine Test Procedure
    The NAS panel did not specifically discuss or recommend a metric to
evaluate the fuel consumption of heavy-duty engines. However, as noted
above they did recommend the use of a load-specific fuel consumption
metric for the evaluation of vehicles.\64\ An analogous metric for
engines would be the amount of fuel consumed per unit of work. Thus,
EPA is proposing that GHG emission standards for engines under the CAA
would be expressed as g/bhp-

hr; NHTSA's proposed fuel consumption standards under EISA, in turn,
would be represented as gal/100 bhp-hr. This metric is also consistent
with EPA's current standards for non-GHG emissions for these engines.
---------------------------------------------------------------------------

    \64\ See NAS Report, Note 19, at page 39.
---------------------------------------------------------------------------

    EPA's criteria pollutant standards for engines require that
manufacturers demonstrate compliance over the transient Heavy-duty FTP
test cycle; the steady-state SET test cycle; and the not-to-exceed test
(NTE test). EPA created this multi-layered approach to criteria
emissions control in response to engine designs that optimized
operation for lowest fuel consumption at the expense of very high
criteria emissions when operated off the regulatory cycle. EPA's use of
multiple test procedures for criteria pollutants helps to ensure that
manufacturers calibrate engine systems for compliance under all
operating conditions. With regard to GHG and fuel consumption control,
the agencies believe it is more appropriate to set standards based on a
single test procedure, either the Heavy-duty FTP or SET, depending on
the primary expected use of the engine. For engines used primarily in
line-haul combination tractor trailer operations, we believe the
steady-state SET procedure more appropriately reflects in-use engine
operation. By setting standards based on the most representative test
cycle, we can have confidence that engine manufacturers will design
engines for the best GHG and fuel consumption performance relative to
the most common type of expected engine operation. There is no
incentive to design the engines to give worse fuel consumption under
other types of operation, relative to the most common type of
operation, and we are not concerned if manufacturers further calibrate
these designs to give better in-use fuel consumption during other
operation, while maintaining compliance with the criteria emissions
standards as such calibration is entirely consistent with the goals of
our joint program.
    Further, we are concerned that setting standards based on both
transient and steady-state operating conditions for all engines could
lead to undesirable outcomes. For example, turbocompounding is one
technology that the agencies have identified as a likely approach for
compliance against our proposed HHD SET standard described below.
Turbocompounding is a very effective approach to lower fuel consumption
under steady driving conditions typified by combination tractor trailer
operation and is well reflected in testing over the SET test procedure.
However, when used in driving typified by transient operation as we
expect for vocational vehicles and as is represented by the Heavy-duty
FTP, turbocompounding shows very little benefit. Setting an emission
standard based on the Heavy-duty FTP only for engines intended for use
in combination tractor trailers could lead manufacturers to not apply
turbocompounding because the full benefits are not demonstrated on the
Heavy-duty FTP even though it can be a highly cost-effective means to
reduce GHG emissions and lower fuel consumption in more steady state
applications.
    The current non-GHG emissions engine test procedures also require
the development of regeneration emission rates and frequency factors to
account for the emission changes during a regeneration event (40 CFR
86.004-28). EPA and NHTSA are proposing to exclude the CO2
emissions and fuel consumption increases due to regeneration from the
calculation of the compliance levels over the defined test procedures.
We considered including regeneration in the estimate of fuel
consumption and GHG emissions and have decided not to do so for two
reasons. First, EPA's existing criteria emission regulations already
provide a strong motivation to engine manufacturers to reduce the
frequency and duration of infrequent regeneration events. The very
stringent 2010 NOX emission standards cannot be met by
engine designs that lead to frequent and extend regeneration events.
Hence, we believe engine manufacturers are already reducing
regeneration emissions to the greatest degree possible.
    In addition to believing that regenerations are already controlled
to the extent technologically possible, we believe that attempting to
include regeneration emissions in the standard setting could lead to an
inadvertently lax emissions standard. In order to include regeneration
and set appropriate standards, EPA and NHTSA would have needed to
project the regeneration frequency and duration of future engine
designs in the timeframe of this proposal. Such a projection would be
inherently difficult to make and quite likely would underestimate the
progress engine manufacturers will make in reducing infrequent
regenerations. If we underestimated that progress, we would effectively
be setting a more lax set of standards than otherwise would be
expected. Hence in setting a standard including regeneration emissions
we faced the real possibility that we would achieve less effective
CO2 emissions control and fuel consumption reductions than
we will achieve by not including regeneration emissions. We are seeking
comments regarding regeneration emissions and what approach if any the
agencies should use in reflecting regeneration emissions in this
program.
    In conclusion, for Class 7 and 8 tractors, compliance with the
vehicle standard would be determined by establishing values for the
variable inputs and using the prescribed inputs in GEM and compliance
against the engine standard using the SET engine cycle. The model would
produce CO2 and fuel consumption results that would be
compared against EPA's and NHTSA's respective standards.
(j) Chassis-Based Test Procedure
    The agencies also considered proposing a chassis-based vehicle test
to evaluate Class 7 and 8 tractors based on a laboratory test of the
engine and vehicle together. A ``chassis dynamometer test'' for heavy-
duty vehicles would be similar to the Federal Test Procedure used today
for light-duty vehicles.
    However, the agencies decided not to propose the use of a chassis
test procedure to demonstrate compliance for tractor standards due to
the significant technical hurdles to implementing such a program by the
2014 model year. The agencies recognize that such testing requires
expensive, specialized equipment that is not yet widespread within the
industry. The agencies have only identified approximately 11 heavy-duty
chassis sites in the United States today and rapid installation of new
facilities to comply with model year 2014 is not possible.\65\
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    \65\ For comparison, engine manufacturers typically own a large
number of engine dynamometer test cells for engine development and
durability (up to 100 engine dynamometers per manufacturer).
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    In addition, and of equal if not greater importance, because of the
enormous numbers of truck configurations that have an impact on fuel
consumption, we do not believe that it would be reasonable to require
testing of many combinations of tractor model configurations on a
chassis dynamometer. The agencies evaluated the options available for
one tractor model (provided as confidential business information from a
truck manufacturer) and found that the company offered three cab
configurations, six axle configurations, five front axles, 12 rear
axles, 19 axle ratios, eight engines, 17 transmissions, and six tire
sizes--where each of these options could impact the fuel consumption
and CO2 emissions of the

tractor. Even using representative grouping of tractors for purposes of
certification, this presents the potential for many different
combinations that would need to be tested if a standard was adopted
based on a chassis test procedure.
    Although the agencies are not proposing the use of a complete
chassis based test procedure for Class 7 and 8 tractors, we believe
such an approach could be appropriate in the future, if more testing
facilities become available and if the agencies are able to address the
complexity of tractor configurations issue described above. We request
comments on the potential use of chassis based test procedures in the
future to augment or replace the model based approach we are proposing.
(3) Summary of Proposed Flexibility and Credit Provisions
    EPA and NHTSA are proposing four flexibility provisions
specifically for heavy-duty tractor and engine manufacturers, as
discussed in Section IV below. These are an averaging, banking and
trading program for emissions and fuel consumption credits, as well as
provisions for early credits, advanced technology credits, and credits
for innovative vehicle or engine technologies which are not included as
inputs to the GEM or are not demonstrated on the engine SET test cycle.
    The agencies are proposing that credits earned by manufacturers
under this ABT program be restricted for use to only within the same
regulatory subcategory for two reasons. First, relating credits between
categories is tenuous because of the differences in regulatory useful
lives. We want to avoid having credits from longer useful life
categories flooding shorter useful life categories, adversely impacting
compliance with CO2 or fuel consumption standards in the
shorter useful life category, and we have not based the level of the
standard on such impact on compliance. In addition, extending the use
of credits beyond these designated categories could inadvertently have
major impacts on the competitive market place, and we want to avoid
such results. For example, a manufacturer which has multiple engine
offerings over several regulatory categories could mix credits across
engine categories and shift the burden between them, possibly impacting
the competitive market place. Similarly, integrated manufacturers which
produce both engines and trucks could shift credits between engines and
trucks and have a similar effect. We would like to ensure that this
proposal reduces the CO2 emissions and fuel consumption but
does not inadvertently have such impacts on the market place. However,
we welcome comments on the extension of credits beyond the limitations
we are proposing.
    The agencies are also proposing to provide provisions to
manufacturers for early credits, the use of advanced technologies and
innovative technologies which are described in greater detail in
Section IV.
(4) Deferral of Standards for Tractor and Engine Manufacturing
Companies That Are Small Businesses
    EPA and NHTSA are proposing to defer greenhouse gas emissions and
fuel consumption standards for small tractor or engine manufacturers
meeting the Small Business Administration (SBA) size criteria of a
small business as described in 13 CFR 121.201.\66\ The agencies will
instead consider appropriate GHG and fuel consumption standards for
these entities as part of a future regulatory action. This includes
both U.S.-based and foreign small volume heavy-duty tractor or engine
manufacturers.
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    \66\ See Sec.  1036.150 and Sec.  1037.150.
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    The agencies have identified two entities that fit the SBA size
criterion of a small business.\67\ The agencies estimate that these
small entities comprise less than 0.5 percent of the total heavy-duty
combination tractors in the United States based on Polk Registration
Data from 2003 through 2007,\68\ and therefore that the exemption will
have a negligible impact on the GHG emissions and fuel consumption
improvements from the proposed standards.
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    \67\ The agencies have identified Ottawa Truck, Inc. and Kalmar
Industries USA as two potential small tractor manufacturers.
    \68\ M.J. Bradley. Heavy-duty Vehicle Market Analysis. May 2009.
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    To ensure that the agencies are aware of which companies would be
exempt, we propose to require that such entities submit a declaration
to EPA and NHTSA containing a detailed written description of how that
manufacturer qualifies as a small entity under the provisions of 13 CFR
121.201.

C. Heavy-Duty Pickup Trucks and Vans

    The primary elements of the EPA and NHTSA programs being proposed
for complete HD pickups and vans are presented in this section. These
provisions also cover incomplete HD pickups and vans that are sold by
vehicle manufacturers as cab-chassis (chassis-cab, box-delete, bed-
delete, cut-away van) vehicles, as discussed in detail in Section
V.B(1)(e). Section II.C(1) explains the proposed form of the
CO2 and fuel consumption standards, the proposed numerical
levels for those standards, and the proposed approach to phasing in the
standards over time. The proposed measurement procedure for determining
compliance is discussed in Section II.C(2), and the proposed EPA and
NHTSA compliance programs are discussed in Section II.C(3). Sections
II.C(4) discusses proposed implementation flexibility provisions.
Section II.E discusses additional standards and provisions for
N2O and CH4 emissions, for impacts from vehicle
air conditioning, and for ethanol-fueled and electric vehicles.
(1) What Are the Proposed Levels and Timing of HD Pickup and Van
Standards?
(a) Vehicle-Based Standards
    About 90 percent of Class 2b and 3 vehicles are pickup trucks,
passenger vans, and work vans that are sold by the vehicle
manufacturers as complete vehicles, ready for use on the road. In
addition, most of these complete HD pickups and vans are covered by CAA
vehicle emissions standards for criteria pollutants today (i.e., they
are chassis tested similar to light-duty), expressed in grams per mile.
This distinguishes this category from other, larger heavy-duty vehicles
that typically have only the engines covered by CAA engine emission
standards, expressed in grams per brake horsepower-hour.\69\ As a
result, Class 2b and 3 complete vehicles share much more in common with
light-duty trucks than with other heavy-duty vehicles.
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    \69\ As discussed briefly in Section I and in more detail in
Section V, this regulatory category also covers some incomplete
Class 2b/3 vehicles.
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    Three of these commonalities are especially significant: (1) Over
95 percent of the HD pickups and vans sold in the United States are
produced by Ford, General Motors, and Chrysler--three companies with
large light-duty vehicle and light-duty truck sales in the United
States, (2) these companies typically base their HD pickup and van
designs on higher sales volume light-duty truck platforms and
technologies, often incorporating new light-duty truck design features
into HD pickups and vans at their next design cycle, and (3) at this
time most complete HD pickups and vans are certified to vehicle-based
rather than engine-based EPA standards. There is also the potential for
substantial GHG and fuel consumption reductions from vehicle design
improvements beyond engine changes (such as through optimizing
aerodynamics, weight, tires, and

brakes), and the manufacturer is generally responsible for both engine
and vehicle design. All of these factors together suggest that it is
appropriate and reasonable to set standards for the vehicle as a whole,
rather than to establish separate engine and vehicle GHG and fuel
consumption standards, as is proposed for the other heavy-duty
categories. This approach for complete vehicles is consistent with
Recommendation 8-1 of the NAS Report, which encourages the regulation
of ``the final stage vehicle manufacturers since they have the greatest
control over the design of the vehicle and its major subsystems that
affect fuel consumption.''
(b) Weight-Based Attributes
    In setting heavy-duty vehicle standards it is important to take
into account the great diversity of vehicle sizes, applications, and
features. That diversity reflects the variety of functions performed by
heavy-duty vehicles, and this in turn can affect the kind of technology
that is available to control emissions and reduce fuel consumption, and
its effectiveness. EPA has dealt with this diversity in the past by
making weight-based distinctions where necessary, for example in
setting HD vehicle standards that are different for vehicles above and
below 10,000 lb GVWR, and in defining different standards and useful
life requirements for light-, medium-, and heavy-heavy-duty engines.
Where appropriate, distinctions based on fuel type have also been made,
though with an overall goal of remaining fuel-neutral.
    The joint EPA GHG and NHTSA fuel economy rules for light-duty
vehicles accounted for vehicle diversity in that segment by basing
standards on vehicle footprint (the wheelbase times the average track
width). Passenger cars and light trucks with larger footprints are
assigned numerically higher target levels for GHGs and numerically
lower target levels for fuel economy in acknowledgement of the
differences in technology as footprint gets larger, such that vehicles
with larger footprints have an inherent tendency to burn more fuel and
emit more GHGs per mile of travel. Using a footprint-based attribute to
assign targets also avoids interfering with the ability of the market
to offer a variety of products to maintain consumer choice.
    In developing this proposal, the agencies emphasized creating a
program structure that would achieve reductions in fuel consumption and
GHGs based on how vehicles are used and on the work they perform in the
real world, consistent with the NAS report recommendations to be
mindful of HD vehicles' unique purposes. Despite the HD pickup and van
similarities to light-duty vehicles, we believe that the past practice
in EPA's heavy-duty program of using weight-based distinctions in
dealing with the diversity of HD pickup and van products is more
appropriate than using vehicle footprint. Weight-based measures such as
payload and towing capability are key among the things that
characterize differences in the design of vehicles, as well as
differences in how the vehicles will be used. Vehicles in this category
have a wide range of payload and towing capacities. These weight-based
differences in design and in-use operation are the key factors in
evaluating technological improvements for reducing CO2
emissions and fuel consumption. Payload has a particularly important
impact on the test results for HD pickup and van emissions and fuel
consumption, because testing under existing EPA procedures for criteria
pollutants is conducted with the vehicle loaded to half of its payload
capacity (rather than to a flat 300 lb as in the light-duty program),
and the correlation between test weight and fuel use is strong.\70\
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    \70\ Section II.C(2) discusses our decision to propose that GHGs
and fuel consumption for HD pickups and vans be measured using the
same test conditions as in the existing EPA program for criteria
pollutants.
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    Towing, on the other hand, does not directly factor into test
weight as nothing is towed during the test. Hence only the higher curb
weight caused by heavier truck components would play a role in
affecting measured test results. However towing capacity can be a
significant factor to consider because HD pickup truck towing
capacities can be quite large, with a correspondingly large effect on
design.
    We note too that, from a purchaser perspective, payload and towing
capability typically play a greater role than physical dimensions in
influencing purchaser decisions on which heavy-duty vehicle to buy. For
passenger vans, seating capacity is of course a major consideration,
but this correlates closely with payload weight.
    Although heavy-duty vehicles are traditionally classified by their
GVWR, we do not believe that GVWR is the best weight-based attribute on
which to base GHG and fuel consumption standards for this group of
vehicles. GVWR is a function of not only payload capacity but of
vehicle curb weight as well; in fact, it is the simple sum of the two.
Allowing more GHG emissions from vehicles with higher curb weight tends
to penalize lightweighted vehicles with comparable payload capabilities
by making them meet more stringent standards than they would have had
to meet without the weight reduction. The same would be true for
another common weight-based measure, the gross vehicle combined weight,
which adds the maximum combined towing and payload weight to the curb
weight.
    Similar concerns about using weight-based attributes that include
vehicle curb weight were raised in the EPA/NHTSA proposal for light-
duty GHG and fuel economy standards: ``Footprint-based standards
provide an incentive to use advanced lightweight materials and
structures that would be discouraged by weight-based standards'', and
``there is less risk of `gaming' (artificial manipulation of the
attribute(s) to achieve a more favorable target) by increasing
footprint under footprint-based standards than by increasing vehicle
mass under weight-based standards--it is relatively easy for a
manufacturer to add enough weight to a vehicle to decrease its
applicable fuel economy target a significant amount, as compared to
increasing vehicle footprint'' (74 FR 49685, September 28, 2009). The
agencies believe that using payload and towing capacities as the