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 using the roof height of the tractor to determine the
trailer type required to be used to demonstrate compliance of a vehicle
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 determined by
market foces linked 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.\56\ 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 finalizing separate standards for sleeper cabs and day cabs.\57\
---------------------------------------------------------------------------

    \56\ 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).
    \57\ The agencies note, as discussed in the previous section,
that some day cabs and sleeper cabs will be reclassified as
vocational tractors and if so will not be subject to the combination
tractor standards.
---------------------------------------------------------------------------

    The agencies received comments from industry stakeholders (EMA,
Allison Transmission, Bosch, and the Heavy-Duty Fuel Efficiency
Leadership Group) and ICCT supporting the nine tractor regulatory
subcategories proposed and did not receive any comments which supported
an alternate classification. Thus, to account for the relevant
combinations of these attributes, the agencies are adopting the
classification scheme proposed, segmenting 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
    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. As proposed, the agencies are treating
tractors with adjustable roof fairings as low roof tractors that will
tested with the fairing in its lowest position.
(2) What are the Final Class 7 and 8 Tractor and Engine CO2
Emissions and Fuel Consumption Standards and Their Timing?
    In developing the final standards for Class 7 and 8 tractors and
for the engines used in these tractors, 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 associated
engines, the necessary 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
on whose performance the final tractor standards are predicated are
improvements in aerodynamic design, lower rolling resistance tires,
extended idle reduction technologies, and lightweighting of the
tractor. The technologies on whose performance the final tractor
standards are predicated are engine friction reduction, aftertreatment
optimization, and turbocompounding, among others, as described in RIA
Chapter 2.4. The agencies' evaluation showed that these technologies
are available today, but have very low application rates on current
vehicles and engines. 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 RIA Chapter 2, explaining as well the
basis for the agencies' conclusion not to adopt standards which are
less stringent or more stringent.
(a) Tractor Standards
    The agencies are finalizing the following standards for Class 7 and
8 combination tractors in Table 0-1, using the subcategorization
approach that was proposed. 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 finalizing standards starting for that model year
predicated on performance of those technologies. EPA is finalizing more
stringent tractor standards for the 2017 model year which reflect the
CO2 emissions reductions required for 2017 model year
engines. (As explained in Section II.B(3)(h)(v) below, engine
performance is one of the inputs into the 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 final standards apply
throughout the useful life period as described in Section V. As
proposed, and as discussed further in Section IV below, manufacturers
may generate and use credits from Class 7 and 8 combination tractors to
show compliance with the standards.
    NHTSA is finalizing 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 within EISA. The 2014 and 2015 model year standards are
voluntary in that manufacturers are not subject to them unless they
opt-in to the standards.\58\ Manufacturers that opt in become subject
to NHTSA standards for all regulatory categories. NHTSA is also
adopting new tractor standards for the 2017 model year which reflect
additional improvements in only the heavy-duty engines. As proposed,
NHTSA is not implementing an in-use compliance program for fuel
consumption because it does not anticipate that there will be notable
deterioration of fuel consumption over the useful life of the vehicle.
---------------------------------------------------------------------------

    \58\ Once a manufacturer opts into the NHTSA program it must
stay in the program for all the optional MYs.
---------------------------------------------------------------------------

    As explained more fully in Section III and Chapter 2 of the RIA,
EPA and NHTSA are not adopting more stringent tractor standards for
2014-2017 MY. The final tractor standards are based on

the maximum application rates of available technologies considering the
available lead time, and we explain in Section III and Chapter 2 of the
RIA that use of additional technologies, or further application of the
technologies already mentioned would be either infeasible in the lead
time afforded, or uneconomic.

               Table II-1--Heavy-Duty Combination Tractor Emissions and Fuel Consumption Standards
----------------------------------------------------------------------------------------------------------------
                                                                      Day cab                     Sleeper cab
                                                     -----------------------------------------------------------
                                                            Class 7             Class 8             Class 8
----------------------------------------------------------------------------------------------------------------
                                     2014 Model Year CO2 Grams per Ton-Mile
----------------------------------------------------------------------------------------------------------------
Low Roof............................................                 107                  81                  68
Mid Roof............................................                 119                  88                  76
High Roof...........................................                 124                  92                  75
----------------------------------------------------------------------------------------------------------------
                          2014-2016 Model Year Gallons of Fuel per 1,000 Ton-Mile \59\
----------------------------------------------------------------------------------------------------------------
Low Roof............................................                10.5                 8.0                 6.7
Mid Roof............................................                11.7                 8.7                 7.4
High Roof...........................................                12.2                 9.0                 7.3
----------------------------------------------------------------------------------------------------------------
                                     2017 Model Year CO2 Grams per Ton-Mile
----------------------------------------------------------------------------------------------------------------
Low Roof............................................                 104                  80                  66
Mid Roof............................................                 115                  86                  73
High Roof...........................................                 120                  89                  72
----------------------------------------------------------------------------------------------------------------
                          2017 Model Year and Later Gallons of Fuel per 1,000 Ton-Mile
----------------------------------------------------------------------------------------------------------------
Low Roof............................................                10.2                 7.8                 6.5
Mid Roof............................................                11.3                 8.4                 7.2
High Roof...........................................                11.8                 8.7                 7.1
----------------------------------------------------------------------------------------------------------------

    The standard values shown above differ somewhat from the proposal,
reflecting refinements made to the GEM in response to comments. For
example, the agencies received comments from stakeholders concerned
that the 2017 MY tractor standards appeared to be backsliding because
the reductions were not in line with the reductions expected from the
2017 MY engine standards. The agencies reviewed the issue and found
that the engine maps we created in the GEM for the 2017 model year for
the proposal did not appropriately reflect the engine improvements.
Therefore, the agencies developed new fuel maps for the GEM v2.0 which
fully reflect the engine improvements due to the 2017 MY standards.\60\
These changes to the GEM did not impact our estimates of the relative
effectiveness of the greenhouse gas emissions and fuel consumption
improving technologies modeled in this final action nor the overall
cost or benefits estimated for these final vehicle standards.
---------------------------------------------------------------------------

    \59\ As noted above, manufacturers may voluntarily opt-in to the
NHTSA fuel consumption program in 2014 or 2015. Once a manufacturer
opts into the NHTSA program it must stay in the program for all the
optional MYs.
    \60\ See RIA Chapter 4 for the engine fuel maps used in GEM
v2.0.
---------------------------------------------------------------------------

    Based on our analysis, the 2017 model year standards for
combination tractors and engines represent up to a 23 percent reduction
in CO2 emissions and fuel consumption over a 2010 model year
baseline tractor (the baseline sleeper cab does not include idle
shutdown technology), as detailed in Section III.A.2. In considering
the feasibility of vehicles to comply with the standards, EPA also
considered the potential for CO2 emissions to increase
during the regulatory useful life of the product. As we discuss
separately in the context of deterioration factor (DF) testing, we have
concluded that CO2 emissions are likely to stay the same or
actually decrease in-use compared to new certified configurations. In
general, engine and vehicle friction decreases as products wear in
leading to reduced parasitic losses and lower CO2 emissions.
Similarly, tire rolling resistance falls as tires wear due to the
reduction in tread height. In the case of aerodynamic components, we
project no change in performance through the regulatory life of the
vehicle since there is essentially no change in their physical form as
vehicles age. Similarly, weight reduction elements such as aluminum
wheels are not projected to increase in mass through time, and hence,
we can conclude will not deteriorate with regard to CO2
performance in-use. Given all of these considerations, EPA is confident
in projecting that the standards finalized today will be technical
feasible throughout the regulatory useful life of the program.
(b) Standards for Engines Installed in Combination Tractors
    EPA is adopting GHG standards and NHTSA is adopting fuel
consumption standards for new heavy-duty engines. This section
discusses the standards for engines used in Class 7 and 8 combination
tractors and also provides some overall background information. We also
note that the agencies are adopting standards for heavy-duty engines
used in vocational vehicles. However, as explained further below,
compliance with the standards would be measured using different test
procedures, corresponding with actual vehicle use, depending on whether
the vehicle in which the engine is installed is a Class 7 and 8
combination tractor or a vocational vehicle.
    The heavy-duty engine standards vary depending on the type of
vehicle in which they are installed, as well as whether the engines are
compression ignition or spark ignition. The agencies are adopting
separate engine fuel consumption and GHG emissions standards for
engines installed in combination tractors versus engines installed in
vocational vehicles. Also, for the purposes of the GHG engine emissions
and engine fuel consumption standards, the agencies are adopting engine
subcategories that match EPA's

existing criteria pollutant emissions regulations for heavy-duty
highway engines which established four regulatory service classes that
represent the engine's intended and primary vehicle application.\61\
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 service class. The engines in these four
regulatory service classes range in size between approximately five
liters and sixteen liters. This subcategory structure enables the
agencies to set standards that appropriately reflect the technology
available for engines installed in each type of vehicle, and that are
therefore technologically feasible for these engines. This is the same
engine classification scheme the agencies proposed, and there were no
adverse comments in response to the proposal.
---------------------------------------------------------------------------

    \61\ See 40 CFR 86.90-2.
---------------------------------------------------------------------------

    Heavy heavy-duty diesel and medium heavy-duty diesel engines are
used today in combination tractors. The following section refers to the
engine standards for these types of engines. This section does not
cover gasoline or light heavy-duty diesel engines because they are not
used in combination tractors.
    In the NPRM, the agencies proposed CO2 and fuel
consumption standards for HD diesel engines to be installed in Class 7
and 8 combination tractors as shown in Table II-2.\62\
---------------------------------------------------------------------------

    \62\ The agencies note that the CO2 and fuel
consumption standards for Class 7 and 8 combination tractors do not
cover gasoline or LHDD engines, as those are not used in Class 7 and
8 combination tractors.

            Table II-2--Proposed Heavy-duty Diesel Engine Standards for Engines Installed in Tractors
----------------------------------------------------------------------------------------------------------------
                                                     Effective 2014 model year       Effective 2017 Model Year
                                                 ---------------------------------------------------------------
                                                                  Voluntary fuel                       Fuel
                                                   CO2 standard     consumption    CO2 standard     consumption
                                                    (g/bhp-hr)    standard  (gal/   (g/bhp-hr)    standard  (gal/
                                                                    100 bhp-hr)                     100 bhp-hr)
----------------------------------------------------------------------------------------------------------------
MHD diesel engine...............................             502            4.93             487            4.78
HHD diesel engine...............................             475            4.67             460            4.52
----------------------------------------------------------------------------------------------------------------

    The agencies proposed to require diesel engine manufacturers to
achieve, on average, a three percent reduction in fuel consumption and
CO2 emissions for the 2014 standards over the baseline MY
2010 performance for the engines.\63\ The agencies' preliminary
assessment of the findings of the 2010 NAS Report and other literature
sources indicated that there are technologies available to reduce fuel
consumption by this amount in the time frame in the lead time provided
by the rules. These technologies include improved turbochargers,
aftertreatment optimization, and low temperature exhaust gas
recirculation.
---------------------------------------------------------------------------

    \63\ The baseline HHD diesel engine performance in MY 2010 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. The
baseline MHD diesel engine performance on the SET cycle is 518 g
CO2/bhp-hr (5.09 gallon/100-bhp-hr) in MY 2010. Further
discussion of the derivation of the baseline can be found in Section
III.
---------------------------------------------------------------------------

    The agencies also proposed to require diesel engine manufacturers
to achieve, on average, a six percent reduction in fuel consumption and
CO2 emissions for the 2017 MY standards over the baseline MY
2010 performance for MHD and HHD diesel engines required to use the
SET-based standard. The agencies stated that additional reductions
could likely be achieved through the increased refinement of the
technologies projected to be implemented for 2014, plus the addition of
turbocompounding, which the agencies' analysis showed would require a
longer development time and would not be available in MY 2014. The
agencies therefore proposed to provide additional lead time to allow
for the introduction of this additional technology, and to wait until
2017 to increase stringency to levels reflecting application of this
technology.
    The agencies proposed that the MHD and HHD diesel engine
CO2 standards for Class 7 and 8 combination tractors would
become effective in MY 2014 for EPA, with more stringent CO2
standards becoming effective in MY 2017, while NHTSA's fuel consumption
standards would become effective in MY 2017, which would be both
consistent with the EISA four-year minimum lead-time requirements and
harmonized with EPA's timing. The agencies explained that the three-
year timing, besides being required by EISA, made sense because EPA's
heavy-duty highway engine program for criteria pollutants had begun to
provide new emissions standards for the industry in three year
increments, which had caused the heavy-duty engine product plans to
fall largely into three year cycles reflecting this regulatory
environment. To further harmonize with EPA, NHTSA proposed voluntary
fuel consumption standards for MHD and HHD diesel engines that are
equivalent to EPA CO2 standards for MYs 2014-2016, allowing
manufacturers to opt into the voluntary standards in any of those model
years.\64\ NHTSA proposed that manufacturers could opt into the program
by declaring their intent to opt in to the program at the same time
they submit the Pre-Certification Compliance Report, and that a
manufacturer opting into the program would begin tracking credits and
debits beginning in the model year in which they opt into the program.
Both agencies proposed to allow manufacturers to generate and use
credits to achieve compliance with the HD diesel engine standards,
including averaging, banking, and trading (ABT) and deficit carry-
forward. The agencies sought comment on the proposed MHD and HHD engine
standards and timing.
---------------------------------------------------------------------------

    \64\ Once a manufacturer opts into the NHTSA program it must
stay in the program for all the optional MYs and remain standardized
with the implementation approach being used to meet the EPA emission
program.
---------------------------------------------------------------------------

    The agencies received comments from EMA, Navistar, Cummins, ACEEE,
Center for Biological Diversity, Detroit Diesel Corporation, American
Lung Association, and the Union of

Concerned Scientists. Comments were divided with respect to the
proposed levels of stringency. While Cummins and DDC expressed support
for the CO2 and fuel consumption standards for diesel
engines, and EMA and Navistar stated the standards could be met if the
flexibilities outlined in the NPRM are finalized as proposed, Navistar
also stated that the model year 2017 standard may not be feasible since
what the agencies characterized as existing technologies are not in
production for all manufacturers. In contrast, environmental groups and
NGOs stated that the standards did not reflect the potential reductions
outlined in the 2010 NAS study and should be more stringent. CBD argued
that the standards were not set at the maximum feasible level by
definition, because the agencies had said that they were based on the
use of existing technologies. In addition, the Center for Neighborhood
Technology encouraged the agencies to implement the rules as soon as
possible, beginning in the 2012 model year.
    In light of the above comments, the agencies re-evaluated the
technical basis for the heavy-duty engine standards. The baseline HHD
diesel engine performance in 2010 model year on the SET is estimated at
490 g CO2/bhp-hr (4.81 gal/100 bhp-hr), based on our
analysis of 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
estimated to be 518 g CO2/bhp-hr (5.09 gallon/100-bhp-hr)
for the 2010 model year. Further discussion of the derivation of the
baseline can be found in Section III. The agencies believe that the MY
2014 standards can be achieved by most manufacturers through the use of
technologies time frame such as improved aftertreatment systems,
friction reduction, improved auxiliaries, turbochargers, pistons, and
other components. These standards will require diesel engine
manufacturers to achieve on average a three percent reduction in fuel
consumption and CO2 emissions over the baseline 2010 model
year levels.
    However, in recognizing that some manufacturers have engines that
would not meet the standard even after applying technologies that
improve GHG emissions and fuel consumption by three percent, the
agencies are finalizing both the proposed ABT provisions for these
engines and also an optional alternate engine standard for 2014 model
year, described in more detail below. We believe that concerns
expressed by Navistar regarding the 2014 MY standards will be addressed
by this alternative standard. The agencies also continue to believe
that the 2017 MY standards are achievable using the above approaches
and, in the case of SET certified engines, turbocompounding. While
Navistar commented that the 2017 MY standard may be challenging because
not all manufacturers are presently producing the technologies that may
be required to meet the standards, the agencies believe that since
manufacturers that may require turbocompounding to meet the standards
will not have to do so until 2017 MY, there will be sufficient lead
time for all manufacturers to introduce this technology. As noted
above, by MY 2017 all MHD and HHD engines installed in combination
tractors should have gone through a redesign during which all needed
technology can be applied. We note that we are finalizing these
standards as proposed based on the assessment that most manufacturers
(not just Navistar) will need to make improvements to existing engine
systems in order to meet the standards. EPA's HD diesel engine
CO2 emission standards and NHTSA's HD diesel engine fuel
consumption standards for engines installed in tractors are presented
in Table II-3. As explained above, the first set of standards take
effect with MY 2014 (mandatory standards for EPA, voluntary standards
for NHTSA), and the second set take effect with MY 2017 (mandatory for
both agencies).

             Table II-3--Final Heavy-duty Diesel Engine Standards for Engines Installed in Tractors
----------------------------------------------------------------------------------------------------------------
                                                     Effective 2014 model year       Effective 2017 model year
                                                 ---------------------------------------------------------------
                                                                  Voluntary fuel                       Fuel
                                                   CO2 standard     consumption    CO2 standard     consumption
                                                    (g/bhp-hr)    standard  (gal/   (g/bhp-hr)    standard  (gal/
                                                                    100 bhp-hr)                     100 bhp-hr)
----------------------------------------------------------------------------------------------------------------
MHD diesel engine...............................             502            4.93             487            4.78
HHD diesel engine...............................             475            4.67             460            4.52
----------------------------------------------------------------------------------------------------------------

    The agencies have also decided to remove NHTSA's proposed Pre-
Certification Compliance Report requirement. Instead, manufacturers
must submit their decision to opt into NHTSA's voluntary standards for
the 2014 through 2016 model years as part of its certification process
with EPA. Once a manufacturer opts into the NHTSA program it must stay
in the program for all the subsequent optional model years.
Manufacturers that opt in become subject to NHTSA standards for all
regulatory categories. The declaration statement must be entered prior
to or at the same time the manufacturer submits its first application
for a certificate of conformity. NHTSA will begin tracking credits and
debits beginning in the model year in which a manufacturer opts into
its program.
    Compliance with the CO2 emissions and fuel consumption
standards will be evaluated based on the SET engine test cycle. In the
NPRM, the agencies proposed standards based on the SET cycle for MHD
and HHD engines used in tractors due to these engines' primary use in
steady state operating conditions (typified by highway cruising).
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 will be required to meet the standard based on the SET, which
is a steady state test cycle.
    The agencies gave full consideration to the need for engine
manufacturers to redesign and upgrade their engines during the MYs
2014-2017 to meet standards, and fully considered the cost-
effectiveness of the standards and the available lead time. The final
two-step CO2 emission and fuel consumption standards
recognize the opportunity for technology improvements over the
rulemaking time frame, while reflecting the typical engine
manufacturers' product plan cycles. 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 and flexibilities needed to incorporate technology that will
achieve the final GHG and fuel consumption standards within the normal
engine redesign process. This is an important aspect of the final
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.\65\ This time period will also provide
manufacturers the opportunity to plan for compliance using a multi-year
time frame, again in alignment with their normal business practice.
Further details on lead time, redesigns and technical feasibility can
be found in Section III.
---------------------------------------------------------------------------

    \65\ See 75 FR at 25467-68 for further discussion of the
negative cost implications of establishing requirements outside of
the redesign cycle.
---------------------------------------------------------------------------

    The agencies continue to believe the standards for MHD and HHD
diesel engines installed in combination tractors are the most stringent
technically feasible in the time frame established in this regulation.
The standards will require a 3 percent reduction in engine fuel
consumption and GHG emissions in 2014 MY based on improvements to
engine components and aftertreatment systems. The 2017 MY standards
will require a 6 percent reduction in fuel consumption and GHG
emissions over a 2010 model year baseline and assumes the introduction,
for some engines, of technologies such as turbocompounding. The
standards, however, are not premised on the introduction of
technologies that are still in development--such as Rankine bottoming
cycle--since these approaches cannot be introduced without further
technical development or engine re-design.\66\
---------------------------------------------------------------------------

    \66\ See RIA Chapter <IP_ADDRESS>.
---------------------------------------------------------------------------

    Additional discussion on technical feasibility is included in
Section III below and in Chapter 2 of the RIA.
    The agencies recognize, however, that the schedule of changes for
the final standards may not be the most cost-effective one for all
manufacturers. The agencies also sought comment as to whether an
alternate phase-in schedule for the HD diesel engine standards for
combination tractors should be considered. In developing the proposal,
heavy-duty engine manufacturers stated that the phase-in of the GHG and
fuel consumption standards should be aligned with the On Board
Diagnostic (OBD)\67\ phase-in schedule, which includes new requirements
for heavy-duty vehicles in the 2013 and 2016 model years. The agencies
did not adopt this suggestion in the proposal, explaining that the
credit averaging, banking and trading provisions would provide
manufacturers with considerable flexibility to manage their GHG and
fuel efficiency standard compliance plans--including the phase-in of
the new heavy-duty OBD requirements--but requested comment on whether
EPA and NHTSA should provide an alternate phase-in schedules that would
more explicitly accommodate this request in the event that
manufacturers did not agree that the ABT provisions mitigated their
concern about the GHG/fuel consumption standard phase-in. See 75 FR at
74178.
---------------------------------------------------------------------------

    \67\ On-board diagnostics (OBD) is a computer-based emissions
monitoring system that was first required in 2007 for vehicles under
14,000 pounds (65 FR 59896, Oct. 6, 2000) and in 2010 for vehicles
over 14,000 pounds (74 FR 8310, Feb. 24, 2009).
---------------------------------------------------------------------------

    In response, Cummins, Engine Manufacturers Association, and DTNA
commented that their first choice was a delay in the OBD effective date
for one year to the 2014 model year. The industry's second choice was
to provide manufacturers with an optional GHG and fuel consumption
phase-in that aligns their product development plans with their current
plans to meet the OBD regulations for EPA and California in the 2013
and 2016 model years. These commenters argued that meeting the OBD
regulation in the 2013 model year already poses a significant
challenge, and that having to meet GHG and fuel consumption standards
beginning in 2014 could require them to redesign and recertify their
products just one year later. They argued that bundling design changes
where possible can reduce the burden on industry for complying with
regulations, so aligning the introduction of the OBD, GHG, and fuel
consumption standards could help reduce manufacturers' burden for
product development, validation and certification.
    In order to provide additional flexibility for manufacturers
looking to align their technology changes with multiple regulatory
requirements, the agencies are finalizing an alternate ``OBD phase-in''
option for meeting the standards for MHD and HHD diesel engines
installed in tractors (in addition to engines installed in vocational
vehicles as noted below in Section II.D), which delivers equivalent
CO2 emissions and fuel consumption reductions as the primary
standards for the engines built in the 2013 through 2017 model years,
as shown in Table II-4. The optional OBD phase-in schedule requires
that engines built in the 2013 and 2016 model years to achieve greater
reductions than the engines built in those model years under the
primary program, but requires fewer reductions for the engines built in
the 2014 and 2015 model years.

 Table II-4--Comparison of CO2 reductions for the HHD and MHD Tractor Standards Under the Alternative OBD Phase-
                                             In and Primary Phase-In
----------------------------------------------------------------------------------------------------------------
                                             HHD Tractor engines                    MHD Tractor engines
                                   -----------------------------------------------------------------------------
                                                               Difference                             Difference
                                      Primary      Optional   in lifetime    Primary      Optional   in lifetime
                                      phase-in     phase-in    CO2 engine    phase-in     phase-in    CO2 engine
                                      standard     standard    emissions     standard     standard    emissions
                                     (g/bhp-hr)   (g/bhp-hr)     (MMT)      (g/bhp-hr)   (g/bhp-hr)     (MMT)
----------------------------------------------------------------------------------------------------------------
Baseline..........................          490          490           --          518          518           --
2013 MY Engine....................          490          485           14          518          512           17
2014 MY Engine....................          475          485          -28          502          512          -28
2015 MY Engine....................          475          485          -28          502          512          -28
2016 MY Engine....................          475          460           42          502          487           42
2017 MY Engine....................          460          460            0          487          487            0
Net Reductions (MMT)..............  ...........  ...........            0  ...........  ...........            3
----------------------------------------------------------------------------------------------------------------

    The technologies for the 2013 model year optional standard include
a subset of technologies that could be used to meet the primary 2014
model year standard. The agencies believe this approach is appropriate
because the shorter lead time provided for manufacturers selecting this
option limits the technologies which can be applied. However, in order
to maintain equivalent CO2 emissions and fuel consumption
reduction over the 2013 through 2017 model year period, it is necessary
for the 2016 model year standard to be equal to the 2017 model year
standard, using the same technology paths described for the primary
engine program. If a manufacturer selects this optional phase-in, then
the engines must be certified starting in the 2013 model year and
continue using this phase-in through 2016 model year. That is, once
electing this compliance path, manufacturers must adhere to it.\68\
Manufacturers may opt into the optional OBD phase-in through the
voluntary NHTSA program, but must opt in in the 2013 model year and
continue using this phase-in through the 2016 model year. Manufacturers
that opt in to the voluntary NHTSA program in 2014 and 2015 will be
required to meet the primary phase-in schedule and may not adopt the
OBD phase-in option. Table II-5 below presents the final HD diesel
engine CO2 emission standards under the ``OBD phase-in''
option.
---------------------------------------------------------------------------

    \68\ See Sec.  1036.150(e).

  Table II-5--Optional Heavy-Duty Engine Standard Phase-in Schedule for
                             Tractor Engines
------------------------------------------------------------------------
                                   MHD Diesel engine   HHD Diesel engine
------------------------------------------------------------------------
                 Effective 2013 Through 2015 Model Year
------------------------------------------------------------------------
CO2 Standard (g/bhp-hr).........                 512                 485
Voluntary Fuel Consumption                      5.03                4.76
 Standard (gallon/100 bhp-hr)...
------------------------------------------------------------------------
                   Effective 2016 Model Year and Later
------------------------------------------------------------------------
CO2 Standard (g/bhp-hr).........                 487                 460
Fuel Consumption (gallon/100 bhp-               4.78                4.52
 hr)............................
------------------------------------------------------------------------

    Although the agencies believe that the standards for the HD diesel
engines installed in combination tractors are generally appropriate,
cost-effective, and technologically feasible in the rulemaking time
frame, we also recognize that when regulating a category of engines for
the first time, there will be individual products that may deviate
significantly from the baseline level of performance, whether because
of a specific approach to criteria pollution control, or due to engine
calibration for specific applications or duty cycles. In the current
fleet of 2010 and 2011 model year engines used in combination tractors,
NHTSA and EPA understand that there is a relatively small group of
legacy engines that are up to approximately 25 percent worse than the
average baseline for other engines. For this group of legacy MHD and
HHD diesel engines installed in tractors, when compared to the typical
performance levels of the majority of the engines in the fleet and the
fuel consumption/GHG emissions reductions that the majority of engines
would achieve through increased application of technology, the same
reduction from the industry baseline may not be possible at reasonably
comparable cost given the same amount of lead-time, because these
products may require a total redesign in order to meet the standards.
Manufacturers of the MHD and HHD diesel engines installed in tractors
with atypically high baseline CO2 and fuel consumption
levels may also, in some instances, have a limited line of engines
across which to average performance to meet the generally-applicable
standards.
    To account for this possibility, the agencies requested comment in
the NPRM on the establishment of an optional alternative MHD and HHD
engine standard for those engines installed in combination tractors
which would be set at 3 percent below a manufacturer's 2011 engine
baseline emissions and fuel consumption, or alternatively, at 2 percent
below a manufacturer's 2011 baseline. The agencies also requested
comment on extending this optional standard one year (to the 2017 MY)
for a single engine family at a 6 percent level below the 2011
baseline.\69\ This option would not be available unless and until a
manufacturer had exhausted all available credits and credit
opportunities, and engines under the optional standard could not
generate credits.
---------------------------------------------------------------------------

    \69\ See 75 FR at 74178-74179.
---------------------------------------------------------------------------

    In comments to the NPRM, Navistar supported the alternative engine
standard, but recommended that it be set at 2 percent below the
manufacturer's 2011 baseline. They also supported the extension to 2017
MY at 6 percent. Navistar provided CBI in support of its comments.
Volvo, DTNA, environmental groups, NGOs, and the New York State
Department of Environmental Conservation opposed the optional engine
standard, arguing that existing flexibilities are sufficient to allow
compliance with the standards and that all manufacturers should be held
to the same standards.
    Based on the CBI submitted by Navistar, the agencies found that a
large majority of the HD diesel engines used in Class 7 and 8
combination tractors were relatively close to the average baseline,
with some above and some below, but also that some legacy MHD and HDD
diesel engines were far enough away from the baseline that they could
not meet the generally-applicable standards with application of
technology that would be available for those specific engines by 2014.
The agencies continue to believe that an interim alternative standard
is needed for these products, and that an interim standard reflects a
legitimate difference between products starting from different fuel
consumption/GHG emitting baselines. As explained in the proposal, it is
legally permissible to accommodate short term lead time constraints
with alternative standards. Commenters did not dispute that there are
legacy engine families with significantly higher CO2
emissions and fuel consumption baselines, and that these engines
require longer lead time to meet the principal standards in the early
model years of the program. Although the agencies acknowledge the view
that all manufacturers should be subject to the same burden for meeting
the primary standards, the agencies believe that, in the initial years
of a new program,

additional flexibilities should be provided. The GHG standards and fuel
consumption standards are first-time standards for these engines, so
the possibility of significantly different baselines is not
unexpected.\70\ Moreover, the agencies do not believe that the
alternative standard affords a relative competitive advantage to the
higher emitting legacy engines: the same level of improvement at the
same cost will be required of those tractor engines, and in addition,
by 2017 MY, those tractor engines will be required to make the
additional improvements to meet the same standards as other engines. We
believe that the concern expressed by Navistar regarding the 2014 MY
standards will be addressed by this alternative. The agencies also
continue to believe the 2017 MY standards are achievable using the
above approaches and, in the case of MHD and HHD engines installed in
tractors, turbocompounding. While Navistar commented that the 2017 MY
standard may be challenging, the agencies believe that since
manufacturers which may need to use turbocompounding to meet the
standards will not have to do so until 2017 MY, there will be
sufficient lead time for all engine manufacturers to introduce this
technology. Thus, the agencies are finalizing a regulatory alternative
whereby a manufacturer, for an interim period of the 2014-2016 model
years, 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. 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. This is similar to EPA's approach in the
light-duty rule for handling a certain subset of vehicles that were
deemed unable to meet the generally-applicable GHG standards during the
2012-2015 time frame due to higher initial baseline conditions, and
which therefore needed alternate standards in those model years.\71\
---------------------------------------------------------------------------

    \70\ See 75 FR at 74178.
    \71\ See 75 FR 25414-25419.
---------------------------------------------------------------------------

    The agencies stress that this is a temporary and limited option
being implemented to address diverse manufacturer needs associated with
complying with this first phase of the regulations. As codified in 40
CFR 1036.620 and 49 CFR 535.5(d), this optional standard will be
available only for the 2014 through 2016 model years, because we
believe that manufacturers will have had ample opportunity to make
appropriate changes to bring their product performance into line with
the rest of the industry after that time. As proposed, the final rules
require that manufacturers making use of these provisions for the
optional standard would need to exhaust all credits available to this
averaging set prior to using this flexibility and would not be able to
generate emissions credits from other engines in the same regulatory
averaging set as the engines complying using this alternate approach.
    The agencies note again that manufacturers choosing to utilize this
option in MYs 2014-2016 will have to make a greater relative
improvement in MY 2017 than the rest of the industry, since they will
be starting from a worse level--for compliance purposes, emissions from
engines certified and sold at the three percent level will be averaged
with emissions from engines certified and sold at more stringent levels
to arrive at a weighted average emissions for all engines in the
subcategory. Again, this option can only be taken if all other credit
opportunities have been exhausted and the manufacturer still cannot
meet the primary standards. If a manufacturer chooses this option to
meet the EPA emission standards in the MY 2014-2016, and wants to opt
into the NHTSA fuel consumption program in these same MYs it must
follow the exact path followed under the EPA program utilizing
equivalent fuel consumption standards. Since the NHTSA standards are
optional in 2014, manufacturers may choose not to adopt either the
alternative engine standard or the regular voluntary standard by not
participating in the NHTSA program in 2014 and 2015.
    Some commenters argued that manufacturers could game the standard
by establishing an artificially high 2011 baseline emission level. This
could be done, for example, by certifying an engine with high fuel
consumption and GHG emissions that is either: (1) Not sold in
significant quantities; or (2) later altered to emit fewer GHGs and
consume less fuel through service changes. In order to mitigate this
possibility, the agencies are requiring that the 2011 model year
baseline must be developed by averaging emissions over all engines in
an engine family certified and sold for that model year so as to
prevent a manufacturer from developing a single high GHG output engine
solely for the purpose of establishing a high baseline. As an
alternative, if a manufacturer does not certify all engine families in
an averaging set to the alternate standards, then the tested
configuration of the engine certified to the alternate standard must
have the same engine displacement and its rated power within 5 percent
of the highest rated power of the baseline tested configuration. In
addition, the tested configuration of the engine certified to the
alternate standard must be a configuration sold to customers. These
three requirements will prevent a manufacturer from producing an engine
with an artificially high power rating and therefore produce
artificially low grams of CO2 emissions and fuel consumption
per brake horsepower. In addition, the tested configurations must have
a BSFC equivalent to or better than all other configurations within the
engine family which will prevent a manufacturer from creating a
baseline configuration with artificially high CO2 emissions
and fuel consumption.
(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 finalizing would apply to
individual vehicles and engines. NHTSA is adopting an approach which
does not include in-use standards.
    EPA proposed 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 to address measurement variability
inherent in comparing results among different laboratories and
different engines. The agency proposed a two percent adjustment factor
and requested comments and additional data during the proposal to
assist in developing an appropriate factor level. The agency received
additional data during the comment period which identified production
variability which was not accounted for at proposal. Details on the
development of the final adjustment factor are included in RIA Chapter
3. Based on the data received, EPA determined that the adjustment
factor in the final rules should be higher than the proposed level of
two percent. EPA is finalizing a three 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.
    We are finalizing regulatory text (in Sec.  1036.150) to allow
engine manufacturers to used assigned

deterioration factors (DFs) without performing their own durability
emission tests or engineering analysis. However, the engines would
still be required to meet the standards in actual use without regard to
whether the manufacturer used the assigned DFs. This allowance is being
adopted as an interim provision applicable only for this initial phase
of standards.
    Manufacturers will be allowed to use an assigned additive DF of 0.0
g/bhp-hr for CO2 emissions from any conventional engine
(i.e., an engine not including advance or innovative technologies).
Upon request, we could allow the assigned DF for CO2
emissions from engines including advance or innovative technologies,
but only if we determine that it would be consistent with good
engineering judgment. We believe that we have enough information about
in-use CO2 emissions from conventional engines to conclude
that they will not increase as the engines age. However, we lack such
information about the more advanced technologies.
    EPA is also finalizing the proposed provisions requiring 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 is adopting provisions where the existing engine useful
life periods, as included in Table II-6, be broadened to include
CO2 emissions for both engines (See 40 CFR 1036.108(d)) and
tractors (See 40 CFR 1037.105).

           Table II-6--Tractor and Engine Useful Life Periods
------------------------------------------------------------------------
                                                      Years      Miles
------------------------------------------------------------------------
Medium Heavy-Duty Diesel Engines..................         10    185,000
Heavy Heavy-Duty Diesel Engines...................         10    435,000
Class 7 Tractors..................................         10    185,000
Class 8 Tractors..................................         10    435,000
------------------------------------------------------------------------

(3) Test Procedures and Related Issues
    The agencies are finalizing 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. Consistent with the
proposal, the test procedures related to the tractors are all new,
while the engine test procedures already established were built
substantially on EPA's current non-GHG emissions test procedures,
except as noted. This section discusses the final simulation model
developed for demonstrating compliance with the tractor standard and
the final engine test procedures.
(a) Vehicle Simulation Model
    We are finalizing as proposed separate engine and vehicle-based
emission standards to achieve the goal of reducing emissions and fuel
consumption for both combination tractors and engines. Engine
manufacturers are subject to the engine standards while the Class 7 and
8 tractor manufacturers are required to install certified engines in
their tractors. The tractor manufacturer is also subject to a separate
vehicle-based standard which utilizes a vehicle 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.
    Consistent with the proposal, NHTSA and EPA are finalizing a
procedure 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.\72\ The EPA developed the Greenhouse gas Emissions
Model (GEM) for the specific purpose of this rulemaking 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 EPA and finalized 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 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
sought comments regarding other software packages which would better
serve the compliance purposes of the rules than the GEM, but did not
receive any recommendations.
---------------------------------------------------------------------------

    \72\ See 2010 NAS Report. Note 21, Recommendation 8-4. Page 190.
---------------------------------------------------------------------------

    The 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 the GEM based on the chassis test results from
two combination tractors tested at Southwest Research Institute. The
validation work conducted on this vehicle was 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 2 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 utilizing in compliance testing. Since the time of the
proposal, the EPA also conducted a validation of the GEM relative to a
commonly used vehicle simulation software, GT-Power. The results of
this validation found that the two software programs predicted the fuel
efficiency of each subcategory of tractor to be within 2 percent. Test
to test variation for heavy-duty vehicle chassis testing can be higher
than 4 percent due to driver variation alone. The final simulation
model is described in greater detail in Chapter 4 of the RIA and is
available for download by at (http://www.epa.gov/otaq/climate/regulations.htm).
    After proposal, the agencies conducted a peer review of GEM version
1.0 which was proposed. In addition, we requested comment on all
aspects of

this approach to compliance determination in general and to the use of
the GEM in particular. The agencies received comments from stakeholders
and made changes for the release of GEM v2.0 to address concerns raised
in the comments, along with the comments received during the peer
review process. The most noticeable changes to the GEM include
improvements to the graphical user interface (GUI). In response to
comments, the agencies have reduced the amount of information required
in the Identification section; linked the inputs to the selected
subcategory while graying-out the items that are not applicable to the
subcategory; and added batch modeling capability to reduce the
compliance burden to manufacturers. In addition, substantial work went
into model validations and benchmarking against vehicle test data and
other commonly used vehicle simulation models.
    The model also includes a new driver model, a simplified electric
system model, and revised engine fuel maps to better reflect the 2017
model year engine standards. The model in the final rulemaking uses the
targeted vehicle driving speed to estimate vehicle torque demand at any
given time, and then the power required to drive the vehicle is derived
to estimate the required accelerator and braking pedal positions. If
the driver misses the vehicle speed target, a speed correction logic
controlled by a PID controller is applied to adjust necessary
accelerator and braking pedal positions in order to match targeted
vehicle speed at every simulation time step. The enhanced driver model
used in the final rulemaking with its feed-forward driver controls more
realistically models driving behavior. The GEM v1.0, the proposed
version of the model, had four individual components to model the
electric system--starter, electrical energy system, alternator, and
electrical accessory. For the final rulemaking, the GEM v2.0 has a
single electric system model with a constant power consumption level.
Based on comments received, the agencies revisited the 2017 model year
proposed fuel maps, specifically the low load area, which was
extrapolated during the proposal and (incorrectly) generated negative
improvements. The agencies redeveloped the fuel maps for the final
rulemaking to better predict the fuel consumption of engines in this
area of the fuel consumption map. Details of the changes are included
in RIA Chapter 4.
    To demonstrate compliance, a Class 7 and 8 tractor manufacturer
will measure the performance of specified tractor systems (such as
aerodynamics and tire rolling resistance), input the values into the
GEM, and compare the model's output to the standard. The rules require
that a tractor manufacturer provide the inputs for each of following
factors for each of the tractors it wishes 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-1.
[GRAPHIC] [TIFF OMITTED] TR15SE11.001

    For the aerodynamic assessment, tire rolling resistance, and
tractor weight reduction, the input values for the simulation model
will be determined by the manufacturer through conducting tests using
the test procedures finalized

by the agencies in this action and described below. The agencies are
allowing several testing alternatives for aerodynamic assessment
referenced back to a coastdown test procedure, a single procedure for
determination of the coefficient of rolling resistance (CRR) for tires,
and a prescribed method to determine tractor weight reduction. The
agencies have finalized 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 finalizing standards for Class 7 and 8
combination tractors that would be expressed in terms of moving a ton
(2,000 pounds) of freight over one mile. Thus, NHTSA's final 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 final CO2 vehicle standards would be represented
as grams of CO2 per ton-mile. The model converts
CO2 emissions to fuel consumption using the CO2
grams per ton mile estimated by GEM and an assumed 10,180 grams of
CO2 per gallon of diesel fuel.
    This approach tracks the recommendations of the NAS report. 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 adopting, 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
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 vehicle can go up. Based on this general approach, it can
be estimated that for every 1,200 pounds in mass reduction across all
Class 7 and 8 tractors on the road, that total 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
vehicle. There was strong consensus in the public comments for adopting
the proposed metrics for tractors.
(c) Vehicle Aerodynamic Assessment
    The aerodynamic drag of a vehicle is determined by the vehicle's
coefficient of drag (Cd), frontal area, air density and speed. As noted
in the NPRM, quantifying truck aerodynamics as an input to the GEM
presents technical challenges because of the proliferation of vehicle
configurations, the lack of a clearly preferable standardized test
method, and subtle variations in measured aerodynamic values among
various test procedures. Class 7 and 8 tractor aerodynamics are
currently developed by manufacturers using a range of techniques,
including wind tunnel testing, computational fluid dynamics, and
constant speed tests.
    Consistent with our discussion at proposal, we believe a broad
approach allowing manufacturers to use these multiple different test
procedures to demonstrate aerodynamic performance of its tractor fleet
is appropriate given that no single test procedure is superior in all
aspects to other approaches. 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)). However, we also
recognize the need for consistency and a level playing field in
evaluating aerodynamic performance.
    The agencies are retaining an aerodynamic bin structure for the
final rulemaking, but are adjusting the method used to determine the
bins. To address the consistency and level playing field concerns,
NHTSA and EPA proposed that manufacturers use a two-part screening
approach for determining the aerodynamic inputs to the GEM. The first
part would have required the manufacturers to assign each vehicle
aerodynamic configuration based on descriptions of vehicle
characteristics to one of five aerodynamics bins created by EPA and
NHTSA. The proposed assignment by bin would have fixed (by rule) the
aerodynamic characteristics of the vehicle. However, the agencies,
while working with industry, concluded for the final rulemaking that an
approach which identified a reference aerodynamic test method and a
procedure to align results from other aerodynamic test procedures with
the reference method is a simpler, more accurate approach than
deciphering and interpreting written descriptions of aerodynamic
components.
    Therefore, we are finalizing an approach, as described in Section
V.B.3.d and Sec.  1037.501, which uses an

enhanced coastdown procedure as a reference method and defines a
process for manufacturers to align drag results from each of their own
test methods to the reference method results. Manufacturers will be
able to use any aerodynamic evaluation method in demonstrating a
vehicle's aerodynamic performance as long as the method is aligned to
the reference method. The results from the aerodynamic testing will be
the single determining factor for aerodynamic bin assignments.
    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,\73\ the wind average drag coefficient is
about 15 percent higher than the zero degree coefficient of drag. In
addition, the agencies received comments that supported the use of wind
averaged drag results for the aerodynamic determination. The agencies
considered finalizing the use of a wind averaged drag coefficient in
this regulatory program, but ultimately decided to finalize 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 the reference method is coastdown testing
which is not capable of determining wind averaged yaw. Wind tunnels are
currently the only tool which can accurately assess the influence of
wind speed and direction on a vehicle'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 overall technology effectiveness or change the
kinds of technology decisions made by the tractor manufacturers in
developing equipment to meet our final standards. However, the agencies
are adopting provisions which allow manufacturers to generate credits
reflecting performance of technologies which improve the aerodynamic
performance in crosswind conditions, similar to those experienced by
vehicles in use through innovative technologies, as described in
Section IV.
---------------------------------------------------------------------------

    \73\ See 2010 NAS Report, Note 21, Finding 2-4 on page 39.
---------------------------------------------------------------------------

    As just noted, the agencies are adopting an approach for this final
action where the manufacturer would determine a tractor's aerodynamic
drag force using their own aerodynamic assessment tools and correlating
the results back to the reference aerodynamic test method of enhanced
coastdown testing. The manufacturer determines the appropriate
predefined aerodynamic bin based on the correlated test results and
then inputs the predefined Cd value for that aerodynamic bin into the
GEM. Coefficient of drag and frontal area of the tractor-trailer
combination go hand-in-hand to determine the force required to overcome
aerodynamic drag. The agencies proposed that the Cd value would be a
GEM input derived by the manufacturer and that the agencies would
specify the vehicle's frontal area for each regulatory subcategory. The
agencies sought and received comment recommending an alternate approach
where the aerodynamic input tables (as shown in Table 0-7 and Table 0-
8) represent the drag force as defined as Cd multiplied by the frontal
area. Because both approaches are essentially equivalent and the use of
CdA more directly relates back to the aerodynamic testing, the agencies
are finalizing the use of CdA as recommended by manufacturers.
    The agencies are finalizing aerodynamic technology bins which
divide the wide spectrum of tractor aerodynamics into five bins (i.e.,
categories) for high roof tractors. The first high roof category, Bin
I, is designed to represent tractor bodies which prioritize appearance
or special duty capabilities over aerodynamics. These Bin I 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 high
roof aerodynamics category is Bin II which roughly represents the
aerodynamic performance of the average new tractor sold today. The
agencies developed this bin to incorporate conventional tractors which
capitalize on a generally aerodynamic shape and avoid classic features
which increase drag. High roof tractors within Bin III build on the
basic aerodynamics of Bin II tractors with added components to reduce
drag in the most significant areas on the tractor, such as integral
roof fairings, side extending gap reducers, fuel tank fairings, and
streamlined grill/hood/mirrors/bumpers, similar to SmartWay trucks
today. The Bin IV aerodynamic category for high roof tractors builds
upon the Bin III tractor body with additional aerodynamic treatments
such as underbody airflow treatment, down exhaust, and lowered ride
height, among other technologies. And finally, Bin V 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 had proposed five aerodynamic bins for each tractor
regulatory subcategory. The agencies received comments from ATA, EMA/
TMA, and Volvo indicating that this approach was not consistent with
the aerodynamics of low and mid roof tractors. High roof tractors are
consistently paired with box trailer designs, and therefore
manufacturers can design the tractor aerodynamics as a tractor-trailer
unit and target specific areas like the gap between the tractor and
trailer. In addition, the high roof tractors tend to spend more time at
high speed operation which increases the impact of aerodynamics on fuel
consumption and GHG emissions. On the other hand, low and mid roof
tractors are designed to pull variable trailer loads and shapes. They
may pull trailers such as flat bed, low boy, tankers, or bulk carriers.
The loads on flat bed trailers can range from rectangular cartons with
tarps, to a single roll of steel, to a front loader. Due to these
variables, manufacturers do not design unique low and mid roof tractor
aerodynamics but instead use derivatives from their high roof tractor
designs. The aerodynamic improvements to the bumper, hood, windshield,
mirrors, and doors are developed for the high roof tractor application
and then carried over into the low and mid roof applications. As
mentioned above, the types of designs that would move high roof
tractors from a Bin III to Bins IV and V include features such as gap
reducers and integral roof fairings which would not be appropriate on
low and mid roof tractors. The agencies considered and largely agree
with these comments and are therefore finalizing only two aerodynamic
bins for low and mid roof tractors. The agencies are reducing the
number of bins to reflect the actual range of aerodynamic technologies
effective in low and mid roof tractor applications. Thus, the agencies
are differentiating the aerodynamic performance for low and mid roof
applications into two bins--conventional and aerodynamic.\74\
---------------------------------------------------------------------------

    \74\ As explained in Section IV, there are no ABT implications
to this change from proposal, since all Class 8 combination tractors
are considered to be a single averaging set for ABT purposes.
Similarly, all Class 7 tractors are considered to be a single
averaging set for ABT purposes.

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

    For high roof combination tractor compliance determination, a
manufacturer would use the aerodynamic results determined through
testing to establish the appropriate bin. The manufacturer would then
input into GEM the Cd value specified for each bin as defined in Table
II-7 and Table II-8. For example, if a manufacturer tests a Class 8
sleeper cab high roof tractor and the test produces a CdA value between
5.8 and 6.6, the manufacturer would assign this tractor to the Class 8
Sleeper Cab High Roof Bin III. The manufacturer would then use the Cd
value identified for Bin III of 0.60 as the input to GEM.
    The Cd values in Table II-7 and Table II-8 differ from proposal
based on a change in the reference method (enhanced coastdown
procedure) and additional testing conducted by EPA. Details of the test
program and results are included in RIA Chapter <IP_ADDRESS>.

 Table II-7--Aerodynamic Input Definitions to GEM for High Roof Tractors
------------------------------------------------------------------------
                                     Class 7             Class 8
                                  --------------------------------------
                                     Day cab      Day cab    Sleeper cab
                                  --------------------------------------
                                    High roof    High roof   High roof >
------------------------------------------------------------------------
                 Aerodynamic Test Results (CdA in m\2\)
------------------------------------------------------------------------
Bin I............................       >= 8.0       >= 8.0       >= 7.6
Bin II...........................      7.1-7.9      7.1-7.9      6.7-7.5
Bin III..........................      6.2-7.0      6.2-7.0      5.8-6.6
Bin IV...........................      5.6-6.1      5.6-6.1      5.2-5.7
Bin V............................       <= 5.5       <= 5.5       <= 5.1
------------------------------------------------------------------------
                      Aerodynamic Input to GEM (Cd)
------------------------------------------------------------------------
Bin I............................         0.79         0.79         0.75
Bin II...........................         0.72         0.72         0.68
Bin III..........................         0.63         0.63         0.60
Bin IV...........................         0.56         0.56         0.52
Bin V............................         0.51         0.51         0.47
------------------------------------------------------------------------

    The CdA values in Table II-8 are based on testing using the
enhanced coastdown test procedures adopted for the final rulemaking,
which includes aerodynamic assessment of the low and mid roof tractors
without a trailer. The removal of the trailer significantly reduces the
CdA value of mid roof tractors with tanker trailers because of the poor
aerodynamic performance of the tanker trailer. The agencies developed
the Cd input for each of the low and mid roof tractor bins to represent
the Cd of the tractor, its frontal area, and the impact of the Cd value
due to the trailer such that the GEM value is representative of a
tractor-trailer combination, as it is for the high roof tractors.

                                     Table II-8--Aerodynamic Input Definitions to GEM for Low and Mid Roof Tractors
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Class 7                                      Class 8
                                                                   ------------------------------------------------------------------------------------------
                                                                                Day Cab                          Day Cab            Sleeper
                                                                                ----------------------------------------------------------------      Cab
                                                                                ------------
                                                                                Low Roof     Mid Roof     Low Roof     Mid Roof    Low
                                                                                Roof
------------------------------------------------------------------------------------------------------------------------------------------------ ------------
                                                     Aerodynamic Test Results (CdA in m\2\)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bin I.............................................................       >= 5.1       >= 5.6       >= 5.1       >= 5.6       >= 5.1       >= 5.6
Bin II............................................................       <= 5.0       <= 5.5       <= 5.0       <= 5.5       <= 5.0       <= 5.5
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                          Aerodynamic Input to GEM (Cd)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Bin I.............................................................         0.77         0.87         0.77         0.87         0.77         0.87
Bin II............................................................         0.71         0.82         0.71         0.82         0.71         0.82
--------------------------------------------------------------------------------------------------------------------------------------------------------

(d) Tire Rolling Resistance Assessment
    NHTSA and EPA are finalizing as proposed 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.\75\
The agencies believe the ISO test procedure is appropriate for this
program because the procedure is the same one used by NHTSA in its fuel
efficiency tire labeling program \76\ and is consistent with the
testing 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 tractor. The
results would be expressed as a rolling resistance coefficient (CRR)
and measured as kilogram per metric ton (kg/metric ton). The agencies
are finalizing as proposed 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 will use the steer and
drive tire rolling resistance inputs and distribute 15 percent of the
gross weight of the tractor and trailer to the steer axle, 42.5 percent
to the drive axles, and 42.5 percent to the trailer axles.\77\ The
trailer tires' rolling resistance is 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.\78\
---------------------------------------------------------------------------

    \75\ 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
    \76\ 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).
    \77\ 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).
    \78\ 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.
---------------------------------------------------------------------------

    EPA and NHTSA conducted additional evaluation testing on HD trucks
tires used for tractors, and also for vocational vehicles. The agencies
also received several comments on the suitability of low rolling
resistance tires for various HD vehicle applications. The summary of
the agencies' findings and a response to issues raised by commenters is
presented in Section II.D(1)(a).
(e) Weight Reduction Assessment
    The agencies proposed that the tractor standards reflect improved
CO2 emissions and fuel consumption performance of a 400
pound weight reduction in Class 7 and 8 tractors through the
substitution of single wide tires and light-weight wheels for dual
tires and steel wheels. This approach was taken since there is a large
variation in the baseline weight among trucks that perform roughly
similar functions with roughly similar configurations. Because of this,
the only effective way to quantify the exact CO2 and fuel
consumption benefit of mass reduction using GEM is to estimate baseline
weights for specific components that can be replaced with light weight
components. If the weight reduction is specified for light weight
versions of specific components, then both the baseline and weight
differentials for these are readily quantifiable and well-understood.
Lightweight wheels are commercially available as are single wide tires
and thus data on the weight reductions attributable to these two
approaches are readily available.
    The agencies received comments on this approach from Volvo, ATA,
MEMA, Navistar, American Chemistry Council, the Auto Policy Center,
Iron and Steel Institute, Arvin Meritor, Aluminum Association, and
environmental groups and NGOs. Volvo and ATA stated that not all fleets
can use single wide tires and if this is the case the 400 pound weight
reduction target cannot be met. Volvo stated that without the use of
single wide drive tires, a 6x4 tractor will have a maximum weight
reduction of 300 pounds if the customer selects all ten wheels to be
outfitted with light weight aluminum wheels. A number of additional
commenters--including American Chemistry Council, The Auto Policy
Center, Iron and Steel Institute, Aluminum Association, Arvin Meritor,
MEMA, Navistar, Volvo, and environmental and nonprofit groups--stated
that manufacturers should be allowed to use additional light weight
components in order to meet the tractor fuel consumption and
CO2 emissions standards. These groups stated that weight
reductions should not be limited to wheels and tires. They asked that
cab doors, cab sides and backs, cab underbodies, frame rails, cross
members, clutch housings, transmission cases, axle differential carrier
cases, brake drums, and other components be allowed to be replaced with
light-weight versions. Materials suggested for substitution included
aluminum, light-weight aluminum, high strength steel, and plastic
composites. The American Iron and Steel Institute stated there are
opportunities to reduce mass by replacing mild steel--which currently
dominates the heavy-duty industry--with high strength steel.
    In addition, The American Auto Policy Center asked that
manufacturers be allowed to use materials other than aluminum and high
strength steel to comply with the regulations. DTNA asked that weight
reduction due to engine downsizing be allowed to receive credit. Volvo
requested that weight reductions due to changes in axle configuration
be credited. They used the example of a customer selecting a 4 X 2 over
a 6 X 4 axle tractor. In this case, they assert there would be a 1,000
pound weight savings from removing an axle.
    As proposed, many of the material substitutions could have been
considered as innovative technologies for tractors and hence eligible
for off cycle credits (so that the commenters overstated that these
technologies were `disallowed'). Nonetheless in response to the above
summarized comments, the agencies evaluated whether additional
materials and components could be used directly for compliance with the
tractor weight reduction through the primary program (i.e. be available
as direct inputs to the GEM). The agencies reviewed comments and data
received in response to the NPRM and additional studies cited by
commenters. A summary of this review is provided in the following
paragraphs.
    TIAX, in their report to the NAS, cited information from Alcoa
identifying several mass reduction opportunities from material
substitution in the tractor cab components which were similar to the
ones identified by the Aluminum Association in their comments to this
rulemaking.\79\ TIAX included studies submitted by Alcoa showing the
potential to reduce the weight of a tractor-trailer combination by
3,500 to 4,500 pounds.\80\ In addition, the U.S. Department of Energy
has several projects underway to improve the freight efficiency of
Class 8 trucks which provide relevant data: \81\ DOE reviewed
prospective lightweighting alternative materials and found that
aluminum has a potential to reduce mass by 40 to 60 percent, which is
in line with the estimates of mass reductions of various components
provided by Alcoa, and by the Aluminum Association in their comments
and as cited in the TIAX report. These combined studies, comments, and
additional data provided information on specific components that could
be replaced with aluminum components.
---------------------------------------------------------------------------

    \79\ TIAX, LLC. ``Assessment of Fuel Economy Technologies for
Medium- and Heavy-Duty Vehicles,'' Final Report to National Academy
of Sciences, November 19, 2009. Pages 4-62 through 4-64.
    \80\ Alcoa. ``Improving Sustainability of Transport: Aluminum is
Part of the Solution.'' 2009.
    \81\ Schutte, Carol. U.S. Department of Energy, Vehicle
Technologies Program. ``Losing Weight--an enabler for a Systems
Level Technology Development, Integration, and Demonstration for
Efficient Class 8 Trucks (SuperTruck) and Advanced Technology
Powertrains for Light-Duty Vehicles.''
---------------------------------------------------------------------------

    With regard to high strength steel, the Iron and Steel Institute
found that the use of high strength steel and redesign can reduce the
weight of light-duty trucks by 25 percent.\82\ Approximately

10 percent of this reduction results from material substitution and 15
percent from vehicle re-design. While this study evaluated light-duty
trucks, the agencies believe that a similar reduction could be achieved
in heavy-duty trucks since the reductions from material substitution
would likely be similar in heavy-trucks as in light-trucks. U.S. DOE,
in the report noted above, identified opportunities to reduce mass by
10 percent through high strength steel.\83\ This study was also for
light-duty vehicles.
---------------------------------------------------------------------------

    \82\ American Iron and Steel Institute. ``A Cost Benefit
Analysis Report to the North American Steel Industry on Improved
Materials and Powertrain Architectures for 21st Century Trucks.''
    \83\ Schutte, Carol. U.S. Department of Energy, Vehicle
Technologies Program. ``Losing Weight--an enabler for a Systems
Level Technology Development, Integration, and Demonstration for
Efficient Class 8 Trucks (SuperTruck) and Advanced Technology
Powertrains for Light-Duty Vehicles''.
---------------------------------------------------------------------------

    The agencies considered other materials such as plastic composites
and magnesium substitutes but were not able to obtain weights for
specific components made from these materials. We have therefore not
included components made from these materials as possible substitutes
in the primary program, but they may be considered through the
innovative technology/off-cycle credits provision. We may consider
including these materials as part of the primary compliance option in a
subsequent regulation if data become available.
    Based on this analysis, the agencies developed an expanded list of
weight reduction opportunities for the final rulemaking that may be
reflected in the GEM, as listed in Table II-9. The list includes
additional components, but not materials, from those proposed. For high
strength steel, the weight reduction value is equal to 10 percent of
the presumed baseline component weight, as the agencies used a
conservative value based on the DOE report. We recognize that there may
be additional potential for weight reduction in new high strength steel
components which combine the reduction due to the material substitution
along with improvements in redesign, as evidenced by the studies done
for light-duty vehicles. In the development of the high strength steel
component weights, we are only assuming a reduction from material
substitution and no weight reduction from redesign, since we do not
have any data specific to redesign of heavy-duty components nor do we
have a regulatory mechanism to differentiate between material
substitution and improved design. We are finalizing for wheels that
both aluminum and light weight aluminum are eligible to be used as
light-weight materials. Aluminum, but not light-weight aluminum, can be
used as a light-weight material for other components. The reason for
this is that data were available for light weight aluminum for wheels
but were not available for other components.
    The agencies received comments on the proposal from the American
Chemistry Council highlighting the role of plastics and composites in
heavy-duty vehicles. As they stated, composites can be low density
while having high strength and are currently used in applications such
as oil pans and buses. The DOE mass reduction program demonstrated for
heavy vehicles proof of concept designs for hybrid composite doors with
an overall mass savings of 40 percent; 30 percent mass reduction of a
hood system with carbon fiber sheet molding compound; 50 percent mass
reduction from composite tie rods, trailing arms, and axles; and
superplastically formed aluminum body panels.\84\ While the agencies
recognize these opportunities, we do not believe the technologies have
advanced far enough to quantify the benefits of these materials because
they are very dependent on the actual composite material. The agencies
may consider such lightweighting opportunities in future actions, but
are not including them as part of this primary program. Manufacturers
which opt to pursue composite and plastic material substitutions may
seek credits through the innovative technology provisions.
---------------------------------------------------------------------------

    \84\ Schutte, Carol. U.S. Department of Energy, Vehicle
Technologies Program. ``Losing Weight--an enabler for a Systems
Level Technology Development, Integration, and Demonstration for
Efficient Class 8 Trucks (SuperTruck) and Advanced Technology
Powertrains for Light-Duty Vehicles''.
---------------------------------------------------------------------------

    With regard to Volvo's request that manufacturers be allowed to
receive credit for trucks with fewer axles, the agencies recognize that
vehicle options exist today which have less mass than other options.
However, we believe the decisions to add or subtract such components
will be made based on the intended use of the vehicle and not based on
a crediting for the mass difference in our compliance program. It is
not our intention to create a tradeoff between the right vehicle to
serve a need (e.g. one with more or fewer axles) and compliance with
our final standards. Therefore, we are not including provisions to
credit (or penalize) vehicle performance based on the subtraction (or
addition) of specific vehicle components. Table II-9 provides weight
reduction values for different components and materials.

                   Table II-9--Weight Reduction Values
------------------------------------------------------------------------

------------------------------------------------------------------------
       Weight reduction technology        Weight reduction (lb per tire/
                                                      wheel)
------------------------------------------------------------------------
Single Wide Drive Tire with:
    Steel Wheel.........................                84
    Aluminum Wheel......................                139
    Light Weight Aluminum Wheel.........                147
Steer Tire or Dual Wide Drive Tire with:
    High Strength Steel Wheel...........                 8
    Aluminum Wheel......................                21
    Light Weight Aluminum Wheel.........                30
------------------------------------------------------------------------
      Weight reduction technologies          Aluminum      High strength
                                              weight       steel weight
                                             reduction       reduction
                                               (lb.)           (lb.)
------------------------------------------------------------------------
Door....................................              20               6
Roof....................................              60              18
Cab rear wall...........................              49              16
Cab floor...............................              56              18
Hood Support Structure..................              15               3

Fairing Support Structure...............              35               6
Instrument Panel Support Structure......               5               1
Brake Drums--Drive (4)..................             140              11
Brake Drums--Non Drive (2)..............              60               8
Frame Rails.............................             440              87
Crossmember--Cab........................              15               5
Crossmember--Suspension.................              25               6
Crossmember--Non Suspension (3).........              15               5
Fifth Wheel.............................             100              25
Radiator Support........................              20               6
Fuel Tank Support Structure.............              40              12
Steps...................................              35               6
Bumper..................................              33              10
Shackles................................              10               3
Front Axle..............................              60              15
Suspension Brackets, Hangers............             100              30
Transmission Case.......................              50              12
Clutch Housing..........................              40              10
Drive Axle Hubs (8).....................             160               4
Non Drive Front Hubs (2)................              40               5
Driveshaft..............................              20               5
Transmission/Clutch Shift Levers........              20               4
------------------------------------------------------------------------

    EPA and NHTSA are specifying the baseline vehicle weight for each
regulatory vehicle subcategory (including the tires, wheels, frame, and
cab components) in the GEM in aggregate based on weight of vehicles
used in EPA's aerodynamic test program, but allow manufacturers to
specify the use of light-weight components. The GEM then quantifies the
weight reductions based on the pre-determined weight of the baseline
component minus the pre-determined weight of the component made from
light-weight material. Manufacturers cannot specify the weight of the
light-weight component themselves, only the material used in the
substitute component. The agencies assume the baseline wheel and tire
configuration contains dual tires with steel wheels, along with steel
frame and cab components, because these represent the vast majority of
new vehicle configurations today. The weight reduction due to
replacement of components with light weight versions will be reflected
partially in the payload tons and partially in reducing the overall
weight of the vehicle run in the GEM. The specified payload in the GEM
will be set to the prescribed payload plus one third of the weight
reduction amount to recognize that approximately one third of the truck
miles are travelled at maximum payload, as discussed below in the
payload discussion. The other two thirds of the weight reduction will
be subtracted from the overall vehicle weight prescribed in the GEM.
    The agencies continue to believe that the 400 pound weight target
is appropriate to use as a basis for setting the final combination
tractor CO2 emissions and fuel consumption standards. The
agencies agree with the commenter that 400 pounds of weight reduction
without the use of single wide tires may not be achievable for all
tractor configurations. As noted, the agencies have extended the list
of weight reduction components in order to provide the manufacturers
with additional means to comply with the combination tractors and to
further encourage reductions in vehicle weight. The agencies considered
increasing the target value beyond 400 pounds given the additional
reduction potential identified in the expanded technology list;
however, lacking information on the capacity for the industry to change
to these lightweight components across the board by the 2014 model
year, we have decided to maintain the 400 pound target. The agencies
intend to continue to study the potential for additional weight
reductions in our future work considering a second phase of vehicle
fuel efficiency and GHG regulations. In the context of the current
rulemaking for HD fuel consumption and GHG standards, one would expect
that reducing the weight of medium-duty trucks similarly would, if
anything, have a positive impact on safety. However, given the large
difference in weight between light-duty and medium-duty vehicles, and
even larger difference between light-duty vehicles and heavy-duty
vehicles with loads, the agencies believe that the impact of weight
reductions of medium- and heavy-duty vehicles would not have a
noticeable impact on safety for any of these classes of vehicles.\85\
---------------------------------------------------------------------------

    \85\ For more information on the estimated safety effects of
this rule, see Chapter 9 of the RIA.
---------------------------------------------------------------------------

(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.\86\ 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 tractor cab itself than to pull off the road and find
accommodations.\87\ During this rest period a driver will idle the
tractor engine in order to provide heating or cooling, or to run on-
board appliances. In some cases the engine can idle in excess of 10
hours. During this period, the engine will consume approximately 0.8
gallons of fuel and emit over 8,000 grams of CO2 per hour.
An average tractor engine can consume 8 gallons of fuel and emit over
80,000 grams of CO2 during overnight idling in such a case.
---------------------------------------------------------------------------

    \86\ 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/.
    \87\ The agencies note that some sleeper cabs may be classified
as vocational tractors and therefore are expected to primarily
travel locally and would not benefit from an idle reduction
technology.
---------------------------------------------------------------------------

    Idling reduction technologies (IRT) 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 adopting a provision for use of
extended idle reduction technology as an input to the GEM for Class 8
sleeper cabs. As discussed further in Section III, if a manufacturer
wishes to receive credit for using IRT to meet the standard, then an
automatic main engine shutoff must be programmed and enabled, such that
engine shutdown occurs after 5 minutes of idling, to help ensure the
reductions are realized in-use. A discussion of the provisions the
agencies are adopting for allowing an override of this automatic
shutdown can be found in RIA Chapter 2. 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 final standards and using these
technologies as the inputs to the GEM. The default value (5 g
CO2/ton-mile or 0.5 gal/1,000 ton-mile) for the use of
automatic engine shutdown (AES) with idle reduction technologies was
determined as the difference between a baseline main engine with idle
fuel consumption of 0.8 gallons per hour that idles 1,800 hours and
travels 125,000 miles per year, and a diesel auxiliary power unit
operating in lieu of main engine during those same idling hours. The
agencies received various comments from ACEEE and MEMA regarding the
assumptions used to derive the idle reduction value. ACEEE argued that
the agencies should use a fuel consumption rate of 0.47 gallon/hour for
main engine idling based on a paper written by Kahn. MEMA argued that
the agencies should use a main engine idling fuel consumption rate of
0.87 gal/hr, which is the midpoint of a DOE calculator reporting fuel
consumption rates from 0.64 to 1.15 gal/hr at idling conditions, and
between 800 and 1200 rpm with the air conditioning on and off,
respectively. The agencies respectfully disagree with the 0.47 gal/hr
recommendation because the same paper by Kahn shows that while idling
fuel consumption is 0.47 gal/hr on average at 600 rpm, CO2
emissions increase by 25 percent with A/C on at 600 rpm, and increase
by 165 percent between 600 rpm and 1,100 rpm with A/C on.\88\ MEMA
recommended using 2,500 hours per year for APU operation. They cited
the SmartWay Web site which uses 2,400 hours per year (8 hours per day
and 300 days per year). Also, they cited an Argonne study which assumed
7 hours per day and 303 days per year, which equals 2,121 hours per
year. Lastly, they referred to the FMCSA 2010 driver guidelines which
reduce the number of hours driven per day by one to two hours, which
would lead to 2,650 to 2,900 hours per year. The agencies reviewed
other studies to quantify idling operations, as discussed in greater
detail in RIA Section <IP_ADDRESS>, and believe that the entirety of the
research does not support a change from the proposed calculation.
Therefore, the agencies are finalizing the calculation as proposed.
Additional details regarding the comments, calculations, and agency
decisions are included in RIA Section <IP_ADDRESS>.
---------------------------------------------------------------------------

    \88\ See Gaines, L., A. Vyas, J. Anderson. ``Estimation of Fuel
Used by Idling Commercial Trucks,'' Page 9 (2006).
---------------------------------------------------------------------------

    The agencies are adopting a provision to allow manufacturers to
provide an AES system which is active for only a portion of a vehicle's
life. In this case, a discounted idle reduction value would be entered
into GEM. A discussion of the calculation of a discounted IRT credit
can be found in Section III. Additional details on the emission and
fuel consumption reduction values are included in RIA Section <IP_ADDRESS>.
(g) Vehicle Speed Limiters
    The NPRM proposed to allow combination tractors that use vehicle
speed limiters (VSL) to include the maximum governed speed value as an
input to the GEM for purposes of determining compliance with the
vehicle standards. The agencies also proposed not to assume the use of
a mandatory vehicle speed limiter because of concerns about how to set
a realistic application rate that avoids unintended consequences. See
75 FR at 74223. Governing the top speed of a vehicle can reduce fuel
consumption and GHG emissions, because fuel consumption and
CO2 emissions increase proportionally to the square of
vehicle speed.\89\ Limiting the speed of a vehicle reduces the fuel
consumed, which in turn reduces the amount of CO2 emitted.
The specific input to the GEM would be the maximum governed speed limit
of the VSL that is programmed into the powertrain control module (PCM).
The agencies stressed in the NPRM that in order to obtain a benefit in
the GEM, a 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.'' If the top speed could be easily overridden, the fuel
consumption/CO2 benefits of the VSL might not be realized,
and the agencies did not want to allow the technology to be used for
compliance if the technology could be disabled easily and the real
world benefits not achieved.
---------------------------------------------------------------------------

    \89\ See 2010 NAS Report, Note 21, Page 28. Road Load Force
Equation defines the aerodynamic portion of the road load as
[frac12] * Coefficient of Drag * Frontal Area * air density *
vehicle speed squared.
---------------------------------------------------------------------------

    Both the Center for Biological Diversity (CBD) and New York State
Department of Transportation and Environmental Conservation commented
that the application of speed limiters should be used to set the
tractor standards.\90\ CBD urged the agencies to reconsider the
position and adopt a speed limitation technology. NY State commented
that the technologies are cost effective, reduce emissions, and appear
to be generally acceptable to the trucking industry. They continued to
say that the vehicle speed limit could be set without compromising
operational logistics.
---------------------------------------------------------------------------

    \90\ One commenter mistakenly thought that the agencies were
rejecting consideration of VSLs due to perceived jurisdictional
obstacles. In fact, both the CAA and EISA allow consideration of VSL
technology and the agencies considered the appropriateness of basing
standards on performance of the technology.
---------------------------------------------------------------------------

    Many commenters (Cummins, Daimler, EMA/TMA, ATA, AAPC, NADA)
supported the use of VSLs as an input to the GEM, but requested
clarification of what the specific requirements would be to ensure the
VSL setting would not be capable of being easily overridden. Cummins
and Daimler requested that the final rules explicitly allow vehicle
manufacturers to access and adjust the VSL control feature for setting
the maximum governed speed, arguing that the diverse needs of the
commercial vehicle industry warrant flexibility in electronic control
features, and that otherwise supply chain issues \91\ may result from
the use of VSLs. NADA and EMA/TMA also requested that VSLs have
override features and be adjustable, citing various needs for
flexibility by the fleets. EMA/TMA and ATA requested that VSLs be
adjustable downward by fleets in order to obtain greater benefit in
GEM, if company policies change or if a subsequent vehicle owner needs
a different VSL setting. EMA/TMA stated that the agencies should
prohibit tampering with VSLs, and both EMA and TRALA requested more
information on how the agencies intended to address tampering with
VSLs.
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    \91\ Commenters stated that OEMs need access for setting
appropriate trims for managing the VSL, otherwise significant supply
chain issues could result such as parts shortages caused by the need
for unique speed governed PCMs.
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    In addition to features governing the maximum vehicle speed,
commenters requested adding other programmable flexibilities to
mitigate potential drawbacks to VSLs. Cummins, DTNA,

and EMA/TMA requested that a programmable ``soft top'' speed be added
to PCMs which would allow a vehicle to exceed the speed limit setting
governed by a VSL for a short period of time. A ``soft top'' feature
could be used for a limited duration in order to maneuver and pass
other on-road vehicles at speeds greater than that governed by the VSL.
The commenters argued this was important for vehicle passing and
safety-related situations where, without a soft top feature, it could
be possible for speed limited trucks to obstruct other vehicles on the
road and cause severe road congestion.
    ATA and EMA/TMA also requested that manufacturers be allowed to
program a mileage based expiration into the VSL control feature, in
order to preserve the value of vehicles for second owners who may
require operation at higher speeds. ATA further commented that
manufacturers should be allowed to account for additional GEM input
benefits if the speed governor is reprogrammed to a lower speed within
the useful life of the vehicle.
    After carefully considering the comments, the agencies have
decided, for these final rules, to retain most of the elements in the
proposal. Manufacturers will be allowed to implement a fixed maximum
governed vehicle speed through a VSL feature and to use the maximum
governed vehicle speed as an input to the GEM for certification. Also
consistent with the proposal, the agencies are not premising the final
standards on the use of VSLs. The comments received from stakeholders
did not address the agencies' concerns discussed in the proposal,
specifically the risk of requiring VSL in situations that are not
appropriate from an efficiency perspective because it may lead to
additional vehicle trips to deliver the same amount of freight.\92\ The
agencies continue to believe that we are not in a position to determine
how many additional vehicles would benefit from the use of a VSL with a
setting of less than 65 mph (a VSL with a speed set at or above 65 mph
will show no CO2 emissions or fuel consumption benefit on
the drive cycles included in this program). The agencies further
believe that manufacturers will not utilize VSLs unless it is in their
interest to do so, so that these unintended consequences should not
occur when manufacturers use VSLs as a compliance strategy. We will
monitor the industry's use of VSL in this program and may consider
using this technology in standard setting in the future.
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    \92\ See 75 FR at page 74223.
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    The agencies have decided to adopt commenters' suggestions to allow
adjustable lower limits that can be set and governed by VSLs
independent of the one governing the maximum certified speed limit to
provide the desired flexibility requested by the trucking industry. We
believe that this flexibility would not decrease the anticipated fuel
consumption or CO2 benefits of VSLs because the adjustable
limits would be lower values. Issues identified by the commenters
including the ability to change delivery routes requiring lower
governed speeds or when a fleet's business practices change resulting
in a desire for greater fuel consumption savings are not in conflict
with the purpose and benefit of VSLs. As such, the agencies have
decided to allow a manufacturer to install features for its fleet
customers to set their own lower adjustable limits below the maximum
VSL specified by the agencies. However, the agencies have decided to
not allow any additional benefit in the GEM to a manufacturer for
allowing a lower governed speed in-use than the certified maximum limit
for this first phase of the HD National Program because we can only be
certain that the VSL will be at the maximum setting.
    Both agencies also agree that manufacturers can provide a ``soft
top'' and expiration features to be programmed into PCMs to provide
additional flexibility for fleet owners and so that fleets who purchase
used vehicles have the ability to have different VSL policies than the
original owner of the vehicle. Although the agencies considered
limiting the soft top maximum level due to safety and fuel consumption/
GHG benefit concerns, we have decided to allow the soft top maximum
level to be set to any level higher than the maximum speed governed by
the VSL. This approach will provide drivers with the ability to better
navigate through traffic. However, the agencies are requiring that
manufacturers providing a soft top feature must design the system so it
cannot be modified by the fleets and will not decrement the vehicle
speed limit causing the vehicle to decelerate while the driver is
operating a vehicle above the normal governed vehicle speed limit. For
example, if a manufacturer designs a vehicle speed limiter that has a
normal governed speed limiter setting of 62 mph, and a ``soft top''
speed limiter value of 65 mph, the algorithm shall not cause the
vehicle speed to decrement causing the vehicle to decelerate while the
driver is operating the vehicle at a speed greater that 62 mph (between
62 and 65 mph). The agencies are concerned that a forced deceleration
when a driver is attempting to pass or maneuver could have an adverse
impact on safety.
    In using a soft top feature, a manufacturer will be required to
provide to the agencies a functional description of the ``soft top''
control strategy including calibration values, the speed setting for
both the hard limit and the soft top and the maximum time per day the
control strategy could allow the vehicle to operate at the ``soft top''
speed limit at the time of certification. This information will be used
to derive a factor to discount the VSL input used in the GEM to
determine the fuel consumption and GHG emissions performance of the
vehicle. The agencies also agree with comments that VSLs should be
adjustable so as not to potentially limit a vehicle's resale value.
However, manufacturers choosing the option to override the VSL after a
specified number of miles would be required to discount the benefit of
the VSL relative to the tractor's full lifetime miles. The VSL discount
benefits for using soft-top and expiration features must be calculated
using Equation II-1.\93\ Additional details regarding the derivation of
the discounted equation are included in RIA Chapter 2. The agencies are
also requiring that any vehicle that has a ``soft top'' VSL to identify
the use of the ``soft top'' VSL on the vehicle emissions label.
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    \93\ See Sec.  1037.640.
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Equation II-1: Discounted Vehicle Speed Limiter Equation

VSL input for GEM = Expiration Factor * [Soft Top Factor* Soft Top VSL
+ (1-Soft Top Factor) * VSL] + (1-Expiration Factor)*65 mph
    The agencies will require that the VSL algorithm be designed to
assure that over the useful life of the vehicle that the vehicle will
not operate in the soft top mode for more miles than would be expected
based on the values used in Equation 0-1, as specified by the
expiration factor and the soft top factor. In addition, any time the
cumulative percentage of operation in the soft top mode (based on
miles) exceeds the maximum ratio that could occur at the full lifetime
mileage, or at the expiration mileage if used, the algorithm must not
allow the vehicle to exceed the VSL value. In this case, the soft top
feature remain disabled until the vehicle mileage reaches a point where
the ratio no longer meets this condition.
    In response to the comments about how the agencies will evaluate

tampering, NHTSA and EPA have added a number of requirements in these
final rules relating to the VSL control feature. VSL control features
should be designed so they cannot be easily overridden. Manufacturers
must ensure that the governed speed limit programmed into the VSL must
also be verifiable through on-board diagnostic scanning tools, and must
provide a description of the coding to identify the governed maximum
speed limit and the expiration mileage both at the time of the initial
vehicle certification and in-use. The agencies believe both
manufacturers and fleets should work toward maintaining the integrity
of VSLs, and the agencies may conduct new-vehicle and in-use random
audits to verify that inputs into GEM are accurate.
    The agencies are aware that some fleets/owners make changes to
vehicles, such as installing different diameter tires, changing the
axle (final drive) ratio and transmission gearing, such that a vehicle
could travel at speeds higher than the speed limited by its VSL.
Vehicles subject to FMCSA requirements must be in compliance with 49