It is worth noting that these first three advantages are also beneficial for the marketplace.  In these respects, the separate engine standards allow each manufacturer to be confident that its competitors are playing by the same rules.  The agencies believe that the absence of a separate engine standard would leave open the possibility that a manufacturer might choose to cut corners with respect to in-use compliance margins, the NOx-CO2 tradeoff, or transient controls.  Concerns that competitors might take advantage of this can put a manufacturer in a difficult situation.  On the other hand knowing that the agencies are ensuring all manufacturers are complying fully can eliminate these concerns.
Finally, the existence of meaningful separate engine standards allows the agencies to exempt certain vehicles from some or all of the vehicle standards and requirements without forgoing the engine improvements.  A good example of this is the off-road vehicle exemption in 40 CFR 1037.631 and 49 CFR 535.3(g), which exempts vehicles "intended to be used extensively in off-road environments" from the vehicle requirements.  The engines used in such vehicles must still meet the engine standards of 40 CFR part 1036 and 49 CFR 535.5(d).  The agencies see no reason why efficient engines cannot be used in such vehicles.  However, without separate engine standards, there would be no way to require them to be efficient.
In the past there has been some confusion about the Phase 1 separate engine standards somehow preventing the recognition of engine-vehicle optimization that vehicle manufacturers perform to minimize a vehicle's overall fuel consumption.  It was not the existence of separate engine standards that prevented recognition of this optimization. Rather it was that the agencies did not allow manufacturers to enter inputs into GEM that characterized unique engine performance.  For Phase 2 we are proposing to require that manufacturers input such data because we intend for GEM to recognize this engine-vehicle optimization.  The continuation of separate engine standards in Phase 2 does not undermine in any way the recognition of this optimization in GEM.
The agencies request comment on the advantages and disadvantages of the proposal to maintain separate engine standards and to increase the stringency of the CI engine standards.  We would also welcome suggested alternative approaches that would achieve the same goals.  It is important to emphasize that the agencies see the advantages of separate engine standards as fundamental to the success of the program and do not expect to adopt alternative approaches that fall short of these goals.
Note that commenters opposing separate engine standards should also be careful distinguish between concerns related to the stringency of the proposed engine standards, from concerns inherent to any separate engine standards whatsoever.  When meeting with manufacturers prior to this proposal, the agencies heard many concerns about the potential problems with separate engines standards that were actually concerns about separate engine standards that are too stringent.  However, we see these as two different issues.  The agencies do recognize that setting engine standards at a high stringency could increase the cost to comply with the vehicle standard, if lower-cost vehicle technologies are available.  Additionally, the agencies recognize that setting engine standards at a high stringency may promote the use of large-displacement engines, which have inherent heat transfer and efficiency advantages over smaller displacement engines over the engine test cycles, though a smaller engine may be more efficient for a given vehicle application.  Thus we encourage commenters supporting the separate engine standards to address the possibility of unintended consequences such as these.
Proposed Vehicle Simulation Model  -  Phase II GEM
For tractors and vocational vehicle chassis, the agencies propose that manufacturers would be required to meet vehicle-based standards, and certification to these standards would be facilitated by the required use of the vehicle simulation computer program called, "Greenhouse gas Emissions Model" or "GEM."  GEM was created for Phase 1 for the exclusive purpose of certifying tractors and vocational chassis.  The agencies are proposing to modify GEM and to require vehicle manufacturers to provide additional inputs into GEM to represent the engine, transmission, drive axle(s), and loaded tire radius.  For Phase 1, GEM used agency default values for all of these parameters.  Under the proposed approach for Phase 2, vehicle manufacturers would be able to use these technologies, plus additional technologies to demonstrate compliance with the applicable standards.  The additional technologies include lightweight thermoplastic materials, automatic tire inflation systems, advanced cruise control systems, engine stop-start idle reduction systems, and axle configurations that decrease the number of drive axles to comply with the standards.
Description of the Proposed Modifications to GEM
As explained above, GEM is a computer program that was originally developed by EPA specifically for manufacturers to use to certify to the Phase 1 tractor and vocational chassis standards.  GEM mathematically combines the results of vehicle component test procedures with other vehicle attributes to determine a vehicle's certified levels of fuel consumption and CO2 emissions.  For Phase 1 the required inputs to GEM include vehicle aerodynamics information, tire rolling resistance, and whether or not a vehicle is equipped with certain lightweight high-strength steel or aluminum components, a tamper-proof speed limiter, or tamper-proof idle reduction technologies for tractors.  The vocational vehicle inputs to GEM for Phase 1 only included tire rolling resistance.  For Phase 1 the GEM's inputs did not include engine test results or attributes related to a vehicle's powertrain; namely, its transmission, drive axle(s), or loaded tire radius.  Instead, for Phase 1 the agencies specified a generic engine and powertrain within GEM, and for Phase 1 these cannot be changed in GEM.
For this proposal GEM has been modified and validated against a set of experimental data that represents over 130 unique vehicle variants.  EPA believes this new version of GEM is an accurate and cost-effective alternative to measuring fuel consumption and CO2 over a chassis dynamometer test procedure.  Some of the key proposed modifications would necessitate required and optional vehicle component test procedures to generate additional GEM inputs.  The results of which would provide additional inputs into GEM.  These include a new required engine test procedure to provide steady-state engine fuel consumption and CO2 inputs into GEM.  We are also seeking comment on a newly developed engine test procedure that also captures transient engine performance for use in GEM.  We are proposing to require inputs that describe the vehicle's transmission type, and its number of gears and gear ratios.  We are proposing an optional powertrain test procedure that would provide inputs to override the agencies' simulated engine and transmission in GEM.  We are proposing to require inputs that describe the vehicle's drive axle(s) type (e.g., 6x4 or 6x2) and axle ratio.  We are also seeking comment on an optional axle efficiency test procedure to override the agencies' simulated axle in GEM.  We are proposing to significantly expand the number of technologies that are recognized in GEM.  These include recognizing lightweight thermoplastic materials, automatic tire inflation systems, advanced cruise control systems, engine stop-start idle reduction systems, and axle configurations that decrease the number of drive axles.  We are seeking comment on recognizing (outside of the GEM simulation) additional technologies such as high efficiency glass and low global warming potential air conditioning refrigerants. To better reflect real-world operation, we are also proposing to revise the vehicle simulation computer program's urban and rural highway duty cycles to include changes in road grade.  We are seeking comment on whether or not these duty cycles should also simulate driver behavior in response to varying traffic patterns.  We are proposing a new duty cycle to capture the performance of technologies that reduce the amount of time a vehicle's engine is at idle during a workday when the vehicle is not moving.  And to better recognize that vocational vehicle powertrains are configured for particular applications, we are proposing to further subdivide the vocational chassis category into three different vehicle speed categories, where GEM weights the individual duty cycles' results of each of the speed categories differently  Section 4.2 of the RIA details all these modifications.  This section briefly describes some of the key proposed modifications to GEM.
    Simulating Engines for Vehicle Certification
Before describing the proposed approach for Phase 2, this section first reviews how engines are simulated for vehicle certification in Phase 1.  GEM for Phase 1 simulates the same generic engine for any vehicle in a given regulatory sub-category with a data table of steady-state engine fuel consumption mass rates (g/s) versus a series of steady-state engine output shaft speeds (revolutions per minute, rpm) and loads (torque, N-m).  This data table is also sometimes called a "fuel map" or an "engine map", although the term "engine map" can mean other kinds of data in different contexts.  The engine speeds in this map range from idle to maximum governed speed and the loads range from engine motoring (negative load) to the maximum load of an engine.  When GEM runs over a vehicle duty cycle, this data table is linearly interpolated to find a corresponding fuel consumption mass rate at each engine speed and load that is demanded by the simulated vehicle operating over the duty cycle.  The fuel consumption mass rate of the engine is then integrated over each duty cycle in GEM to arrive at the total mass of fuel consumed for the specific vehicle and duty cycle. Under Phase 1, manufacturers were not allowed to input their own engine fuel maps to represent their specific engines in the vehicle being simulated in GEM.  Because GEM was programmed with fixed engine fuel maps for Phase 1 that all manufacturers had to use, interpolation of the tables themselves over each of the three different GEM duty cycles did not have to closely represent how an actual engine might operate over these three different duty cycles.
In contrast, for Phase 2 we are proposing a new and required steady-state engine dynamometer test procedure for manufacturers to use to generate their own engine fuel maps to represent each of their engine families in GEM.  The proposed Phase 2 approach is consistent with the 2014 NAS Phase 2 First Report recommendation.  To validate this approach we compared the results from 28 individual engine dynamometer tests.  Three different engines were used to generate this data, and these engines were produced by two different engine manufacturers.  One engine was tested at three different power ratings (13 liters at 410, 450 & 475 hp) and one engine was tested at two ratings  (6.7 liters  at 240 and 300 hp), and other engine with one rating (15 liters 455 hp) service classes.  For each engine and rating our proposed steady-state engine dynamometer test procedure was conducted to generate an engine fuel map to represent that particular engine in GEM.  Next, with GEM we simulated various vehicles in which the engine could be installed.  For each of the GEM duty cycles we are proposing, namely the urban local (ARB Transient), urban highway with road grade (55 mph), and rural highway with road grade (65 mph) duty cycles, we determined the GEM result for each vehicle configuration, and we saved the engine output shaft speed and torque information that GEM created to interpolate the steady-state engine map for each vehicle configuration  We then had this same engine output shaft speed and torque information programmed into an engine dynamometer controller, and we had each engine perform the same duty cycles that GEM demanded of the simulated version of the engine.  We then compared the GEM results based on GEM's linear interpolation of the engine maps to the measured engine dynamometer results.  We concluded that for the 55 mph and 65 mph duty cycles, GEM's interpolation of the steady-state data tables was sufficiently accurate versus the measured results.  This is an outcome one would reasonably expect because even with changes in road grade, the 55 mph and 65 mph duty cycles do not demand rapid changes in engine speed or load.  The 55 mph and 65 mph duty cycles are nearly steady-state, as far as engine operation is concerned, just like the engine maps themselves.  However, for the ARB Transient cycle, we observed a consistent bias, where GEM consistently under-predicted fuel consumption and CO2 emissions.  This low bias over the 28 engine tests ranged from 4.2 percent low to 7.8 percent low.  The mean was 5.9 percent low and the 90[th] percentile value was 7.1 percent low.  These observations are consistent with the fact that engines generally operate less efficiently under transient conditions than under steady-state conditions.
A number of reasons explain this consistent trend.  For example, under rapidly changing engine conditions, it is generally more challenging to program an engine electronic controller to respond with optimum fuel injection rate and timing, exhaust gas recirculation valve position, variable nozzle turbo-charger vane position and other set points than it is to do so under steady-state conditions.  Transient heat and mass transfer within the intake, exhaust, and combustion chambers also tend to increase turbulence and enhance energy loss to engine coolant during transient operation.  Furthermore, because exhaust emissions control is more challenging under transient engine operation, engineering tradeoffs sometimes need to be made between fuel efficiency and transient emissions control.  Special calibrations are typically also required to control smoke and manage exhaust temperatures during transient operation for a transient cycle.  We are confident that this low bias in GEM would continue to exist well into the future if we were to test additional engines.  However, with the range of the results that we have generated so far we are somewhat less confident in proposing a single numerical value to correct for this effect over the ARB Transient duty cycle.  Based on the data we have collected so far, we are conservatively proposing to apply a 5.0 percent correction factor to GEM's ARB Transient results.  Note that adjustment would be applied internal to GEM, and no manufacturer input or action would be needed.  This means that for GEM fuel consumption and CO2 emissions results that were generated using the steady-state engine map representation of an engine in GEM, a 1.05 multiplier would be applied to only the ARB Transient result.  If a manufacturer chooses to perform the optional powertrain test procedure we are proposing, then this 1.05 multiplier to the ARB Transient would not apply (since we know of no bias in that optional powertrain test).  For the same reason, if we were to replace the proposed steady-state engine map in GEM with the alternative approach detailed in draft RIA Appendix A, then this 1.05 multiplier would not apply.  We request comment on whether or not this single value multiplier is an appropriate way to correct between steady-state and transient engine fuel consumption and CO2 emissions, specifically over the ARB Transient duty cycle.  We also request comment on the magnitude of the multiplier itself.  For example, for the proposal we have chosen a 1.05 multiplier correction value because it is conservative but still near the mean bias we observed.  However, for the tests we have conducted on current technology engines, a 1.05 multiplier would mean that about one half of these engines would be penalized by powertrain testing (or if we utilized the alternative engine approach in Appendix A) because the actual measured transient impact would be slightly higher than 5 percent.  While these tests were performed on current technology powertrains rather than the kind of optimized powertrains we project for Phase 2, these results raise still some concerns for us.  Because we intend to incentivize powertrain testing and not penalize it, and because we also encourage constructive comments on the alternative approach in Appendix A, we also request comment on increasing the magnitude of this ARB Transient multiplier toward the higher end of the biases we observed.  For example, we request comment on increasing the proposed multiplier from 1.05 to 1.07, which is close to the 90[th] percentile of the results we have collected so far.  Using this higher multiplier would imply that only about 10 percent of engines powertrain tested or tested under the alternative approach in Appendix A would show worse fuel consumption over the ARB Transient than its respective representation in a steady-state data table in GEM.  This would mean that the remaining 90 percent of engines powertrain tested would receive additional credit in GEM.  Using 1.07 would essentially guarantee that any powertrain that was significantly more efficient than current powertrains would receive meaningful credit for the improvement.  However, this value would also provide credits for many current powertrain designs.
We also request comment as to whether or not there might be certain vehicle sub-categories or certain small volume vocational chassis, where using the Phase 1 approach of using a generic engine table might be more appropriate.  We also request comment as to whether or not the agencies should provide default generic engine maps in GEM for Phase 2 and allow manufacturers to optionally override these generic maps with their own maps, which would be generated according to our proposed engine dynamometer steady-state test procedure.
    Simulating Human Driver Behavior and Transmissions for Vehicle Certification
GEM for Phase 1 simulates the same generic human driver behavior and manual transmission for all vehicles.  The simulated driver responds to changes in the target vehicle speed of the duty cycles by changing the simulated positions of the vehicle's accelerator pedal, brake pedal, clutch pedal, and gear shift lever.  For simplicity in Phase 1 the GEM driver shifted at ideal points for maximum fuel efficiency and the manual transmission was simulated as an ideal transmission that did not have any delay time (i.e., torque interruption) between gear shifts and did not have any energy losses associated with clutch slip during gear shifts.
In GEM for Phase 2 we are proposing to allow manufacturers to select one of three types of transmissions to represent the transmission in the vehicle they are certifying: manual transmission, automated manual transmission, and automatic transmission.  We are currently in the process of developing a dual-clutch transmission type in GEM, but we are not proposing to allow its use in Phase 2 at this time.  Because production of heavy-duty dual clutch transmissions has only begun in the past few months, we do not yet have any experimental data to validate our GEM simulation of this transmission type.  Therefore, we are requesting comment on whether or not there is additional data available for such validation.  Should such data be provided in comments, we may finalize GEM for Phase 2 with a fourth transmission types for dual clutch transmissions. We are also considering an option to address dual clutch transmissions through a post-simulation adjustment as discussed in Chapter 4 of the draft RIA.
In the proposed modifications to GEM, the driver behavior and the three different transmission types are simulated in the same basic manner as in Phase 1, but each transmission type features a unique combination of driver behavior and transmission responses that match both the driver behavior and the transmission responses we measured during vehicle testing of these three transmission types.  In general the transmission gear shifting strategy for all of the transmissions is designed to shift the transmission so that it is always in the most efficient gear for the current vehicle demand, while staying within certain limits to prevent unrealistically high frequency shifting.  Some examples of these limits are torque reserve limits (which vary as function of engine speed), minimum time-in-gear and minimum fuel efficiency benefit to shift to the next gear.  Some of the differences between the three transmission types include a driver "double-clutching" during gear shifts of the manual transmission only, and "power shifts" and torque converter torque multiplication, slip, and lock-up in automatic transmissions only.  Refer to Chapter 4 of the draft RIA for a more detailed description of these different simulated driver behaviors and transmission types.
We considered an alternative approach where transmission manufacturers would provide vehicle manufacturers with detailed information about their automated transmissions' proprietary shift strategies for representation in GEM.  NAS also recommended this approach.  The advantages of this approach include a more realistic representation of a transmission in GEM and potentially the recognition of additional fuel efficiency improving strategies to achieve additional fuel consumption and CO2 emissions reductions.  However, there are a number of technical and policy disadvantages of this approach.  One disadvantage is that it would require the disclosure of proprietary information between competing companies because some vehicle manufacturers produce their own transmissions and also use other suppliers' transmissions. There are technical challenges too.  For example, some transmission manufacturers have upwards of 40 different shift strategies programmed into their transmission controllers.  Depending on in-use driving conditions, some of which are not simulated in GEM (e.g., changing payloads, changing tire traction) a transmission controller can change its shift strategy.  Representing dynamic switching between multiple proprietary shift strategies would be extremely complex to simulate in GEM.  Furthermore, if the agencies were to propose requiring transmission manufacturers to provide shift strategy inputs for use in GEM, then the agencies would have to devise a compliance strategy to monitor in-use shift strategies, including a driver behavior model that could be implemented as part of an in-use shift strategy test.  This too would be very complex.  If manufacturers were subject to in-use compliance requirements of their transmission shift strategies, this could lead to restricting the use of certain shift strategies in the heavy-duty sector, which would in turn potentially lead to sub-optimal vehicle configurations that do not improve fuel efficiency or adequately serve the wide range of customer needs; especially in the vocational vehicle segment.  For example, if the agencies were to restrict the use of more aggressive and less fuel efficient in-use shift strategies that are used only under heavy loads and steep grades, then certain vehicle applications would need to compensate for this loss of capability through the installation of over-sized and over-powered engines that are subsequently poorly matched and less efficient under lighter load conditions.  Therefore, as a policy consideration to preserve vehicle configuration choice and to preserve the full capability of heavy-duty vehicles today, the agencies are intentionally not requiring transmission manufacturers to submit detailed proprietary shift strategy information to vehicle manufacturers to input into GEM.  This is not unlike Phase 1, where unique transmission and axle attributes were not recognized at all in GEM.  Instead, the agencies are proposing that vehicle manufacturers choose from among the three transmission types that the agencies have already developed, validated, and programmed into GEM.  The vehicle manufacturers would then enter into GEM their particular transmission's number of gears and gear ratios.  The agencies recognize that designing GEM like this would exclude a potentially significant reduction from the GEM simulation.  However, if a manufacturer chooses to use the optional powertrain test procedure, then the agencies' transmission types in GEM would be overridden by the actual data collected during the powertrain test, which would recognize the actual benefit of the transmission.  Note that the optional powertrain test procedure is only advantageous to a vehicle manufacturer if an actual transmission is more efficient and has a superior shift strategy compared to its respective transmission type simulated in GEM.
    Simulating Axles for Vehicle Certification
In GEM for Phase 1 the axle ratio of the primary drive axle and the energy losses assumed in the simulated axle itself were the same for all vehicles.  For Phase 2 we are proposing that the vehicle manufacturer input into GEM the axle ratio of the primary drive axle.  This input would recognize the intent to operate the engine at a particular engine speed when the transmission is operating in its highest transmission gear; especially for the 55 mph and 65 mph duty cycles in GEM.  This input facilitates GEM's recognition of vehicle designs that take advantage of operating the engine at the lowest possible engine speeds.  This is commonly known as "engine down-speeding", and the general rule-of-thumb for heavy-duty engines is that for every 100 rpm decrease in engine speed, there can be about a 1 percent decrease in fuel consumption and CO2 emissions.  Therefore, it is important that GEM allow this value to be input by the vehicle manufacturer.  Axle ratio is also straightforward to verify during any in-use compliance audit.
We are proposing a fixed axle ratio energy efficiency of 95.5 percent at all speeds and loads, but are requesting comment on whether this pre-specified efficiency is reasonable.  However, we know that this efficiency actually varies as a function of axle speed and axle input torque.  Therefore, as an exploratory test we have created a modified version of GEM that has as an input a data table of axle efficiency as a function of axle speed and axle torque.  The modified version of GEM subsequently interpolates this table over each of the duty cycles to represent a more realistic axle efficiency at each point of each duty cycle.  We have also created a draft axle ratio efficiency test procedure that requires the use of a dynamometer test facility.  The draft test procedure includes initial feedback that we have received from axle manufacturers and our own engineering judgment.  Refer to 40 CFR 1037.515 of the Phase 2 proposed regulations, which contain this draft test procedure.  This test procedure could be used to generate the results needed to create the axle efficiency data table for input into GEM.  However, the agencies have not yet conducted experimental tests of axles using this draft test procedure so we are reluctant to propose this test procedure as either mandatory or even optional at this time.  Rather we request comment as to whether or not we should finalize this test procedure and either require its use or allow its use optionally to determine an axle efficiency data table as an input to GEM, which would override the fixed axle efficiency we are proposing at this time.  We also request comment on improving or otherwise refining the test procedure itself.  Note that the agencies believe that allowing the GEM default axle efficiency to be replaced by manufacturer inputs only makes sense if the manufacturer inputs is are the results of a specified test procedure that we could verify by our own independent testing of the axle.
In addition to proposing to require the primary drive axle ratio input into GEM (and potentially  an option to input an actual axle efficiency data table), we are also proposing that the vehicle manufacturer input into GEM whether or not one or two drive axles are driven by the engine.  When a heavy-duty vehicle is equipped with two rear axles where both are driven by the engine, this is called a "6x4" configuration.  "6" refers to the total number of wheel hubs on the vehicle.  In the 6x4 configuration there are two front wheel hubs for the two steer wheels and tires plus four rear wheel hubs for the four rear wheels and tires (or more commonly four sets of rear dual wheels and tires). "4" refers to the number of wheel hubs driven by the engine.  These are the two rear axles that have two wheel hubs each.  Compared to a 6x4 configuration a 6x2 configuration decreases axle energy loss due to friction and oil pumping in two driven axles, by driving only one axle.  The decrease in fuel consumption and CO2 emissions associated with a 6x2 versus 6x4 axle configuration is estimated to be 2.5 percent.   Therefore, in the proposed Phase 2 version of GEM, if a manufacturer simulates a 6x2 axle configuration, GEM decreases the overall GEM result by 2.5 percent.  Note that GEM will similarly decrease the overall GEM result by 2.5 percent for a 4x2 tractor or Class 8 vocational chassis configuration if it has only two wheel hubs driven.  Note that we are not proposing that GEM have an option to increase the overall GEM result by some percentage by selecting, say, a 6x6 or 8x8 option if the front axle(s) are driven.  Because these configurations are only manufactured for specialized vehicles that require extra traction for off-road applications, they are very low volume sales and their increased fuel consumption and CO2 emissions are not significant in comparison to the overall reductions of the proposed Phase 2 program.  Note that 40 CFR 1037.631 (for off-road vocational vehicles), which is being continued from the Phase 1 program, would likely exempt many of these vehicles from the vehicle standards.
Instead of directly modeling 6x4 or 6x2 axle configuration,  we are proposing use of a post-simulation adjustment approach discussed in Chapter 4 of the drat RIA to model benefits of different axle configuration.
    Simulating Accessories for Vehicle Certification
Phase 1 GEM uses a fixed power consumption value to simulate the fuel consumed for powering accessories such as power steering pumps and alternators.  While the agencies are not proposing any changes to this approach for Phase 2, we are requesting comment on whether or not we should allow some manufacturer input to reflect the installation of accessory components that result in lower accessory loads.  For example, we could consider an accessory load reduction GEM input based on installing a number of qualifying advanced accessory components that could be in production during Phase 2.  We request comment on identifying such advanced accessory components, and we request comment on defining these components in such a way that they can be unambiguously distinguished from other similar components that do not decrease accessory loads.  We also request comment on how much of a decrease in accessory load should be programmed into GEM if qualifying advanced accessory components are installed.
    Aerodynamics for Tractor, Vocational Vehicle, and Trailer Certification
For GEM in Phase 2 the agencies propose to simulate aerodynamic drag in largely the same manner as in Phase 1.  For vocational chassis we propose to continue to use the same prescribed products of drag coefficient times vehicle frontal area (Cd*A) that were predefined for each of the vocational subcategories in Phase 1.  For tractors we propose to continue to use an aerodynamic bin approach similar to the one that exists in Phase 1 today.  This approach requires tractor manufacturers to conduct a certain amount of coast-down vehicle testing, although manufacturers have the option to conduct scaled wind tunnel testing and/or computational fluid dynamics modeling.  The results of these tests determine into which bin a vehicle is assigned.  Then in GEM the aerodynamic drag coefficient for each vehicle in the same bin is the same.  This approach helps to account for limits in the repeatability of aerodynamic testing and it creates a compliance margin since any test result which keeps the vehicle in the same aerodynamic bin is considered compliant.   However, for Phase 2 we are proposing new boundary values for the bins themselves and we are adding two additional bins in order to recognize further advances in aerodynamic drag reduction beyond what was recognized in Phase 1.  Furthermore, while Phase 1 GEM used predefined frontal areas for tractors while the manufacturers input a Cd value, the agencies propose that manufacturers would use a measured frontal area value for each tractor configuration for Phase 2.  See 40 CFR 1037.521.
In addition to these proposed changes we are proposing a number of aerodynamic drag test procedure improvements.  One proposed improvement is to update the so-called standard trailer that is prescribed for use during aerodynamic drag testing of a tractor  -  that is, the hypothetical trailer modeled in GEM to represent a trailer paired with the tractor in actual use.  In Phase 1 a non-aerodynamic 53-foot long box-shaped dry van trailer was specified as the standard trailer for tractor aerodynamic testing (see 40 CFR 1037.501(g)).  For Phase 2 we are proposing to modify this standard trailer for tractor testing to make it more similar to the trailers we would require to be produced during the Phase 2 timeframe.  More specifically, we would prescribe the installation of aerodynamic trailer skirts and low rolling resistance tires on the reference trailer, as discussed in further in Section III.E.2.  As explained more fully in Sections III and IV below, the agencies believe that tractor-trailer pairings will be optimized aerodynamically to a significant extent in-use (such as using high-roof cabs when pulling box trailers), and that this real-world optimization should be reflected in the certification testing.  We also request comment on whether or not the Phase 2 standard trailer should include the installation of other aerodynamic devices such as a nose fairing, an under tray, or a boat tail or trailer tail.  Would a standard trailer including these additional components make the tractor program better?
Another proposed aerodynamic test procedure improvement is intended to better account for average wind yaw angle to better reflect the true impact of aerodynamic features on the in-use fuel consumption and CO2 emissions of tractors.  Refer to the proposed test procedures in 40 CFR 1037.521 for further details of these aerodynamic test procedures.
For GEM in Phase 2 the agencies are proposing to use GEM for trailer certification in much the same way that GEM is used for tractor certification in Phase 1.  However, the only technologies recognized by GEM for trailer certification are aerodynamic technologies, tire technologies (including tire rolling resistance and automatic tire inflation systems), and some weight reduction technologies.  Similar to tractor certification, we propose that trailer manufacturers may at their option conduct some amount of aerodynamic testing (e.g., coast-down testing, scale wind tunnel testing, computational fluid dynamics modeling, or possibly aerodynamic component testing) and use this information in GEM.  In this case the agencies propose the configuration of a reference tractor for conducting trailer testing.  Refer to Section IV of this preamble and to 40 CFR 1037.501 of the proposed regulations for details on the proposed reference tractor configuration for trailer test procedures.  Note that for trailers we are proposing a simplified interim certification option that would not require conducting aerodynamic testing of a complete trailer or the use of GEM.  Complete trailer testing and use of GEM would be an option that trailer manufacturers could elect to use during the phase-in period if they determined that the GEM approach would allow their trailer technologies to be better recognized as compared to the proposed simplified trailer certification approach.
     Tires and Tire Inflation Systems for Truck and Trailer Certification
    	For GEM in Phase 1 vehicle manufacturers input the tire rolling resistance of steer and drive tires directly into GEM.  The agencies prescribed an internationally recognized tire rolling resistance test procedure, ISO 28580, for determining the tire rolling resistance value that is input into GEM, as described in 40 CFR 1037.520(c).  For Phase 2 we are proposing to continue this same approach and the use of ISO 28580, and we propose to expand these requirements to trailer tires as well.  We request comment on whether specific modifications to this test procedure would improve its accuracy, repeatability or its test lab to test lab variability.
    In addition to tire rolling resistance, we are proposing that for Phase 2 vehicle manufacturers enter into GEM the tire manufacturer's specified tire loaded radius for the vehicle's drive tires.  This value is commonly reported by tire manufacturers already so that vehicle speedometers can be adjusted appropriately.  This input value is needed so that GEM can accurately convert simulated vehicle speed into axle speed, transmission speed, and ultimately engine speed.
    For tractors and trailers, we propose to allow manufacturers to specify whether or not an automatic tire inflation system is installed.  If one is installed, GEM would assign a 1 percent decrease in the overall fuel consumption and CO2 emissions simulation results for tractors, and a 1.5 percent decrease for trailers.  This would be done through post-simulation adjustments discussed in Chapter 4 of the draft RIA.  In contrast, we are not proposing to assign any decrease in fuel consumption and CO2 emissions for tire pressure monitoring systems.  We do recognize that some drivers would respond to a warning indication from a tire pressure monitoring system, but we are unsure how to assign a fixed decrease in fuel consumption and CO2 emissions for tire pressure monitoring systems.  We would estimate that the value would be less than any value we would assign for an automatic tire inflation system.  We request comment on whether or not we should assign a fixed decrease in fuel consumption and CO2 emissions for tire pressure monitoring systems, and if so, we request comment on what would be an appropriate assigned fixed value.
    Weight Reduction for Tractor, Vocational Chassis and Trailer Certification
We propose for Phase 2 that GEM continues the weight reduction recognition approach in Phase 1, where the agencies prescribe fixed weight reductions, or "deltas", for using certain lightweight materials for certain vehicle components.  In Phase 1 the agencies published a list of weight reductions for using high-strength steel and aluminum materials on a part by part basis.  For Phase 2 we propose to use these same values for high-strength steel and aluminum parts for tractors and for trailers and we have scaled these values for use in certifying the different weight classes of vocational chassis.  In addition we are proposing a similar part by part weight reduction list for tractor parts made from thermoplastic material.  We are also proposing to assign a fixed weight increase to natural gas fueled vehicles, scaled by vehicle weight class, to reflect the weight increase of natural gas fuel tanks versus gasoline or diesel tanks.  For tractors we are proposing to continue the same mathematical approach in GEM to assign 1/3 of a total weight decrease to a payload increase and 2/3 of the total weight decrease to a vehicle mass decrease.  For Phase 1 these ratios were based on the average frequency that a tractor operates at its gross combined weight rating.  Therefore, we propose to use these ratios for trailers in Phase 2.  For vocational chassis, for which Phase 1 did not address weight reduction, we propose a 50/50 ratio.  In other words, for vocational chassis in GEM we propose to assign 1/2 of a total weight decrease to a payload increase and 1/2 of the total weight decrease to a vehicle mass decrease.  We request comment on whether or not this 50/50 ratio is appropriate for vocational chassis.
    GEM Duty Cycles for Tractor, Vocational Chassis and Trailer Certification
In Phase 1, there are three GEM vehicle duty cycles that represented stop-and-go city driving (ARB Transient), urban highway driving (55 mph), and rural interstate highway driving (65 mph).  In Phase 1 these cycles were time-based.  That is, they were specified as a function of simulated time and the duty cycles ended once the specified time elapsed in simulation.  The agencies propose to use these three drive cycles in Phase 2, but with some revisions.  First the agencies propose that GEM would simulate these cycles on a distance-based specification, rather than on a time-based specification.  A distance-based specification ensures that even if a vehicle in simulation does not always achieve the target vehicle speed, the vehicle will have to continue in simulation for a longer period of time to complete the duty cycle.  This ensures that vehicles are evaluated over the complete distance of the duty cycle and not just the portion of the duty cycle that a vehicle completes in a given time period.  A distance-based duty cycle specification also facilitates a straightforward specification of road grade as a function of distance along the duty cycle.  For Phase 2 the agencies are proposing to enhance the 55 mph and 65 mph duty cycles by adding representative road grade to exercise the simulated vehicle's engine, transmission, axle, and tires in a more realistic way.  A flat road grade profile over a constant speed test does not present many opportunities for a transmission to shift gears, and may have the unintended consequence of enabling underpowered vehicles or excessively downsped drivetrains to generate credits.  The road grade profile proposed is the same for both the 55 mph and 65 mph duty cycles, and the profile was based on real over-the-road testing the agencies directed under an agency-funded contract with Southwest Research Institute.  See Section III.E for more details on development of the proposed road grade profile.  The agencies are continuing to evaluate alternate road grade profiles including actual sections of restricted access highway with road grades that are statistically similar to the national road grade profile as well as purely synthetic road grade profiles.  We request comments on the proposed road grade profile, and would welcome additional statistical evaluations of this road grade profile and other road grade profiles for comparison.  We believe that the enhancement of the 55 mph and 65 mph duty cycles with road grade is consistent with the NAS recommendation regarding road grade.
We recognize that even with the proposed road grade profile, GEM may continue to under predict the number of transmission shifts of vehicles on restricted access highways if the model simulates constant speeds.  We request comment on other ways in which the proposed 55 mph and 65 mph duty cycles could be enhanced.  For example, we request comment on whether a more aggressive road grade profile would induce a more realistic and representative number of transmission gear shifts.  We also request comment on whether we should consider varying the vehicle target speed over the 55 mph and/or 65 mph duty cycles to simulate human driver behavior reacting to traffic congestion.  This would increase the number of shifts during the 55 mph and 65 mph duty cycles, though it may be possible for an equivalent effect to be achieved by assigning a greater weighting to the transient cycle in the GEM composite test score.

    Workday Idle Operation for Vocational Vehicle Certification
In the Phase 1 program, reduction in idle emissions was recognized only for sleeper cab tractors, and only with respect to hotelling idle, where a driver needs power to operate heating, ventilation, air conditioning and other electrical equipment in order to use the sleeper cab to eat, rest, or conduct other business.  As described in Section V, the agencies are now proposing to recognize in GEM technologies that reduce workday idle emissions, such as automatic stop-start systems and automatic transmissions that shift to neutral at idle.  Many vocational vehicle applications operate on patterns implicating workday idle cycles, and the agencies are proposing test procedures in GEM to account specifically for these cycles and potential controls.  GEM would recognize these idle controls in two ways.  For technologies like neutral-idle that address idle that occurs during the transient cycle (representing the type of operation that would occur when the vehicle is stopped at a stop light), GEM would interpolate lower fuel rates from the engine map.  For technologies like start-stop and auto-shutdown that eliminate some of the idle that occurs when a vehicle is stopped or parked, GEM would assign a value of zero fuel rate for what we are proposing as an "idle cycle".  This idle cycle would be weighted along with the 65 mph, 55 mph, and ARB Transient duty cycles according to the vocational chassis duty cycle weighting factors that we are proposing for Phase 2.  These weighting factors are different for each of the three vocational chassis speed categories that we are proposing for Phase 2.  While we are not proposing to apply this idle cycle for tractors, we do request comment on whether or not we should consider a applying this idle cycle to certain tractor types, like day cabs that could experience more significant amounts of time stopped or parked as part of an urban delivery route.  We also request comment on whether or not start-stop or auto-shutdown technologies are being developed for tractors; especially for Class 7 and 8 day cabs that could experience more frequent stops and more time parked for deliveries.
Validation of the Proposed GEM
     After making the proposed changes to GEM, the agencies validated the model in comparison to over 130 vehicle variants, consistent with the recommendation made by the NAS in their Phase 2-First Report.  As is described in Chapter 4 of the Draft RIA, good agreement was observed between GEM simulations and test data over a wide range of vehicles.  In general, the model simulations agreed with the test results within +-5 percent on an absolute basis.  As pointed out in Chapter 4.3.2 of the RIA, relative accuracy is more relevant to this rulemaking.  This is because all of the numeric standards proposed for tractors, trailers and vocational chassis are derived from running GEM first with Phase 1 "baseline" technology packages and then with various candidate Phase 2 technology packages.  The differences between these GEM results are examined to select stringencies.  In other words, the agencies used the same version of GEM to establish the standards as was used to evaluate baseline performance for this rulemaking.  Therefore, it is most important that GEM accurately reflects relative changes in emissions for each added technology.  For vehicle certification purposes it is less important that GEM's absolute value of the fuel consumption or CO2 emissions are accurate compared to laboratory testing of the same vehicle.  The ultimate purpose of this new version of GEM will be to evaluate changes or additions in technology, and compliance is demonstrated on a relative basis to the numerically standards that were also derived from GEM.  Nevertheless, the agencies concluded that the absolute accuracy of GEM is generally within +-5 percent, as shown in Figure II-1.  Chapter 4.3.2 of the draft RIA shows that relative accuracy is even better, +-2-3 percent.

Figure II-1: GEM Validation Data
In addition to this successful validation against experimental results, the agencies have also initiated a peer review of the proposed GEM source code.  This peer review has been submitted to Docket # EPA-HQ-OAR-2014-0827.
Supplements to GEM Simulation
As in Phase 1, for most tractors and vocational vehicles, compliance with the Phase 2 g/ton-mile vehicle standards could be evaluated by directly comparing the GEM result to the standard.  However, in Phase 1, manufacturers incorporating innovative or advanced technologies could apply improvement factors to lower the GEM result slightly before comparing to the standard.  For example, a manufacturer incorporating a launch-assist mild hybrid that was approved for a 5 percent benefit would apply a 0.95 improvement factor to its GEM results for such vehicles.  In this example, a GEM result of 300 g/ton-mile would be reduced to 285 g/ton- mile.
For Phase 2, the agencies are proposing to largely continue the existing Phase 1 innovative technology approach.  We are also proposing to create a parallel option specifically related to innovative powertrain designs.  These proposals are discussed below.
    Innovative/Off-Cycle Technology Procedures
In Phase 1 the agencies adopted an emissions credit generating opportunity that applied to new and innovative technologies that reduce fuel consumption and CO2 emissions, that were not in common use with heavy-duty vehicles before model year 2010 and are not reflected over the test procedures or GEM (i.e., the benefits are "off-cycle").  See 76 FR at 57253.  As was the case in the development of Phase 1, the agencies are proposing to continue this approach for technologies and concepts with CO2 emissions and fuel consumption reduction potential that might not be adequately captured over the proposed Phase 2 duty cycles or are not proposed inputs to GEM.  Note, however, that the agencies are proposing to refer to these technologies as off-cycle rather than innovative.  See Section I for more discussion of innovative and off-cycle technologies.
We recognize that the Phase 1 testing burden associated with the innovative technology credit provisions discouraged some manufacturers from applying.  To streamline recognition of many technologies, default values have been integrated directly into GEM.  For example, automatic tire inflation systems and 6x2 axles both have fixed default values, recognized through a post-simulation adjustment approach discussed in Chapter 4 of the draft RIA.  This is similar to the technology "pick list" from our light-duty programs.  See 77 FR at 62833-35 (Oct. 15, 2012).  If manufacturers wish to receive additional credit beyond these fixed values, then the innovative/off-cycle technology credit provisions would provide the regulatory path toward that additional recognition.
Beyond the additional technologies that the agencies have added to GEM, the agencies also believe there are several emerging technologies that are being developed today, but would not be accounted for in GEM as we are proposing it because we do not have enough information about these technologies to assign fixed values to them in GEM.  Any credits for these technologies would need to be based on the off-cycle technology credit generation provisions.  These require the assessment of real-world fuel consumption and GHG reductions that can be measured with verifiable test methods using representative operating conditions typical of the engine or vehicle application.
As in Phase 1, the agencies are proposing to continue to provide two paths for approval of the test procedure to measure the CO2 emissions and fuel consumption reductions of an off-cycle technology used in the HD tractor.  See 40 CFR 1037.610 and 49 CFR 535.7.  The first path would not require a public approval process of the test method.  A manufacturer can use "pre-approved" test methods for HD vehicles including the A-to-B chassis testing, powerpack testing or on-road testing.  A manufacturer may also use any developed test procedure which has known quantifiable benefits.  A test plan detailing the testing methodology is required to be approved prior to collecting any test data.  The agencies are also proposing to continue the second path which includes a public approval process of any testing method which could have questionable benefits (i.e., an unknown usage rate for a technology).  Furthermore, the agencies are proposing to modify its provisions to better clarify the documentation required to be submitted for approval aligning them with provisions in 40 CFR 86-1869-12 and NHTSA is separately proposing to prohibit credits from technologies addressed by any of its crash avoidance safety rulemakings (i.e., congestion management systems).  We welcome recommendations on how to improve or streamline the off-cycle technology approval process.
  Sections III and V describe tractor and vocational vehicle technologies, respectively, that the agencies anticipate may qualify for these off-cycle credit provisions.
    Powertrain Testing
The agencies are proposing a powertrain test option to allow for a robust way to quantify the benefits of CO2 reducing technologies that are a part of the powertrain (conventional or hybrid) that are not captured in the GEM simulation.  Powertrain testing and certification was included as one of the NAS recommendations in the Phase 2  - First Report.  Some of these improvements are transient fuel control, engine and transmission control integration and hybrid systems.  To limit the amount of testing, the powertrain would be divided into families and powertrains would be tested in a limited number of simulated vehicles that cover the range of vehicles in which the powertrain would be installed.  The powertrain test results would then be used to override the engine and transmission simulation portion of GEM.
The largest proposed change from the Phase 1 powertrain procedure is that only the advanced powertrain would need to be tested (as opposed to the Phase 1 requirement where both the advanced powertrain and the conventional powertrain had to be tested).  This change is possible because the proposed GEM simulation uses the engine fuel map and torque curve from the actual engine in the vehicle to be certified.  For the powertrain results to be used broadly across all the vehicles that the powertrain would go into, a matrix of 8 to 9 tests would be needed per vehicle cycle.  These tests would cover the range of coefficient of drag, coefficient of rolling resistance, vehicle mass and axle ratio of the vehicles that the powertrain will be installed in.  The main output of this matrix of tests would be CO2 per positive work measured at the output of the transmission as a function of positive work and average transmission output speed over average vehicle speed.  This matrix of test results would then be used to calculate the vehicle's CO2 emissions by taking the work per ton-mile from the GEM simulation and multiplying it by the interpolated work specific CO2 mass emissions from the powertrain test.
Along with proposing changes to how the powertrain results are used, the agencies are also proposing changes to the procedures that describe how to carry out a powertrain test.  The changes are to give additional guidance on controlling the temperature of the powertrains intake-air, oil, coolant, block, head, transmission, battery, and power electronics so that they are within their expected ranges for normal operation.  The equations that describe the vehicle model are proposed to be changed to allow for input of the axle's efficiency, driveline rotational inertia, as well as the mechanical and electrical accessory loads.
Production Vehicle Testing for Comparison to GEM
The agencies are is proposing to require tractor and vocational vehicle manufacturers to annually chassis test 5 production vehicles over the GEM cycles to verify that relative reductions simulated in GEM are being achieved in actual production.  See 40 CFR 1037.665.  We would not expect absolute correlation between GEM results and chassis testing.  GEM makes many simplifying assumptions that do not compromise its usefulness for certification, but do cause it to produce emission rates different from what would be measured during a chassis dynamometer test.  Given the limits of correlation possible between GEM and chassis testing, we would not expect such testing to accurately reflect whether a vehicle was compliant with the GEM standards.  Therefore, we are proposing to not apply compliance liability to such testing.  Rather, this testing would be for informational purposes only.  However, we do expect there to be correlation in a relative sense.  Vehicle to vehicle differences showing a 10 percent improvement in GEM should show a similar percent improvement with chassis dynamometer testing.  Nevertheless, manufacturers would not be subject to recall or other compliance actions if chassis testing did not agree with the GEM results on a relative basis.  Rather, the agencies would continue evaluate in-use compliance by verifying GEM inputs and testing in-use engines.
EPA believes this chassis test program is necessary because of our experience implementing regulations for heavy-duty engines.  In the past, manufacturers have designed engines that have much lower emissions on the duty cycles than occur during actual use.  By proposing this simple test program, we hope to be able to identify such issues earlier and to dissuade any attempts to design solely to the certification test.  We also expect the results of this testing to help inform the need for any further changes to GEM.
As already noted in Section II. B. (1) , it can be expensive to build chassis test cells for certification.  However, EPA is proposing to structure this pilot-scale program to minimize the costs.  First, we are proposing that this chassis testing would not need to comply with the same requirements as would apply for official certification testing.  This would allow testing to be performed in developmental test cells with simple portable analyzers.  Second, since the proposed program would require only 5 tests per year, manufacturers without their own chassis testing facility would be able to contract with a third party to perform the testing.  Finally, EPA proposes to apply this testing to only those manufacturers with annual production in excess of 20,000 vehicles.
Proposed Engine Test Procedures and Engine Standards
For the most part, the proposed Phase 2 engine standards are a continuation of the Phase 1 program, but with more stringent standards for compression-ignition engines.  Nevertheless, the agencies are proposing important changes related to the test procedures and compliance provisions.  These changes are described below.
As already discussed in Section II. B. the agencies are proposing a regulatory structure in which engine technologies are evaluated using engine-specific test procedures as well using GEM, which is vehicle-based.  We are proposing separate standards for each procedure.  The proposed engine standards described in Section II. D. (2) and the proposed vehicle standards described in Sections III and V are based on the same engine technology, which is described in Section II. D. (2) .  We request comment on whether the engine and vehicle standards should be based on the same projected technology.   As described below, while the agencies projected the same engine technology for engine standards and for vehicle standards, we separately projected the technology that would be appropriate for:
         * Gasoline vocational engines and vehicles
         * Diesel vocational engines and vehicles
         * Tractor engines and vehicles
Before addressing the engine standards and engine technology in Section II. D. (2) , the agencies describe the test procedures that would be used to evaluate these technologies in Section II. D. (1) below.  We believe that without first understanding the test procedures, the numerical engine standards would not have the proper context.
Engine Test Procedures
The Phase 1 engine standards relied on the engine test procedures specified in 40 CFR part 1065.  These procedures were previously used by EPA to regulate criteria pollutants such as NOx and PM, and few changes were needed to employ them for purposes of the Phase 1 standards.  The agencies are proposing significant changes to two areas for Phase 2:  (1) cycle weighting; and (2) GEM inputs.  (Note that EPA is also proposing some minor changes to the basic part 1065 test procedures, as described in Section XIII).
The diesel (i.e., compression-ignition) engine test procedure relies on two separate engine test cycles.  The first is the Heavy-duty Federal Test Procedure (Heavy-duty FTP) that includes transient operation typified by frequent accelerations and decelerations, similar to urban or suburban driving.  The second is the Supplemental Engine Test (SET) which includes 13 steady-state test points.  The SET was adopted by EPA to address highway cruise operation and other nominally steady-state operation.  However, it is important to note that it was intended as a supplemental test cycle and not necessarily to replicate precisely any specific in-use operation.
The gasoline (i.e., spark-ignition) engine test procedure relies on a single engine test cycle: a gasoline version of Heavy-duty FTP.  The agencies are not proposing changes to the gasoline engine test procedures.
It is worth noting that EPA sees great value in using the same test procedures for measuring GHG emissions as is used for measuring criteria pollutants.  From the manufacturers' perspective, using the same procedures minimizes their test burden.  However, EPA sees additional benefits.  First, as already noted in Section II. B. (2) (b), requiring engine manufacturers to comply with both NOx and CO2 standards using the same test procedures discourages alternate calibrations that would trade NOx emissions against fuel consumption depending how the engine or vehicle is tested.  Second, this approach leverages the work that went into developing the criteria pollutant cycles.  Taken together, these factors support our decision to continue to rely on the Part 1065 test procedures with only minor adjustments, such as those described in Section II. D. (1) (a).  Nevertheless, EPA would consider more substantial changes if they were necessary to incentivize meaningful technology changes, similar to the changes being made to GEM for Phase 2 to address additional technologies.
    SET Cycle Weighting
The SET cycle was adopted by EPA in 2000 and modified in 2005 from a discrete-mode test to a ramped-modal cycle to broadly cover the most significant part of the speed and torque map for heavy-duty engines, defined by three non-idle speeds and three relative torques.  The low speed is often called the "A speed", the intermediate speed is often called the "B speed", and the high speed is often called the "C speed."  As is shown in Table II-1, the SET weights these three speeds at 23 percent, 39 percent, and 23 percent.
            Table II-1 SET Modes Weighting Factor in Phase 1
                                 Speed, % Load
                        Weighting factor in Phase 1 (%)
                                     Idle
                                      15
                                    A, 100
                                       8
                                     B, 50
                                      10
                                     B, 75
                                      10
                                     A, 50
                                       5
                                     A, 75
                                       5
                                     A, 25
                                       5
                                    B, 100
                                       9
                                     B, 25
                                      10
                                    C, 100
                                       8
                                     C, 25
                                       5
                                     C, 75
                                       5
                                     C, 50
                                       5
                                     Total
                                      100

                                 Total A Speed
                                      23
                                 Total B Speed
                                      39
                                 Total C Speed
                                      23

The C speed is typically in the range of 1800 rpm for current HHD engine designs.   However, it is becoming less common for engines to operate often in such a high speed in real world driving condition, and especially not during cruise vehicle speed between 55 and 65 mph.  The agencies receive confidential business information from a few vehicle manufacturers that support this observation.  Thus, although the current SET represents highway operation better than the FTP cycle, it is not an ideal cycle to represent future highway operation.  Furthermore, given the recent trend configure drivetrains to operate engines at speeds down to a range of 1150-1200 rpm at vehicle speed of 65mph.  This trend would make the typical highway engine speeds even further away from C speed.
     To address this issue, the agencies are proposing new weighting factors for the Phase 2 GHG and fuel consumption standards.  The proposed new SET mode weightings move most of C weighting to "A" speed, as shown in Table II-2.  It would also slightly reduce the weighting factor on the idle speed.
  The agencies request comment on the proposed reweighting.
      Table II-2 Proposed SET Modes Weighting Factor in Phase 2
                                 Speed/% Load
                   Proposed Weighting factor in Phase 2 (%)
                                     Idle
                                      12
                                    A, 100
                                       9
                                     B, 50
                                      10
                                     B, 75
                                      10
                                     A, 50
                                      12
                                     A, 75
                                      12
                                     A, 25
                                      12
                                    B, 100
                                       9
                                     B, 25
                                       9
                                    C, 100
                                       2
                                     C, 25
                                       1
                                     C, 75
                                       1
                                     C, 50
                                       1
                                     Total
                                      100

                                 Total A Speed
                                      45
                                 Total B Speed
                                      38
                                 Total C Speed
                                       5

    Measuring GEM Engine Inputs
Although GEM does not apply directly to engine certification, implementing the Phase 2 GEM would impact engine manufacturers.  To recognize the contribution of the engine in GEM the engine fuel map, full load torque curve and motoring torque curve have to be input into GEM.  To insure the robustness of each of those inputs, a standard procedure has to be followed.  Both the full load and motoring torque curve procedures are already defined in 40CFR part 1065 for engine testing.  However, the fuel mapping procedure being proposed would be new.  The agencies have compared the proposed procedure against other accepted engine mapping procedures with a number of engines at various labs including EPA's NVFEL, Southwest Research Institute sponsored by the agencies, and Environment Canada's laboratory.  The proposed procedure was selected because it proved to be accurate and repeatable, while limiting the test burden to create the fuel map. This proposed provision is consistent with NAS's recommendation (3.8).
 One important consideration is the need to correct measured fuel consumption rates for the carbon and energy content of the test fuel.  For engine tests, we propose to continue the Phase 1 approach, which is specified in 40 CFR 1036.530.  We propose a similar approach to GEM fuel maps in Phase 2.
The agencies are proposing that engine manufacturers must certify fuel maps as part of their certification to the engine standards, and that they be required to provide those maps to vehicle manufacturers.  The one exception to this requirement would be for cases in which the engine manufacturer certifies based on powertrain testing, as described in Section II. D. (1) (c).  In such cases, engine manufacturers would not be required to also certify the otherwise applicable fuel maps.  We are not proposing that vehicle manufacturers be allowed to develop their own fuel maps for engines they do not manufacture.
    Engine Test Procedures for Replicating Powertrain Tests
As described in Section C. (3) (b), the agencies are proposing a powertrain test option to quantify the benefits of CO2 reducing powertrain technologies.  These powertrain test results would then be used to override the engine and transmission simulation portion of GEM.  The agencies are proposing to require that any manufacturer choosing to use this option also measure engine speed and engine torque during the powertrain test so that the engine's performance during the powertrain test could be replicated in a non-powertrain engine test cell.  Subsequent engine testing would be conducted using the normal part 1065 engine test procedures, and g/hp-hr CO2 results would be compared to the levels the manufacturer reported during certification.  Such testing would apply for both confirmatory and selective enforcement audit testing.
    CO2 from Urea SCR Systems
For diesel engines utilizing urea SCR emission control systems for NOx reduction, the agencies are proposing to allow correction of the final engine fuel map and powertrain duty cycle CO2 emission results to account for the contribution of CO2 from the urea injected into the exhaust.  This urea could contribute up to 1 percent of the total CO2 emissions from the engine.  Since current urea production methods use gaseous CO2 captured from the atmosphere (along with NH3), CO2 from urea consumption does not represent a net carbon emission.  This adjustment is necessary so that fuel maps developed from CO2 measurements would be consistent with fuel maps from direct measurements of fuel flow rates.  Thus, we are only proposing to allow this correction for emission tests where CO2 emissions are determined from direct measurement of CO2 and not from fuel flow measurement, which would not be impacted by CO2 from urea.
We note that this correction would be voluntary for manufacturers, and expect that some manufacturers may determine that the correction is too small to be of concern.  The agencies will use this correction with any engines for which the engine manufacturer applied the correction for its fuel maps during certification.
We are not proposing this correction for engine test results with respect to the engine CO2 standards.  Both the Phase 1 standards and the proposed standards for CO2 from diesel engines are based on test results that included CO2 from urea.  In other words, these standards are consistent with using a test procedure that does not correct for CO2 from urea.  We request comment on whether it would be appropriate to allow this correction for the Phase 2 engine CO2 standards, but also adjust the standards to reflect the correction.  At this time, we believe that reducing the numerical value of the CO2 standards by 1 g/hp-hr would make the standards consistent with measurement that are corrected for CO2 from urea.  However, we also request comment on the appropriateness of applying a 2 g/hp-hr adjustment should we determine it would better reflect the urea contribution for current engines.
    Potential Alternative Certification Approach
In Section II. D. (1) (b), we explained that although GEM does not apply directly to engine certification, implementing the Phase 2 GEM would impact engine manufacturers by requiring that they measure engine fuel maps.  In Section II. B. (2) , the agencies noted that some stakeholders may have concerns about the proposed regulatory structure that would require engine manufacturers to provide detailed fuel consumption maps for GEM.  Given such concerns, the agencies are requesting comment on an approach that could mitigate the concerns by allowing both vehicle and engine to use the same driving cycles for certification.  The detailed description of this alternative certification approach can be seen in Appendix A of the draft RIA.  We are requesting comment on allowing this approach as an option, or as a replacement to the proposed approach.  Commenters supporting this approach should address possible impacts on the stringency of the proposed standards.
This approach utilizes GEM with a default engine fuel map pre-defined by the agency to run a number of pre-defined vehicle configurations over three certification cycles.  Engine torque and speed profile would be obtained from the simulations, and would be used to specify engine dynamometer commands for engine testing.  The results of this testing would be a CO2 map as function of the integrated work and the ratio of averaged engine speed (N) to averaged vehicle speed (V) defined as (N/V) over each certification cycle.  In vehicle certification, vehicle manufacturers would run GEM with the to-be-certified vehicle configuration and the agency default engine fuel map separately for each GEM cycle.  Applying the total work and N/V resulted from the GEM simulations to the CO2 map obtained from engine tests would determine CO2 consumption for vehicle certification.  For engine certification, we are considering allowing the engine to be certified based on one of the points conducted during engine alternative CO2 map tests mentioned above rather than based on the FTP and SET cycle testing.
Proposed Engine Standards for CO2 and Fuel Consumption
We are proposing to maintain the existing Phase 1 regulatory structure for engine standards, which had separate standards for spark-ignition engines (such as gasoline engines) and compression-ignition engines (such as diesel engines), but we are proposing changes to how these standards would apply to natural gas fueled engines.  As discussed in Section II. B. (2) (b), the agencies see important advantages to maintaining separate engines standards, such as improved compliance assurance and better control during transient engine operation.
Phase 1 also applied different test cycles depending on whether the engine is used for tractors, vocational vehicles, or both, and we propose to continue this as well.   We assume that CO2 at the end of Phase 1 is the baseline of Phase 2.   Table II-3 shows the Phase 1 CO2 standards for diesel engines, which serve as the baseline for our analysis of the proposed Phase 2 standards.
Table II-3 Phase 2 Baseline CO2 Performance (g/bhp-hr)
LHDD - FTP
MHDD - FTP
HHDD - FTP
                                   MHDD-SET
HHDD - SET
576
576
555
                                      487
460
The gasoline engine baseline CO2 is 627 (g/bhp-hr).  The agencies used the baseline engine to assess the potential of the technologies described in the following sections. As described below, the agencies are proposing new compression-ignition engine standards for Phase 2 that would require additional reductions in CO2 emissions and fuel consumption beyond the baseline.  However, as also described below in Section II. D. (2) (b), we are not proposing more stringent CO2 or fuel consumption standards for new heavy-duty gasoline engines.  Note, however, that we are projecting some small improvement in gasoline engine performance that would be recognized over the vehicle cycles.
For heavy-heavy-duty diesel engines to be installed in Class 7 and 8 combination tractors, the agencies are proposing the standards shown in Table II-4.  The proposed MY 2027 standards for engines installed in tractors would require engine manufacturers to achieve, on average, a 4.2 percent reduction in fuel consumption and CO2 emissions beyond the Phase 1 standard.  We propose to adopt interim engine standards in MY 2021 and MY 2024 that would require diesel engine manufacturers to achieve, on average, 1.5 percent and 3.7 percent reductions in fuel consumption and CO2 emissions, respectively.
Table II-4 Proposed Phase 2 Heavy-duty Tractor Engine Standards for Engines over the SET Cycle
Model Year
                                   Standard
                           Medium Heavy-Duty Diesel
                            Heavy Heavy-Duty Diesel
2021-2023
                                     CO2
                                  (g/bhp-hr)
                                      479
                                      453

                     Fuel Consumption (gallon/100 bhp-hr)
                                     4.71
                                     4.45
2024 -2026
                                     CO2
                                  (g/bhp-hr)
                                      469
                                      443

                     Fuel Consumption (gallon/100 bhp-hr)
                                     4.61
                                     4.35
2027 and Later
                                     CO2
                                  (g/bhp-hr)
                                      466
                                      441

                     Fuel Consumption (gallon/100 bhp-hr)
                                     4.58
                                     4.33

For compression-ignition engines fitted into vocational vehicles, the agencies are proposing MY 2027 standards that would require engine manufacturers to achieve, on average, a 4.0 percent reduction in fuel consumption and CO2 emissions beyond the Phase 1 standard.  We propose to adopt interim engine standards in MY 2021 and MY 2024 that would require diesel engine manufacturers to achieve, on average, 2.0 percent and 3.5 percent reductions in fuel consumption and CO2 emissions, respectively.
Table II-5presents the CO2 and fuel consumption standards the agencies propose for compression-ignition engines to be installed in vocational vehicles.  The first set of standards would take effect with MY 2021, and the second set would take effect with MY 2024.
Table II-5 Proposed Vocational Diesel Engine Standards over the Heavy-Duty FTP Cycle
Model Year
Standard
Light Heavy-Duty Diesel
Medium Heavy-Duty Diesel
Heavy Heavy-Duty Diesel
2021-2023
CO2 Standard (g/bhp-hr)
565
565
544

Fuel Consumption Standard (gallon/100 bhp-hr)
5.55
5.55
5.34
2024 -2026
CO2 Standard (g/bhp-hr)
556
556
536

Fuel Consumption (gallon/100 bhp-hr)
5.46
5.46
5.26
2027 and Later
CO2 Standard (g/bhp-hr)
553
553
533

Fuel Consumption (gallon/100 bhp-hr)
5.43
5.43
5.23
Although both EPA and NHTSA are proposing to begin the Phase 2 engine standards, EPA considered proposing Phase 2 standards that would begin before MY 2021  -  that is with less lead time.  NHTSA is required by statute to provide four models years of lead time, while EPA is required only to provide lead time "necessary to permit the development and application of the requisite technology" (CAA Section 202 (a)(2)).  However, as noted in Section I, lead time cannot be separated for other relevant factors such as costs, reliability, and stringency.  Proposing these standards before 2021 could increase the risk of reliability issues in the early years.  Given the limited number of engine models that each manufacturer produces, managing that many new standards would be problematic (i.e., new Phase 1 standards in 2017, new Phase 2 EPA standards in 2018, 2019, or 2020, new standards in 2021, 2024, and again in 2027).   Considering these challenges, EPA determined that earlier model year standards would not be appropriate, especially given the value of harmonizing the NHTSA and EPA standards.
    Feasibility of the Diesel (Compression-Ignition) Engine Standards
In this section, the agencies discuss our assessment of the feasibility of the proposed engine standards and the extent to which they would conform to our respective statutory authority and responsibilities.  More details on the technologies discussed here can be found in the Draft RIA Chapter 2.3.  The feasibility of these technologies is further discussed in draft RIA Chapter 2.7 for tractor and vocational vehicle engines.  Note also, that the agencies are considering adopting engine standards with less lead time, and may do so in the Final Rules.  These standards are discussed in Section II. D. (2) (e).
Based on the technology analysis described below, the agencies can project a technology path exists to allow manufacturers to meet the proposed final Phase 2 standards by 2027, as well as meeting the intermediate 2021 and 2024 standards.  The agencies also project that manufacturers would be able to meet these standards at a reasonable cost and without adverse impacts on in-use reliability.  Note that the agencies are still evaluating whether these same standards could be met sooner, as was analyzed in Alternative 4.
In general, engine performance for CO2 emissions and fuel consumption can be improved by improving combustion and reducing energy losses.  More specifically, the agencies have identified the following key areas where fuel efficiency can be improved:
         * Combustion optimization
         * Turbocharging system
         * Engine friction and other parasitic losses
         * Exhaust aftertreatment
         * Engine breathing system
         * Engine downsizing
         * Waste heat recovery
         * Transient control for vocational engines only
The agencies are proposing to phase-in the standards from 2021 through 2027 so that manufacturers could gradually introduce these technologies.  For most of these improvements, the agencies project manufacturers could begin applying them to about 45-50 percent of their heavy-duty engines by 2021, 90-95 percent by 2024, and ultimately apply them to 100 percent of their heavy-duty engines by 2027.  However, for some of these improvements (such as waste heat recovery and engine downsizing) we project lower application rates in the Phase 2 time frame.  This phase-in structure is consistent with the normal manner in which manufacturers introduce new technology to manage limited R&D budgets and well as to allow them to work with fleets to fully evaluate in-use reliability before a technology is applied fleet-wide.  The agencies believe the proposed phase-in schedule would allow manufacturers to complete these normal processes.  As described in Section II. D. (2) (e), the agencies are also requesting comment on whether manufacturers could complete these development steps more quickly so that they could meet these standards sooner.
Based on our technology assessment described below, the proposed engine standards appear to be consistent with the agencies' respective statutory authorities.  All of the technologies with high penetration rates above 50 percent have already been demonstrated to some extent in the field or in research laboratories, although some development work remains to be completed.  We note that our feasibility analysis for these engine standards is not based on projecting 100 percent application for any technology until 2027.  We believe that projecting less than 100 percent application is appropriate and gives us confidence that the interim standards would be feasible.
The agencies have carefully considered the costs of applying these technologies, which are summarized in Section II. D. (2) (d).  These costs appear to be reasonable on both a per engine basis, and when considering payback periods.  The engine technologies are discussed in more detail below.  Readers are encouraged to see the draft RIA Chapter 2 for additional details (and underlying references) about our feasibility analysis.
Combustion Optimization
Although manufacturers are making significant improvements in combustion to meet the Phase 1 engine standards, the agencies project that even more improvement would be possible after 2018.  For example, improvements to fuel injection systems would allow more flexible fuel injection capability with higher injection pressure, which can provide more opportunities to improve engine fuel efficiency.  Further optimization of piston bowls and injector tips would also improve engine performance and fuel efficiency.  We project that a reduction of up to 1.0 percent is feasible in the 2024 model year through the use of these technologies, although it would likely apply to only 95 percent of engines until 2027.
Another important area of potential improvement is advanced engine control incorporating model based calibration to reduce losses of control during transient operation.  Improvements in computing power and speed would make it possible to use much more sophisticated algorithms that are more predictive than today's controls.  Because such controls are only beneficial during transient operation, they would reduce emission over the FTP cycle, and during in-use operation, they would not reduce emissions over the SET cycle.  Thus the agencies are projecting model based control reductions only for vocational engines.  Although this control concept is not currently available, we project model based controls achieving a 2 percent improvement in transient emissions could be in production for some engine models by 2021.  By 2027, we project over one-third of all vocational diesel engines would incorporate model-based controls.
Turbocharging System
Many advanced turbocharger technologies can be potentially added into production in the time frame between 2021 and 2027, and some of them are already in production, such as mechanical or electric turbo-compound, more efficient variable geometry turbine, and Detroit Diesel's patented asymmetric turbocharger.  A turbo compound system extracts energy from the exhaust to provide additional power.  Mechanical turbo-compounding includes a power turbine located downstream of the turbine which in turn is connected to the crankshaft to supply additional power.  On-highway demonstrations of this technology began in the early 1980s.  It was used first in heavy duty production by Detroit Diesel for their DD15 and DD16 engines and reportedly provided a 3 to 5 percent fuel consumption reduction.  Results are duty cycle dependent, and require significant time at high load to see a fuel efficiency improvement.  Light load factor vehicles can expect little or no benefit.  Volvo reports two to four percent fuel consumption improvement in line haul applications, which could be in production even by 2020
Engine Friction and Parasitic Losses
The friction associated with each moving part in an engine results in a small loss of engine power.  For example, frictional losses occur at bearings, in the valve train, and at the piston-cylinder interface.  Taken together such losses represent a large fraction of all energy lost in an engine.  For Phase 1, the agencies projected a 1-2 percent reduction in fuel consumption due to friction reduction.  However, new information leads us to project that an additional 1.4 percent reduction would be possible for some engines by 2021 and all engines by 2027.  These reductions would be possible due to improvements in bearing materials, lubricants, and new accessory designs such as variable-speed pumps.
Aftertreatment Optimization
All diesel engines manufacturers are already using diesel particulate filter (DPF) to reduce particulate matter (PM) and selective catalytic reduction (SCR) to reduce NOx emissions.  The agencies see two areas in which improved aftertreatment systems can also result in lower fuel consumption.  First, increased SCR efficiency could allow re-optimization of combustion for better fuel consumption because the SCR would be capable of reducing higher engine-out NOx emissions.  Second, improved designs could reduce backpressure on the engine to lower pumping losses.  The agencies project the combined impact of such improvements could be 0.6 percent or more.
Engine Breathing System
Various high efficiency air handling (for both intake air and exhaust) processes could be produced in the 2020 and 2024 time frame.  To maximize the efficiency of such processes, induction systems may be improved by manufacturing more efficiently designed flow paths (including those associated with air cleaners, chambers, conduit, mass air flow sensors and intake manifolds) and by designing such systems for improved thermal control.  Improved turbocharging and air handling systems would likely include higher efficiency EGR systems and intercoolers that reduce frictional pressure loss while maximizing the ability to thermally control induction air and EGR.  EGR systems that often rely upon an adverse pressure gradient (exhaust manifold pressures greater than intake manifold pressures) must be reconsidered and their adverse pressure gradients minimized.  Other components that offer opportunities for improved flow efficiency include cylinder heads, ports and exhaust manifolds to further reduce pumping losses by about 1 percent.
Engine Downsizing
Proper sizing of an engine is an important component of optimizing a vehicle for best fuel consumption.  This Phase 2 rule would improve overall vehicle efficiency, which would result in a drop in the vehicle power demand for most operation.  This drop moves the vehicle operating points down to a lower load zone, which can move the engine away from the sweet spot.  Engine downsizing combined with engine down speeding can allow the engine to move back to higher loads and lower speed zone, thus achieving slightly better fuel economy in the real world.  However, because of the way engines are tested, little of the benefit of engine downsizing would be detected during engine testing (if power density remains the same) because the engine test cycles are normalized based on the full torque curve.  Thus the current engine test is not the best way to measure the true effectiveness of engine downsizing.  Nevertheless, we project that some small benefit would be measured over the engine test cycles  -  perhaps up to a one-quarter percent improvement in fuel consumption.  Note that a bigger benefit would be observed during GEM simulation, better reflecting real world improvements.  This is factored into the vehicle standards.  Thus, the agencies see no reason to fundamentally revise the engine test procedure at this time.
Waste Heat Recovery
More than 40 percent of all energy loss in an engine is lost as heat to the exhaust and engine coolant.  For many years, manufacturers have been using turbochargers to convert some of the waste heat in the exhaust into usable mechanical power than is used to compress the intake air.  Manufacturers have also been working to use a Rankine cycle-based system to extract additional heat energy from the engine.  Such systems are often called waste heat recovery (WHR) systems.  The possible sources of energy include the exhaust, recirculated exhaust gases, compressed charge air, and engine coolant.  The basic approach with WHR is to use waste heat from one or more of these sources to evaporate a working fluid, which is passed through a turbine or equivalent expander to create mechanical or electrical power, then re-condensed.
Prior to the Phase 1 Final Rule, the NAS estimated the potential for WHR to reduce fuel consumption by up to 10 percent.  However, the agencies do not believe such levels would be achievable within the Phase 2 time frame.  There currently are no commercially available WHR systems for diesel engines, although research prototype systems are being tested by some manufacturers.  The agencies believe it is likely a commercially-viable WHR capable of reducing fuel consumption by over three percent would be available in the 2021 to 2024 time frame.  Cost and complexity may remain high enough to limit the use of such systems in this time frame.  Moreover, packaging constraints and transient response challenges would limit the application of WHR systems to line-haul tractors.  Refer to RIA Chapter 2 for a detailed description of these systems and their applicability.  The agencies project that WHR recovery could be used on 1 percent of all tractor engines by 2021, on 5 percent by 2024, and 15 percent by 2027.
The net cost and effectiveness of future WHR systems would depend on the sources of waste heat.  Systems that extract heat from EGR gases may provide the side benefit of reducing the size of EGR coolers or eliminating them altogether.  To the extent that WHR systems use exhaust heat, they would increase the overall cooling system heat rejection requirement and likely require larger radiators.  This could have negative impacts on cooling fan power needs and vehicle aerodynamics.  Limited engine compartment space under hood could leave insufficient room for additional radiator size increasing.  On the other hand, WHR systems that extract heat from the engine coolant, could actually improve overall cooling.
Technology Packages for Diesel Engines Installed in Tractors
Typical technology packaged for diesel engines installed in tractors basically includes most technologies mentioned above, which includes  combustion optimization, turbocharging system, engine friction and other parasitic losses, exhaust aftertreatment, engine breathing system, and engine downsizing.  Depending on the technology maturity of WHR and market demands, a small number of tractors could install waste heat recovery device with Rankine cycle technology.  During the stringency development, the agencies received strong supports from various stakeholders, where they graciously provided many confidential business information (CBI) including both technology reduction potentials and estimated market penetrations. Combining those CBI data with the agencies' engineering judgment, Table II-4 lists those potential technologies together with the agencies' estimated market penetration for tractor engine.   Those reduction values shown as "SET reduction" are relative to Phase 1 engine, which is shown in Table II-6.  It should be pointed out that the stringency in Table II-6  are developed based on the proposed SET reweighting factors l shown in Table II-2.
        Table II-6 Projected Tractor Engine Technologies and Reduction
                                   SET Mode
                     SET weighted reduction (%)  2020-2027
                           Market penetration (2021)
                           Market penetration (2024)
                           Market penetration (2027)
                          Turbo compound with clutch
                                     1.9%
                                      5%
                                      10%
                                      10%
                              WHR (Rankine cycle)
                                     3.3%
                                      1%
                                      5%
                                      15%
            Parasitic/Friction (Cyl Kits,  pumps, FIE), lubrication
                                     1.3%
                                      45%
                                      95%
                                     100%
                           Aftertreatment (lower dP)
                                     0.6%
                                      45%
                                      95%
                                     100%
              EGR/Intake & exhaust manifolds/Turbo /VVT/Ports
                                     1.1%
                                      45%
                                      95%
                                     100%
                             Combustion/FI/Control
                                     1.0%
                                      45%
                                      95%
                                     100%
                                  Downsizing
                                     0.2%
                                      10%
                                      20%
                                      30%
                            Weighted reduction (%)

                                     1.5%
                                     3.7%
                                     4.2%
Technology Packages for Diesel Engines Installed in Vocational Vehicles
For compression-ignition engines fitted into vocational vehicles, the agencies are proposing MY 2021 standards that would require engine manufacturers to achieve, on average, a 2.0 percent reduction in fuel consumption and CO2 emissions beyond the baseline that is the Phase 1 standard.  Beginning in MY 2024, the agencies are proposing engine standards that would require diesel engine manufacturers to achieve, on average, a 3.5 percent reduction in fuel consumption and CO2 emissions beyond the Phase 1 baseline standards for all diesel engines including LHD, MHD, and HHD.  The agencies are proposing these standards based on the performance of reduced parasitics and friction, improved aftertreatment, combustion optimization,  superchargers with VGT and bypass, model-based controls, improved EGR cooling/transport, and variable valve timing (only in LHD and MHD engines).  The percent reduction for the MY2021, MY2024, and MY2027 standards is based on the combination of technology effectiveness and market adoption rate projected.
Most of the potential engine related technologies discussed previously can be applied here.  However, neither the waste heat technologies with the Rankine cycle concept nor turbo-compound would be applied into vocational sector due to the inefficient use of waste heat energy with duty cycles and applications with more transient operation than highway operation.  Given the projected cost and complexity of such systems, we believe that for the Phase 2 time frame manufacturers will focus their development work on tractor applications (which would have better payback for operators) rather than vocational applications. In addition, the benefits due to engine downsizing, which can be seen in tractor engines, may not be clearly seen in vocational sector, again because this control technology produces few benefits in transient operation.
One of the most effective technologies for vocational engines is the optimization of transient control.  It would be expected that more advanced transient control including different levels of model based control and neural network control package could provide substantial benefits in vocational engines due to the extensive transient operation of these vehicles.  For this technology, the use of the FTP cycle would drive engine manufacturers to invest more in transient control to improve engine efficiency.  Other effective technologies would be parasitic/friction reduction, as well as improvements to combustion, air handling systems, turbochargers, and aftertreatment systems.  Table II-7 below lists those potential technologies together with the agencies' projected market penetration for vocational engines.  Again, similar to tractor engine, the technology reduction and market penetration are estimated by combining the CBI data together with the agencies' engineering judgment.  Those reduction values shown as "FTP reduction" are relative to a Phase 2 baseline engine, which is shown in Table II-3.  The weighted reductions combine the emission reduction values weighted by the market penetration of each technology).
       Table II-7 Projected Vocational Engine Technologies and Reduction
                                  Technology
                   GHG Emissions Reduction         2020-2027
                            Market Penetration 2021
                            Market Penetration 2024
                            Market Penetration 2027
                              Model based control
                                     2.0%
                                      25%
                                      30%
                                      40%
                              Parasitic /Friction
                                     1.5%
                                      60%
                                      90%
                                     100%
                              EGR/Air/VVT /Turbo
                                     1.0%
                                      50%
                                      90%
                                     100%
                                  Improved AT
                                     0.5%
                                      50%
                                      90%
                                     100%
                            Combustion Optimization
                                     1.0%
                                      50%
                                      90%
                                     100%
                        Weighted reduction (%)-L/M/HHD

                                     2.0%
                                     3.5%
                                     4.0%
Summary of the Agencies' Analysis of the Feasibility of the Proposed Diesel Engine Standards
The proposed HD Phase 2 standards are based on adoption rates for technologies that the agencies regard, subject to consideration of public comment, as the maximum feasible for purposes of EISA Section 32902 (k) and appropriate under CAA Section 202 (a) for the reasons given above.  The agencies believe these technologies can be adopted at the estimated rates for these standards within the lead time provided, as discussed in draft RIA Chapter 2.  The 2021 and 2024 MY standards are phase-in standards on the path to the 2027 MY standards and were developed using less aggressive application rates and therefore have lower technology package costs than the 2027 MY standards.
As described in Section II. D. (2) (d) below, the cost of the proposed standards is estimated to range from $270 to $1,698 per engine.  This is slightly higher than the costs for Phase 1, which were estimated to be $234 to $1,091 per engine.  Although the agencies did not separately determine fuel savings or emission reductions due to the engine standards apart from the vehicle program, it is expected that the fuel savings would be significantly larger than these costs, and the emission reductions would be roughly proportional to the technology costs when compared to the corresponding vehicle program reductions and costs.  Thus, we regard these standards as cost-effective.  This is true even without considering payback period.  The proposed phase-in 2021 and 2024 MY standards are less stringent and less costly than the proposed 2027 MY standards.  Given that the agencies believe the proposed standards are technically feasible, are highly cost effective, and highly cost effective when accounting for the fuel savings, and have no apparent adverse potential impacts (e.g., there are no projected negative impacts on safety or vehicle utility), the proposed standards appear to represent a reasonable choice under Section 202(a) of the CAA and the maximum feasible under NHTSA's EISA authority at 49 U.S.C. 32902(k)(2).
    Basis for Continuing the Phase 1 Spark-Ignited Engine Standard
Today most SI-powered vocational vehicles are sold as incomplete vehicles by a vertically integrated chassis manufacturer, where the incomplete chassis shares most of the same technology as equivalent complete pickups or vans, including the powertrain.  The number of such incomplete SI-powered vehicles is small compared to the number of completes.  Another, even less common way that SI-powered vocational vehicles are built is by a non-integrated chassis manufacturer purchasing an engine from a company that also produces complete and/or incomplete HD pickup trucks and vans.  The resulting market structure leads manufacturers of heavy-duty SI engines to have little market incentive to develop separate technology for vocational engines that are engine-certified.  Moreover, the agencies have not identified a single SI engine technology that we believe belongs on engine-certified vocational engines that we do not also project to be used on complete heavy-duty pickups and vans.
In light of this market structure, when the agencies considered the feasibility of more stringent Phase 2 standards for SI vocational engines, we identified the following key questions:
         1. Will there be technologies available that could reduce in-use emissions from vocational SI engines?
         2. Would these technologies be applied to complete vehicles and carried-over to engine certified engines without a new standard?
         3. Would these technologies be applied to meet the vehicle-based standards described in Section V?
         4. What are the drawbacks associated with setting a technology-forcing Phase 2 standard for SI engines?
With respect to the first and second questions, as noted in Chapter 2.6 of the draft RIA, the agencies have identified improved lubricants, friction reduction, and cylinder deactivation as technologies that could potentially reduce in-use emissions from vocational engines; and the agencies have further determined that to the extent these technologies would be viable for complete vehicles, they would also be applied to engine-certified engines.  Nevertheless, significant uncertainty remains about how much benefit would be provided by these technologies.  It is possible that the combined impact of these technologies would be one percent or less.  With respect to the third question, we believe that to the extent these technologies are viable and effective, they would be applied to meet the vehicle-based standards for vocational vehicles.
At this time, it appears the fourth question regarding drawbacks is the most important.  The agencies could propose a technology forcing standard for vocational SI engines based on a projection of each of these technologies being effective for these engines.   However, as already noted in Section I, the agencies see value in setting the standards at levels that would not require every projected technology to work as projected.  Effectively requiring technologies to match our current projections would create the risk that the standards would not be feasible if even a single one of technologies failed to match our projections.  This risk is amplified for SI engines because of the very limited product offerings, which provide far fewer opportunities for averaging than exist for CI engines.  Given the relatively small improvement projected, and the likelihood that most or all of this improvement would result anyway from the complete pickup and van standards and the vocational vehicle-based standard, we do not believe such risk is justified.  Nevertheless, we request comment on adopting more a stringent standard in the 2024 to 2027 time frame that would be 1-2 percent lower than the Phase 1 standard.
    Engine Improvements Projected for Vehicles over the GEM Duty Cycles
Because we are proposing that tractor and vocational vehicle manufacturers represent their vehicles' actual engines in GEM for vehicle certification, the agencies aligned our engine technology effectiveness assessments for both the separate engine standards and the tractor and vocational vehicle standards for each of the regulatory alternatives considered.  This was an important step because we are proposing to recognize the same engine technologies in both the separate engine standards and the vehicle standards, which each have different test procedures for demonstrating compliance.  As explained earlier in Section II. D. (1) , compliance with the tractor separate engine standards is determined from a composite of the Supplemental Engine Test (SET) procedure's 13 steady-state operating points.  Compliance with the vocational vehicle separate engine standards is determined over the Federal Test Procedure's (FTP) transient engine duty cycle.  In contrast, compliance with the vehicle standards is determined using GEM, which calculates composite results over a combination of 55 mph and 65 mph steady-state vehicle cycles and the ARB Transient vehicle cycle.  Note that we are also proposing a new workday idle cycle for vocational vehicles.  Each of these duty cycles emphasizes different engine operating points; therefore, they can each recognize certain technologies differently.
Our first step in aligning our engine technology assessment at both the engine and vehicle levels was to start with an analysis of how we project each technology to impact performance at each of the 13 individual test points of the SET steady-state engine duty cycle.  For example, engine friction reduction technology would be expected to have the greatest impact at the highest engine speeds, where frictional energy losses are the greatest.  As another example, turbocharger technology is generally optimized for best efficiency at steady-state cruise vehicle speed.  For an engine this is near its lower peak-torque speed and at a moderately high load that still offers sufficient torque reserve to climb modest road grades without frequent transmission gear shifting.  The agencies also considered the combination of certain technologies causing synergies and dis-synergies with respect to engine efficiency at each of these test points.  See RIA Chapter 2 for further details.
Next we estimated unique brake-specific fuel consumption values for each of the 13 SET test points for two hypothetical MY2018 tractor engines that would be compliant with the Phase 1 standards.  These were a 15 liter displacement 455 horsepower engine and an 11 liter 350 horsepower engine.  We then added technologies to these engines that we determined were feasible for MY2021, MY2024, and MY 2027, and we determined unique improvements at each of the 13 SET points.  We then calculated composite SET values for these hypothetical engines and determined the SET improvements that we could use to propose more stringent separate tractor engine standards for MY2021, MY2024, and MY 2027.
To align our engine technology analysis for vehicles to the SET engine analysis described above, we then fit a surface equation through each engine's SET points versus engine speed and load to approximate their analogous fuel maps that would represent these same engines in GEM.  Because the 13 SET test points do not fully cover an engine's wide range of possible operation, we also determined improvements for an additional 6 points of engine operation to improve the creation of GEM fuel maps for these engines.  Then for each of these 8 tractor engines (two each for MY2018, MY2021, MY2024, and MY2027) we ran GEM simulations to represent low-, mid-, and high-roof sleeper cabs and low-, mid-, and high-roof day cabs.  Class 8 tractors were assumed for the 455 horsepower engine and Class 7 tractors (day cabs only) were assumed for the 350 horsepower engine. Each GEM simulation calculated results for the 55 mph, 65 mph, and ARB Transient cycles, as well as the composite GEM value associated with each of the tractor types.  After factoring in our Alternative 3 projected market penetrations of the engine technologies, we then compared the percent improvements that the same sets of engine technology caused over the separate engines' SET composites and the various vehicles' GEM composites.  Compared to their respective MY2018 baseline engines, the two engines of different horsepower showed the same percent improvements.  All of the tractor cab types showed nearly the same relative improvements too.  For example, for the MY2021 Alternative 3 engine technology package in a high roof sleeper tractor, the SET engine composites showed a 1.5 percent improvement and the GEM composites a 1.6 percent improvement.  For the MY2024 Alternative 3 engine technology packages, the SET engine composites showed a 3.7 percent improvement and the GEM composites a 3.7 percent improvement.  For MY2027 Alternative 3 engine technology packages, the SET engine composites showed a 4.2 percent improvement and the GEM composites a 4.2 percent improvement.  We therefore concluded that tractor engine technologies will improve engines and tractors proportionally, even though the separate engine and vehicle certification test procedures have different duty cycles.
We then repeated this same process for the FTP engine transient cycle and the GEM vocational vehicle types.  For the vocational engine analysis we investigated four engines: 15 liter displacement engine at 455 horsepower rating, 11 liter displacement engine at 345 horsepower rating, a 7 liter displacement engine at a 200 horsepower rating and a 270 horsepower rating.  These engines were then used in GEM over the light-heavy, medium-heavy, and heavy-heavy vocational vehicle configurations.  Because the technologies were assumed to impact each point of the FTP in the same way, the results for all engines and vehicles were 2.0 percent improvement in MY2021, 3.5 percent improvement in MY2024, and 4.0 percent improvement in MY2027.  Therefore, we arrived at the same conclusion that vocational vehicle engine technologies are recognized at the same percent improvement over the FTP as the GEM cycles.  We request comment on our approach to arrive at this conclusion.
    Engine Technology Package Costs for Tractor and Vocational Engines (and Vehicles)
As described in Chapters 2 and 7 of the draft RIA, the agencies estimated costs for each of the engines technologies discussed here.  All costs are presented relative to engines projected to comply with the model year 2017 standards  -  i.e., relative to our baseline engines.  Note that we are not presenting any costs for gasoline engines (SI engines) because we are not proposing to change the standards.
Our engine cost estimates include a separate analysis of the incremental part costs, research and development activities, and additional equipment.  Our general approach used elsewhere in this action (for HD pickup trucks, gasoline engines, Class 7 and 8 tractors, and Class 2b-8 vocational vehicles) estimates a direct manufacturing cost for a part and marks it up based on a factor to account for indirect costs.  See also 75 FR 25376.  We believe that approach is appropriate when compliance with proposed standards is achieved generally by installing new parts and systems purchased from a supplier.  In such a case, the supplier is conducting the bulk of the research and development on the new parts and systems and including those costs in the purchase price paid by the original equipment manufacturer.  The indirect costs incurred by the original equipment manufacturer need not include much cost to cover research and development since the bulk of that effort is already done.  For the MHD and HHD diesel engine segment, however, the agencies believe that OEMs will incur costs not associated with the purchase of parts or systems from suppliers or even the production of the parts and systems, but rather the development of the new technology by the original equipment manufacturer itself.  Therefore, the agencies have directly estimated additional indirect costs to account for these development costs.  The agencies used the same approach in the Phase 1 HD rule. EPA commonly uses this approach in cases where significant investments in research and development can lead to an emission control approach that requires no new hardware.  For example, combustion optimization may significantly reduce emissions and cost a manufacturer millions of dollars to develop but would lead to an engine that is no more expensive to produce.  Using a bill of materials approach would suggest that the cost of the emissions control was zero reflecting no new hardware and ignoring the millions of dollars spent to develop the improved combustion system.  Details of the cost analysis are included in the draft RIA Chapter 2.  To reiterate, we have used this different approach because the MHD and HHD diesel engines are expected to comply in part via technology changes that are not reflected in new hardware but rather reflect knowledge gained through laboratory and real world testing that allows for improvements in control system calibrations  -  changes that are more difficult to reflect through direct costs with indirect cost multipliers.  Note that these engines are also expected to incur new hardware costs as shown in Table II-8  through Table II-11. EPA also developed the incremental piece cost for the components to meet each of the 2021 and 2024 standards.  The costs shown in Table II-12 include a low complexity ICM of 1.15 and assume the flat-portion of the learning curve is applicable to each technology.

Tractor Engine Package Costs
Table II-8 Proposed MY2021 Tractor Diesel Engine Component Costs Inclusive of Indirect Cost Markups and Adoption Rates (2012$)

                                   Medium HD
                                   Heavy HD
Aftertreatment system (improved effectiveness SCR, dosing, DPF)
                                                                             $7
                                                                             $7
Valve Actuation
                                                                            $82
                                                                            $82
Cylinder Head (flow optimized, increased firing pressure, improved thermal management)
                                                                             $3
                                                                             $3
Turbocharger (improved efficiency)
                                                                             $9
                                                                             $9
Turbo Compounding
                                                                            $50
                                                                            $50
EGR Cooler (improved efficiency)
                                                                             $2
                                                                             $2
Water Pump (optimized, variable vane, variable speed)
                                                                            $43
                                                                            $43
Oil Pump (optimized)
                                                                             $2
                                                                             $2
Fuel Pump (higher working pressure, increased efficiency, improved pressure regulation)
                                                                             $2
                                                                             $2
Fuel Rail (higher working pressure)
                                                                             $5
                                                                             $5
Fuel Injector (optimized, improved multiple event control, higher working pressure)
                                                                             $5
                                                                             $5
Piston (reduced friction skirt, ring and pin)
                                                                             $1
                                                                             $1
Valve Train (reduced friction, roller tappet)
                                                                            $39
                                                                            $39
Waste Heat Recovery
                                                                           $105
                                                                           $105
"Right sized" engine
                                                                           -$40
                                                                           -$40
Total
                                                                           $314
                                                                           $314
         Note: "Right sized" diesel engine is a smaller, less costly engine than the engine it replaces.
Table II-9 Proposed MY2024 Tractor Diesel Engine Component Costs Inclusive of Indirect Cost Markups and Adoption Rates (2012$)

                                   Medium HD
                                   Heavy HD
Aftertreatment system (improved effectiveness SCR, dosing, DPF)
                                                                            $14
                                                                            $14
Valve Actuation
                                                                           $166
                                                                           $166
Cylinder Head (flow optimized, increased firing pressure, improved thermal management)
                                                                             $6
                                                                             $6
Turbocharger (improved efficiency)
                                                                            $17
                                                                            $17
Turbo Compounding
                                                                            $92
                                                                            $92
EGR Cooler (improved efficiency)
                                                                             $3
                                                                             $3
Water Pump (optimized, variable vane, variable speed)
                                                                            $84
                                                                            $84
Oil Pump (optimized)
                                                                             $4
                                                                             $4
Fuel Pump (higher working pressure, increased efficiency, improved pressure regulation)
                                                                             $4
                                                                             $4
Fuel Rail (higher working pressure)
                                                                             $9
                                                                             $9
Fuel Injector (optimized, improved multiple event control, higher working pressure)
                                                                            $10
                                                                            $10
Piston (reduced friction skirt, ring and pin)
                                                                             $3
                                                                             $3
Valve Train (reduced friction, roller tappet)
                                                                            $75
                                                                            $75
Waste Heat Recovery
                                                                           $502
                                                                           $502
"Right sized" engine
                                                                           -$85
                                                                           -$85
Total
                                                                           $904
                                                                           $904
         Note: "Right sized" diesel engine is a smaller, less costly engine than the engine it replaces.

Table II-10 Proposed MY2027 Tractor Diesel Engine Component Costs Inclusive of Indirect Cost Markups and Adoption Rates (2012$)

                                   Medium HD
                                   Heavy HD
Aftertreatment system (improved effectiveness SCR, dosing, DPF)
                                                                            $14
                                                                            $14
Valve Actuation
                                                                           $169
                                                                           $169
Cylinder Head (flow optimized, increased firing pressure, improved thermal management)
                                                                             $6
                                                                             $6
Turbocharger (improved efficiency)
                                                                            $17
                                                                            $17
Turbo Compounding
                                                                            $87
                                                                            $87
EGR Cooler (improved efficiency)
                                                                             $3
                                                                             $3
Water Pump (optimized, variable vane, variable speed)
                                                                            $84
                                                                            $84
Oil Pump (optimized)
                                                                             $4
                                                                             $4
Fuel Pump (higher working pressure, increased efficiency, improved pressure regulation)
                                                                             $4
                                                                             $4
Fuel Rail (higher working pressure)
                                                                             $9
                                                                             $9
Fuel Injector (optimized, improved multiple event control, higher working pressure)
                                                                            $10
                                                                            $10
Piston (reduced friction skirt, ring and pin)