Summary

BACKGROUND

Medium- and heavy-duty vehicles (MHDVs) are a significant contributor to energy consumption and greenhouse gas (GHG) emissions in the transportation sector, accounting for approximately 22 percent of U.S. transportation energy consumption.¹ Unlike the light-duty vehicle sector, which has long been subject to corporate average fuel economy standards, the fuel consumption of MHDVs has only recently begun to be regulated at the federal level. This regulation of MHDV fuel efficiency was mandated by Congress in 2007 in the Energy Independence and Security Act of 2007 (EISA), P.L. 110-140. Section 101 of EISA required the U.S. Department of Transportation (DOT) to promulgate fuel efficiency standards for MHDVs. The statute anticipates that these standards would be updated over time and requires DOT to provide 4 years of lead time between promulgation and enforcement of fuel efficiency standards, and also requires a period of 3 years of stability once the standards are in effect. On May 21, 2010, President Barack Obama directed the National Highway Traffic Safety Administration (NHTSA), on behalf of DOT, to issue MHDV fuel economy standards in close coordination with GHG emission standards to be promulgated for the same vehicles by the U.S. Environmental Protection Agency (EPA).

Section 108 of EISA also requires the secretary of transportation to contract with the National Academy of Sciences to undertake a study on the technologies and costs for improving fuel efficiency in MHDVs. Upon completion of the National Research Council (NRC) Phase One Report² and its own study of fuel efficiency standards for MHDVs, DOT was instructed to promulgate by rulemaking a fuel efficiency program for MHDVs that is “designed to achieve the maximum feasible improvement” in fuel economy and to “adopt and implement appropriate test methods, measurement metrics, fuel economy standards, and compliance and enforcement protocols that are appropriate, cost-effective, and technologically feasible for commercial medium- and heavy-duty on-highway vehicles and work trucks” (49 U.S.C. § 32902(k)(2)).

Figure S-1 provides a schematic of the different phases of the regulation, the model year (MY) vehicles included, and the types of MHDVs that are considered in the standards.

___________________

¹ Davis, S.C., S.W. Diegel, and R.G. Boundy. 2014. Transportation Energy Data Book: Edition 33. Oak Ridge, TN: Oak Ridge National Laboratory. March.

² National Research Council. 2010. Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles. Washington, DC: The National Academies Press.

The committee issued its Phase Two First Report in 2014.³ The Summary chapter from the 2014 report is provided as Appendix E for reference. It provided guidance for the Phase II rule, which was directed at the post-2018 time frame. The present report is the final report of the NRC Phase Two study and covers a broader range of technologies and issues focused on the 2022 to 2030 time frame.

The Summary captures the overarching report themes of vehicle technology progress, alternative technology and approaches, economic assessment and considerations, future regulatory framework, and interim evaluation. Given the broad scope of the statement of task (SOT), it focuses only on the most significant recommendations. The associated findings are addressed in the individual chapters. Chapter 1 contains a detailed mapping of the SOT items to the report chapters, but briefly, the report is organized with a discussion of MHDV regulation structure and compliance (Chapters 2 and 3), followed by powertrain (Chapter 4) and power demand reduction (Chapter 5) technologies and fuel consumption benefits (Chapter 6), hybrid and electric and battery technologies (Chapters 6–8), freight efficiency (Chapter 9), intelligent transportation systems and automation (Chapter 10), and manufacturing, cost-benefit, and alternative regulatory approaches (Chapters 11–13). A number of appendixes follow with detailed information.

VEHICLE TECHNOLOGY PROGRESS

The energy efficiency of the two widely used conventional engine platforms—compression ignition (i.e., diesel) and spark ignition—can and is still being improved. Diesel engines using the well-known diffusion-dominated compression-ignition (CI) combustion are presently the most efficient engines for MHDVs, with

___________________

³ National Research Council. 2014. Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two: First Report. Washington, DC: The National Academies Press.

progress evident for further reductions in CO₂ and fuel consumption, and NO_x emissions. Supported by the U.S. Department of Energy’s SuperTruck initiative, demonstration of 55 percent peak engine efficiency in a research vehicle environment⁴ may occur in the next few years. Improvements in waste-heat recovery will be a necessary precursor to reaching such efficiencies with current production engine architectures.

Spark-ignition (SI) engines continue to evolve and improve, with potential to reach more than 40 percent peak brake thermal efficiency while still achieving stringent criteria emissions with relatively low-cost aftertreatment. Even higher efficiency would be achievable in technology pathways where a high fuel octane number is used. Such pathways are well suited to renewable fuels such as ethanol or fuels with low carbon, like natural gas or propane. Based on emerging experimental and modeling results, the expected efficiency of SI engines could exceed the Phase II regulatory requirements, suggesting such engines could attain more stringent regulations depending on the extent that advanced technologies for passenger vehicle engines are adapted to MHDV gasoline engines and based on duty cycle considerations.

The current regulatory structure, which focuses on engine and truck fuel consumption and GHG emission standards, does not appear to have regulatory flexibility to address advanced fuels and methods of improving the efficiency of goods (i.e., freight) movement. For example, increases in heavy-duty vehicle size and weight limits could reduce total system fuel consumption; however, the authority to make such changes lies with Congress.

For Class 8 combination tractor-trailers, a total weight reduction of at least 4,000 pounds appears achievable, which would produce approximately 3 to 4 percent reduction in fuel consumption compared to trucks without lightweighting features, depending on duty cycle. Since most trucks operate at less than maximum weight limit, reduced weight benefits fuel consumption as well as load-specific fuel consumption (LSFC), with the impact of weight reduction greatest in the smaller truck classes.

The committee’s technology review, projections, and simulations indicate that, depending on vehicle class and the progress in engine efficiency within each, roughly 12 to 19 percent reduction in LSFC⁵ is technologically feasible for MHDVs in the 2030 time frame compared to the committee’s 2019 baseline. This expected feasible reduction pertains especially to Class 8 combination vehicles and their drive cycles that consume most of the fuel in the MHDV sector (whereas hybrid vehicles may achieve even greater reductions in fuel consumption in certain duties). Economic feasibility of such an efficiency improvement requires further analyses. This reduction is without the effects of significant changes in fuels or overall operational efficiencies. The committee also conducted simulations under an aggressive set of assumptions for engine efficiency (e.g., 55 percent peak thermal for a combination tractor) and key vehicle parameters,⁶ post-2027, and found roughly a 30 percent reduction over the 2019 baseline for the vehicle classes larger than a Class 2b pickup truck. These ambitious CO₂ reductions at the vehicle level will need to be evaluated for sufficiency relative to meeting any national goals and international agreements to which the United States is a party. Substantial reductions greater than 30 percent in CO₂ compared to a 2019 baseline may necessitate approaches beyond the vehicle such as efficiency gains from fuels, operations, and so forth.

Recommendation: NHTSA, in coordination with EPA, should evaluate and quantify the life-cycle GHG emissions and fuel consumption of all fuels and technologies whose use could contribute to meeting a third phase of standards, and take them into consideration in developing a third phase of regulation. It will be critically important to incorporate a life-cycle perspective in those instances where some fuel-technology pathways’ life-cycle emissions may lead to an increase, rather than a decrease, in emissions. However, given the resources needed for detailed life-cycle analysis and uncertainty characterization, and given the resource constraints from the agencies, we would recommend assessing carefully which fuel-technology pathways may deserve specific attention in a life-cycle perspective. (Recommendation 2-7)

___________________

⁴ The next phase of the SuperTruck program calls for 55 percent engine efficiency of a Class 8 tractor-trailer with 65,000-pound gross combined vehicle weight at 65 mph. The peak thermal efficiency may be slightly higher.

⁵ LSFC is measured in units of volume of fuel consumed per mass of payload per distance traveled (e.g., gallons per 1,000 ton-mile).

⁶ Reflecting aggressive improvements in aerodynamic drag, rolling resistance, and mass reduction.

Recommendation: NHTSA, in cooperation with EPA, should establish what MHDV GHG and fuel consumption reductions need to be achieved in the 2030 to 2050 time frame, consistent with national goals and international agreements to which the United States is a party. (Recommendation 2-2)

Recommendation: Engine manufacturers, with appropriate engagement of NHTSA and EPA, should allow and promote use of biodiesel and renewable diesel in their engines. NHTSA, in concert with EPA, is encouraged to continue some types of incentives for use of biomass-derived diesel fuel, provided that analyses continue to show overall life-cycle GHG reduction. The agencies are encouraged to seek harmony and synergy between their separate rules for renewable fuels and tailpipe regulations to enable further GHG reduction and petroleum displacement. (Recommendation 4-7)

Recommendation: NHTSA and EPA, through their representation in or coordination with the relevant entities within the U.S. Department of Commerce, the U.S. Department of Energy, and the Office of Science and Technology Policy, should prioritize development and application of additive manufacturing, materials joining processes, nanostructured materials, and other yet-to-be-identified promising manufacturing innovations on those parts and systems that offer the greatest potential for fuel consumption and GHG reduction. The progress of these technologies, their prioritization status, and prognosis for effective commercialization within the Phase III regulatory period should be included in the interim evaluation proposed by this report. (Recommendation 11-5)

Recommendation: Future MHDV fuel consumption standards should include expectations for weight reduction adoption, with the likely potential for 3 to 4 percent reduction in load-specific fuel consumption at market-acceptable return on investment. (Recommendation 5-11)

Recommendation: Government and industry should continue the development of higher-efficiency SI gasoline and natural gas engines for vocational vehicles and should continue to ensure substantial CO₂ and fuel consumption reductions are realized, because (1) higher efficiency appears feasible and (2) market forces may cause a shift toward the SI engines. (Recommendation 6-2)

ALTERNATIVE TECHNOLOGY AND APPROACHES

Implementation of new propulsion technologies, new low-carbon fuels, and more efficient freight operations and logistics offers the opportunity to reduce fuel consumption and GHG emissions beyond what is achievable from improving the efficiency of conventional MHDVs—which may be necessary to meet future climate goals. There are numerous alternative-configuration combustion engines. Many of these are merely alternative mechanisms to carry out thermodynamic processes very similar to conventional engines, but there are a few that provide clear enhancements via changing the basic cycles or reducing a prominent loss mechanism (such as heat transfer or friction). Few alternative concepts have reached a scale of development where they could be tested in a MHDV system for performance and emission requirements. With limited data found on alternative configurations, the magnitude of improvement over advanced conventional engines is not readily predictable and will depend on prevailing emission requirements.

For example, progress in understanding and demonstrating the benefits and challenges for kinetics-dominated combustion has continued, but there are still many recipes of the phenomena in flux, depending on fuel properties and stratification modes. Full-scale heavy-duty engines have been successfully demonstrated on test stands, and light-duty vehicle demonstrations have been conducted. A full commercial application is still pending.

Further, waste-heat recovery (WHR) used in Class 8 over-the-road vehicles potentially offers significant cost-effective fuel savings. Expected progress in WHR technology suggests this technology will see increasing penetration in Class 8 combination tractors. There are many approaches to waste-heat conversion to power that can provide up to 4 percent efficiency improvements in modern truck engines. This effect is comparable to other engine improvements in combustion, air handling, friction, etc., and even comparable to many vehicle technology improvements. The WHR systems have proven technically feasible in a research vehicle, yet carry challenges

in their weight, packaging, thermal response, and cost. Progress in addressing the challenges is evident. The Regulatory Impact Analysis⁷ noted a potential 25 percent penetration in some Class 8 segments by the end of the Phase II rule period.

Hybridization

With respect to hybridization of commercial vehicles, several international light-duty vehicle manufacturers and Tier 1 battery suppliers are projecting costs for plug-in hybrid-electric or battery electric vehicle battery packs that will achieve $120/kWh by 2020 and $100/kWh or less by 2025. At these cost levels, significant market growth in electrified light-duty vehicles can be expected worldwide by 2030. However, due to the duty cycle, service life, and other boundary conditions for commercial vehicles, the battery-system costs are expected to reduce significantly by 2030 but will remain somewhat higher than light-duty battery systems.

Yet, the specific energy, charge and discharge rates, vehicle duty cycles, service life, and reliability requirements for commercial vehicles will limit the potential for direct carryover of battery systems from light-duty vehicles. Additional research and development, above that being done for light-duty applications, is necessary and could delay the market penetration of electrified commercial vehicles. However, international regulatory incentives to promote combustion-free powertrains could support earlier introduction of electrified commercial vehicles than would normally occur in the technology and manufacturing cost-development cycle.

In 2027 and beyond, stop-start technology applications are expected to have payback periods that would make them attractive in many applications to private firms. The greater fuel savings, however, that are possible with the application of mild and strong hybrids are expected to be less attractive to private firms, given their relatively long payback periods. However, technological developments and likely cost evolution and potential life-cycle benefits results suggest that hybridization is a technology that is “next up” for meeting more stringent post–Phase II standards.

Fuel Considerations

Further, petroleum-derived diesel fuel will likely remain the dominant CI engine fuel through the time period of this study (approximately 2030). Regarding changes to diesel fuel to reduce GHG emissions, the most effective measure would be additional use of biomass-derived fuel components (in contrast to changing diesel fuel performance specifications). Renewable diesel fuel (hydrogenation-derived renewable diesel) and biodiesel are both well developed, commercially available, and suitable for this path. They offer overall GHG reduction of up to about 80 percent relative to petroleum-derived diesel.

Since SI engines fueled with gasoline-based fuels are economically attractive for some market segments, GHG reductions with these engines can be enhanced by improving the performance properties of the fuel, such as octane number and maintaining or increasing the content of renewable fuels. The effect of a moderate increase in octane number (research octane number) on efficiency is 5 to 10 percent improvement, whereas the GHG reduction is on the order of 30 percent if renewable ethanol is the high-octane-number blending material.^8,9

Improved Freight Movement Efficiency

The relatively high cost and long payback periods of “next-up” technologies—in particular, mild and strong hybrids—which will be necessary to meet aggressive reductions in fuel consumption in many of the medium-

___________________

⁷ NHTSA and EPA. 2016. Regulatory Impact Analysis, Final Rule for Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles, Phase II. Washington, DC: NHTSA and EPA.

⁸ Leone, T.G., J.E. Anderson, R.S. Davis, A. Iqbal, R.A. Reese, M.H. Shelby, and W.M. Studzinski. (2015). The effect of compression ratio, fuel octane rating, and ethanol content on spark-ignition engine efficiency. Environmental Science & Technology 49(18):10778-10789. doi: 10/1021/acs.est.5b01420.

⁹ Theiss, T., T. Alleman, A. Brooker, A. Elgowainy, et al. Summary of High-Octane, MidLevel Ethanol Blends Study. ORNL/TM-2016/42, Oak Ridge National Laboratory, 2016.

and heavy-duty truck segments, suggest that future efforts to increase fuel efficiency should look beyond vehicle technology solutions alone. Consideration should be given to actions that increase the efficiency of the overall freight system, as is described in Chapter 2.

A more integrated approach to systemic improvement in fuel efficiency would, however, require closer cooperation among government agencies than takes place today. A range of opportunities exists to improve energy efficiency and reduce GHG emissions in freight transportation, as detailed in Chapters 9 and 10. For example, modifying truck size and weight standards, facilitating intermodal shipments, and truck platooning could improve the fuel efficiency of freight shipments. Taking advantage of these opportunities will require action and leadership by the federal government, state and local governments (who own and operate the highway system), and private industry.

In considering methods and technologies for improving the efficiency of freight operations, the committee found that higher weight limits and longer combination vehicles could significantly improve productivity and therefore reduce the overall distance traveled in the heavy-vehicle long-haul transportation sector. In addition, the development of freight transfer facilities near urban areas would increase the use of more agile, fuel efficient, and less polluting vehicles for “last-mile” freight movements and would facilitate the early adoption of autonomous vehicles. As such, automated operation that enables truck platooning has the opportunity to save fuel and GHG emissions achieved through decreases in the drag of both trucks.

The commercialization and deployment of advanced technologies, fuels, and freight movement methods that are significantly different from those currently in use may need to start as early as 2030 if ambitious national GHG emissions reduction and fuel-economy goals are established for the 2050 time frame. Because of the long lead time needed to develop such advanced technologies and strategies, planning and preparation for such measures must begin well before the target dates for commercialization and implementation.

Recommendation: NHTSA should coordinate with EPA to identify a portfolio of technologies and options that could achieve national GHG emission and fuel-economy goals for the 2030 to 2050 time frame and to identify the research, planning, and preparation needed to commercialize and implement such technologies and options in the relevant time frame. (Recommendation 2-3)

Recommendation: As SI engines continue to be improved, NHTSA and EPA should reassess the future balance in MHDVs between SI and CI, and the reductions in GHG emissions and fuel consumption that might be achieved with a more challenging efficiency requirement for SI engines, including an optimized low-carbon or renewable fuel. (Recommendation 4-1)

Recommendation: NHTSA, together with EPA, the Department of Energy (DOE), and the Department of Defense (DOD), should maintain a technology assessment of developments and progress in alternative-configuration engines which evaluates them, analytically and experimentally, against benchmarks and fundamental criteria. (Recommendation 4-5)

Recommendation: Industry and government should continue to research, develop, and apply waste-heat recovery (WHR) systems where technical and economic considerations are reasonable to capture this opportunity to reduce fuel consumption. (Recommendation 4-6) Since hybrid technologies and WHR potentially could play increasing roles in achieving reductions in fuel consumption in the post-2027 period, developments in the cost and efficiency of these technologies should be monitored and be included in a formal interim review of fuel-consumption standards. (Recommendation 12-1)

Recommendation: NHTSA should coordinate with EPA to engage other agencies in the rulemaking process, such as DOE, Federal Motor Carrier Safety Administration, and Federal Highway Administration, who have authorities that can facilitate commercialization of low-carbon fuels and more efficient freight movement methods. NHTSA, in cooperation with EPA, should evaluate how incentives or other regulatory provisions can be incorporated to

facilitate implementation of fuels and freight movement approaches that lie outside of NHTSA and EPA authorities. (Recommendation 2-3)

Recommendation: NHTSA and the U.S. Department of Transportation should consider urging Congress to adopt size and weight regulations that are in line with those of other North American trade partners. (Recommendation 9-4)

ECONOMIC ASSESSMENT AND CONSIDERATIONS

The costs and benefits of specific measures to reduce fuel consumption can be estimated accurately in the near term. The committee had to consider technologies and approaches for medium- and heavy-duty vehicles that could be introduced in model year 2028 or later. Their costs and benefits cannot be estimated with accuracy at this time.

The committee chose to use the NHTSA Lifetime Benefits and Costs Evaluations and the NHTSA and EPA Regulatory Impact Analysis as the foundation of its evaluations. The analysis done by these agencies provided insight into the “marginal cost” and “marginal benefits” of going beyond the rule. The committee assumed that the Phase II rule would take effect and the agencies would be considering a rule to take effect in the 2027 period and beyond. Under this assumption, the required 2.5 percent per annum improvement (needed to comply with the 2027 step of the Phase II rule) would already have been met and further improvements are being considered. In order to meet the higher standard, additional technology will need to be applied to the new vehicle fleet.

In its review of the Regulatory Impact Analysis,¹⁰ the committee found greater reductions are achieved, according to the results shown in Table 10-15 of that document, by the more widespread use of electrification technologies—electronic power steering and accessories, 12-volt stop-start, and strong hybrids. Other technologies either plateau at the high rates, such as eight-speed automatic transmission or turbocharging. Stop-start, mild hybrids, and strong hybrids appear to be a key incremental technology necessary to move beyond the proposed rule and can be used to measure the marginal cost—that is, the incremental cost of increasing fuel economy beyond the proposed rule—as well as the incremental benefit of compliance. Mass reduction and aerodynamic improvements also play a role in moving from 2.5 to 4.0 percent per annum improvement.

The committee’s own analysis, referenced in Chapters 6 through 8, generally supports the conclusions of the analysis of NHTSA and EPA. In addition, it finds the following:

• WHR used in Class 8 over-the-road vehicles potentially offers significant cost-effective fuel savings in the post-2027 period. Expected progress in WHR technology suggests that in the post-2027 period this technology will see increasing penetration in Class 8 tractors.
• In 2027 and beyond, stop-start technology applications are expected to have payback periods that would make them attractive in many applications to private firms. The greater fuel savings, however, that are possible with the application of mild and strong hybrids are expected to be less attractive to private firms, given their relatively long payback periods.
• Considering 10-year fuel savings, however, breakeven fuel prices are either below or at the social cost of fuel¹¹ in many hybrid applications. These results suggest that hybridization is a technology that is “next up” for meeting more stringent post–Phase II standards. Only in Class 2b does the breakeven fuel price for full hybrids exceed the social cost of fuel.
• If the anticipated cost reductions and efficiency gains are in fact consistently achieved, in the post-2027 period increases in fuel efficiency beyond the Phase II rule are likely to be met with increasing applications

___________________

¹⁰ NHTSA (National Highway Traffic Safety Administration) and EPA (Environmental Protection Agency). 2016. Regulatory Impact Analysis, Final Rule for Greenhouse Gas Emissions and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles, Phase II. Washington, DC: NHTSA and EPA.

¹¹ The social cost of fuel includes the private cost of the fuel itself as well as its external costs, including the cost to society of carbon emissions (the social cost of carbon), the societal cost of other pollutants, and any national security costs associated with oil consumption. The payback analysis of private firms excludes these external costs in the evaluation of fuel-saving technology. Furthermore, the 10-year fuel savings metric assumes that the factors underlying the relatively short payback periods used by private firms, such as the uncertainties and lack of information—discussed in Chapter 13—will be resolved over time and with more widespread use of the technology.

• of hybrid technologies, including stop-start, mild, and strong hybrids. The technology penetration will vary depending on vehicle class and duty cycle.

• The cost of technology tends to fall over time as experience accumulates and firms invest in research and development. Projecting these cost developments is difficult because of the variability in experiences—in the characteristics of specific technologies and in the level of firm investments. In order to capture learning effects, NHTSA and EPA use a complicated algorithm to project how technology costs will evolve over time. While there is ample evidence of cost reduction through learning, the empirical evidence does not support these agencies’ complex procedure.

Recommendation: NHTSA and EPA should employ a simpler and more transparent method and rationale on how the unit costs of technologies will evolve, either over time or as a function of the production capacity, in their future assessment. Two options the agencies should consider include (1) assuming specific costs per unit over time for each of the technologies under study, informed by manufacturers’ and experts’ elicitation of likely costs in the future, and (2) applying simple parametric one-factor learning curves, complemented with a sensitivity analysis, to assess how high or low these learning factors would need to be for a technology to be more economically appealing than another. NHTSA and EPA also are encouraged to do ex post assessments of their forecasts of learning effects. (Recommendation 12-6)

FUTURE REGULATORY FRAMEWORK

NHTSA and EPA currently lack reliable data on real-world vehicles that can be used to establish a credible regulatory baseline. It is essential for evaluating the effectiveness and success of the regulatory program and identifying future regulatory priorities and directions.

An effective method of determining in-use fuel consumption of trucks, and thereby of determining the overall effectiveness of the regulatory program, is not currently feasible technologically. Such a method is necessary to assess any differential between the LSFC of an individual vehicle model as certified pre-sale using simulation and the LSFC achieved by such vehicles on the road. The data stream this creates will allow NHTSA to identify opportunities to improve the effectiveness and reduce the cost of the program.

In dealing with MHDV fuel consumption and emissions, the question arises of whether to adopt the same regulatory approach for all classes of MHDVs or different approaches for different classes. If one adopts different strategies, there is a risk of artificially distorting owner choices. Because of differential regulatory impacts on vehicle cost or performance, a buyer may shift to a less regulated class, causing a less efficient vehicle to end up in use, thereby frustrating the purpose of the regulation. However, if there is significant heterogeneity across classes, applying the same regulatory strategy to all classes may lead to an outcome determined by the lowest common denominator. In particular, if it becomes possible to measure simultaneously fuel use, vehicle weight, and distance traveled, there is reason to anticipate that telematics systems that permit in-use measurement of vehicle fuel use will be widely adopted in Class 8b vehicles well ahead of other classes, making it more practical to formulate a performance standard for those sectors.

Given that NHTSA’s Phase II rule covers model years through 2027, NHTSA and EPA have sufficient time to explore potential in-use compliance concepts and approaches. The available time should allow stakeholder involvement in a deliberative process prior to the issuance of any post-2027 regulations to establish the objectives to be achieved and assess and develop an in-use compliance concept that best meets the objectives.

Recommendation: NHTSA and EPA should commit resources to collecting GHG emission and real-world fuel consumption data for a large and representative national sample of pre-control trucks and for each model year subject to the Phase I and Phase II standards, with priority given to those categories of trucks with the greatest fuel consumption. These data could be used to assess the effectiveness of Phase I and early Phase II standards. If the resources for collecting these data exceed those available to the agencies, the agencies should consider requiring the regulated industry to provide the needed data or fund its collection. (Recommendation 3-8)

Recommendation: NHTSA, in coordination with EPA, should develop an effective in-use compliance method that would allow the overall performance of the regulatory program to be quantified, identify whether groups of in-use trucks may not be in compliance, and provide insight into truck operating conditions where GHG emissions and fuel consumption of future trucks could be further reduced. (Recommendation 3-6)

Recommendation: NHTSA, in coordination with EPA, should undertake studies and establish a dialog with stakeholders to identify the most feasible method of determining on a continuous basis the effectiveness of the MHDV fuel consumption and GHG emission program, including in-use compliance. (Recommendation 3-7)

Recommendation: NHTSA and EPA should also evaluate if actual in-use emissions and fuel consumption could become the principal metric for determining compliance, including the costs, complexities, and benefits of such an approach, and if implemented which regulated entity should be responsible for complying with emissions in use based on considerations of practicality, feasibility, and fairness. NHTSA and EPA should also determine whether a compliance program based on in-use emissions could supplant the need for engine emission test and simulation model-specific standards now in place, and if in-use compliance could be extended for the full life cycle of vehicles. (Recommendation 3-7)

INTERIM EVALUATION

The long time period during which NHTSA’s Phase II regulations on fuel consumption will be in effect—through model year 2027—creates an opportunity and need for a midcourse evaluation of the preparations for any future regulations. This would evaluate the implementation progress of the Phase II regulations and other developments in technology availability and feasibility. The Phase II standards—covering model years 2019 to 2027—and any follow-on regulations that may then be in the early stages of formulation, both will depend on many assumptions about technology availability, cost, implementation, and effectiveness. An interim evaluation would provide an opportunity to assess those assumptions and projections and to make a determination on whether any adjustments may be appropriate in the preparations for any future rulemaking. This interim evaluation could also coincide with the next National Academies report, required every 5 years, which could feed into that evaluation in the same way the recently published report on light-duty vehicles¹² (LDVs) will contribute to the 2017 midterm evaluation of the LDV standards.

An interim evaluation of its MHDV regulation in the 2021–2022 time period would help improve the latter’s overall effectiveness and value contribution. Its primary focus would be on preparations for any future regulations beyond the Phase II standards.

Recommendation: NHTSA, in coordination with EPA, should conduct an interim evaluation of the MHDV program in the 2021–2022 time period, focusing on adjustments to and preparations for future revisions to the regulations. (Recommendation 2-5)

The interim evaluation would address the list of tasks enumerated in Chapter 2 and related to the themes of this Summary. All of the report findings and recommendations are discussed thoroughly in each of the chapters. An outline of the report structure, its associated topics, and the committee scope are addressed in Chapter 1.

___________________

¹² National Research Council. 2015. Cost, Effectiveness, and Deployment of Fuel Economy Technologies for Light-Duty Vehicles. Washington, DC: The National Academies Press. https://doi.org/10.17226/21744.