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Introduction

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 (Davis et al., 2014). Unlike the light-duty vehicle sector, which has long been subject to corporate average fuel economy (CAFE) 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 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 the 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.¹

Section 108 of EISA also requires the secretary of transportation to contract with the National Academy of Sciences (NAS) to undertake a study on the technologies and costs for improving fuel efficiency in MHDVs. Upon completion of the NAS report and its own study of fuel efficiency standards for MHDVs, the 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)).

The key events in implementing the EISA requirement for MHDV standards are shown in Figure 1-1. The NAS, through its operating arm the National Research Council (NRC), issued a report on March 31, 2010, titled Technologies and Approaches to Reducing the Fuel Consumption of Medium- and Heavy-Duty Vehicles (henceforth the “NRC Phase One Report”) (NRC, 2010). On May 21, 2010, shortly after the release of the NRC report, President Barack Obama directed the National Highway Traffic Safety Administration (NHTSA), on behalf of the DOT, to issue MHDV fuel economy standards in close coordination with GHG emissions standards to be promulgated for the same vehicles by the EPA (White House, 2010). Given the connection between fuel economy and GHG emissions, a coordinated approach to fuel economy and GHG standards would reduce regulatory costs and

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¹ These timing requirements only apply to the National Highway Traffic Safety Administration (NHTSA) MHDV fuel efficiency standards, not to the accompanying Environmental Protection Agency (EPA) MHDV CO2 standards, which are subject to the Clean Air Act rather than EISA requirements.

burdens and minimize inconsistent regulatory requirements by allowing manufacturers to build one set of vehicles to comply with both sets of standards.

On September 15, 2011, NHTSA and EPA finalized joint Phase I rules to establish a comprehensive Heavy-Duty National Program to reduce GHG emissions and fuel consumption for on-road medium- and heavy-duty vehicles. NHTSA adopted final fuel consumption standards under its statutory authority provided by EISA, and EPA adopted carbon dioxide emission standards under its Clean Air Act authority. The coordinated rules were tailored to the same three regulatory categories of heavy-duty vehicles: (i) combination tractors, (ii) heavy-duty pickup trucks and vans, and (iii) vocational vehicles. The EPA GHG emission standards, which were not subject to the EISA 4-year lead-time requirement, commenced with model year (MY) 2014, whereas NHTSA’s fuel efficiency standards were voluntary in MYs 2014 and 2015 and became mandatory in MY 2016, in order to comply with EISA’s lead-time requirement (EPA and NHTSA, 2015).

In June 2013, President Barack Obama issued The President’s Climate Action Plan, which states that the administration plans to work with stakeholders “to develop post-2018 fuel economy standards for heavy-duty vehicles to further reduce fuel consumption through the application of advanced cost-effective technologies and continue efforts to improve the efficiency of moving goods across the United States” (White House, 2013).

As NHTSA and EPA began working on a second round of standards, the NRC (2014) issued another report—Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two: First Report—authored by the present committee and providing recommendations for the Phase II standards. Key recommendations of that report were for NHTSA and EPA to consider various suggested improvements in the certification and compliance procedures using the Greenhouse Gas Emissions Model (GEM), to adopt fuel efficiency and GHG emission standards for natural gas engines and vehicles, to regulate trailers, to develop and

monitor a baseline for fleet emissions that can be used for measuring real-world emissions, and to consider a low-rolling-resistance performance standard for all new tires. The summary of this report is reproduced in Appendix F.

In July 2015, EPA and NHTSA published a proposed second round of standards—known as Phase II—which were finalized in 2016 (EPA and NHTSA, 2016). The regulations create fuel efficiency and CO₂ standards for the same three categories of medium- and heavy-duty vehicles covered in Phase I: (1) combination tractors, (2) heavy-duty pickups and vans, and (3) vocational vehicles. In addition, for the first time, the federal regulations would regulate trailers pulled by combination tractors, with EPA’s CO₂ standards starting in 2018 and NHTSA’s fuel efficiency standards starting in 2021. NHTSA and EPA estimate that these more stringent Phase II standards would, over the course of the program through 2027, conserve approximately 1.8 billion barrels of oil and cut GHG emissions by approximately 1 billion metric tons, cumulative. Figure 1-2 provides a schematic of the different phases of the regulation, the model year vehicles included, and the types of MHDVs that are considered in the standards.

This third report by the National Academies of Science, Engineering, and Medicine on the NHTSA/EPA MHDV program focuses on a possible third phase of regulations to be promulgated by these agencies in the next

decade (i.e., in the 2020s). The timing for implementation of a third phase of standards would be affected by several factors that are different for fuel efficiency and GHG emissions. Under EISA, NHTSA must provide 4 years of lead time and 3 years of stability when adopting or revising fuel efficiency standards. These discrete timing provisions do not apply to EPA’s regulatory authority under the Clean Air Act (CAA), which specifies that standards “shall take effect after such period as the Administrator finds necessary to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period” (CAA §202(a)(2)). It is therefore possible for EPA to implement its GHG standards before NHTSA can enforce its fuel efficiency standards. The Phase I standards reflected these different requirements with EPA implementing GHG standards with the 2014 models, while NHTSA’s fuel efficiency standards became mandatory in 2016. The Phase II standards will not be fully implemented until 2027. EPA’s third set of GHG standards could begin with the 2028 model year provided they were adopted early enough to provide adequate lead time. NHTSA’s fuel efficiency standards could not go into effect until 2030 due to the statutory 3-year stability requirement. However, to date both standards have been designed to be met with a single engine and vehicle design. Thus the implementation date for the third set of standards will likely be established by the EPA GHG standards, and could be as early as the 2028 model year.

The committee’s work has focused on addressing the technological and regulatory issues related to future regulatory activities regarding MHDV fuel efficiency and GHG emissions, including a potential third phase of rulemakings in the future. The committee’s work was directed at, and guided by, the committee’s statement of task reproduced in Box 1-1. Table 1-1 shows which elements of the statement of task are addressed by which chapters.

REFERENCES

TABLE 1-1 Relationship Between Statement of Task Items and Report Chapters