Fuel consumption and emissions of medium- and heavy-duty vehicles

Tractor-trailers, buses, commercial trucks, and other heavy vehicles are significant contributors in the transportation sector to energy consumption and greenhouse gas (GHG) emissions, accounting for approximately 22 percent of energy use by U.S. transportation.

The fuel consumption of medium- and heavy-duty vehicles (MHDVs) has only recently begun to be regulated at the federal level. To provide periodic advice on establishing fuel economy metrics and standards that are appropriate, cost-effective, and technologically feasible for commercial MHDVs, the Energy Independence and Security Act of 2007 mandated a series of studies from the National Academies.

The newest report in this series addresses the technological and regulatory issues related to future regulations for MHDV fuel efficiency and GHG emissions.  It recommends the National Highway Traffic Safety Administration (NHTSA) and U.S. Environmental Protection Agency (EPA) conduct an interim evaluation of MHDV regulations in 2021-2022 to ensure and improve their effectiveness and value. This evaluation should address vehicle technologies, fuel mix, efficiency of the freight system, and future regulatory frameworks.

Industry, NHTSA, EPA, and other relevant agencies should promote the use of biodiesel and renewable diesel in MHDV engines, prioritize the development and application of additive manufacturing and other promising manufacturing innovations, improve freight movement efficiency, and collect real-world fuel consumption and GHG emissions data to establish a regulatory baseline – which is essential for evaluating the effectiveness of regulations and identifying future priorities, the report says.

"One key finding is on the importance of thinking about medium- and heavy-duty transportation systems, rather than just technologies," said associate professor of energy resources engineering Inês Azevedo, who contributed to several chapters in the report. "For example, if we were to think about natural gas medium- and heavy-duty vehicles, one would think that they could be a good way to reduce greenhouse gas emissions – but that's only the case if we can reduce the leakage rate from the natural gas system."

This new report is preceded by a 2014 report that provided guidance to NHTSA and EPA as they developed a “Phase II Rule” on fuel consumption and greenhouse gas emissions of MHDVs for the post-2018 time frame.

Azevedo is also a senior fellow at the Stanford Woods Institute for the Environment.

This story was adapted from a press release issued by the National Academies of Sciences, Engineering, and Medicine.