White paper

Comparative assessment of heavy-duty vehicle regulatory design options for U.S. greenhouse gas and efficiency regulation

As regulatory agencies in the U.S. work on the second phase of heavy-duty vehicle greenhouse gas (GHG) and efficiency standards, one of the key decisions they face concerns the regulatory certification pathways. The question of whether to maintain separate standards for the engine and the full vehicle, as in the first phase of the regulation, is hotly debated. In addition, the agencies must decide what upgrades to the testing and certification procedures can be made based on lessons learned from Phase 1.

This analysis develops six possible options for certification, using Phase 1 and publicly expressed industry viewpoints as a guide. The authors then evaluate these options based on seven criteria developed to compare the certification procedures’ relative merits.

Key findings:

  1. The benefits of maintaining separate engine standards outweigh any potential disadvantages.
  2. Physical testing of the powertrain (i.e., the engine plus the transmission) in a new test procedure will be necessary in order to capture and promote transmission and engine-transmission integration improvements.
  3. Some unique inputs about the actual powertrain in a vehicle are necessary in EPA’s Greenhouse gas Emission Model (GEM) simulations to ensure that all fuel-saving technologies and approaches are properly incentivized and accounted for.
  4. More research is needed to determine the appropriate level of engine information to input into GEM to properly credit all efficiency improvements while balancing resource constraints for both industry and government.
  5. A research plan that tracks and compares real-world engine, truck, and tractor-trailer efficiency with certification values for select, high-volume products in 2015–2020 is warranted.