Designing the Next Fuel Efficiency and Greenhouse Gas Emissions Rule for Heavy-Duty Vehicles

Blog Post | March 04, 2014 - 11:46 am
By Siddiq Khan, Senior Researcher

The president recently announced that a second phase of fuel efficiency and [no-glossary]greenhouse gas[/no-glossary] standards for heavy-duty vehicles will be proposed in March of 2015, with rule adoption a year later. Some aspects of the program are likely to change from the first phase of the standards. In anticipation of such changes, ACEEE has posted a working paper entitled Structural Options for Phase 2 Heavy-Duty Vehicle Fuel Efficiency and Greenhouse Gas Standards.

The first fuel efficiency and greenhouse emissions standards for big trucks and other heavy-duty vehicles were adopted in 2011. They are essentially component-based standards, aimed primarily at improving engine efficiency, tire efficiency, and aerodynamic improvements. In an earlier report, we made the case that the next phase of the program should be based on evaluation of the full vehicle, which would help to drive advanced transmissions, trailer improvements, and integrated vehicle and powertrain strategies. Adding these efficiency opportunities could increase the fuel savings from heavy-duty fuel efficiency standards to over a million barrels of oil per day by 2030.

Our new white paper looks more closely at structural options for the second phase. Moving to a full-vehicle standard without a separate engine standard would promote efficiency improvements throughout the vehicle while giving truck manufacturers full flexibility in achieving the standard. But what could be lost in this approach?

Engine manufacturers would no longer have a direct signal to spur sustained investment in advanced technologies, and coordination with engine criteria pollutant standards already in place would become more complex. The paper evaluates the existing program structure and the full-vehicle approach relative to six criteria, including promotion of advanced technologies, ability to capture real-world vehicle performance, and compliance flexibility. The paper also discusses the option of replacing engine standards with standards for the engine and transmission together, in order to capture the efficiency potential of powertrain integration.

All options present substantial challenges. More data and further analysis are needed to better understand these challenges and how they can be resolved. Our preliminary recommendation is a combined approach, which would retain separate engine (or engine plus transmission) standards with overlaying standards that would cover the real-world performance of the full vehicle.