Adapting US heavy-duty vehicle emission standards to support a zero-emission commercial truck and bus fleet

This paper proposes to US EPA a regulatory approach that offers high certainty of reaching near-term goals for deployment of zero-emission heavy-duty vehicles (HDVs) and sets the stage for the longer-term transition to zero-emission HDVs. The approach could achieve two interrelated goals: major reductions in greenhouse gases (GHGs), oxides of nitrogen (NOx), and particulate matter (PM) from heavy-duty (HD) vehicles, and the start of the transition to zero-emission MD and HD vehicles of all types. These goals are consistent with President Biden’s call for new standards for heavy-duty engines and vehicles. If designed appropriately, our proposals could jump-start the national transition to electric heavy-duty vehicles and take advantage of the infrastructure investments and fiscal policies the president is pursuing through legislation.

New motor vehicle standards are one of several effective policies to support the transition to a zero-emission fleet. For many decades US EPA set new vehicle emission standards under Section 202 of the Clean Air Act, focusing on the incremental improvement of internal combustion engine-powered vehicles. The result has been steadily cleaner ambient air and significant public health and welfare benefits.  But the urgency of the climate crisis suggests the need for deeper, more rapid, and more sustained emission reductions than those delivered by previous vehicle and engine standards. This need points to the role of zero-emission powertrains as a leapfrog solution over continued incremental improvements. Delivering the technology transition to zero-emission powertrains in the commercial truck and bus fleet requires an effective adaptation of the existing U.S. regulatory framework for internal combustion engines and the vehicles they power.

We propose two basic regulatory steps to extend the current approach to zero-emission vehicles. First, the EPA can take advantage of new vehicle and engine standards applied to MY 2027-2029 to jumpstart the transition to zero-emission vehicles in the near-term, and to update tailpipe NOx emission standards applicable to internal combustion engines. Second, it can use a Phase 3 GHG rulemaking applicable to MY 2030 and later engines and vehicles to lay the groundwork for a comprehensive, longer-term transition to zero-emission vehicles for the entire heavy-duty category. These two regulatory actions present a ripe opportunity for EPA to define the minimum pace of the transition to zero-emission HDVs in coming years.

The design of new standards will shape the outcome. We propose two basic regulatory frameworks. In one approach we call ‘Dual Averaging Sets’, EPA could set separate requirements for zero-emission vehicles and for vehicles powered by internal combustion engines. In another approach we call ‘Single Combined Averaging Set,’ EPA could combine these requirements into one fleet-wide average. Under both approaches the standards would reflect the projected use of zero-emission technology for minimum specified percentages of vehicles and the cleanest and most efficient technologies for the remaining vehicles powered by internal combustion engines.

This paper recommends option 1 over option 2. Option 1 provides high certainty that the projected transition to a percentage of zero-emission vehicles will occur. It does this by requiring a percentage of vehicles to meet standards based on zero-emission technology. It also provides high certainty that the overall level of projected GHG, NOx, and PM reductions would be achieved.

It is critical that we achieve the long-term goal of broadly transitioning to zero-emission vehicles with their elimination of tailpipe criteria pollutant, air toxic, and greenhouse gas emissions over the full life of the vehicle. EPA has regulatory design options such as Option 1 outlined in this paper that can clearly and reliably start the transition to that goal.

image of a truck on a highway

Freight truck on a rural highway