The U.S. Environmental Protection Agency (EPA) has proposed new measures to reduce pollution from heavy-duty vehicles and engines starting in model year (MY) 2027. The new rule is long overdue — the last set of trucks standards were developed over two decades ago. Unfortunately, the agency’s proposal is weaker than existing state action and fails to advance the deployment of zero-emission trucks at the pace needed to address the urgent public health crisis caused by tailpipe exhaust.
The proposal sets new engine standards to reduce health-harming air pollutants emitted by heavy-duty gasoline and diesel engines and updates the agency’s old greenhouse gas standards for certain commercial vehicle categories, like school and transit buses, delivery trucks, and short haul tractors.
EPA is responsible for slashing air pollution, protecting communities, and addressing the climate crisis. To do so, EPA must meet the moment by finalizing the strongest fossil fuel engine standards possible and set us on a trajectory to zero out truck tailpipe emissions.
The Need For Urgent Action
EPA’s proposal builds on President Biden’s recent Executive Order on Strengthening American Leadership in Clean Cars and Trucks, to set emissions standards for air pollutants from new motor vehicles and their engines.
Strong standards are vital, as emissions from heavy-duty vehicles — which range from U-Haul trucks, to school buses, to 18-wheelers — emanate from our roads, ports, and warehouses and into communities, homes, and playgrounds, poisoning our air and lungs. Across the country, tailpipe fumes envelop the communities living near freight activity, which are often — by design — low-income communities and communities of color.
Heavy-duty vehicles are the largest mobile source of nitrogen oxides (NOx), which react in the atmosphere to form health harming air pollutants like ozone and particulate matter (PM). These pollutants are linked to respiratory diseases, cardiovascular problems, and other adverse health impacts that lead to hospitalization, ER visits, and premature deaths.
Transportation is also the largest source of greenhouse gas (GHG) emissions in the United States, making up 29 percent of all emissions. Within this sector, heavy-duty vehicles, which account for less than 10 percent of vehicles on the road, pollute above their weight class, contributing 23 percent of sectoral emissions.
In many ways, EPA’s proposal is a half-hearted attempt to catch up to the states who have blazed ahead to protect their residents by adopting tough new vehicle emission standards including the “Advanced Clean Trucks” and “Heavy-Duty Omnibus” rules. Together, these regulations will accelerate the transition to zero-emission trucks and buses while cutting NOx pollution from new fossil fuel engines by 90 percent, once fully implemented in 2027. The Heavy-Duty Omnibus rule — a superior version of EPA’s proposal adopted by three leading states — works by comprehensively overhauling exhaust emission standards, test procedures, and other emissions-related requirements for on-road trucks for model years 2024 and beyond. State action to curb NOx displays the level of ambition that should, at a minimum, be pursued by EPA.
Breaking Down The Proposed Rule
EPA’s proposal contains two parts: new NOx and PM standards for heavy-duty vehicles beginning in 2027 and minor revisions to the existing GHG emission standards for heavy-duty trucks in 2027.
New NOx And PM Requirements
For NOx and PM, the proposal includes two options under consideration: a mediocre Option 1 and an unacceptable weak Option 2. EPA also evaluated an “alternative proposal” that was generally more stringent, but the agency dismissed it as infeasible, despite the fact states have already gone further. Importantly, the proposal closes existing loopholes by regulating the substantial pollution from regular operations such as low speed driving, idling, and stop-and-go traffic that previous rules have not addressed.
Option 1 would implement NOx standards in two steps, intending to align with some aspects of the states’ Heavy-Duty Omnibus rule by 2031. By 2031, the expectation is that NOx standards would be 90 percent lower than today’s standards. EPA estimates that if this option is adopted, heavy-duty vehicle NOx emissions would drop 60 percent by 2045.
The greatest failure of Option 1 (and the entire proposal) is EPA’s explicit decision to ignore zero emission vehicle (ZEV) technology. How could EPA ignore something as big as this electric transit bus?
Not only does the proposal do nothing to accelerate the transition to ZEVs — the best available technology to control NOx, PM, and GHG emissions — it completely ignores the rapidly growing ZEV market, driven by state adoption of the Advanced Clean Truck rule.
This is a fatal flaw because the NOx standard relies on a “fleet average.” That means new heavy-duty vehicles must, on average, emit less NOx. For example, if you produce 100 trucks and 50 are ZEV, and 50 are highly polluting diesel trucks, you can, on average, still meet the NOx standard. And this gets worse over time as ZEV adoption picks up thanks to state actions to propel the market forward and the increasingly attractive economics of ZEVs.
A major difference between Option 1 and existing state action is that it unnecessarily delays aligning with the Heavy-Duty Omnibus rule for four years. Instead of requiring the same stringency in 2027, EPA wants to delay lifesaving emission reductions until 2031, allowing dirtier engines that will be on our roads for decades to be sold for four additional years.
Not all of Option 1 misses the mark. There is a general alignment with the Heavy-Duty Omnibus Rule on particulate matter standards and on warranty and useful life provisions (which cover the engine’s minimum allowed warranty and expected duration of utility for a certain number of years, miles and/or hours). Longer warranty periods make it less likely for owners to tamper with emissions controls and more likely to make the repairs they need sooner rather than later, ensuring that the emission reduction systems continue to work like they should while in operation.
Option 2 is unacceptably weak, failing to adequately address NOx pollution from heavy-duty vehicles and including only one level of standard with no additional ramp up in stringency. This option never reaches the stringency of state action. Not only does this option lack ambition on the deployment of ZEVs, but it also fails to align with the Heavy-Duty Omnibus rule in key areas, including NOx emission limits and useful life provisions.
Option 2 is essentially a giveaway to the highest polluters in the engine manufacturing industry and shouldn’t be seriously considered by EPA.
Lastly, EPA offers an Alternative option. The Alternative is more stringent than either Option 1 or 2, as it has a shorter lead time, greater NOx reductions, and longer useful life periods. EPA believes the Alternative to be infeasible in the MY 2027 timeframe and that it needs additional supporting data that refutes the agency’s initial conclusions to consider adopting it in the final rule. But states have already demonstrated otherwise and experience shows that every time industry has claimed a tailpipe standard was infeasible, they’ve generally met the mark early and at a lower cost than projected.
Minor GHG Rule Updates
The second part of the proposal involves small changes to the “Phase 2” GHG standards for medium- and heavy-duty vehicles, that were finalized in 2016. Unfortunately, EPA again fails to adequately understand and characterize the ZEV technology market, so the updates fall short.
The targeted revisions will only impact a portion of all trucks and buses, specifically, school buses, transit buses, delivery trucks, and short haul tractors, for MY 2027 through 2029.
While EPA claims its revisions are intended to both lower the overall level of GHG emissions and incentivize zero and near-zero emissions vehicle development, the rule is insufficient on both accounts.
The new GHG stringency levels misjudge ZEV penetration levels for MY 2027 in its baseline assumptions by estimating that the overall percentage of heavy-duty ZEVs in MY 2027 will be approximately 1.5 percent. This is absurdly low and will be met even if only California complies with its existing Advanced Clean Truck rule. Considering five other states have already adopted the same rule and more will soon follow, the proposed EPA rule wouldn’t move the needle at all. To give meaning to President Biden’s “Executive Order on Strengthening American Leadership in Clean Cars and Trucks,” EPA needs to account for the baseline required by state law and set a standard that moves the market for zero-emission vehicles beyond that business-as-usual path.
EPA Must Step Up And Finalize A Stronger Rule
To align with the President Biden and EPA Administrator Regan’s often repeated equity goals, EPA must set standards that adequately address the high levels of NOx pollution and GHG pollution that disproportionately burdens low-income communities and communities of color.
On the NOx and PM portion of the proposal, EPA must adopt the strongest diesel engine standards possible. This would include an enhanced version of Option 1 in addition to a national zero-emission truck requirement – which would help slash truck pollution, increase the number of zero-emission trucks on the road, and bring health benefits more quickly to the communities that need them most.
On the GHG rule update, EPA must set stringency levels that build upon the foundation state rules have already laid and incentivizes additional electrification.
Anything less leaves too much on the table and fails to provide the relief from dirty air that environmental justice communities have been denied for too long.
Next Steps & How You Can Help
A lot must be done to get the agency’s proposal to where it needs to be. Over the next month, NRDC, and other public-interest groups will push back on industry opposition and advocate for stronger standards. Every voice counts — you too can help by telling EPA to adopt a stronger rule.
In the end, EPA must step up to protect our air and live up to President Biden’s executive order, which states correctly: “America must lead the world on clean and efficient cars and trucks.”
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