The Environmental Protection Agency has proposed significant changes to its 2027 heavy-duty diesel emissions rule that could reduce the cost of next-generation trucks while easing some of the uncertainty that has complicated fleet buying decisions.

The EPA proposed rule would leave in place the stringent nitrogen oxide (NOx) emissions standard scheduled to take effect with 2027 model-year heavy-duty diesel engines. However, it would delay some of the rule's costly implementation requirements, including longer useful-life requirements and expanded emissions warranties, while eliminating mandatory diesel exhaust fluid (DEF) engine derates.

EPA estimates the proposed changes would reduce costs by up to $6,000 per engine, though 2027 trucks are still expected to cost more than today's models.

The proposal comes after truck and engine manufacturers spent the past several years warning that while they could meet the lower NOx emissions standard, the rule's durability, warranty and enforcement provisions would add significantly to the cost and complexity of new trucks.

Reaction to Proposal

The Truck and Engine Manufacturers Association welcomed the proposal but emphasized the need for the agency to move quickly.

"As EPA moves forward, it is critical that the rule be finalized by the end of the year to provide manufacturers with the regulatory certainty necessary for compliance planning, go-to-market strategies, and product availability," the association said.

American Trucking Associations President and CEO Chris Spear joined EPA Administrator Lee Zeldin during the announcement, with ATA describing the proposal as rolling back "onerous, unachievable" provisions adopted by the previous administration.

Environmental organizations criticized the proposal, arguing that weakening durability, warranty and inducement provisions could reduce real-world emissions performance over a truck's lifetime.

Could EPA Change Affect Fleet Buying Plans?

The proposal also could affect when fleets decide to buy trucks.

Uncertainty about the final cost of EPA 2027-compliant trucks has made it nearly impossible for manufacturers to set prices and for fleets to plan replacement cycles. OEMs have repeatedly said that without the original rule's warranty and useful-life requirements, price increases could be substantially lower than originally anticipated.

Nevertheless, Class 8 orders have been heating up this year. Freight rates have been rising. Some fleets are looking to add trucks as business improves. Others are simply replacing equipment they held onto longer than planned during the freight recession. In many cases, it's probably a little of both.

ACT Research and FTR both report that manufacturers are rapidly filling available 2026 production slots as improving freight conditions and regulatory uncertainty continue to drive demand.

"Strong orders this month, adding to an already full Class 8 backlog, suggest either higher-than-expected industry builds into year-end or orders increasingly spilling into the first half of 2027," said Carter Vieth, research analyst at ACT Research. He noted that improving freight conditions continue to support demand.

"As we say, truckers only buy trucks when they make money."

FTR reported June Class 8 orders reached the second-highest June total since it began tracking the market. Year-to-date orders are up 125% from a year ago, with remaining 2026 build slots expected to fill quickly. The firm said the market is shifting from one driven primarily by demand to one constrained by production capacity.

"The bigger question now is not demand, but how much of the 2026 backlog converts to production before uncertainty over EPA, tariffs, and USMCA reshapes fleet timing for 2027," said Dan Moyer, senior analyst, commercial vehicles, at FTR.

If finalized, EPA's proposal could remove one of the biggest unknowns facing fleets as they weigh whether to secure one of the remaining 2026 build slots or wait for 2027 models.

What Would Change?

While the proposal has been described by supporters as a rollback of the Biden administration's 2027 heavy-duty emissions rule, it leaves the rule's centerpiece intact: the requirement that heavy-duty diesel engines reduce NOx emissions to 0.035 grams per horsepower-hour.

Instead, EPA is proposing changes to how manufacturers demonstrate compliance and how those emissions systems are supported throughout a truck's service life.

Among the proposed changes:

• Delay the expanded useful-life requirements until 2030.
• Maintain the current five-year/100,000-mile emissions warranty rather than expanding warranty coverage beginning in 2027.
• Replace mandatory DEF-related speed and power derates with visible and/or audible dashboard warnings.
• Allow manufacturers to temporarily sell engines that don't fully meet the new standard by paying EPA nonconformance penalties while they complete the transition.

According to EPA, the proposal would preserve nearly 90% of the NOx reductions expected under the original rule while reducing costs and giving manufacturers greater flexibility during the transition.

What's Next?

The proposal is now open for a 45-day public comment period, after which EPA will review comments before issuing a final rule.