U.S. EPA unveils new emissions standards for Model Year 2027 and beyond

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The U.S. Environmental Protection Agency (EPA) has adopted a new set of emissions standards for heavy-duty vehicles and engines that will apply beginning in Model Year 2027 – placing a particular focus on nitrogen oxides (NOx).

NOx emissions will be 80% tighter than those that apply today, while mandated warranties on emissions controls will be 2.8 to 4.5 times longer. Manufacturers will also have to demonstrate that the engine designs will prevent drivers from tampering with electronic emission controls.

The final standards will also target emissions during a broader range of operating conditions, such as low-load situations which generate lower exhaust temperatures that reduce the effectiveness of selective catalytic reduction-based emissions control systems. The low-load conditions are believed to account for more than half of the NOx emissions during a vehicle’s typical workday, EPA says.

engine assembly
(File photo: John G. Smith)

Heavy-duty vehicles will need to limit NOx emissions to 0.035 grams per horsepower-hour during typical conditions, 0.050 grams at low load, and 10.0 grams at idle.

The rule is expected to reduce the NOx from heavy-duty vehicles by more than 40% as early as 2040, as new vehicles are introduced into the U.S. fleet. By 2045, when most of the regulated fleet will have turned over, the emissions will be half the levels seen without the changes.

It’s the first update to clean air standards for heavy-duty trucks in more than 20 years. Canada has traditionally adopted emissions-related standards set by the U.S.

Reaction to new emissions rules

“EPA is taking significant action to protect public health, especially the health of 72 million people living near truck freight routes in America, including our most vulnerable populations in historically overburdened communities,” EPA Administrator Michael S. Regan said in a press release.

“This is just the first action under EPA’s Clean Trucks Plan to pave the way toward a zero-emission future. These rigorous standards, coupled with historic investments from the Inflation Reduction Act and the Bipartisan Infrastructure Law, will accelerate [U.S. President Joe] Biden’s ambitious agenda to overhaul the nation’s trucking fleet, deliver cleaner air, and protect people and the planet.”

EPA estimates that, by 2045, the stronger rules will help to realize up to 2,900 fewer premature deaths, 6,700 fewer hospital admissions and emergency department visits, and 78,000 fewer lost workdays, among other benefits.

“It is clear the rule is very stringent and will be challenging to implement,” Truck and Engine Manufacturers Association president Jed R. Mandel said in a statement.

“Our members are fully committed to working with the EPA and other stakeholders for its successful implementation. Ultimately, the success or failure of this rule hinges on the willingness and ability of trucking fleets to invest in purchasing the new technology to replace their older, higher-emitting vehicles.”

EPA received more than 260,000 public comments on the rules.

Limits and allowances

Family Emissions Limit caps are set at 65 mg of NOx per horsepower-hour for Model Years 2027-30, and 50 mg/hp-hr for Model 2031 and beyond. Current caps are set at about 200 mg/hp-hr.

But EPA says it is not finalizing an allowance for manufacturers to generate NOx emission credits from heavy-duty zero-emission vehicles, citing concerns that allowing ZEVs to generate NOx emissions credits would lead to fewer emissions reductions than intended.

Manufacturers will have to demonstrate that emissions controls in the largest heavy-duty engines will keep NOx emissions at 35 mg/hp-hr over the equivalent of 750,000 miles (1.2 million km).

Warranties on emissions controls will extend to 450,000 miles (725,000 km), compared to 100,000 miles (160,000 km) today, while the “useful life” of the equipment will extend to 650,000 miles (1 million km) from 435,000 miles (700,000 km).

“The revised warranty periods are expected to result in better maintenance, including maintenance of emission-related components, and less tampering, which would help to ensure the benefits of the emission controls in use,” EPA notes in the rule. “In addition, longer regulatory warranty periods may lead engine manufacturers to simplify repair processes and make them more aware of system defects that need to be tracked and reported to EPA.”

Updates to maintenance instructions will also include minimum maintenance intervals for certain emission-related components.

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John G. Smith is the editorial director of Newcom Media's trucking and supply chain publications -- including Today's Trucking, trucknews.com, TruckTech, Transport Routier, and Road Today. The award-winning journalist has covered the trucking industry since 1995.


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  • I’m sure glad I don’t have to live by these new regs but we all will have to live WITH them. If you think we have supply issues now , you aint seen nothin’ yet

  • This is good news but what they really need to do is get the dirty, pre-emission trucks and rule cheating glider kits off the road. My 10 year old emission equipped truck blows total zeros on it’s test every year. Yes I had to spend a few grand to fix it but it was worth it.