Key Elements of EPA's 2027 Low-NOx Rule

The Environmental Protection Agency’s final rule on emissions from heavy-duty diesel engines, “Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards,” was published Dec. 20, 2022 — but it wasn’t much of a Christmas gift for the trucking industry.  

The rule sets very aggressive standards for NOx (Nitrogen Oxides) reductions and leaves engine makers precious little time to test and implement the technology required to meet the requirements.  

And, when the industry is done complying with the NOx reduction mandates in 2027, a new set of greenhouse-gas-reduction mandates, GHG Phase 3, kicks in — to be followed by multi-pollutant standards proposed for light- and medium-duty vehicles that will affect model years 2027 and beyond. 

What’s in the New EPA's 2027 Low-NOx Rule?  

Beginning with model-year 2027 vehicles, the final rule calls for NOx emissions to be slashed to 0.035 grams per horsepower-hour (also expressed as 35 milligrams) during normal operation, 0.05 grams at low load, and 10 grams at idle. Current standards do not take engine load into account, and basically ignore low-load, idle, and start-up conditions when the aftertreatment system is cold and not functioning at optimum efficiency.  The 0.035 mg standard is an 82.5% reduction in NOx emissions from the current standard of 2 milligrams. 

The new rules increase the defined useful life of regulated vehicles by 1.5 to 2.5 times from 435,000 miles out to 650,000 miles.  

Emissions systems warranties will increase by 2.8 to 4.5 times, or from today’s 100,000 miles to 450,000 miles for MY2027 trucks. These longer useful life and warranty periods are intended to ensure that vehicles remain compliant with EPA’s emissions standards as they age.   

Future Truck Emissions Regulations 

By the end of March, EPA is expected to release proposals for the final two steps in its Clean Truck Plan, including the Phase 3 greenhouse-gas-emission standard for heavy-duty engines beginning with MY2027.  

The industry should hear sometime this spring whether EPA will grant a waiver requested by the California Air Resources Board that could cut the congressionally mandated lead time on new emissions systems from four model years to two.  

The Truck and Engine Manufacturers Association filed a lawsuit in May 2022 seeking to ensure that CARB follows requirements established by Congress that heavy-duty on-highway engine and vehicle manufacturers be provided at least four full model years of lead time before new emission standards become effective. A few months later, EMA withdrew the litigation amidst uproar from environmental groups, which painted the lawsuit as challenging emissions rules in general. 

Withdrawing the suit doesn’t change the fact that more lead time would, as EMA President Jed Mandel put it, “… maximize the likelihood of the smooth and successful implementation of new emission standards.”  

In the early months of 2023, however, smooth and successful implementation of EPA’s low-NOx final rules is anything but certain. 

This article appeared in the cover story of the March 2023 issue of Heavy Duty Trucking.