WASHINGTON, D.C. – The U.S. Environmental Protection Agency (EPA) is looking to further reduce the NOx produced by heavy trucks – particularly under low-load conditions when the vehicles are idling, moving slowly, or in stop-and-go traffic.

Details of the regulatory plans have emerged in a call for comments on the agency’s Cleaner Trucks Initiative, under an Advanced Notice of Proposed Rule (ANPR).

Ongoing Canadian-based research into medium-duty vehicles will also have a role to play in the process. The EPA plans to use Environment and Climate Change Canada’s full vehicle testing being performed on this side of the border, exploring advanced technologies available in the market today.

“EPA expects this study will inform our baseline engine performance for medium-heavy duty engines,” the EPA says.

While NOx emissions in the U.S. have dropped by more than 40% over a decade, heavy-duty vehicles are expected to continue to be a leading mobile source in 2028. Those NOx emissions contribute to unwanted ozone and particulate matter.

“There is more work to be done,” the EPA says in the submission, noting that the EPA last revised the NOx standards in 2001. “We have an opportunity to modernize the requirements to better reflect the capability of available emissions control technologies.”

The EPA’s National Vehicle and Fuel Emissions Laboratory, and the Southwest Research Institute, are now investigating technologies such as cylinder deactivation and intake valve closing to reduce airflow and increase exhaust temperatures. That is expected to help aftertreatment systems control emissions while also reducing fuel consumption – the primary focus of current emissions-related programs. The latest generation of aftertreatment configurations and formulas are also being investigated.

For gasoline engines used in heavy-duty applications, regulators are looking to keep three-way catalysts warm for improved cold starts and low-load emissions, as well as material changes to reduce the need for engine protection modes that increase emissions during high-load applications.

Another study is looking at the accuracy, repeatability, noise, interference and response times of current NOx sensors.

To help manufacturers, meanwhile, the EPA is looking for a way to demonstrate aftertreatment durability through an accelerated catalyst aging procedure.

“We have the opportunity to build on and repeat our past success, but to do so we need the agency to lead a collaborative, data-driven process to determine both the feasibility and cost-effectiveness of any future regulations,” said Jed Mandel, president of the Truck and Engine Manufacturers Association. “Through the Cleaner Trucks Initiative, EPA can assure that any future regulations are not only cost-effective, but also provide sufficient regulatory lead time, stability and certainty.”

It wasn’t the only organization to comment.

“Since 1985, newly manufactured trucks have reduced NOx emissions by over 98%, but our work is not yet done,” said American Trucking Associations executive vice-president of advocacy Bill Sullivan. “ATA is committed to continuing to work closely with EPA on developing the next generation of low-NOx emitting trucks through the Cleaner Trucks Initiative. To this end, the trucking industry seeks one national, harmonized NOx emissions standard that will result in positive environmental progress while not compromising truck performance and delivery of the nation’s goods.”

Todd Spencer, president of the Owner-Operator Independent Drivers Association (OOIDA) said that “serious problems with earlier rulemakings have left small-business truckers justifiably wary of new emissions reduction proposals. However, over the last year, representatives of the EPA have gone to great lengths to fully understand how new policies may affect our members, which wasn’t standard practice under previous administrations.”

More information is available through the Cleaner Trucks Initiative web page.

• An original version of this story has been updated to include comments from the ATA and OOIDA.