California air quality enforcers approve rule limiting emissions from idling trucks


  • California has passed a sweeping new rule limiting nitrogen oxide emissions from trucks.
  • The rule potentially sets up another conflict with the Trump Administration over the state’s authority to enact air quality regulations.
  • “We were hoping for a national effort,” said Mike Tunnell, director of environmental affairs for the American Trucking Associations. “We are disappointed the state has decided to go it alone.”

California clean air regulators have approved a new rule aimed at dramatically limiting emissions from slow-moving and idling trucks, arousing the ire of trucking groups and potentially setting up another conflict with the Trump Administration over the state’s authority to enact air quality regulations.

Members of the California Air Resources Board (CARB) on Friday unanimously voted to adopt the “Heavy-Duty Omnibus ( HD Omnibus)” rule. The phased-in regulation would require current NOx (nitrogen oxides) standards be cut about 75% below current standards beginning in 2024 and 90% below current standards in 2027. 

Trucking groups argue the new rule doesn’t give manufacturers enough time to develop technologies that would meet the standards, and that the industry will now have to make trucks for two different markets: California and the rest of the country.

“We were hoping for a national effort,” Mike Tunnell, director of environmental affairs for the American Trucking Associations, told FreightWaves. “We are disappointed the state has decided to go it alone.”

In early 2018, the Trump administration surprised many environmental groups by announcing  that the EPA would propose a new Clean Trucks Initiative in early 2020, also aimed at reducing NOx emissions. 

But earlier this year that initiative was put on hold. California regulators, having worked with the federal agency on the national standard, decided to move ahead with their own NOx rulemaking. 

The EPA “continues to work on the Cleaner Trucks Initiative, which was personally launched by EPA Administrator [Andrew] Wheeler,”  an EPA spokesperson said.

 “As with any large regulatory effort,” she said, “schedules get adjusted on a regular basis.”

Timelines in dispute

NOx emissions are among the primary contributors to smog. The proposed reductions will be equivalent to removing 16 million light-duty cars from the road, according to CARB, reducing health impacts to California port communities that see a disproportionate number of heavy-duty trucks on their streets.

Encompassing several action items, the Omnibus rule requires manufacturers to comply with the stricter emissions standards, overhaul engine testing procedures to better reflect real-world traffic conditions and further extend engine warranties to ensure limited emissions of NOx .

Jed Mandel, president of the Engine and Truck Manufacturers Association, said in a statement that CARB’s timeline for implementation  is not “technologically feasible or cost effective.”

Additionally, the requirements “fail to provide the statutorily required minimum lead time for manufacturers to develop the technologies.”

Engine manufacturer Cummins is working to meet CARB’s proposed 2024 standard with advanced internal combustion engines and powertrains, including alternative fuel options, spokesperson Katie Zarich said in an email to FreightWaves.

Still, “concerns remain with the sweeping changes to certification and compliance requirements proposed in the HD Omnibus regulation,” she said.

“We understand the unique air quality issues California faces and share CARB’s goal to improve real-world NOx emissions from heavy-duty vehicles.” To achieve this goal, Cummins has recommended changes to the new rule aimed at bringing “efficient, reliable, and cost-effective power to our customers and to ensure the regulation is successful in achieving the air quality benefits sought in California.”

A double standard

Another thorn in the side of the trucking industry is that the more stringent NOx rule will take effect at the same time as the Advanced Clean Truck regulation adopted by CARB in late June 2020. That rule requires truck manufacturers to sell an increasing percentage of electric trucks starting in 2024.

The simultaneous rules account for the fact that “vast numbers” of fossil- fuel powered trucks will continue to be sold in California, said CARB chairwoman  Mary Nichols during a hearing on the Omnibus rule last week.

“Even as California ramps up the numbers of zero-emission electric and fuel-cell trucks on our roads over the next decade and beyond, tens of thousands of new internal combustion trucks will still be sold in our state,” she said. “This [Omnibus] regulation ensures that conventional diesel trucks will run as cleanly as possible at every point in their duty cycle.” 

Mandel countered that the compounding and overlapping nature of the two regulatory mandates that CARB approved this summer threatens California’s commercial truck market.

Instead of purchasing “expensive, complicated and unproven new vehicles in California,” truck operators and freight shippers are likely to maintain old trucks longer and seek solutions outside the state, he asserted.

The disconnect between state and national standards means that out-of-state trucks (representing about 60% of vehicle miles traveled) won’t have to meet the California NOx standards. California air quality agencies and the trucking industry alike were pushing for a single national standard, albeit for different reasons.

“We really believe national uniformity is the key,” Tunnell said, “whether it’s other parts of the country or trucks from other states.” The industry hasn’t faced dual NOx standards since the late ‘80s, he said. “It wasn’t optimal.”

California vs. Trump

The EPA spokesperson declined to comment on when the federal agency planned to move forward with the Clean Trucks Initiative, but Tunnell said the association is working with the agency on a standard to take effect in 2027.

Meanwhile, the state will need a federal waiver before it can actually  implement the omnibus regulation in 2024. The EPA spokesperson declined to comment on that process, which could put California on another collision course with the Trump Administration.

Earlier this month CARB signed a deal with five automakers to cut greenhouse gases from passenger vehicles instead of  abiding by weaker federal standards put in place by the Trump administration.  The deal followed the administration’s decision to block California’s longstanding authority to set its own, more stringent air quality standards.

Other states are expected to adopt a similar low-NOx rule, once the California regulation is finalized.

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