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Truck Engine Makers Wary of Looming California, EPA Pollution Plans (Corrected)

April 26, 2019, 10:30 AMUpdated: May 1, 2019, 12:52 PM

The Trump administration and California are crafting their own plans for addressing air pollution from diesel engines, and the nation’s engine makers and trucking industry fear they could be caught in a costly state-versus-federal vise by this time next year.

California wants to slash the federal standard for emissions of nitrogen oxide—a key cause of asthma and heart disease—by 90 percent from the limit that’s governed truck engines for nearly two decades. But the Environmental Protection Agency is working on its own target that may not be as stringent, although it has yet to release specific details.

Any updated standards would apply only to future model-year heavy duty diesel truck models, and no earlier than model-year 2024.

While the stricter rules would not apply to the more than 13 million diesel trucks currently on the nation’s roads, diesel engine makers are leery of California’s plan, especially if its standard goes into effect before the EPA’s, which looks likely.

“When it comes to heavy-duty truck emissions standards, this is the first time that California and the EPA have been out of sync,” said Sarah Dirndorfer, spokeswoman for the Diesel Technology Forum, the nonprofit education arm of diesel engine makers including Cummins Inc., Daimler AG, and the Volvo Group. “So we’re all working with quite a bit of uncertainty as to how it will all shake out.”

Uncertainty Over the Gap

Both California and the EPA are expecting to issue proposed diesel engine standards at the start of next year. But California, which started its regulatory process earlier than EPA, is looking to finalize its standards later in 2020. The EPA is unlikely to set national standards before 2021 at the earliest.

Since the Clean Air Act requires the EPA and California to give engine manufacturers four years lead time to make engines compliant with the newly finalized standards, California’s emissions limits could be imposed a year or more before the EPA’s.

The disparity in the effective dates worries the industry players involved.

“So what happens in those gap years? Curtailed product offerings in California?” asked Alan Schaeffer, executive director of the Diesel Technology Forum. “Hard to know at this point. So much speculation about what might happen and when.”

Logistical Nightmare

Nitrogen oxide (NOx) emission limits for diesel trucks nationwide have remained unchanged since the final days of the Clinton administration despite the key role NOx pollution plays in forming ground-level ozone and fine airborne particle pollution. And the EPA estimates that heavy duty trucks across the nation will be responsible for one-third of NOx emissions from transportation in 2025.

While tougher standards would be a challenge for truckers to meet, competing standards in California and the rest of the country could be worse, setting up a logistical nightmare for the nation’s trucking industry.

“We, along with the rest of the trucking industry, have supported harmonized national standards, and we continue to engage in discussions with EPA and CARB [the California Air Resources Board] on ways to achieve real-world NOx reductions,” said Claes Eliasson, a spokesman for the Volvo Group.

The automobile industry is already caught between California’s decision to pursue Obama-era greenhouse gas limits for newer passenger cars, and the Trump administration’s plan to reconsider those standards.

Although most internal combustion passenger vehicles in the U.S. use gasoline, most major commercial trucks still use diesel-powered engines, according to the Diesel Technology Forum.

Heavy duty diesel engines already contribute a third of total statewide emissions in California, which is also struggling to meet national air quality standards for ozone and fine airborne particle pollution in the central and southern parts of the state.

Even if it sticks with a 90 percent reduction in allowable NOx, “it is not clear that California will propose standards that are stringent enough to handle their severe pollution problems,” said Luke Tonachel, clean vehicles and fuel group director for the nonprofit Natural Resources Defense Council.

California’s Goal: Achievable or Feasible?

The California Air Resources Board set an optional 90 percent NOx reduction goal for heavy duty diesel engines in 2013, and decided to pursue a mandatory standard three years later. Around the same time, California’s South Coast Air Quality Management District joined several air quality agencies around the country to petition the Obama administration’s EPA to consider the same goal. The EPA in December 2016 agreed, but left it to the Trump administration to respond.

Despite failing to hear from EPA, the state agency forged ahead with its plans, charging the San Antonio-based Southwest Research Institute to test diesel-powered truck engines to see if that 90 percent goal could be met.

Based on initial results of those tests released last week by the California Air Resources Board, staff members suggested the state seek to phase in NOx emissions reductions starting with model year 2024, at 25 to 40 percent of the current standard. They recommended seeking steeper cuts in engines for model years 2027 and beyond to eventually reach the 90 percent limit.

But the staff said these were initial recommendations and could change after further engine tests.

California has separately certified that 10 engines powered by natural gas and liquefied petroleum gas have been able to meet that 90 percent NOx reduction goal.

“The question is not whether the California goal is achievable but whether it is economically feasible,” the diesel forum’s Schaeffer said.

Technical Challenges

Only 36 percent (about 4.9 million) of all commercial trucks in the country have advanced diesel technology to meet the current nitrogen oxide standard of 0.2 grams per brakehorsepower-hour, which was set in 2001 and deployed in diesel engines belonging to model years 2011 and beyond.

The remaining 64 percent of commercial trucks nationwide (8.7 million) are older models operating under prior emission limits because trucking companies have not bought relatively newer fleets with more stringent controls, Schaeffer said.

Last November, the EPA said it would join California through its 2018 Cleaner Trucks Initiative to craft a single, national standard for nitrogen oxide pollution. But the EPA is not giving any clues on where it plans to set the upcoming standards.

“By working closely with states and the private sector, we will reduce NOx emissions from heavy-duty trucks, which is not required by statute or court order, but makes sense to do,” the EPA told Bloomberg Environment.

“The goal is always to harmonize,” agreed Daniel Sperling, a CARB member and founding director of the Institute of Transportation Studies at the University of California, Davis. “This is one of the few environmental actions [EPA] actually proposed to take action on.”

Real-Word Conditions

Engine makers like Cummins want both California and federal regulators to consider real-world driving conditions, not just laboratory emissions tests, in setting new rules.

“Much of the attention is on the nitrogen oxide limits, the numerical standard, but there are a whole range of stringent requirements that truck engines have to meet,” said Brian Mormino, Cummins’ executive director for environmental strategy and compliance.

Trucks also have to meet higher fuel efficiency and low carbon dioxide emissions standards starting with model years 2021.

One challenge for engine makers is to design a typical four-stroke diesel engine that will reduce NOx emissions without compromising the ability to lower carbon dioxide emissions, a greenhouse gas. For example, lower startup engine temperatures decrease carbon dioxide emissions, but result in greater nitrogen oxide emissions.

San Diego-based Achates Power is testing a two-stroke, opposing-piston engine that has shown to reduce nitrogen oxide emissions by 90 percent and to lower carbon dioxide emissions. But this diesel engine has not been used in any commercial trucks, said Schaeffer.

The ideal is to have standards that are based on sound science, economically achievable and don’t cause disruption in the marketplace, Glen Kedzie, vice president at the American Trucking Associations, said in an interview.

Truckers’ Dilemma

If California were to craft tougher-than-national standards, truckers could be in a bind. Trucks have to travel across the country and they cannot afford to avoid driving through California, by itself one of the largest economies in the world, Kedzie said.

Truckers with business in the state could be tempted to “pre-buy” fleets of trucks before the more stringent standards take effect, he said. But such an approach would defeat the purpose of reducing ozone-forming emissions.

If California and the EPA can’t agree, the state is considering another option: allowing engine manufacturers to use “emission credits” to comply with the tougher law. That would work by essentially allowing manufacturers to earn credits for making engines that reach the NOx standard before the compliance date.

“California has a history of not wanting to wait,” Sperling said. “With the U.S. EPA you don’t always know what’s going to happen.”

(Corrected to reflect that the 40 percent figure in the 19th paragraph referred to proposed standards and corrected details about the state's emissions credit program in penultimate paragraph.)

To contact the reporter on this story: Amena H. Saiyid in Washington at

To contact the editors responsible for this story: Gregory Henderson at; Anna Yukhananov at