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California could phase out diesel locomotives

CARB expected to take up regulation on zero emissions

Union Pacific could be required to use zero-emissions locomotives if the California Air Resources Board approves regulation calling for the use of such locomotives. (Photo: Jim Allen/FreightWaves)

The California Air Resources Board is poised to take action this week on a proposed regulation that seeks to reduce locomotive emissions in the state by phasing out diesel locomotives and requiring zero-emissions locomotives within a certain time frame.

“In the absence of federal action to address harmful emissions from locomotives, CARB is developing regulatory concepts to reduce criteria pollutants, toxic air contaminants, and greenhouse gas emissions for locomotives in-use,” CARB says on its website. “These concepts are intended to be implemented statewide, and provide an opportunity for the railroads to better address regional pollution and long-standing environmental justice concerns with communities near railyards. The goal of the regulatory concepts is to accelerate immediate adoption of advanced cleaner technologies for all locomotive operations.”

The proposed regulation, which would apply to both passenger and freight rail operations that involve travel to seaports, rail yards and other locations, consists of the following:

  • In 2024:
    • Locomotive operators would need to fund a trust account based on how much emissions their locomotives produce and that account would help fund the purchase of cleaner locomotives or the upgrade of existing locomotives.
    • Locomotives with automatic shutoff devices would not be permitted to idle for longer than 30 minutes, except for certain circumstances such as maintaining air brake pressure or providing heat or cooling to the locomotive cab.
    • Locomotives operating in the state would be required to register with CARB and locomotive activity, emission levels and idling data would be reported annually.
  • In 2030:
    • Locomotives must be 23 years old or younger in order to be used in California.
    • “All switch, industrial and passenger locomotives with an original engine build date of 2030 or newer would be required to operate in a ZE [zero-emission] configuration — i.e., qualify as either a ZE locomotive or ZE capable locomotive to operate in California.”
  • In 2035:
    • “All Class I line haul locomotives with an original engine build date of 2035 and beyond would be required to operate in a ZE configuration — i.e., qualify as either a ZE locomotive or ZE capable locomotive to operate in California.”

CARB estimates that between 2023 and 2050, this regulation statewide would reduce approximately 7,455 tons of particulate matter (PM), 389,630 tons of NOx emissions and 21.9 million metric tons of greenhouse gas emissions. The agency says that would be equivalent to removing all heavy-duty diesel trucks from California’s roads for all of 2030.


CARB projects in 2022, locomotives used in passenger and freight operations emitted more than 640 tons per year of PM2.5 and over 29,800 tons per year of NOx emissions.

Rail industry, environmental advocates differ on rule’s usefulness

This week’s deliberations will be the latest in a debate that has been going on for years on whether to regulate locomotive emissions. This proposed regulation was released in November 2022.

The American Short Line and Regional Railroad Association (ASLRRA) has said the regulation could render a number of short line railroads operating in California to become “financially insolvent.” 

“CARB has dramatically underestimated the cost of the Proposed Rule. While the rule proposes extremely onerous recordkeeping and anti-idling requirements, the spending account provision provides the most severe burden to small businesses,” ASLRRA said in an April 2021 statement to CARB. 


The trade association also said costs for new locomotives that could be compliant range between $5 million and $7 million for each locomotive.

“Combined with necessary infrastructure upgrades needed for things like hydrogen fueling or battery recharging, other regulations from local air districts in some parts of the state mandating additional improvements such as exhaust scrubbers in shop facilities, and new indirect emission source rules, these new regulations would significantly destabilize the state’s short line railroad industry, which already operates on relatively small profit margins,” ASLRRA said. “The result of such a destabilization would be California shippers cut off from rail service, impacting their cost structure and ability to compete effectively in the U.S. and world economies.”

ASLRRA also questioned the legality of the regulation since locomotives — including the ones that travel to California from out of state — participate in interstate commerce. 

Environmental advocate Earthjustice said the regulation would clean up the air in communities situated nearby rail yards.

“There are few places where this dirty diesel locomotive pollution is more saturated than in communities located near railyards. Southern California’s Inland Empire and Los Angeles regions are all too familiar with locomotive pollution,” Earthjustice senior associate attorney Yasmine Agelidis said Wednesday on the group’s website. “Not only do these areas suffer from some of the worst air quality in the country, but of the 18 major railyards in California, at least 10 are situated in this region.”

Agelidis also pointed to an environmental analysis by CARB that determined that trucks and not trains would be the cleaner mode to move cargo in 2023. 

This would be due to the shift toward zero-emissions trucks in California, per CARB regulations. CARB is seeking to accelerate a target requiring zero-emission vehicles in California’s trucking sector to 2036 from 2040. 

CARB’s regulation on locomotive emissions would affect Class I railroads Union Pacific (NYSE: UNP) and BNSF (NYSE: BRK.B). Both railroads have been involved in testing alternatively powered locomotives with state officials.


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Joanna Marsh

Joanna is a Washington, DC-based writer covering the freight railroad industry. She has worked for Argus Media as a contributing reporter for Argus Rail Business and as a market reporter for Argus Coal Daily.