California Air Resources Board

CARB is committed to reducing air pollution to protect public health. We encourage industries to reduce their emissions and look forward to continued partnership in these efforts. CARB is working with industry to create and test zero‑emission locomotive technologies. As discussed in CARBʼs Mobile Source Strategy, such technologies are critical to the Stateʼs ability to protect public health, address climate change, and meet both State and federal air quality standards. CARB is also researching technologies and strategies that will support the passenger and freight rail goals discussed in the State Rail Plan.

Background

Overthepast20years,CARBhasworkedtoreduceemissionsfromlocomotivesbyenteringintoenforceableagreementswiththerailroads.WhileprogresshasbeenmadethroughtheCARBemissionreductionagreementswiththeClass1Railroads,additionalemissionreductionsfromtherailsectorarecriticaltomeetthecriteriapollutantstandardsacrossthestate.In2017,CARBalsopetitionedU.S.EPAtocreateanew,cleaneremissionsstandardsforlocomotives.

OnNovember9,2022, the United States Environmental Protection Agency (U.S.EPA)respondedtoCARB'spetition,stating:

• U.S. EPA will develop options for possible regulatory actions, examine current locomotive rules, and consider appropriate actions to ensure that their rules continue to meet Clean Air Act (CAA) requirements.
• U.S. EPA will undertake a notice and comment rulemaking process to reconsider existing locomotive preemption regulations to ensure they don’t inappropriately limit California’s and other states’ authorities under the CAA to address their air quality issues.
• U.S. EPA noted that the passing of the Inflation Reduction Act (IRA) provides an enormous opportunity for locomotives to transition to zero emissions and committed to explore opportunities to leverage these historic resources moving forward. 

Additionally, the State of California has placed additional emphasis on protecting local communities from the harmful effects of air pollution through the passage of Assembly Bill (AB) 617 (C. Garcia, Chapter 136, Statutes of 2017).  AB 617 is a significant piece of air quality legislation that highlights the need for further emission reductions in communities with high exposure burdens.

In the absence of federal action to address harmful emissions from locomotives, CARB approved the In‑Use Locomotive Regulation (Regulation) to reduce criteria pollutants, toxic air contaminants, and greenhouse gas emissions for locomotives in‑use. This Regulation would have been implemented statewide and provided an opportunity for locomotive operators to better address regional pollution and long‑standing environmental justice concerns with communities near railyards and other locomotive operations. In November 2023, CARB requested authorization for the Regulation from U.S. EPA. However, in January 2025 CARB withdrew its authorization request because it was not going to be approved by the Regulation’s compliance dates. To prevent confusion and uncertainty for California locomotive operators, CARB repealed the Regulation in June 2025.