California Air Resources Board

• Class I locomotive operators are those earning revenue greater than $1.05 billion annually.
• Two Class I operators operate locomotives in California: Union Pacific and BNSF Railway Company.

Class I Locomotive Types

Line Haul Locomotives are large locomotives that haul freight long distances across the country.

• Line haul locomotives are typically powered by 4,400 horsepower engines.
• Class I operators operate about 11,000‑12,000 unique line haul locomotives annually in California.

Switch locomotives, called “Class I switchers” in this fact sheet, are smaller locomotives that pull freight throughout railyards or for short distances outside railyards.

• Switchers are powered by engines with 2,300 horsepower or less.
• Switchers tend to be older and create more harmful emissions in the communities where they operate.
• Class I operators operate about 500‑600 switchers in California.

Emissions

• Diesel‑powered locomotives emit particulate matter (PM2.5) and oxides of nitrogen (NOx).
  • These pollutants are harmful to human health, causing illness and premature death.
• Class I locomotives create about 95% of all locomotive emissions statewide.

The charts below show emissions of PM2.5 and NOx by locomotive type.

Statewide PM2.5 Emissions by Locomotive Type (2022)

Due to insufficient inventory data, historic locomotives are not included in this figure. 

Statewide NOx Emissions by Locomotive Type (2022)

Due to insufficient inventory data, historic locomotives are not included in these figures.   

Continued Reliance on Older Locomotives

Class I operators report their South Coast Air Basin data to CARB through a voluntary agreement.[1] The chart below shows continued reliance on older, dirtier Tier 0 and Tier 1 locomotives and very slow uptake of newer, cleaner Tier 4 locomotives.

South Coast Air Basin Locomotive Operation by Engine Tier (2010 - 2024)

Locomotive Emissions Compared to Truck Emissions

Heavy‑duty trucks move much of the same freight as locomotives. The chart below shows heavy‑duty truck emissions compared with emissions from line haul locomotives moving the same amount of freight under current emission requirements. [1][2]

Total PM2.5 Emissions in Communities Within 20 Miles of the Ports

[1] CARB Truck vs. Train Emission Analysis. (weblink: https://ww2.arb.ca.gov/resources/fact-sheets/truck-vs-train-emissions-analysis)

[2]Based on the projected average mix of trucks and trains in California in the given year

• Starting in 2020, heavy-duty trucks will create less PM2.5 than line haul locomotives hauling the same freight.
• Beyond 2023, future CARB regulations such as the Advance Clean Trucks Regulation bring truck emissions to zero (CARB Advanced Clean Trucks Regulation; https://ww2.arb.ca.gov/rulemaking/2019/advancedcleantrucks)