Locomotive Fact Sheets

Locomotives Overview

Locomotives are self‑propelled off‑road equipment used to push or pull rail‑mounted cars carrying freight or passengers.
Locomotives travel throughout the state to seaports, railyards and other locations that are near where people work and live.
Locomotives can be powered diesel or zero emission (ZE) sources such as batteries, hydrogen fuel cells, or overhead catenary.
Diesel‑powered locomotives, the most common type of locomotive in California, emit multiple air pollutants, including diesel particulate matter, fine particulate matter (PM2.5), oxides of nitrogen (NOx) and greenhouse gases (GHG).
Exposure to toxic and harmful diesel emissions is known to lead to cancer and increases in asthma, cardiopulmonary illness, hospitalizations, and premature mortality.
Communities near rail operations bear a disproportionate health burden due to their proximity to harmful emissions.

There are several types of locomotive operators in California. Select a locomotive type to view the fact sheet.

Locomotive Emissions

As of 2022, diesel locomotives are projected to produce:
- Over 640 tons per year of PM2.5
- Over 29,800 tons per year of NOx
Zero emission locomotives produce zero tailpipe PM2.5 and NOx emissions.
Locomotive emission standards, called Tiers, are described in the graphs below. Tier 0 is the dirtiest diesel locomotive standard, and Tier 4 is the cleanest diesel locomotive standard. The standards are divided between two locomotive power levels, referred to as line haul (locomotives greater than 2,300 horsepower) and switch (locomotives 1,006 ‑ 2,300 horsepower)

Line Haul Locomotive Emission Standards

Historic locomotives are not included in this PM2.5 graphic due to insufficient population data.

Switch Locomotive Emission Standards

Switch locomotive emission standards

Historic locomotives are not included in this PM2.5 graphic due to insufficient population data.

2020 California Locomotive Population by Tier

Pie chart showing the population breakdown of California locomotives by Tier. Over 90 percent are Tier 3 or older.

Historic locomotives are not included in this population graphic due to insufficient population data.

The graphs below show percent reductions (in tons per day) of PM2.5 and NOx that will be achieved in each operating type by 2050.

Statewide PM2.5 Locomotive Emissions by Type

This graph shows the PM2.5 emissions in 2025, 2037, and 2050 from all locomotive operator types in California

Historic locomotives are not included in this PM2.5 graphic due to insufficient population data.

Statewide NOx Locomotive Emissions by Type

This graph shows the NOx emissions in 2025, 2037, and 2050 from all locomotive operator types in California

Historic locomotives are not included in this NOx graphic due to insufficient population data.

Decrease in Cancer Risk from the Transition to Tier 4 Locomotives

Cancer Risk: Using a conservative approach, CARB staff modelled cancer risk assuming all locomotive use in California is at an average of Tier 4 emission levels. In the two railyards modelled, it is estimated cancer risk will decrease by over 90%.

bar chart showing decreases in cancer risk due to exposure to locomotive emission under the regulation

Zero Emission Locomotives

Locomotives can be powered by ZE sources like batteries, hydrogen fuel cell, and overhead catenary. Select a ZE source below to learn about how they can be used with locomotives.

Incentive Funding for New Technology

Based on development timelines for new technology, CARB staff estimate that ZE passenger and switch locomotives will be commercially available by 2030, and ZE line haul locomotives by 2035. CARB released the Technical Support Document: Zero Emission Locomotive Conversion along with the regulatory package prior to the Board hearing.

CARB offers grant funding to upgrade or replace locomotives to Tier 4 or ZE. Visit CARB Incentives for Locomotives for more information.