The American Lung Association’s 2025 State of the Air report delivered a sobering message: nearly half of people living in the United States are breathing unhealthy levels of air pollution. While cars and trucks are often at the center of conversations around vehicle emissions, there’s a critical and often-overlooked aspect of our transportation sector that contributes significantly to unhealthy air. Locomotives, a.k.a. the engines that power trains, are a leading source of harmful, lung-damaging air pollution.
The engines that haul goods across the country and transport people between cities are most often powered by diesel. These diesel-powered locomotives are extremely polluting communities surrounding railways, and they contribute to the climate change health crisis. Many have been in operation for decades and still rely on outdated technology that spews harmful pollutants and gases into the air we breathe.
The Pollution Problem on Our Tracks
The majority of America’s locomotive fleet is old. Trains built as far back as the 1970s are still on the rails today. These engines release a dangerous mix of emissions, including particulate matter, nitrogen oxides and greenhouse gases. These pollutants cause health emergencies such as asthma attacks, cancer, lung and heart disease and even premature death.
Locomotive emissions impact air quality around the country, especially in communities surrounding rail yards and train routes. Millions of Americans live and work near train tracks, many of them in lower-income and disadvantaged communities that already bear a heavy burden of environmental health risks. Children, older adults and people with existing health conditions are especially vulnerable.
Is Train Travel Sustainable?
It is true that trains are a more efficient way to move large quantities of people and goods when compared to cars and trucks. They use less fuel per ton or per passenger, and they help reduce roadway congestion. Passenger trains, especially, are a key part of a cleaner transportation future.
However, while trains themselves are efficient, the engines that power them are often not. For the people living near rail corridors, their communities are being filled with locomotive emissions that should have been improved decades ago.
Outdated Standards, Outdated Technology
Unlike cars and trucks, which have seen steadily improving emissions regulations over the years, locomotives are still regulated under a system that hasn’t been meaningfully updated in nearly two decades.
The Environmental Protection Agency (EPA) introduced a tiered system for regulating locomotive emissions. The “Tier 4” locomotives, introduced in 2008, are the cleanest diesel-powered trains under current rules. They emit significantly less particulate matter and nitrogen oxides than older models. But here’s the catch: there's no requirement for older trains to be upgraded or replaced. That means trains built under the looser Tier 0, 1, 2, or 3 standards, dating all the way back to 1973, are still on the tracks today.
Many rail companies take advantage of regulatory loopholes that allow them to refurbish older locomotives instead of investing in cleaner or zero-emission alternatives. These rebuilds can keep a polluting train on the tracks for decades longer, with only minimal upgrades. The United States is ready for new locomotive standards that can greatly improve public health and reduce cancer risk.
A Clear Path Forward: Modernize Standards and Embrace Zero-Emission Technology
We now have the tools and technology to dramatically cut emissions from locomotives. Zero-emission electric locomotives are already in use. Newer, more efficient engines are readily available. But without stronger federal regulations to push the industry forward, progress will remain slow.
That’s why EPA must act now to modernize locomotive emissions standards. We need a new Tier 5 standard that reflects today’s technological advances. We need to close the loopholes that let the oldest, dirtiest trains stay in service indefinitely. Finally, we need growing awareness and support to make the case for zero-emission locomotives to be implemented across the country. EPA has an opportunity to finally require older, high-polluting locomotives to meet stronger, up-to-date standards through more efficient technology.
Cleaning up our locomotive fleet is not just an environmental imperative; it’s a public health necessity. Communities near rail yards and train routes deserve clean air and protection from the harmful effects of diesel pollution. By updating standards and transitioning to cleaner, more efficient technologies, we can reduce emissions, safeguard lung health and make our transportation system sustainable.
Advancing public health, reducing cancer risk, and pushing the rail sector toward a cleaner and more efficient future is of the utmost importance, and the U.S. EPA must take action to modernize emissions standards for locomotives to reflect the growth of zero-emission technologies in this field. Let’s get on the right track.
Blog last updated: June 25, 2025
