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Published : 14 Dec 2025, 08:41 PM
BNSF Railway, one of the crown jewels of Warren Buffett’s sprawling Berkshire Hathaway conglomerate, calls itself an environmental leader in the US rail industry with the cleanest locomotive fleet in North America.
“When you see our orange locomotives’ and freight cars’ steel wheels moving on steel rails, think green,” BNSF says in its latest sustainability overview.
But the company is the largest player in an industry that has a pollution problem: US freight railroads are a major source of pollution, chuffing out more nitrogen oxide, the primary component of smog, than all the nation’s coal-fired power plants combined, according to a Reuters calculation using government data.
US railroads together produced about 485,000 tons of nitrogen oxide in 2024, compared to 452,000 tons emitted by US coal-fired power plants, according to a Reuters calculation of reported annual fuel consumption multiplied by the EPA’s 2023 weighted-average emission rates.
BNSF, the nation's largest freight railroad, accounts for about a third of that total, producing 161,500 tons of smog-causing nitrogen oxide in 2024, according to the data. “We don't dispute your number. BNSF is the biggest Class I railroad by volume,” BNSF said in an email.
BNSF's position as largest in the rail industry, as well as its profitability, will be challenged if regulators approve the planned $85 billion merger of Union Pacific and Norfolk Southern, which would create the first US coast-to-coast freight rail operator, Morningstar railroad analyst Greggory Warren said.
Reuters shared its calculations with four industry experts and all agreed it was a fair methodology. About 80 percent of the industry's NOx tons are produced by Class I railroads, the industry term for the six major railroads with more than $1 billion in annual revenue.
Details on the rail industry’s recent NOx emissions performance, BNSF’s share of those emissions, and the factors driving the ongoing high levels of pollution have not previously been reported.
Railroad locomotive pollution causes an estimated $48 billion in healthcare costs and 3,100 premature deaths annually in the United States, according to the EPA’s Co-Benefits Risk Assessment tool.
“Americans don’t realise how much harmful pollution comes from old diesel locomotives,” said Bill Magavern, policy director for the Coalition for Clean Air, a California group that advocates for public health. “EPA should require the railroad companies to modernise their fleets,” he said.
The EPA declined to comment specifically on rail pollution for this story, but said: "The Trump EPA is committed to enhancing our ability to deliver clean air, water, and land for all Americans.”
AGING FREIGHT LOCOMOTIVES
The railroad industry’s poor emissions performance is due mainly to the fact that it has largely stopped replacing its aging fleet of locomotives. The average age of US locomotives is about 28 years, compared with 20 years in 2009, according to EPA and industry reports.
That's a problem because federal emissions standards for locomotives depend on how old they are with the oldest grandfathered into the lightest limits.
With no requirement to retire old locomotives, the US freight rail industry has dragged its feet on buying new ones, a dynamic amplified by industry fears that new regulations under future administrations could render their investments obsolete, according to Environmental Protection Agency data, and interviews with analysts and railroad executives.
Senator Edward Markey, a Massachusetts Democrat, says railroads have lost their taste for innovation. "Our air pollution standards for railroads have an engine-sized loophole in them, which companies are using to... keep old, dirty trains on the tracks," Markey said in a statement to Reuters.
The rail industry says that it is the cleanest option available to move freight over land, and cites data from the US Department of Transportation. A locomotive can move a ton of freight about 500 miles on a gallon of fuel, which is three to four times more efficient than trucks.
The Association of American Railroads said it was also unfair to compare rail to power plants, saying locomotives have little choice but to burn diesel. "These power plants have multiple other viable options for generation – coal, natural gas, hydropower, wind, nuclear, etc. That is not the case for rail," the trade group told Reuters.
BNSF, meanwhile, told Reuters that it is working to reduce its emissions through efficiency and technology improvements, and stands by its claim to have the cleanest fleet in the industry based on the outright number of modern locomotives in its possession.
BNSF said 360 of its 6,780 total are modern locomotives subject to the strictest federal emissions standards, called Tier 4, the largest outright number in the industry.
That's just 5 percent of the company's total fleet that is active or in storage, according to Surface Transportation Board data. By contrast, rival Canadian National has nearly 300 Tier 4 locomotives, making up about 27 percent of its total fleet, according to analysts and CN press releases about new locomotive orders.
Tier 4 locomotives operated by BNSF's nearest competitors number about 270 at Union Pacific; about 225 at CSX Corp.; and about 80 at Norfolk Southern, according to EPA data, company press releases and trade industry reports.
BNSF spent $394 million on 165 new and rebuilt locomotives from 2020 to 2024. That was down 69 percent from the prior five years when it spent $1.26 billion on 558 locomotives, as replacement of aging engines—some lasting up to 40 years—slowed sharply, according to BNSF annual reports filed with the US Surface Transportation Board.
CLEANEST FLEET?
BNSF's high emissions, however, are not just the result of its size.
BNSF’s fuel economy is the worst among the country’s six major railroads, according to railroad operating statistics filed with the US Surface Transportation Board, the industry’s economic regulator.
In 2024, BNSF burned 1.14 gallons of diesel for every ton of weight it moved 1,000 miles, an industry metric called a gross ton mile. Union Pacific burned 1.08 gallons to move the same weight the same distance, and the most efficient, Canadian National, burned 0.88 gallons, according to the data.
Railroad industry analysts interviewed by Reuters said one reason for BNSF's low fuel economy is that it handles more intermodal freight than peers.
These high-priority shipping containers need to move faster than regular freight because they are typically more time-sensitive, said Jason Kuehn, a railroad analyst and vice president at consulting firm Oliver Wyman.
BNSF's intermodal shipments totaled 5.3 million in 2024, or nearly 60 percent more than No. 2 Union Pacific, according to company disclosures.
Analysts said BNSF's efficiency is also likely hurt by its limited adoption of precision-scheduled railroading, an industry practice meant to reduce costs and fuel use through longer trains, fewer locomotives, and less idling time. Fuel efficiency can also be hindered by mountainous terrain and congestion on a railroad's network.
BNSF declined to comment on the reasons behind its relatively low fuel economy, but maintains it is an environmental leader in the industry based on its adoption of new locomotives, which allow it to burn fuel more cleanly.
“BNSF has the most modern platform locomotives in the rail industry, the basis for our cleanest fleet statement,” the company told Reuters.
It declined to provide details on its fleet-wide emissions intensity, and Reuters was unable to verify if it was better than rivals.
Tier 4 locomotives can reduce NOx emissions by about 80 percent compared to Tier 3 models, according to the EPA.
FEAR OF REGULATION
The main reason railroads stopped spending big money on new locomotives is because they are worried new regulations - including proposed zero-emissions standards in California - could quickly make them obsolete.
"These locomotives have a lifespan of 40 to 45 years, and you're saying they won't be able to use those because we'll have zero emissions," said Roger Nober, director of George Washington University’s Regulatory Studies Center who retired as BNSF’s chief legal officer in 2023.
"Railroads don’t see that as an efficient use of their capital."
In 2008, the EPA hoped to clean up freight rail by setting new standards for locomotives, including higher standards for new Tier 3 and Tier 4 models. But rather than encourage replacement of old locomotives, rail companies have slowed down their purchases of new locomotives dramatically.
In 2008, the EPA estimated that at least 30 percent of freight locomotives would be operating under the strictest limits by 2025. But as of 2023 only 6.5 percent of 19,303 active locomotives operated by the big six railroads meet that limit, according to the EPA.
Before 2008, American railroads replaced their locomotives at a 4 percent rate per year, according to the US Office of Transportation and Air Quality. By 2024, the industry replacement rate had dropped to 0.5 percent per year.
Neither BNSF nor its rivals provide exact data on the model years of active locomotives in their national fleets.
One key battle for the industry has been opposing California's proposed emissions standard, which would have banned locomotives older than 23 years from operating in the state, and required all locomotives to be zero-emissions by 2035.
Because California is such a large market, it can effectively set the national standard.
Officials at the California Air Resources Board (CARB) estimated that by 2050 the stricter rules would have reduced 7,400 tons of diesel soot, 386,000 tons of NOx and cut cancer risk for those living near rail operations by up to 90 percent.
But it would have also barred 65 percent of active freight locomotives from operating in the state, rail officials say.
A week before Donald Trump’s inauguration as US president in January, California withdrew the proposal.
Trump has been a frequent critic of CARB and was expected to block the initiative by denying California the waiver it would have needed to set state pollution rules that are tougher than federal ones.
In May, House Republicans introduced the Locomotives Act, which would prevent California from securing such waivers. The bill has been referred to the Energy and Commerce Committee.
FIGHTING GREEN TECHNOLOGY
The rail industry has also lobbied hard against the adoption of clean technologies. BNSF told the EPA last year at a public hearing that their test of a battery-electric locomotive failed to deliver enough power to move tons of freight over long distances.
"The battery had two megawatts of usable energy,” John Lovenburg, BNSF’s vice president for environment and sustainability, said. “That’s roughly 1/40th of the energy we will need for line-haul locomotives.”
Electric locomotives are viable for shorter routes and replacing diesel locomotives in switch yards, but for long distances they're limited by battery weight, said Alex Scott, a professor of supply chain management at the University of Tennessee.
Battery-electric locomotives are not prevalent in the United States and other parts of the world. But in China, India and Russia, a majority of their freight locomotives draw their power from overhead electric lines, or catenary systems.
That sort of electrification in North America would cost more than $1.1 trillion for 139,000 miles of track used by the six major railroads, according to a February 2025 study by the Association of American Railroads.
"The railroad industry is slow to adopt new things because if you have problems, it's not just your problem," Scott explained. "You're creating problems for your customers and other railroads because they share track all of the time."
