Like a mirage speeding across the dusty desert outside Pueblo, Colorado, the first hydrogen-fuel-cell passenger train in the United States is getting warmed up on its test track. Made by the Swiss manufacturer Stadler and known as the FLIRT (for “Fast Light Intercity and Regional Train”), it will soon be shipped to Southern California, where it is slated to carry riders on San Bernardino County’s Arrow commuter rail service before the end of the year. In the insular world of railroading, this hydrogen-powered train is a Rorschach test. To some, it represents the future of rail transportation. To others, it looks like a big, shiny distraction.

In the quest to decarbonize the transportation sector—the largest source of greenhouse-gas emissions in the United States—rubber-tired electric vehicles tend to dominate the conversation. But to reach the Biden administration’s goal of net-zero emissions by 2050, other forms of transportation, including those on steel wheels, will need to find new energy sources too. 

The best way to decarbonize railroads is the subject of growing debate among regulators, industry, and activists. Things are coming to a head in California, which recently enacted rules requiring all new passenger locomotives operating in the state to be zero-emissions by 2030 and all new freight locomotives to meet that threshold by 2035. Federal regulators could be close behind.

The debate is partly technological, revolving around whether hydrogen fuel cells, batteries, or overhead electric wires offer the best performance for different railroad situations. But it’s also political: a question of the extent to which decarbonization can, or should, usher in a broader transformation of rail transportation. For decades, the government has largely deferred to the will of the big freight rail conglomerates. Decarbonization could shift that power dynamic—or further entrench it. 

So far, hydrogen has been the big technological winner in California. Over the past year, the California Department of Transportation, known as Caltrans, has ordered 10 hydrogen FLIRT trains at a cost of $207 million. After the Arrow service, the next rail line to receive hydrogen trains is scheduled to be the Valley Rail service in the Central Valley. That line will connect Sacramento to California High-Speed Rail, the under-construction system that will eventually link Los Angeles and San Francisco.

In its analysis of different zero-­emissions rail technologies, Caltrans found that hydrogen trains, powered by onboard fuel cells that convert hydrogen into electricity, had better range and shorter refueling times than battery-electric trains, which function much like electric cars. Hydrogen was also a cheaper power source than overhead wire (or simply “electrification,” in industry parlance), which would cost an estimated $6.8 billion to install on the state’s three main intercity routes. (California High-Speed Rail and its shared track on the Bay Area’s Caltrain commuter service will both be powered by overhead wire, since electrification is necessary to reach speeds of over 100 miles per hour.)  

Further complicating the electrification option, installing overhead wire on the rest of California’s passenger network would require the consent of BNSF and Union Pacific, the two major freight rail carriers that own most of the state’s tracks. The companies have long opposed the installation of wire above their tracks, which they say could interfere with double-stacked freight trains. 

Electrifying all 144,000 miles of the nation’s freight rail tracks would cost hundreds of billions of dollars, according to a report by the Association of American Railroads (AAR), an industry trade group, and even electrifying smaller sections of track would result in ongoing disruptions to train traffic and shift freight customers from trains to trucks, the group claims. Electrification would also require the cooperation of electric utilities, leaving railroads vulnerable to the grid connection delays that plague renewable-energy developers. 

“We have long stretches of track outside of urbanized areas,” says Marcin Taraszkiewicz, an engineer at the engineering and architecture firm HDR who has worked on Caltrans’s hydrogen train program. Getting power to those rugged places can be a challenge, he says, especially when infrastructure must be designed to resist natural disasters like wildfires and earthquakes: “If that wire goes down, you’re going to be in trouble.” 

The AAR thinks California’s railroad emissions regulations are too much, too soon, especially given that freight rail is already three to four times more fuel efficient than trucking. Last year, the AAR sued the state over its latest railroad emissions regulations, in a case that is still pending. Though the group generally prefers hydrogen to electrification as a long-term solution, it contends that this alternative technology is not yet mature enough to meet the industry’s needs. 

A group called Californians for Electric Rail also views hydrogen as an immature technology. “From an environmental as well as a cost perspective, it’s a really circular and indirect way of doing things,” says Adriana Rizzo, the group’s founder, who is an advocate for electrifying the state’s regional and intercity tracks with overhead wire.

Synthesizing, transporting, and using the tiny hydrogen molecule can be very inefficient. Hydrogen trains currently require roughly three times more energy per mile than trains powered by overhead wire. And the environmental benefits of hydrogen—the ostensible purpose of this new technology—remain largely theoretical, since the vast majority of hydrogen today is produced by burning fossil fuels like methane. Natural-gas utilities have been among the hydrogen industry’s biggest boosters, because they are already able to produce and transport the gas. 

Opinions on the merits of hydrogen trains have been mixed. In 2022, following a pilot program, the German state of Baden-Württemberg determined that this technology would be 80% more expensive to operate over the long run than other zero-emissions alternatives. 

Kyle Gradinger, assistant deputy director for rail at Caltrans, thinks there’s been some “Twittersphere exaggeration” about the problems with hydrogen trains. In tests, the hydrogen-powered Stadler FLIRT is “performing as well as we expected, if not better,” he says. Since they also use electric motors, hydrogen trains offer many of the same benefits as trains powered by overhead wire, Gradinger says. Both technologies will be quieter, cleaner, and faster than diesel trains. 

Caltrans hopes to obtain all the hydrogen for its trains from zero-emissions sources by 2030—a goal bolstered by a draft clean-­hydrogen rule issued by the Biden administration in 2023. California is one of seven “hydrogen hubs” in the US, public-private partnerships that will receive billions of dollars in subsidies from the Infrastructure Investment and Jobs Act for developing hydrogen technologies. It’s too early to say whether Caltrans will be able to procure funding for its hydrogen fueling stations and supply chains through these subsidies, Gradinger says, but it’s certainly a possibility. So far, California is the only US state to have purchased hydrogen trains. 

Advocates like Rizzo fear, however, that all this investment in hydrogen infrastructure will get in the way of more transformative changes to passenger rail in California. 

“Why are we putting millions of dollars into buying new trains and putting up all of this infrastructure and then expecting the same crappy service that we have now?” Rizzo says. “These systems could carry so many more passengers.” 

Rizzo’s group, and allies like the Rail Passenger Association of California and Nevada, think decarbonization is an opportunity to install the type of infrastructure that supports the vast majority of fast passenger train services around the world. Though the up-front investment in overhead wire is high, electrification reduces operating costs by providing constant access to a cheap and efficient energy source. Electrification also improves acceleration so that trains can travel closer together, creating the potential for service patterns that function more like an urban metro system than a once-per-day Amtrak route. 

Caltrans has a long-term plan to dramatically increase rail service and speeds, which might eventually require electrification by overhead wire, also known as a catenary system. But at least for the next couple of decades, the agency believes, hydrogen is the most feasible way to meet the state’s ambitious climate goals. The money, the political will, and the stomach for a fight with the freight railroads and utility companies just aren’t there yet.  

“The gold standard is overhead catenary electrification, if you can do that,” Gradinger says. “But we aren’t going to get to a level of service on the intercity side for at least the next decade or two that would warrant investment in electrification.” 

Rizzo hopes that as the federal government puts more railroad emissions regulations in place, the case for electrifying rail by overhead wire will get stronger. Other countries have come to that conclusion: a 2015 policy change in India resulted in the electrification of nearly half the country’s track mileage in less than a decade. The United Kingdom’s Decarbonising Transport Plan states that electrification will be the “main way” to decarbonize the rail industry. 

These changes are still compatible with a robust freight industry. The world’s most powerful locomotives are electric, pulling ore-laden freight trains in South Africa and China. In 2002, Russia finished electrifying the 5,700-mile Trans-Siberian Railway, demonstrating that freight trains running on electric wire can travel very long distances over very harsh terrain.

Things may be starting to shift in the US as well, albeit slowly. BNSF appears to have softened its stance against electrification on a corridor it owns in Southern California, where it has agreed to allow California High-Speed Rail to construct overhead wire on its right of way. Rizzo and her group are looking to make these projects easier by sponsoring state legislation exempting overhead wire from the California Environmental Quality Act. That would prevent situations like a 2015 environmental lawsuit from the affluent Bay Area suburb of Atherton, over tree removal and visual impact, that delayed Caltrain’s electrification project for nearly two years.

New innovations could blur the lines between different kinds of green rail technologies. Caltrain has ordered a battery-­equipped electrified train that has the potential to charge up while traveling from San Francisco to San Jose and then run on a battery onward to Gilroy and Salinas. A similar system could someday be deployed in Southern California, where trains could charge through the Los Angeles metro area and run on batteries over more remote stretches to Santa Barbara and San Diego. 

New hydrogen technologies could also prove transformative for passenger rail. The FLIRT train doing laps in the Colorado desert is version 1.0. In the future, using ammonia as a hydrogen carrier could result in much longer range for hydrogen trains, as well as more seamless refueling. “With hydrogen, there’s a lot more room to grow,” Taraszkiewicz says.

But in a country that has invested little in passenger rail over the past century, new technology can only do so much, Taraszkiewicz cautions. America’s railroads all too often lack passing tracks, grade-separated road crossings, and modern signaling systems. The main impediment to faster, more frequent passenger service “is not the train technology,” he says. “It’s everything else.”

Benjamin Schneider is a freelance writer covering housing, transportation, and urban policy.