America is on the verge of welcoming its first hydrogen-powered passenger train, a development that transportation officials and environmental advocates see as a turning point for sustainable transit. Known as the Zero-Emission Multiple Unit, or ZEMU, the train will soon begin operating on the Arrow line between Redlands and San Bernardino in Southern California. With its debut planned for early 2025, the project is being closely watched as a test case for whether hydrogen rail can become a practical and scalable alternative to diesel trains in the United States.
The initiative is the result of a collaboration between the San Bernardino County Transportation Authority, train manufacturer Stadler Rail, Caltrans, and Metrolink. The ZEMU is powered by a hybrid system that combines hydrogen fuel cells with onboard batteries, a design that enables the train to run without emitting harmful pollutants. The only byproduct of its operation is water vapor. Officials have described the project as a historic first for American railroads, as it will be the first self-powered, zero-emission passenger train to operate in compliance with Federal Railroad Administration standards.
The train itself has traveled a long road before arriving in California. It was built in Switzerland, shipped to Belgium, and then transported across the Atlantic before undergoing safety testing at the Transportation Technology Center in Colorado. By mid-2024, it had been delivered to California, where it entered the second phase of testing along the nine-mile Arrow Corridor. The corridor, which opened in 2022, connects downtown San Bernardino to the University of Redlands and is integrated into Metrolink’s regional commuter rail system.
Community leaders and transportation officials have emphasized that the project represents more than a new train; it represents a step toward a new kind of transit system. Ray Marquez, president of the SBCTA board, called the ZEMU “transformational,” noting that the train not only eliminates emissions but also demonstrates how existing rail infrastructure can be adapted for clean technology. The Arrow Corridor was chosen as a testing ground because of its relatively short length, making it an ideal pilot for a new technology that could one day extend across longer rail networks.
The ZEMU also carries symbolic weight. Its blue-and-white exterior is wrapped in a design meant to resemble water vapor, reminding passengers and communities that the train’s emissions are clean and harmless. Supporters hope the train will encourage the public to think differently about hydrogen and its role in transitioning away from fossil fuels. Unlike traditional electrification, which requires costly installation of overhead wires or third-rail systems, hydrogen trains can operate on existing tracks, making them attractive for regions where full electrification is not financially or technically feasible.
California officials have placed the project squarely within the state’s broader climate goals. Caltrans Secretary Toks Omishakin has praised the train’s environmental benefits, saying it aligns with California’s long-term commitment to achieve carbon neutrality by 2045. For Southern California, where air pollution remains one of the most pressing environmental challenges, the project offers the possibility of cleaner air and quieter, more efficient transportation options.
Yet while excitement around the project is high, questions remain about hydrogen’s long-term role in transit. Producing hydrogen at scale still depends heavily on fossil fuels, particularly natural gas, though efforts are underway to expand production of “green hydrogen” through renewable energy. Hydrogen also poses cost challenges compared with alternatives like battery-powered trains, which are already in use in parts of Europe. Critics argue that hydrogen may be better suited for long-haul applications, such as freight trains and heavy trucks, while battery technology could dominate shorter routes.
Despite these debates, California is pressing ahead. The state has already commissioned additional hydrogen-powered trains for future use on intercity routes. Officials expect as many as ten new units, with the potential for more, to enter service on routes connecting Merced to Sacramento as soon as 2027. These expansions are expected to be supported by the state’s hydrogen strategy, which includes billions of dollars in planned investment for fueling stations, research, and new infrastructure.
The debut of the ZEMU in San Bernardino County is significant not only for the region but also for the country as a whole. North America has lagged behind Europe and parts of Asia in deploying hydrogen trains, where they are already in commercial operation. By proving that the technology can work within the U.S. regulatory and infrastructure environment, the Arrow project could set the stage for other regions to follow.
For residents of San Bernardino County, the train is also a matter of local pride. The county, often overshadowed by larger metropolitan areas in California, has become a national leader in sustainable transit innovation. The Arrow Corridor was originally designed to enhance regional mobility, but now it is being recognized as the proving ground for a clean-energy revolution in passenger rail.
As the first passengers prepare to board in 2025, the ZEMU is more than a new way to travel the nine miles between Redlands and San Bernardino. It is a glimpse into what the future of American rail might look like—a future where trains run clean, operate efficiently on existing infrastructure, and help drive the country toward ambitious climate goals. While the journey to widespread adoption of hydrogen technology is far from complete, the Arrow project demonstrates that meaningful progress is already on track.
