How Hydrogen Trains Work: The Tech Replacing Diesel on Non-Electrified Rails

For decades, the rail industry has been the poster child for sustainable transportation. Yet a surprisingly large share of regional rail services across North America and Europe still runs on diesel. These are lines that were never electrified because installing continuous overhead wires across sprawling, low-density routes is prohibitively expensive.[9]

That is the exact gap hydrogen-powered trains—often called "hydrail"—are designed to close. By generating their own electricity onboard, these trains offer the smooth, quiet performance of an electric locomotive without the need for billions of dollars in catenary wire infrastructure.[8][9]

In late 2025, this technology crossed a major threshold in the United States. The San Bernardino County Transportation Authority (SBCTA) officially launched the Zero-Emission Multiple Unit (ZEMU) into regular passenger service. Built by Swiss manufacturer Stadler, the ZEMU is North America’s first self-powered, zero-emission passenger train fully compliant with Federal Railroad Administration standards.[2][6]

The ZEMU, wrapped in a distinctive blue and white water-vapor design, now operates on the nine-mile Arrow Corridor connecting San Bernardino and Redlands, California. It represents a blueprint for transit agencies looking to eradicate diesel from their commuter networks.[1][6]

While the U.S. is just boarding the hydrail movement, Europe has been laying the track for years. In 2018, French manufacturer Alstom debuted the Coradia iLint in Germany, marking the world's first commercial deployment of a hydrogen fuel cell passenger train.[4]

Since then, the Coradia iLint has expanded its footprint, securing orders in France and Italy, and completing successful trials in Austria, Sweden, and Poland. In the summer of 2023, a pilot project in Quebec, Canada, carried over 10,000 passengers, saving 8,400 liters of diesel and averting 22 tons of carbon dioxide emissions over just four months.[3][7]

But how does a hydrogen train actually work? Despite the name, most hydrail vehicles do not burn hydrogen in a traditional combustion engine. Instead, they are fundamentally electric trains equipped with a mobile power plant.[5][9]

The process begins on the roof of the train, where high-pressure tanks store gaseous hydrogen. This hydrogen is fed into a fuel cell stack, where it meets oxygen drawn from the ambient air.[5][9]

Inside the fuel cell, an electrochemical reaction—essentially reverse electrolysis—strips electrons from the hydrogen atoms. This flow of electrons creates an electrical current that drives the train's traction motors. Because there is no combustion, the only direct byproducts exhausted from the train are heat and pure water vapor.[4][5]

However, fuel cells are best suited for providing a steady, continuous output of power. Rail traction, by contrast, is highly dynamic. Trains require massive surges of energy to accelerate from a dead stop or climb steep gradients.[9]

To solve this, modern hydrogen trains operate as hybrids. The fuel cell is paired with an onboard lithium-ion battery pack. The fuel cell constantly charges the battery, which then handles the peak loads during acceleration. When the train brakes, regenerative motors capture the kinetic energy and feed it back into the battery, maximizing overall efficiency.[5][9]

This hybrid architecture gives hydrogen trains a distinct operational advantage over pure battery-electric models. While battery trains are improving, they still suffer from limited range and long recharging times. A hydrogen train like the Coradia iLint can travel up to 621 miles (1,000 kilometers) on a single tank and can be fully refueled in about 30 minutes.[4][8]

Yet, the hydrail revolution is not without its uncertainties. The true climate benefit of a hydrogen train depends entirely on how the hydrogen itself is produced. Hydrogen is an energy carrier, not a primary energy source, meaning it must be manufactured.[5][9]

Currently, the vast majority of industrial hydrogen is "grey," produced by steam methane reforming of natural gas. While running a train on grey hydrogen still produces 45% fewer emissions than burning diesel, it is not a truly zero-emission lifecycle.[5]

The ultimate goal is "green" hydrogen, which is produced by splitting water via electrolysis powered by renewable energy sources like wind or solar. Until green hydrogen production scales up globally, the environmental promise of hydrail remains partially constrained by the broader energy grid.[7][9]

Infrastructure presents another formidable hurdle. Transitioning to hydrail requires transit operators to build entirely new refueling depots, install high-pressure storage tanks, and secure reliable supply chains for industrial-grade hydrogen.[2][5]

Despite these challenges, the rail industry is heavily investing in the hydrogen ecosystem. Polish manufacturer PESA is currently developing a tri-mode train that can seamlessly switch between hydrogen fuel cells, battery power, and overhead electric lines, optimizing energy use across mixed infrastructure.[3]

Ultimately, hydrogen is not a universal substitute for traditional rail electrification. For high-speed lines and dense urban corridors, continuous overhead wires remain the most efficient solution. But as a targeted tool to decarbonize the sprawling, hard-to-electrify routes where diesel has long been the only practical option, the hydrogen train has definitively arrived.[8][9]