Most trains run on either diesel fuel or electricity, with the split depending on where in the world you are. About 35% of the world’s rail lines are electrified, meaning the majority still rely on diesel-powered locomotives. But that balance is shifting, and newer technologies like hydrogen fuel cells are starting to enter service.
Diesel: Still the Dominant Fuel
Diesel is the workhorse fuel of railroads worldwide, especially for freight. But modern diesel locomotives don’t work the way most people assume. They’re actually hybrids. A massive 12- to 16-cylinder diesel engine doesn’t directly turn the wheels. Instead, it spins a high-voltage electrical generator through a driveshaft, and that generator sends power to electric traction motors mounted at each axle. Those motors are what actually move the train.
This hybrid design exists for a practical reason: the diesel engine can run at a constant, efficient speed regardless of whether the train is crawling uphill or cruising on flat track. The electrical system handles the variable demands of acceleration and speed changes. A typical freight locomotive produces around 3,200 horsepower, and the gear reduction between the traction motors and axle shafts allows speeds up to 125 mph. The result is impressive efficiency. A modern freight train can haul one ton of cargo more than 480 miles on a single gallon of diesel, making rail 3 to 4 times more fuel efficient than trucking the same load.
Electricity: Cleaner and Faster
Electric trains draw power from an external source rather than carrying fuel on board. That power comes in two forms: overhead wires (called catenary systems) or an electrified third rail running alongside the track. Overhead systems typically operate at 25,000 volts AC and are used for high-speed and long-distance rail. Third rail systems run at lower voltages, around 750 volts DC, and are common in subways and urban commuter lines. The lower voltage limits speed and capacity, which is why you won’t see third rail on a bullet train route.
In both cases, traction power substations along the route convert high-voltage electricity from the national grid into the right voltage for the trains. The train picks up this power through a pantograph (the arm on top of the train) or a contact shoe (for third rail), and electric motors convert it directly into motion. No combustion, no exhaust at the point of use.
The emissions advantage is significant. Electric locomotives produce about 0.134 pounds of CO2 per passenger-mile, compared to 0.280 pounds for diesel, less than half. That gap widens further as electrical grids incorporate more renewable energy. Europe leads global electrification at 55% of its rail lines, followed closely by the Asia-Pacific region at 53%. North America lags well behind, with most freight lines still running diesel.
Hydrogen: The Newest Option
Hydrogen fuel cell trains are a relatively new entry, designed to replace diesel on routes where installing overhead electric wires would be too expensive or impractical. These trains carry tanks of compressed hydrogen gas, which reacts with oxygen in a fuel cell to produce electricity. That electricity powers traction motors just like in a diesel-electric locomotive, but the only byproduct is water vapor.
The first commercial hydrogen train, the Coradia iLint, has been operating in northern Germany since 2018. Refueling takes roughly 20 to 60 minutes depending on the setup, and the trains can cover substantial distances on a single fill. In September 2022, an iLint set a world record by traveling 730 miles on one tank of hydrogen. That range makes hydrogen competitive with diesel for regional passenger routes, and several countries are now testing or ordering hydrogen trains for lines that would be costly to electrify.
Maglev: Powered by Magnets
Magnetic levitation trains don’t burn any fuel in the traditional sense. They run entirely on electromagnetic energy, which provides both lift and forward motion. Instead of wheels on rails, maglev trains float above a guideway using powerful magnets, eliminating the friction that limits conventional trains.
There are two main approaches. In electromagnetic suspension (EMS) systems, magnets underneath the train are attracted upward toward the guideway, pulling the train into a hover. A linear motor built into the train generates both the levitation and the propulsive force. In electrodynamic suspension (EDS) systems, superconducting magnets on the train induce currents in the guideway as the train moves, creating a repulsive force that pushes the train upward. EDS systems use a separate mechanism for forward propulsion.
In both designs, an alternating current flowing through motor windings creates a traveling magnetic wave that pulls the train forward without any physical contact. This is essentially a conventional electric motor unrolled into a flat strip and laid along the track. The energy source is grid electricity, fed into the guideway infrastructure. Maglev trains can reach speeds above 370 mph, but the specialized guideway makes them extremely expensive to build, which is why only a handful of commercial maglev lines exist worldwide.
How They Compare on Efficiency
The choice of fuel shapes everything about a rail system’s cost, speed, and environmental footprint. Diesel remains unmatched for flexibility since the locomotive carries its own fuel and can operate anywhere there’s track. Electric trains are faster, quieter, and produce far less carbon per mile, but require substantial infrastructure investment along every inch of the route. Hydrogen splits the difference, offering zero-emission operation without overhead wires, though the refueling infrastructure is still in its early stages.
For freight, diesel’s dominance is likely to continue for years simply because of the vast, unelectrified networks already in place. For passenger rail, especially in Europe and Asia, the trend is clearly toward electrification. And for the rural or regional routes that fall in between, hydrogen is emerging as a practical bridge technology that avoids both diesel emissions and the cost of stringing wires across hundreds of miles of countryside.