Although commonly called diesels, the locomotives actually are electrically driven. The diesel engine drives an alternator, which produces electricity to run electric motors mounted on the locomotive's axles.

In 2026, the power source for trains is transitioning rapidly from diesel to a "hybrid-electric" mix, with Electricity being the dominant force. Most high-speed and commuter rail lines are powered via Overhead Catenary Systems (OCS) or a "Third Rail," which draws electricity directly from the national grid. However, for non-electrified rural lines, we are seeing the rise of Hydrogen Fuel Cells and Battery-Electric locomotives. Hydrogen trains, like the Alstom Coradia iLint, use a chemical reaction between hydrogen and oxygen to generate electricity, emitting only water vapor. Meanwhile, "BEMUs" (Battery Electric Multiple Units) use massive lithium-ion battery packs to bridge gaps between electrified sections of track. While traditional diesel-electric locomotives (which use a diesel engine to run an internal electric generator) still exist for heavy freight in the U.S. and Australia, the industry is moving toward "Bio-Diesel" or "Renewable Diesel" (HVO) as a bridge technology to meet the 2030–2040 net-zero targets for global rail transport.