Locomotives pull (or sometimes even push) a train along the track. Steam locomotives move as pressurized steam created by heating water with a coal, wood or oil fire is fed to cylinders with pistons in them, causing the pistons to move back and forth. The pistons are connected via cranks to the drive wheels which propels the locomotive.

Diesel locomotives work by burning liquid fuel oil in an internal-combustion engine. The engine’s crank shaft turns an electric generator, which sends electricity to traction motors on the trucks of the locomotive. A gear on the traction motor shaft engages a gear on the axle and moves the locomotive wheels. In the following descriptions, (N) indicates narrow gauge and (S) indicates standard gauge.