Why do some trains have two engines?

Not all freight trains have two engines, and not all things that have two engines are freight trains. read more

Not all freight trains have two engines, and not all things that have two engines are freight trains. Locomotives ("engines") are designed to be 'lashed up' so that multiple engines can be controlled by the engineer in the first cab, and used to pull a chain of rail cars (a "consist") regardless of whether the cars are passenger, freight or anything else. read more

A related issue concerns midtrain 'slaves' and 'trailing power', engines in the middle or at the end of a train. These are also controlled from the head end, but via some flavor of radio rather than interengine cables and hoses from the lead locomotive. read more

Some units (called “drones”) have engines and motors but no cab of their own, and have to be controlled from another unit. Others (called “slugs”) have cabs but no engines. But the usual U.S. freight locomotive has a single cab, a diesel engine, an electric generator and traction motors to turn the wheels. read more