Sometimes a train has no separate locomotive, but the prime mover (diesel engine or electric motor) is located on the first car of the train itself, and the car has engineer's cabin. The car is called a "motor unit". Some trains have motors in many or all of the cars. This is called a diesel multiple unit or electric multiple unit. Usually, both ends of the train have engineer's cabins. These trains are especially popular in commuter traffic in large towns and cities. Electric trains get their power from a third rail or from overhead wires.