http://en.wikipedia.org/wiki/Push-pull_train
When operating push-pull the train can be driven from either the locomotive or the alternate cab. If the train is heading in the direction in which the locomotive end of the train is facing, this is considered 'pulling'. If the train is heading in the opposite direction, this is considered 'pushing', and the motorman or engineer is located in the alternate cab. This configuration means that the locomotive never needs to be uncoupled from the train, and ensures fast turnaround times at a railway station terminus