Push-pull
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- Push-pull can also refer to a type of electronic amplifier.
Push-pull is a mode of operation for locomotive-hauled trains. A push-pull train has a locomotive at one end of the train, and an alternative driver's cab (DBSO or DVT in the UK, cab car in the US) at the other end.
The train can be driven either from 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 driver is located in the alternate cab. This configuration ensures that the locomotive never needs to be uncoupled from the train, and ensures fast turnaround times at a railway station terminus.
Alternatively a push-pull train, especially a long one, may have a locomotive on both ends so that there is always one locomotive pushing and one locomotive pulling. In this case caution must be used to make sure that the two locomotives do not put too much stress on the cars from uneven locomotives. This two-locomotive formation is used by the Intercity 125 and its Australian equivalent the XPT. It is usual to arrange things so that auxiliary power is supplied by the trailing locomotive so that the locomotive at the front does more pulling than the locomotive at the rear does pushing.
See also: Rail terminology