Switchback spur (sawtooth siding)

On a switchback (or sawtooth) spur a siding can only be reached by reversing: the train runs past the turnout, stops, and then backs into the spur. Mountain railways use the same principle as a switchback (zig-zag) to gain height in a tight space. For operation the length of the intermediate or tail track is decisive: the locomotive plus at least one car must fit entirely onto it, otherwise the spur is effectively unworkable.