A set of operating rules that permits a following train to enter a block section that is already occupied by another train. The second train must proceed at restricted speed, prepared to stop short of the train ahead. This method is heavily used in congested areas, yards, or station approaches to maximize capacity.
We're on permissive working through the terminal limits, so keep your speed down and watch for the taillights of the local.
Operating under permissive working requires absolute vigilance, as the signaling system will not protect you from rear-ending the train ahead.
Related terms
Block
A group of cars bound for the same destination, kept together so they can be handled as one unit.
Restricted speed
A speed slow enough to stop within half the distance you can see, used whenever the track ahead may be occupied.
Block section
A defined length of track governed by signals that only one train may occupy at a time.