Pre signals have intermittent lights while main signals have constant lights.
Combined pre and warning signals are situated on lines where the distance between the signals is less than 3000 metres. Stop Example 1 . The drawing shows a single-track line with a station to handle trains encountering each other. Two trains are at the moment approaching the station but none of them has reached it yet. The arrows show the directions of incoming trains, and red lines symbolize the ways that are set for the trains.