All trains entering a Single Line Automatic Signalling area not controlled by Centralised Traffic Control system, or an Open Section must, must be scheduled to cross the last train off such a section at the border station irrespective of the time lapse within the same 24 hours or within three hours of the last train off such a section if midnight intervenes.

There are two types of train crossings - commonly referred to in train running parlance as "physical" crossings and "paper" crossings.

PAPER crossings are, in effect, technical crossings which are inserted to indicate to station staff and train crews that the arrival of one train governs the departure of another or conversely the departure of a train is governed by the arrival of another train. As the name suggests such crossings are shown on paper but the trains do not necessarily physically pass one another when running to time. During disrupted or late running, however, the paper crossing provides a safeguard because it is incumbent on station staff and train crews to ensure that all crossings are fulfilled or altered by appropriate instructions.