The safety critical part of a signalling system which prevents unsafe situations arising, such as sending trains onto collision courses, or conflicting route .
Most large signal boxes have interlocking sub-areas which are generally based in buildings housing the control relays etc. for a discrete area of the panel. They may also contain an emergency panel for that area.
In some areas the signal number prefixes may reflect the sub-area. e.g. CQ is the prefix for Glasgow Queen Street interlocking area of Cowlairs box.
Last edited by GeoffM on 15/09/2016 at 03:00