On a
rail transport system,
signalling control is the process by which control is exercised over train movements by way of
railway signals and
block systems to ensure that trains operate safely, over the correct route and to the proper
timetable. Signalling control was originally exercised via a decentralised network of control points that were known by a variety of names including
signal box (International and British),
interlocking tower (North America),
signal poste (France) and
signal cabin (some railways e.g.,
GCR). Currently these decentralised systems are being consolidated into wide scale
signalling centres or
dispatch offices. Whatever the form, signalling control provides an interface between the
human signal operator and the
lineside signalling equipment. The technical apparatus used to control
switches (points),
signals and block systems is called
interlocking.