BRITISH RAILWAYS 1920 - 1970
Block system: absolute block: under this method of working, the railway is divided into individual block sections. No two trains are permitted to occupy the same block section at the same time. The signal which regulates entrance to the block section cannot be cleared until the preceding train completely vacates the section.
: automatic block: a development of the absolute block system used in areas of colour-light signalling. The signals operate automatically according to the running of the preceding trains.
: permissive block: a system used on quadruple tracked lines, where the slow freight-only tracks were permitted to carry more than one train in each block, subject to the requirements of forward visibility.
: intermediate block signalling: on heavy graded lines, an additional signal may be installed on the up-gradient in order to improve the headway between trains. Such an intermediate block signal effectively protects an additional block section.
Cab signalling: an automatic warning system provided in the driver's cab to provide an audible indication of an approaching signal, which if not acknowledged, will actuate an automatic brake system. Also known by its abbreviated form: A.W.S. (A.T.C.: automatic train control before 1959)
Centralised Traffic Control (C.T.C.): a general term for remote control systems, by which points and signals are electrically operated from a distant place using electronic encoded controls.
Detectors: electrical circuit contacts or mechanical detector blades, which are interlinked to the signalling system and provide confirmation that facing poins are correctly set.
Fog signalling: the provision of detonators to give an audible indication of adverse signals in conditions of poor visibility. The detonators, used on non-A.W.S. fitted lines, were emplaced mechanically or by 'fog-men' who also showed supplementary hand-lamp signals.
Interlocking: a failsafe mechanical or electrical system of coordinating point and signal operation whereby such movements are 'interlocked'. Other systems such as level crossing operation are similarly linked to the signalling controls.
Lever collar: a device fitted over a lever handle, which is temporarily out of use.
Lock and block: a system introduced by W.R. Sykes to interlock the signal levers with the block instruments and with train movements, via a treadle operated system.
Overlap: the distance beyond (in advance of) a stop signal which must be free from obstruction before a train is allowed to approach that signal, typically 440yd.
Point locking: a mechanical system of physically locking facing points, interlocked with the signal operation. See also detectors.
Route working: an electro-mechanical system for setting up one route through a section of trackwork by the movement of a single lever. Conventional levers were fitted with electrical contacts designed to actuate the appropriate points and signals.
Signalling relays: electromagnetic switches for electrical circuits.
Single line token: a train-staff or token engraved with the name of the stations at each end of a section to which it applies. The possession of the appropriate token authorises a train to enter a single line section.
Single line working: The following methods were used:
staff and ticket
electric token, tablet or miniature staff
pilotman (during engineering works on double track lines or if token instruments are non-operative)
The exchange of tokens at speed was accomplished in a variety of ways. The simplest used hooped attachments which could be passed from hand to outstretched arm or, from and to receiving and delivering posts. An automatic exchanging apparatus was introduced about 1890 by J. Manson (G.N.S.R.), which was used on other Scottish lines, particularly the H.R. A modified form used on the G. & S.W.R. was effective at speeds of between 4 and 70m.p.h. Another form designed by T. Whitaker (S.D.J.) was also used on the M. & G.N.
Slotting: a mechanical system for coordinating signals under the control of separate signal boxes. In the case of a home and distant assembly on the same post, these signals relate to separate block sections, and such a system prevents the distant signal from showing a clear indication while the home signal shows 'stop'.
Speed signalling: a system based on American practice used between Heaton Lodge and Thornhill junctions, near Mirfield, Yorks between 1932 and 1969. Three colour aspects were shown, to indicate the speed and route to be taken at a junction, plus a fourth red marker light.
Switching out: a system whereby, at times of light traffic, a signal box can be closed down and the adjacent block effectively extended to include the section controlled by that box.
Telegraph rig: the circuitry for connecting signal boxes (telephone, block indicators and bells) and for intra-sectional signalling (repeaters, track circuits, relays, etc) was conventionally carried on telegraph poles. These were typically spaced at 24 (or 32) to the mile.
Track circuit: a system of train detection using relays across electrically isolated sections of track, linked with control circuits for signal and point operation.
Treadle: a mechanical system actuated by the passing of train wheels used prior to the advent of track circuiting. See Lock and block, tunnel signal.
Wrong line working: on double track lines it may be necessary, during track repairs for example, for all trains to use one line. Special arrangements are made to ensure safety, which include the provision of a pilotman to travel on every train which travels over the temporary single line section. In the instance of a succession of trains travelling in the same direction, the pilotman authorises each train to proceed and travels with the last train of the series.
COPYRIGHT © R.D.LAKE 2009