BRITISH RAILWAYS 1920 - 1970
The types of signal are described below. In the case of early semaphore three-aspect signals (see slotted post), the lamps on the posts showed red for 'stop', green for 'caution' and white for 'proceed'. Later, when most signals showed only two aspects, the equivalents of distant signals confusingly also showed red for 'caution'. The white 'clear' signal was clearly not fail-safe and, after 1893, green was adopted for the 'proceed' aspect. White was then regarded as a danger signal. In 1917, the use of yellow lights for distant signals was commenced, in common with the colour of the arms at a later date (see below).
Note that in signalling terms, ‘in advance’ means beyond a given point on the railway when facing the direction of travel, and should not be confused with ‘advance notice’.
Automatic (semaphore): signal actuated by track circuit. In the system first introduced by the N.E.R. in 1905, the signals normally stood at danger until an approaching train occupied the track circuit. Compressed carbon dioxide moved the signal to Clear and gravity to the Stop position.
Backing: signal used at approach of station platform to enable a train to be reversed into a siding clear of the main line; this signal faces the reverse way to normal traffic.
Balanced arm: a lower quadrant signal arm which was pivoted centrally on a horizontal iron bracket (adopted by the G.N.).
Banner: signal used to provide an advanced 'sight' of a signal in areas of restricted visibility. The Sykes banner signal consists of an arm, centrally pivoted, within a circular case having a glazed front.
Blasting: signal, in the (M.R./L.M.S.) form of a board which rotated on a vertical axis, to advise an adjacent quarry that blasting could proceed. The signal showed full face to the quarry at other times.
Calling-on: signal used to permit a train to draw ahead into an occupied section as far as the line is clear e.g. in a long passenger platform which can accommodate two trains. In some cases the signal arms were mounted with a 'C'.
Colour-light: multiple aspect signal has separate illuminated lenses for each aspect displayed. Three-aspect signals have green, yellow, red lenses in descending order. Four-aspect signals have a yellow, green, yellow, red array and show green-double yellow-single yellow-red aspects (at successive signals) to a train approaching an occupied section.
: searchlight signal displays the red, green or amber aspects through a single lens.
Distant: signal, commonly fish-tailed in form, used to provide a warning of the aspect displayed by the next stop signal ahead. This signal provides two indications of the block section ahead: Clear or Caution. Before about 1926-8, distant signals were generally red with a white vee stripe. The colour was then changed to yellow with a black stripe and the lamp colour from red to yellow.
Double arm (bi-directional): signal with two arms mounted in opposing directions on the same post. An economy measure used on single track lines.
Dummy: see ground disc.
Fixed distant: signal which permanently displays the 'Caution' aspect.
Fixed home: signal which permanently displays the 'Stop' aspect. All trains must come to a stand and await further authority to proceed from the signalman. Such signals were used at approaches to swing bridges and at throats of sidings where the points were hand-operated.
Fixed signal: as used in rule-books, literally any permanently positioned signal.
Gallows: signal which is underslung from a bracket in areas of restricted visibility, especially in station areas, where awnings or bridges may otherwise obscure sight of signals.
Ground disc: subsidiary signal mounted at ground level to control shunting movements. Various patterns have been used including a plain white disc with a red stripe and a miniature arm with or without a white backing display plate.
Home: signal providing absolute protection of the block section ahead. This signal gives two indications: Stop or Clear. In complicated layouts the role may be split between 'outer' and 'inner' home signals.
Junction (or bracket) signal: signal which consists of two or more arms mounted on separate posts above (or below) a bracket, to protect a facing junction. Typically, the symmetry of the bracket and posts reflects that of the junction. In the case of a bracket with posts of unequal heights, the highest signal post denotes the main running line.
Junction indicator: a white light array used in conjunction with colour-light signals to indicate the route set at a junction, where the principal route is not to be taken.
Lower quadrant: semaphore signal which pivots from the horizontal position downwards to the lower quadrant.
Miniature: signal in miniaturised form which may act as a banner signal (q.v.) or provide the signalman in his box with a visual indication of the aspect of a signal, out of his sight.
Relief line: signal on a slow running or relief line, distinguished by a ring mounted on the arm in the case of the L.N.W.R. (removed in 1926) and by an 'S' on some other pregrouping lines (see also Shunt ahead).
Repeater: signal used in the sense of a banner signal (q.v.) or instrument in a signalbox, see miniature above.
Route indicator: a mechanically operated display or white light array used in areas of complex trackwork to obviate the need for multiple signal groupings.
Semaphore: a signal which uses a pivoted arm to indicate aspect, generally in two positions
Semaphore, automatic: see automatic signal
Semaphore, out of use: commonly distinguished by an 'X' mounted on the signal arm, where a line is out of use.
Semaphore, 'ringed': some companies, such as the G.W.R. and L.S.W.R., used semaphores mounted with a ring-shaped plate to control siding movements. See also relief line.
Semaphore, three position: an experimental signal introduced in 1916 where the upper-quadrant arm showed horizontal for 'stop', 450 (yellow light) for 'caution', and vertical (green) for 'Clear'. The advent of colour-light signals in the 1920s rendered this semaphore out of date. Compare 'slotted post signal.'
Shunt (ahead): signal which permits a train to proceed for a restricted distance past a home signal in the Stop position. It may take the form of a ground disc or of a semaphore arm, mounted with an 'S'.
Slotted post: early form of semaphore signal where the arm fell invisibly into a slot in the post, when showing a vertical 'Line clear' indication; an horizontal arm indicated 'stop' and the arm at 45o indicated 'caution'.
Slotted: two signals on one post (home and distant, or starter and distant) each controlled by separate signalmen in closely spaced boxes. Mechanical or electrical ‘slotting’ prevents contradictory aspects.
Somersault: signal of the lower quadrant type which pivots into the fully pendant vertical position for 'clear'.
Splitting distant: a junction (bracket) signal with distant signals providing advance notice of junction stop signals ahead.
Starting: home signal positioned at the departure end of a station platform which gives authority to proceed into the next block section. On busy lines an advanced starting signal may be provided beyond the starting signal so that trains can be cleared from the station to await the clearance of the next block section.
Stone (automatic): signals used to give warning of falls of rock, such signals are connected to a system of wires forming a screen on the hillside above. If one or more wires are broken the signal automatically goes to Danger.
Stop Shunt: signal, in the (M.R./L.M.S.) form of a board which rotated on a vertical axis, to protect a crossing from conflicting shunting movements. The signal was operated by the shunter and when it showed full face to one line, this indicated Stop; end on, it indicated Proceed.
Tunnel: small colour-light signal used in tunnels, mechanically operated before the advent of electrical systems. Advanced warning of the signal was provided by a white light and a treadle-operated audible 'banger'.
Upper quadrant: semaphore signal which pivots from the horizontal position upwards to the upper quadrant. Adopted as standard by most companies (not the G.W.R.) in the late 1920s.
COPYRIGHT © R.D.LAKE 2009