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Section 2: Main Signals

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In semaphore signalled areas, lack of space sometimes prevented a semaphore arm being accommodated. In these situations, it was necessary to dispense with the semaphore arm and provide a signal that displayed a red or green light indication by day or night. This creates an anomaly, however, since while semaphore signalling practice allows a green light in one signal to be followed by a red light in the next, the same cannot occur in colour light practice (in normal working). To overcome the risk of confusion, the LMS would fit such signals with a white opal marker bearing a black ring [2.110]. The marker was illuminated only when the signal was exhibiting a green aspect and, where practicable, only if the signal ahead was at 'danger'. The marker advised the driver that the signal was acting like a semaphore signal and he should be prepared to find the next signal at 'danger'.

[2.110] Two-aspect signal at 'clear' with illuminated marker below.
Area: LMS   Usage: Low   Status: Historical

To accommodate increased wartime traffic, the GWR provided intermediate block sections through the Severn Tunnel in 1941. The intermediate block home signal on each line took the form of a two-aspect colour light signal. As a safeguard against lamp failure, the 'danger' aspect consisted of two red lights [2.111]. These signals were removed in 1947.

[2.111] Double Red Aspect.
Area: Severn Tunnel / South London   Usage: Low   Status: Historical

On 28 February 1975 an accident occurred at Moorgate, which was then part of the London Underground's Northern City Line. A loaded passenger train ran at speed through the buffer stop and into the tunnel end wall. As a result, British Rail decided that in future all colour light signals reading into terminal platform lines would show a yellow rather than a green aspect when the line was clear to the buffer stop.

In December 1975, the yellow aspect (see [2.92]) of the single-aspect colour light distant signal on the Gravesend West Branch at Fawkham Junction (Southern Region) was replaced by a yellow fluorescent disc on the existing signal post [2.112].

During bridge construction work on the Riverside branch (Newcastle) in February 1977, the site of the work was protected in each direction by a stop board reading "Stop - Await instructions" (see Section 26). An advance warning board comprising a yellow disc on a white background [2.113] was provided on the Up Branch line to act as a fixed distant signal for the stop board ahead.

[2.112] Fixed Distant Marker.
Area: Fawkham Junction   Usage: Low   Status: Historical
[2.113] Advance Warning Board.
Area: Riverside branch (Newcastle)   Usage: Low   Status: Historical

In May 1977, marker boards were provided on the approaches to the buffer stops at Kirkby station (London Midland Region). Although performing the function of fixed distant signals, these were in the form of advance warning boards of the style more usually associated with level crossings (see [16.10]). Both were replaced by standard reflectorised distant boards in December 1985.

The Liverpool Loop line, opened in 1977, was provided with two-aspect signalling similar to that which was already in widespread use on the London Underground. Two-aspect signalling involves two types of signals, i.e. stop signals and repeater signals. A stop signal shows a red light for "Danger - Stop" or a green light for "Clear - Proceed". Where sighting is good, drivers are expected to be able to stop at a 'Danger' signal with no advance warning. Where sighting of a stop signal is restricted, a repeater signal will be provided in rear. A repeater signal shows a yellow light for "Caution - Be prepared to find next signal at Danger" or a green light for "Clear - Proceed". A repeater signal for a stop signal in advance may be co-located with the preceding stop signal. Where this occurs, the repeater signal is mounted below the stop signal, so that the "Caution" aspect comprises a green light over a yellow light [2.114] and the "Clear" aspect is green over green [2.115]. When the stop signal is displaying a red aspect, no light is shown in the repeater signal below, in contrast to the combined stop and distant colour light signals that once existed on the GWR (see [2.101]).

[2.114] Green Aspect over Yellow Aspect.
Area: Liverpool Loop line   Usage: Low   Status: Current
[2.115] Green Aspect over Green Aspect.
Area: Liverpool Loop line   Usage: Low   Status: Current

With the introduction of the Class 253 & 254 'High Speed Trains' (or 'InterCity 125s') to British Rail, it was found necessary to introduce two additional signal aspects. The new flashing aspects were designed to give the driver advance warning that the junction signal ahead (see Section 6) is showing a 'proceed' aspect applicable to the diverging route. Where there is more than one diverging route, the flashing aspects only refer to the highest speed divergence(s). A flashing single yellow aspect [2.116] means "Preliminary Caution - Be prepared to find the next signal displaying one yellow light, with a route indication for the highest speed diverging route". Where provided, the flashing double yellow aspect [2.117] means "Proceed - Next signal displaying flashing single yellow" and is an indication of a diverging route ahead of the next but one signal. The new aspects were first introduced at Didcot East Junction (Western Region) in March 1979, signals R70 and DM49 on the Down Main line being equipped to display a flashing single yellow and a flashing double yellow aspect, respectively. This installation was soon followed by others on each of the remaining regions apart from, initially, the Southern Region.

[2.116] Flashing Single Yellow Aspect.
Area: All Areas   Usage: High   Status: Current
[2.117] Flashing Double Yellow Aspect.
Area: All Areas   Usage: High   Status: Current

In 1979, a marker board was erected on the approach to the buffer stop at Stourbridge Town station (London Midland Region). Acting as a fixed distant signal, the board displayed an outline of a semaphore distant arm in the 'on' position [2.118].

Between 1980 and 1982, distant boards were being provided in place of fixed semaphore distant signals on various colliery branch lines on the Eastern Region. These comprised a square yellow board with a black chevron [2.119].

[2.118] Distant Board.
Area: Stourbridge Town   Usage: Low   Status: Historical
[2.119] Distant Board.
Area: Eastern Region   Usage: Medium   Status: Historical

In the early 1980s, a 'low cost signalling committee' was formed, tasked with developing proposals aimed at reducing the cost of signalling lightly used lines. Amongst other ideas, these included the emergence of a standard form of reflectorised distant board, following the manufacture of a number of experimental boards for evaluation purposes [2.120 - 2.123]. The style of board that was chosen to become standard [2.123] was first put into use in 1982.

[2.120] Experimental Reflectorised Distant Board.
Area: Unknown   Usage: Low   Status: Historical
[2.121] Experimental Reflectorised Distant Board.
Area: Unknown   Usage: Low   Status: Historical
[2.122] Experimental Reflectorised Distant Board.
Area: Various   Usage: Low   Status: Obsolescent
[2.123] Experimental Reflectorised Distant Board (subsequently adopted as standard). Click Here for Photo
Area: All Areas   Usage: High   Status: Current

To facilitate special test runs of the new Class 91 electric trains on the East Coast Main Line at 140 m.p.h., it was necessary to introduce a new signal aspect. Signals on part of the route, between Peterborough and Stoke Tunnel, were altered in 1988 to be capable of displaying a flashing green aspect [2.124]. For the test trains, a flashing green aspect gives authority to exceed 125 m.p.h. and a steady green (see [2.93]) means reduce speed to 125 m.p.h. For all other trains, a flashing green has the same meaning as a steady green.

[2.124] Flashing Green Aspect.
Area: Peterborough - Stoke Tunnel   Usage: Medium   Status: Obsolescent

An experimental form of distant board appeared at Blaenau Ffestiniog (London Midland Region) in 1989, replacing a fixed semaphore distant signal on the line from Trawsfynydd. The new board had the image of a yellow distant arm on a black background [2.125]. Three self-luminous 'Betalights' were fitted to the front of the arm to give drivers a visible indication during darkness. Betalights had the drawbacks of being radioactive and susceptible to vandalism.

[2.125] Distant Board with Betalights.
Area: Blaenau Ffestiniog   Usage: Low   Status: Historical

In the South London area in 1992 and 1993, while resignalling work was being carried out in connection with the Channel Tunnel project, temporary block working by ticket was implemented over certain lines. The colour light signals at the exits from the affected sections were fixed at 'danger' and a handsignalman appointed at each would instruct the driver to proceed when authorised by the signalman. Because the signals in question had no lamp-proving, their 'danger' aspect comprised two red lights (see [2.111]). In the event of one light failing, the handsignalman would immediately inform the signalman.

Britain's first high speed line was the Channel Tunnel Rail Link (CTRL), the first section of which opened in 2003. The completed line runs between London and the Channel Tunnel. High speed lines do not have lineside signals, because a driver could not reasonably be expected to read and interpret a signal aspect at high speed. Instead, cab signalling is used, with fixed markers placed at the lineside to mark the start of each block section. The CTRL is signalled with a cab signalling system called TVM. This is the same system as used in the Channel Tunnel itself, as well as on the high speed lines in France, where high speed lines had been in operation for many years beforehand. The letters "TVM" stand for 'Transmission Voie-Machine', which means 'Track to Train Transmission'. The British block markers are based on the French 'repères', bearing a yellow triangle on a blue square background [2.126]. The apex of the triangle points towards the line to which it applies. The marker indicates to the driver the position at which the train must come to a stand when a 'stop' indication is shown on the cab signalling display.

[2.126] TVM Block Marker (e.g. applies to the line on the right). Click Here for Photo
Area: CTRL   Usage: High   Status: Current

The European Rail Traffic Management System (ERTMS) is a signalling and management system developed with the backing of the European Union. The objective of ERTMS is to allow seamless operation ("interoperability") across international borders without the problem of having incompatible signalling systems on either side. ERTMS may be overlaid onto ordinary lineside signalling. Alternatively, it may function solely as cab signalling. The standard form of block marker for ERTMS lines with cab signalling is similar to a TVM block marker (see [2.126]), with the triangle replaced by an arrow [2.127]. The arrow points towards the line to which the marker applies. In the unusual situation where a block marker is mounted directly over the line to which it applies, the arrow points down [2.128].

[2.127] ERTMS Block Marker (e.g. applies to the line on the right). Click Here for Photo
Area: All Areas   Usage: High   Status: Current
[2.128] ERTMS Block Marker applicable to the line below.
Area: All Areas   Usage: Low   Status: Current