Home Page > Section 12; pages: 1, 2

Section 12: Signs associated with Train Protection Systems

(Page 1 of 2)


Over the years, various safety systems have been introduced on Britain's railways to help drivers observe and obey signals and, to a lesser degree, speed restrictions. Some were implemented throughout almost the entire network, while others were confined to specific areas or routes. In general, all these systems function either by automatically applying the brakes in the event of a signal being passed at 'danger' (or in anticipation of a signal being passed at 'danger') or by providing audible and/or visual indications inside the driving cab, although usually they do both. Even though the indications primarily occur inside the cab, lineside signs or indicators associated with these systems are sometimes needed.



The mechanical trainstop system is employed on some urban DC electrified railways. Trainstops are installed beside the track at stop signals. When the signal is at 'danger', the trainstop's arm is raised. The tripcock on a train that passes the signal at 'danger' will engage with the trainstop arm and cause a brake application. Tripcock testers and associated indicators are provided on the approaches to lines fitted with trainstops. When a train approaches, the indicator will become illuminated and display the letters "TT" [12.1]. The indication will remain lit until the tripcock on the train operates a treadle close to the indicator. If the indicator continues to show "TT", it must be assumed that the train's tripcock is not in the correct position.

[12.1] Tripcock Test Indicator. Click Here for Photo
Area: Various   Usage: Medium   Status: Current

In 1906, the Great Western Railway introduced its "audible cab signalling" system, which gave the driver an audible indication in the cab when approaching or passing a distant signal (see Section 2). Such faith was placed in the system that it was expected eventually to replace the distant signal at the lineside. The 'clear' indication was given by a bell. For the 'warning' indication, a siren would sound, which the driver could cancel by lifting a lever. From c.1910, the siren was accompanied by an automatic brake application and the system was renamed "Automatic Train Control" (ATC). Widespread fitment took place at distant signals on GWR lines.

Following nationalisation in 1948, British Railways set about developing an improved version of the ATC system as a standard for use across the whole network. The project was given added urgency by a terrible crash at Harrow & Wealdstone on 8 October 1952. The resulting "Automatic Warning System" (AWS) was introduced in 1956. It incorporated a warning horn and bell in the cab in a similar fashion to the ATC system. The horn has to be cancelled by the driver pressing a button. An additional feature of AWS is the visual indicator, originally provided for test purposes but retained and adopted as standard. The indicator shows 'all black' when the train passes over the AWS equipment on the approach to a signal. If the signal is showing 'clear', a bell sounds and the indicator remains 'all black'. If the signal is showing 'caution' or 'danger', then as soon as the warning horn has been cancelled, the indicator changes to a visually striking pattern of black and yellow segments, referred to as the 'sunflower'.


At places where the BR AWS system abutted the Western Region AWS (ex GWR ATC) system, a notice board was provided lettered "B.R. A.W.S." or "W.R. A.W.S.", as appropriate [12.2].

[12.2] Notice Board.
Area: Western Region   Usage: Low   Status: Historical

Before a locomotive equipped with WR AWS apparatus could run over a fourth rail electrified line, its AWS shoe had to be clipped up to avoid the risk of it coming into contact with a live rail. A special high ramp placed in the 'four-foot' allowed the clipping-up of the shoe to be performed automatically. In the 1960s, Western Region diesel multiple units began running into Paddington Suburban station via the electrified lines of the London Underground. Since these units had more than one AWS shoe, it was necessary to ensure that they were all properly clipped up. After a trainborne shoe-checking system proved unsatisfactory, a track-based system was installed, which included a blue light fitted to the signal post at the end of the clipping-up zone [12.3]. The driver was required to see that this light remained lit as the train approached. If the light went out, it meant that one of the shoes was not properly clipped up.

[12.3] WR AWS Shoe Clip-Up Indicator.
Area: London Paddington   Usage: Low   Status: Historical

At some through stations where the track layout is complex and speeds are low (30 m.p.h. or less), AWS equipment was not installed in the station area. The commencement and termination of the AWS gap are marked by lineside signs. The commencement sign is a circular board bearing the letters "AWS" and a diagonal red cross [12.4] while the termination sign bears the letters "AWS" inside a square [12.5]. Normally, no signs are provided to mark the boundaries between AWS fitted lines and non-fitted lines; however, in recent years there has been a tendency to misuse these AWS gap signs for that purpose.

[12.4] Commencement of AWS Gap.
Area: All Areas   Usage: High   Status: Current
[12.5] Termination of AWS Gap.
Area: All Areas   Usage: High   Status: Current

On 6 June 1975, a high speed derailment occurred at Nuneaton, as a result of the lights in a gas-lit temporary speed restriction (T.S.R.) warning board (see [14.14]) being extinguished. As a recommendation of the Ministry of Transport's report into the derailment, provision of AWS equipment was extended to include T.S.R. warning boards. From 1977, a portable temporary AWS magnet was to be installed on the approach to the warning board so that a warning indication would be received in the cab. Where a portable AWS magnet is installed on a single line, a warning indication will be received regardless of the train's direction of travel. Where this situation arises, a cancelling indicator is provided ahead of the magnet, in the opposite direction from the warning board, to advise drivers that the AWS warning just received must be cancelled in the usual way and then disregarded. The original form of cancelling indicator comprised a black square with a white diagonal cross, illuminated during darkness [12.6].

From 1981, cancelling indicators were being permanently installed at locations where it was not practicable to suppress the AWS equipment for moves to which it did not apply. Permanently installed cancelling indicators have a blue background [12.7] and are reflectorised, although a few early examples were floodlit. Temporary illuminated cancelling indicators with a similar blue background were introduced concurrently with blue T.S.R. signs (see Section 14), giving identical colouring to both the temporary and permanent types. The consistency came to an end in 1986, when illuminated cancelling indicators with a yellow background [12.8] were introduced for T.S.R.s, while permanently installed cancelling indicators remained blue and reflectorised. Following the general introduction of reflectorised signs for T.S.R.s in 1997, all cancelling indicators were reflectorised.

[12.6] AWS Cancelling Indicator.
Area: All Areas   Usage: Medium   Status: Historical
[12.7] AWS Cancelling Indicator. Click Here for Photo
Area: All Areas   Usage: High   Status: Current
[12.8] AWS Cancelling Indicator.
Area: All Areas   Usage: High   Status: Current

Simplified bi-directional signalling (SIMBIDS) schemes were introduced from 1988. This is an economical form of bi-directional signalling for use on double tracked railways worked by the Track Circuit Block system where 'wrong direction' movements are normally only made during emergencies or engineering work. A cost-saving feature of SIMBIDS is the absence of AWS for signals that apply in the wrong direction. Additionally, the AWS provided for normal direction signals is not suppressed, nor are any cancelling indicators provided. Lineside signs are provided to mark the start and finish of this special AWS working. Both signs are diagonal and contain the letters "AWS" and while the commencement sign also has a red diagonal cross [12.9], the termination sign does not [12.10]. Further provision of SIMBIDS schemes ceased in 2002.

[12.9] Commencement of Special AWS Working.
Area: All Areas   Usage: Medium   Status: Obsolescent
[12.10] Termination of Special AWS Working.
Area: All Areas   Usage: Medium   Status: Obsolescent

Lineside signs are provided at places where lines signalled with lineside signals abut lines with cab signalling. This situation first arose in 1993, near the U.K. portal of the Channel Tunnel at Dollands Moor in 1993. These signs appear similar to the standard 'AWS gap' signs (see [12.4 & 12.5]) but the colours are reversed [12.11 & 12.12].

[12.11] End of AWS.
Area: Various   Usage: Low   Status: Historical
[12.12] Commencement of AWS.
Area: Various   Usage: Medium   Status: Current

The approach to the cab signalling area is identified by one or more signs at the lineside with the word "cab" on a black background, indicating the commencement of cab signalling [12.13]. The cab signalling is enabled automatically and the AWS is disabled. On the approach to a lineside signalling area, one or more signs indicating the end of cab signalling are provided. These were similar in appearance to the commencement sign, with the addition of a red diagonal stripe [12.14]. The AWS is enabled automatically, followed by the automatic disabling of the cab signalling.

[12.13] Commencement of Cab Signalling.
Area: Various   Usage: Medium   Status: Current
[12.14] End of Cab Signalling.
Area: Various   Usage: Low   Status: Obsolescent

An AWS reminder board was installed at Warwick Parkway station upon its opening in 2000, as a safeguard against a driver forgetting a 'caution' aspect displayed by the previous signal while stopped at the station. The lower part of the board included a picture of an AWS 'sunflower' cab indication underneath the words "check AWS" [12.15]. The board was removed in 2002.

[12.15] AWS Reminder Board.
Area: Warwick Parkway   Usage: Low   Status: Historical

In 2001, signals between Bridlington and Seamer were fitted with AWS equipment, with the exception of the distant signals for Gristhorpe level crossing. To alert drivers to this omission, the posts of the preceding stop signals (one at Seamer South Junction and two at the north end of Filey station) were each fitted with a large board worded "no AWS for Gristhorpe" [12.16]. The boards were removed in 2007 upon the installation of AWS equipment at the signals concerned.

[12.16] "No AWS for Gristhorpe" Sign.
Area: Seamer South Junction / Filey   Usage: Low   Status: Historical

Experimental AWS reminder signs were installed at Hurst Green and Betchworth (Southern Region) in 2002. These bear a large image of a 'sunflower' on a square board with black and yellow surrounds [12.17].

[12.17] AWS Reminder Sign.
Area: Hurst Green / Betchworth   Usage: Low   Status: On Trial