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Section 12; pages:
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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, though usually they do both. Although their indications primarily occur inside the cab, associated lineside signs or indicators are sometimes needed.
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', 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'.
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At places where the BR AWS system abutted the WR AWS (ex GWR ATC) system, a notice board was provided [12.2].
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[12.2] Notice Board.
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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]. If the light went out as a train approached, the driver would know that one of the shoes was not properly clipped-up.
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[12.3] WR AWS Shoe Clip-Up Indicator.
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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 [12.4 & 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.
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[12.4] Commencement of AWS Gap.
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[12.5] Termination of AWS Gap.
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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, an illuminated cancelling indicator [12.6] will be provided ahead of the magnet, in the opposite direction from the warning board. This sign advises the driver that the AWS warning just received must be cancelled in the usual way and then disregarded.
Cancelling indicators may be permanently installed at locations where it is not practicable to suppress the AWS equipment for moves to which it does not apply. Permanently installed cancelling indicators have a blue background [12.7] and are reflectorised rather than being illuminated. Temporary illuminated cancelling indicators with a blue background were introduced concurrently with blue T.S.R. signs (see Section 14). From 1986, cancelling indicators with a yellow background [12.8] were introduced for T.S.R.s but the blue reflectorised version continues to be used for an indicator that is permanently installed. The general introduction of reflectorised signs for T.S.R.s in 1997 also affected the temporary cancelling indicators.
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[12.6] AWS Cancelling Indicator.
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[12.7] AWS Cancelling Indicator.
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[12.8] AWS Cancelling Indicator.
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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 this is that no AWS is provided 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 [12.9] and finish [12.10] of this special AWS working. Further provision of SIMBIDS schemes ceased in 2002.
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[12.9] Commencement of Special AWS Working.
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[12.10] Termination of Special AWS Working.
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Lineside signs are provided at places where lines signalled with lineside signals abut lines with cab signalling. The first such place was 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].
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[12.11] End of AWS.
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[12.12] Commencement of AWS.
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The approach to the cab signalling area is identified by one or more signs at the lineside 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 [12.14]. The AWS is enabled automatically, followed by the automatic disabling of the cab signalling.
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[12.13] Commencement of Cab Signalling.
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[12.14] End of Cab Signalling.
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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.
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[12.15] AWS Reminder Board.
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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.
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[12.16] "No AWS for Gristhorpe" Sign.
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Experimental AWS reminder signs were installed at Hurst Green and Betchworth in 2002 [12.17].
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[12.17] Experimental AWS Reminder Sign (Southern Region).
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