Automatic warning system

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The Automatic Warning System (AWS) is a train control system that has been in use in Great Britain since 1956 . In 1992 about 11,000 kilometers (out of a total of about 16,000 kilometers) of the British Rail network were equipped with it.

functionality

An AWS ramp

About 180 meters before a distant signal or the announcement of a speed limit stop, there is a so-called AWS ramp in the middle of the track. It contains a permanent magnet and an electromagnet with reverse polarity; there is no electromagnet when announcements of speed limits are announced.

AWS ad

A receiver that reacts to these magnetic fields is installed under the vehicle. In the driver's cab there is a bell and a horn (today these tones are often generated electronically), a display of the device status and a confirmation button (alertness button).

When the distant signal shows "Drive free", the electromagnet is activated. This means that the bell rings in the driver's cab and the display goes black.

If, however, the distant signal indicates "expect stop" (and always in the case of slow speed areas), the electromagnet is not active or not available. In this case the horn sounds. The driver now has two to three seconds to operate the alert button. If he fails to do this, an emergency brake is applied .

If you press the alert button in good time, the horn will stop and the display will turn into a pattern of alternating yellow and black sectors (colloquially called "sunflower"). This reminds the driver that he has received a warning and has confirmed it. It is now his job to apply the brakes. However, this is not monitored by the Automatic Warning System.

The Ladbroke Grove rail accident is largely attributed to this lack of brake monitoring.

literature

  • Hall, Stanley (1992): BR Signaling Handbook . Ian Allan, Shepperton. ISBN 0-7110-2052-3
  • Rail Safety and Standards Board Limited (Eds.): AWS and TPWS Handbook . RS / 522 Issue December 3, 2015 (English, 28 pp., Rssb.co.uk [PDF; 1,2 MB ; accessed on April 17, 2017]).