Automatic Warning System
If the signal being approached is displaying a 'clear' aspect, then AWS will sound a bell tone (modern trains have an electronic sounder that makes a distinctive 'ping') and leave the 'sunflower' black.If the next signal is displaying a restrictive aspect (e.g. caution or stop) the AWS audible indicator will sound a continuous alarm.This yellow spoke pattern persists until the train reaches the next AWS magnet and serves as a reminder to the driver of the restrictive signal aspect they passed.As a fail-safe mechanism, if the driver fails to press the AWS acknowledgement button for a warning indication in sufficient time, the emergency brakes will automatically apply, bringing the train to a stop.After stopping, the driver can now press the AWS acknowledgement button, and the brakes will automatically release after a safety time out period has elapsed.AWS works in the same way as for signals, except that a fixed magnet is located at the service braking distance before the speed reduction.Ten years later, Colonel William Yolland of the Railway Inspectorate was calling for a system that not only alerted the driver but also automatically applied the brakes when signals were passed at danger but no satisfactory method of bringing this about was found.In Germany, the Kofler system used arms projecting from signal posts to engage with a pair of levers, one representing caution and the other stop, mounted on the locomotive cab roof.To address the problem of operation at speed, the sprung mounting for the levers was connected directly to the locomotive's axle box to ensure correct alignment.[4] When Berlin's S-Bahn was electrified in 1929, a development of this system, with the contact levers moved from the roofs to the sides of the trains, was installed at the same time.In 1907 Frank Wyatt Prentice patented a radio signalling system using a continuous cable laid between the rails energized by a spark generator to relay "Hertzian Waves" to the locomotive.When the electrical waves were active they caused metal filings in a coherer on the locomotive to clump together and allow a current from a battery to pass.In the final version of the GWR system, the locomotives were fitted with a solenoid-operated valve into the vacuum train pipe, maintained in the closed position by a battery.[7] It was possible for specially equipped GWR locomotives to operate over shared lines electrified on the third-rail principle (Smithfield Market, Paddington Suburban and Addison Road).It was found, however, that the heavy traction current could interfere with the reliable operation of the on-board equipment when traversing these routes and it was for this reason that, in 1949, the otherwise "well proven" GWR system was not selected as the national standard (see below).[7][8] Notwithstanding the heavy commitment of maintaining the lineside and locomotive batteries, the GWR installed the equipment on all its main lines.A non-contact method based on magnetic induction was preferred, to eliminate the problems caused by snowfall and day-to-day wear of the contacts which had been discovered in existing systems.It was successful and British Railways developed the mechanism further by providing a visual indication in the cab of the aspect of the last signal passed.All signal aspects, except green, cause the horn to sound and the indicator disc to change to yellow on black.To verify that the on-train equipment is functioning correctly motive power depot exit lines are fitted with a 'Shed Test Inductor' that produces a warning indication for vehicles entering service.AWS is provided at most main aspect signals on running lines, though there are some exceptions:[1] Because the permanent magnet is located in the centre of the track, it operates in both directions.
Class 27signalClass 43magnetic fieldfail-safewrong-side failure(SPAD)Train Protection & Warning System (TPWS)train stopEdward BuryWilliam YollandRailway Inspectorateaxle boxS-BahnVincent RavenNorth Eastern Railwayspark generatorcohererLondon & South Western RailwayHampton Court branch lineGreat Western RailwaysolenoidresistanceelectrifiedSmithfield MarketAddison RoadWestern RegionMinistry of Transportmagnetic inductionStrowger Automatic Telephone Exchange CompanySouthern RailwayLondon & North Eastern RailwayLondon, Midland & Scottish RailwayLondon, Tilbury and Southend lineBritish RailwaysHarrow & Wealdstone accidentWestern Region of British RailwaysNetwork RailbrakesSt Andrew's crossmotive power depotthird railmilliteslasSectional Appendixderailment at NuneatonTrain Protection & Warning SystemNorthern Ireland RailwaysEast Rail lineMTR CorporationQueenslandAdelaideTaiwan Railways AdministrationEMU100ATS-SN/ATS-PLiberiaAnti Collision DeviceAutomatic track warning systemAutomatic Train ProtectionContinuous Automatic Warning SystemCrocodile (train protection system)Driver reminder applianceIntermittent Inductive Automatic Train StopPositive Train ControlAutomatic Locomotive SignallingThe English Mechanic and World of ScienceDavid & CharlesHM Stationery OfficeRail Safety and Standards BoardRailway Gazette InternationalThe Daily NewsInstitution of Civil EngineersIan Allan PublishingOxford University PressRail EnthusiastRailway signallingBlock systemsAbsolute block signallingAutomatic block signalingCentralized traffic controlCommunications-based train controlDirect traffic controlEuropean Train Control SystemMoving blockRadio Electronic Token BlockTrack Warrant ControlTrain order operationSignalling controlBlock postIntegrated Electronic Control CentreInterlockingLever frameRail operating centreSolid State InterlockingWestlock InterlockingSignalsApplication of railway signalsCab signallingNorth American railroad signalsRailway semaphore signalAxle counterTrack circuitTrack circuit interrupterTreadleTrain protectionAdvanced Civil Speed Enforcement SystemAutomatic train controlAutomatic train operationAutomatic Train Protection (United Kingdom)Automatic train stopAutomatische treinbeïnvloedingBaliseCatch pointsChinese Train Control SystemCityflo 650 CBTCContrôle de vitesse par balisesEBICABIntegra-SignumInteroperable Communications Based SignalingCrocodileKorean Train Control SystemLinienzugbeeinflussungPulse code cab signalingPunktförmige ZugbeeinflussungRS4 CodiciSelTracSistema Controllo Marcia Treno