ATC Ramp

ATC, Automatic Train Control, is a safety device that was invented by the GWR around 1905, it indicates to the driver what the next signal is and will put the brake on at a danger signal if no action is taken. The design was set out out give 2 separate sounds, 1 for clear and another for danger, this being safer than the standard system at the time for bad weather which involved detonators when the line was not clear.

On the locomotive there is a solenoid keeping a valve on the trains vacuum brake system closed, when the engine passes over a ramp a plunger below the engine is lifted, breaking the electrical circuit from the battery to the solenoid, now the solenoid is kept closed by electricity from the ramp, if it is present. The electricity from the ramp will sound a bell in the cab of the locomotive to indicate the next signal is at clear, but if the ramp is 'dead' the solenoid will not be kept closed, allowing air in to the vacuum system through a siren, if this is not cancelled the train will come to a stand still. Thus there is a fail safe system, if the power from the signal box fails the locomotive receives a danger signal.

The photograph shows the cab equipment, the pipe has been pulled out for some reason, but bellow it can be seen the small lever to cancel the warning.

ATC was demonstrated to representatives from the LNER in 1938 after an accident at Castlecary in Scotland, a train of 300 tons was taken past a distant signal at danger and left with the regulator open. The siren in the cab sounded, and was ignored, so the brakes came on and the train was brought to a stop from 69mph in 900yd, which as the ramp was 318yd from the distant signal and the distant was 1,032yd from the home signal gave 400yd before any danger point.

This system was widely introduced on to the GWR's mainlines so that by 1931 2,130 route miles had this system. During 1947 the GWR also demonstrated a system to indicate if there was a single yellow, or double yellow, as they were going to introduce 4-aspect colour lights, this was not done due to nationalisation in 1948. The current AWS in use has several advantages, it has a visual indication in the cab as to the last signal passed, and doesn't use a mechanical plunger but magnets, but still cannot tell the difference between a single or double yellow.