The New Zealand Railways Magazine, Volume 6, Issue 8 (April 1, 1932.)
Britain's Largest Train Control Installation
Britain's Largest Train Control Installation.
The track installation consists of a steel bar, or ramp, 40ft in length, placed between the rails adjacent to the distant signal at a height of 3 1/4 inches above rail level. The lever which operates the distant signal is connected by wire electrically with the ramp. When the signal is in the danger position the ramp is dead, and when in the clear position the action of pulling the lever completes an electric circuit and causes the ramp to be energised. The locomotive has an iron shoe, the bottom of which is 2 1/2 inches above rail level. This makes contact with the ramp as the locomotive passes over. If the signal is at danger and the ramp dead, the action of lifting the shoe opens a valve on the vacuum brake apparatus, causing an application of the brakes throughout the train, and the sounding of a siren in the locomotive cab. On the other hand, should the signal be in the clear position, the ramp is energised, and the electric current passing through the shoe does not interfere with the vacuum brake, but rings an electric bell in the cab. The driver thus has two entirely distinct audible indications of the condition of the signals.