Might be completely wrong here, but I've always assumed that the train rolls over something on the track just before it reaches the station which triggers a message on the board of the station it's approaching and the subsequent stations along the line. This would explain why the gaps between changes on time (e.g. 5m to 4m) often vary significantly - because of he differing distances between the stations. I await my theory being blown out the water.![]()
Works on track circuits and what is known as the Positive Train Identification system. When a driver sets up the train they enter a code for the terminus station. This sets up the route automatically and also the platform displays. Some of the track circuit blocks between stations are quite long due to a lack of signals which explains why a train can go from 5 minutes to 'Due' very quickly. However part of the problem is at terminus stations such as St. James and South Shields. Until the driver changes ends and enters the code then the platform displays at the next station (i.e. Monument plt 3 and Chichester) do not 'know' that there is a train on the way. This data will only be transferred when the driver has input the correct code and has pressed a 'Ready to Start' button. This also explains why at South Gosforth platform 1, when a train is leaving the depot for Pelaw in the peak hours, the displays will show:
South Shields 2 Min
South Hylton 8 Min
But this then can change to:
South Shields Due
Pelaw 2 Min
