Train reporting number
The Railway Clearing House intervened to standardise headcodes, based on four lamp positions, and they were adopted by the majority of lines outside the south of England.
These contained one or more letters or numbers to either uniquely identify a particular train, or denote its route (particularly on busier lines).
Although these numbers were in many places confined to timetables and other documentation, in some busier areas they were actually shown at the head of the train.
This was developed at the same time as a significant programme of electrification and the consequent introduction of a large number of multiple unit trains.
The code system had equivalence with the lamp or disc route-based headcodes in assisting signallers with routing trains.
[1] In 1960, the current format was introduced where train class, route and reporting number information are combined in four characters.
[1] By 1976, the replacement of the huge number of manual signal boxes with centralised power-signalling coupled with computer-based train control and more modern telecommunications systems meant that it was no longer necessary to display headcodes throughout the railway network.
The main purpose of the headcode is to assist the signaller in routing and regulating the train correctly, and it is especially useful if services are disrupted.
After the introduction of the four-character codes, originally it was intended for signallers to visually note the train by the number displayed on its front; with the coming of automated systems the number has been retained internally within timetables and signalling systems but with some exceptions detailed above is no longer displayed on trains.
This emphasises to signallers that the train is to run its booked route as it is recording, not to be diverted without the prior knowledge of the controller.
An unusual situation arose with the opening of the Channel Tunnel: many continental train reporting numbers are all numeric.
The GNER White Rose service from London King's Cross to Leeds formed of a 16 carriage Regional Eurostar set ran with a prefix of 1X due to the train's unusually long length.
[citation needed] Tyne & Wear Metro trains have three-digit numbers which are displayed in the driver's cab window.
Those on the Sunderland line are generally in the range 101 – 112, and the set operates all day on the Newcastle Airport to South Hylton route with this number.
