A small sign featuring a series of numbers, letters and a slider commonly appears at the side of the track on the London Underground, but have you ever wondered what it’s for?
The purpose of a small sign that features prominently beside the track of the London Underground and indeed, overground tracks – has baffled many for years it seems. Each one features a series of numbers and letters and a slider, which prompted one person to seek clarification online.
In the London Underground community on Reddit, they asked: “What’s this for?” The question was also alongside a snap showing the sign at a Tube station. The query was met with the response from several of those in the know, one of whom advised: “Its a Datum Plate, believe they are used for measuring height and track alignment, so it can be checked during engineering works and safety inspections.”
A second person concurred: “This is right on the money. This is the same as the ones on the National Rail network.”
Then a third elaborated further: “Trackmen use it to ensure the track is at the right level to the platform. My understanding is the track and the slider need to be set to level and everything is okay.
“If it’s way off the would be concern the train could collide with platform. My father fitted these many years ago, I remember having a kitchen full of them one upon a time.”
While a fourth pointed out: “Track datum plate some have red sliders, some are green sliders.
“Red is the current installed position. Green is absolute so basically the designed position.”
On YouTube, railway enthusiast user, Railway Mayhem, datum plates hold the “secret” to keeping the railways running smoothly.
“The coloured block is the key – if they have a red block, it shows where the track was when the plate was first installed, ensuring the train stays at the correct distance from the platform edge,” they explained.
“But if it is a newer green block, that indicates that the ideal track position according to new modern standards.
“Taking into account the speed limit and the slope and incline of the track, engineers use the information from the plates along with precise surveying tools to make adjustments ensuring the track is perfectly aligned for safe and smooth train travel.”
The Railway Shop advises on its website: “Datum plates are fixed to structures (bridges, platforms and overhead line masts, etc.) that are located near the track.
“The details on the plate specify the relative position of the track from said structure, which can then be monitored for movement.”
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