Test Coach 'Mercury' (aka Lab 18)

Prior to being incorporated into the Structure Gauging Train, RDB975280 Test Coach Mercury had been used in the late 1970's to monitor the transponders then being fitted to the WCML in connection with the introduction of the C-APT track-to-train communication system for the Advanced Passenger Train.

This was a new development at the time and the benefit of a transponder is that it does not need a power supply and is 'interrogated' by a device on the train as it passes. The same principle is used today for the TASS system on the Voyagers and Pendolinos.

R&DD was pioneering the system in the UK 30 odd years ago.


Here is Test Coach Mercury in the formation of a scheduled passenger train on the WCML around 1974.

Note that it belonged then to the Train Control Group and was based at the Mickleover Test Track

BR official

Transponder in track

This is a closer view of the transponder in the track. Something similar is used today to control tilt on Pendolinos but not on Class 221 Cross Country Voyagers since the tilt system is now isolated.

Author's collection


The coach was part of the Structure Gauging Train (SGT) and is pictured here at Derby on 19th September 2008


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