Tyer's Electric Train Tablet

Tyer's Electric Train Tablet system is a form of railway signalling for single line railways used in several countries; it was first devised in Great Britain by engineer Edward Tyer after the Thorpe rail accident of 1874, which left 21 people dead.

The purpose of the system was to use the tablet as a physical guarantee to the traincrew that their train had exclusive right of way on the single-line section.

The signalling bell associated with the machine is separate so could be located on the block shelf or wall mounted above the instrument.

Tablets are in the form of a disc made of metal or fibre (with a gunmetal weight at the top of the magazine), engraved with the names of the stations between which it is valid, and also provided with notches (also called configurations) or other indentations to ensure that it would fit only one pair of instruments.

They were often painted in distinctive colours as an additional visual identification in areas where consecutive sections could each be controlled using the same type of instrument.

This meant that should a train failure occur in the single line section or a shunt beyond station limits, the tablet had to travel to the receiving instrument by foot or horse.

The later No 6 model however was a restoring design, which enabled the tablet to be placed back into the issuing instrument for shunting out of station limits.

[5] Sri Lanka Railways is currently using this system at several locations, including the Kelani Valley line between Maradana and Avissawella in the Colombo District.

6 tablet instrument was far more widespread in the UK and was adopted by most railway companies on single line installations.

However, as of 2015[update], the Tyer Electric Token Block, using No 7 instruments and coloured perspex tablets, remains in use on the Stranraer Line, between Girvan and Dunragit.

Token machines under the remote control of the Thames Valley Signalling Centre are also still in use between Maidenhead and Bourne End.

[6] Tyer's Tablet working using the No 7 system was used in New Zealand from 1901, as most lines apart from sections near the main centres were single-track.