Tilt Authorisation and Speed Supervision

The Tilt Authorisation and Speed Supervision System, abbreviated as TASS, is an overlay to train protection systems allowing the control the speeds of tilting trains. It is only installed on the West Coast Main Line (UK). Its trainborne part is fitted to British Rail Class 221 and British Rail Class 390.

The history of TASS is connected to the privatization program of the West Coast Main Line which was won by Virgin Trains in 1996. The modernisation plan unveiled by Virgin included ambitious targets to increase the line speed from 110 mph (177 km/h) to 140 mph (225 km/h). This would include the use of tilting trains on the existing tracks.

The tilting train tender was won by Alstom with their Pendolino technology. In the first batch 53 trains were ordered which were delivered between 2001 and 2004 to be introduced as British Rail Class 390. With just three years from the specification to the test trains in August 2000 the British class did not differ heavily from the other Pendolino systems. They had been provided to areas with very different train protection systems before and there was a requirement to include features of the European Rail Traffic Management System at the time.

The system is based on Eurobalises to transmit an additional set of speed restrictions on top of the Automatic Warning System (AWS) or Train Protection & Warning System (TPWS). TASS allows a maximum of 25 mph (40 km/h) extra speed on sections with enough clearance for the tilting trains.

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