The Tilt Authorisation and Speed Supervision System, abbreviated as TASS, is an overlay to train protection systems allowing the control of speeds of tilting trains.
The history of TASS is connected to the modernisation program of the West Coast Main Line conducted by Railtrack and successor Network Rail in the early 2000s.
The tilting train tender was won by Alstom with its Pendolino technology.
The first batch of 53 Class 390s trains delivered between 2001 and 2004, did not differ heavily from the other Pendolino systems.
TASS allows a maximum of 25 mph (40 km/h) extra speed on sections with enough clearance for the tilting trains.