Automatic Train Protection (ATP) is the class of safety systems that supervise a train’s speed and permitted movement and apply the brakes automatically if the driver exceeds a limit or passes a stop signal. In Europe the term covers both the national legacy systems and ETCS, which is designed to replace them.
Most European networks use a national ATP system. Examples include the German systems PZB and LZB, the French KVB and TVM, the Spanish ASFA, the Italian SCMT and the Dutch ATB. Without ATP, a missed signal or an overspeed depends entirely on the driver’s reaction.
The systems differ in how they pass information to the train. PZB and KVB transmit data at fixed points on the track. LZB and TVM transmit continuously, through cable loops or track circuits, and show the permitted speed in the cab.
The cross-border cost
The national systems are not compatible with each other. A train that crosses borders must carry the on-board equipment for each network, either as separate units or as Specific Transmission Modules connected to ETCS.
The Control-Command and Signalling TSI, Commission Implementing Regulation (EU) 2023/1695, treats ETCS as the Class A system. The national systems are Class B systems, listed by the European Union Agency for Railways.
Every extra on-board system adds cost, weight and certification work to a locomotive or multiple unit. Replacing Class B systems with ETCS removes that duplication for trains in cross-border service.