Sifa is short for Sicherheitsfahrschaltung, German for "safety driving switch". It is usually a pedal and/or large press button, which monitors the alertness of the driver. The driver has to repeatedly press a button after a fixed interval; if he fails to do so, the train will carry out an emergency-stop. It complements the external train safety systems: PZB, LZB and ETCS.
In Europe the Zeit-Zeit-Sifa (time-time Sifa) is common. In this system, the engine driver holds a pedal or button down for 30 seconds and must then briefly release the pressure. Thus the system can confirm that the driver is still able to react. If the driver does not react after 30 seconds, the system warns the driver, at first optically, then for a few seconds acoustically. After a further short period of time without any reaction the train is automatically stopped. The Zeit-Weg-Sifa (time-distance Sifa) system takes account of the distance travelled, as well as time, since the last activation.
In electric trains such as those working on U- and S-Bahn lines the Sifa has for a long time been combined with the driving switch. This is where the concept of the dead man's switch first arose. If the button was released (due to the driver falling asleep) the train was automatically stopped.
In order to test the function of the Sifa the driver must carry out a Sifa test run before the train is used in order to check that the train is automatically braked.
After serious accidents as a result of drivers falling asleep, where the pedal was still regularly activated, the Deutsche Reichsbahn in East Germany introduced a special type of Sifa (Sifa86) into service. Here the driver has to acknowledge, by pressing a button, an optical signal at a time and distance interval randomly generated by the system.
- Dead man's switch
- Dead-man's vigilance device
- Train protection system
- Watchdog timer
- Emergency brake
- Hand brake
- "Deadman’s control system UDB". Retrieved 2008-12-24.