Train protection system

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A train protection system is a railway technical installation to ensure safe operation in the presence of human failures.

Contents

[edit] Development

Berlin S-Bahn train stop in its engaged (left) and disengaged (right) position
Berlin S-Bahn train stop in its engaged (left) and disengaged (right) position

[edit] Train stops

Main article: Train stop

The earliest systems were train stops, as still used by the New York Subway, the Toronto Subway, the London Underground and the Berlin S-Bahn. Beside every signal is a moveable clamp, which touches a valve on a passing train if the signal is red, and opens the brake line, applying the emergency brake. If the signal shows green, the clamp is turned away.

Trackside magnets for very simple data communication. Outside and middle of track: Integra-Signum, other two (yellow) magnets: ZUB
Trackside magnets for very simple data communication. Outside and middle of track: Integra-Signum, other two (yellow) magnets: ZUB

[edit] Inductive systems

In this system data is transmitted magnetically between the track and locomotive by means of magnets mounted beside the rails and on the locomotive.

In the Integra-Signum system the trains are influenced only at given locations, for instance whenever a train ignores a red signal, the emergency brakes are applied and the locomotive's motors are shut down. Additionally, they often require the driver to confirm distant signals (e.g. CAWS) that show stop or caution – failure to do so results in the train stopping. This gives sufficient braking distance for trains following each other, however it cannot always prevent accidents in stations where trains cross paths, because the distance from the red signal to the next obstacle may be too short for the train to brake to a halt.

More advanced systems (e.g. PZB, and ZUB) calculate a braking curve that determines if the train can stop before the next red signal, and if not they brake the train. They require that the train driver enter the weight and the type of brakes into the onboard computer. One disadvantage of this kind of system is that the train cannot speed up before the signal if the signal has switched to green, because the onboard computer's information can only be updated at the next magnet. To overcome that problem, some systems allow additional magnets to be placed between distant and home signals, or data transfer from the signalling system to the onboard computer is continuous (e.g. LZB).

[edit] Cab signalling

Main article: Cab signalling

The newest systems use cab signalling, where the trains constantly receive information regarding their relative positions to other trains. The computer shows the driver how fast he may drive, instead of him relying on exterior signals. Systems of this kind are in common use in France, Germany and Japan, where the high speeds of the trains made it impossible for the train driver to read exterior signals, and distances between distant and home signals are too short for the train to brake.

These systems are usually far more than automatic train protection systems, not only do they prevent accidents, but also actively support the train driver. This goes as far as some systems being nearly able to drive the train automatically.

[edit] Future

Because of the many incompatible automatic train protection systems used in Europe and the resulting changes of locomotives at borders (or equipping locomotives with many different systems), efforts have been made to create one common system with different stages of implementation, called the European Train Control System.

[edit] Variants

[edit] International standards

[edit] Country specific legacy systems

[edit] See also


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Railway signalling
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