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Automatic train protection system

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An automatic train protection system (ATPS) is a technical installation on railway lines and trains to ensure safe operation in presence of human failures.

Contents

[edit] Development

[edit] Mechanical locks

The earliest systems were mechanical locks, like the one still used by the Berlin S-Bahn. Alongside every signal is a moveable clamp, which, if the signal is red, touches a valve on a passing train which opens the brake line. That way the emergency brake is activated. If the signal shows green, the clamp is turned away.

Image:Integra-signum-zub.jpg

[edit] Inductive systems

Automatic train protection systems that transmit data via magnetic fields, emitted and received by magnets mounted beside the rails and on locomotives, come in various forms. Simple systems may influence trains 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. Systems like Integra-Signum work this way; additionally, they often ask the train driver to confirm distant signals (e.g. CAWS) that show stop or caution - if he does not confirm within a few seconds, the train is stopped. 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, ZUB) calculate a braking curve, that is they constantly calculate if the train will be able to stop before the next red signal, and if not they brake the train. They require that the train driver enters 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 has to be made continuous (e.g. LZB).

[edit] Cab signalling

The newest systems use cab signalling, where the trains constantly get information about their and other's positions and the computer shows the driver how fast he may drive, instead of exterior signals. Systems of this kind have been common for a long time 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, because they not only prevent accidents, but also support the train driver actively. This goes as far as some systems being able to drive the train nearly 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 modern, universally usable system with different stages of implementation, the European Train Control System.

[edit] Variants

[edit] International standards

[edit] Country specific legacy systems

[edit] See also

da:Togkontrolsystem de:Zugsicherungssystem nl:Treinbeïnvloeding ja:自動列車保障装置 zh:自動列車保障裝置

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