Punktförmige Zugbeeinflussung
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The Punktförmige Zugbeeinflussung, abbreviated to PZB, is a train safety system used in Germany and Austria. The name translates to "influencing trains at certain points" and was chosen to contrast to the Linienzugbeeinflussung (LZB) which means "influencing trains continuously". Previous versions were named Indusi, long form Induktive Zugsicherung, translated "inductive train safety".
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[edit] Equipment
Locomotives and multiple unit cars with operating cabs are equipped with onboard transmitter coils with the superimposed frequencies 500 Hz, 1000 Hz and 2000 Hz. Passive tuned inductors (RLC circuits) are situated at appropriate trackside locations; each inductor resonates at one of the three frequencies, depending on its location. When the leading end of the train passes over one of the trackside inductors, the inductor's presence is detected by the onboard equipment through a change in magnetic flux. This activates the appropriate onboard circuit and triggers whatever action is required based on the location (e.g., an audible/visual warning, enforced speed limit, or enforced stop).
The three frequencies have different meanings to the train:
- 1000 Hz
- warning that the Vorsignal (distant signal) being passed shows "caution"
- 500 Hz
- maximum speed (Vmax) of 65 km/h (40 mph) is enforced
- 2000 Hz
- stop
1000 and 500 Hz activate conditional restrictions. If the train's driver fails to take the required action within the allowed time, the system enforces a stop. A 2000 Hz enforces an unconditional stop. Details of the restrictions vary with different versions of the system, but the common purpose is to enforce the observation of speed reductions and then a stop before a train reaches a red signal. The 2000 Hz inductor is a last resort to stop a train as it overruns a red signal.
[edit] Versions
First prototypes of the system were developed in the 1930s. The Deutsche Bundesbahn specified the system in 1954 and called it Indusi I 54. Minor improvements led to the I 60 system. When a 1000 Hz inductor was encountered, the driver had to acknowledge the caution signal within four seconds. Additionally, a countdown was started to check whether the train had slowed to a specified speed within a specified time frame.
[edit] I 60R
When these systems proved insufficient, I 60R was introduced, which required microprocessors in all locomotives. Instead of checking certain speeds at certain points in time, the new system continuously checked a curve of speed against time. If the train was faster than the curve allowed, a stop could be enforced at any time.
[edit] PZB90
PZB90 is a new version, deployed in the mid-1990s. It features a new restrictive mode as the result of two accidents. In both cases a train had stopped at a station as intended. Then the train accelerated again, despite the signal still showing red. When the train reached the home signal, its speed was sufficient to crash into another train despite the automatic braking enforced by the 2000 Hz inductor.
The new restrictive mode limits speeds after a train stopped before reaching a red signal. Currently, trains are limited to 25 km/h for the first 250 m after a stop and to 40 km/h for an additional 400 m.
[edit] Similar accidents
Failure to control speed after passing signal at stop:
