Punktförmige Zugbeeinflussung

The Punktförmige Zugbeeinflussung (PZB, "point-wise train protection") is an intermittent cab signalling system and train protection system used in Germany, Austria, Slovenia, Croatia, Romania and on one line in Canada. It is also known as Induktive Zugsicherung (Indusi, "inductive train protection").

PZB is a predecessor of the "Linienzugbeeinflussung" ("LZB", "continuous train protection") system.

Introduction

Indusi is a family of intermittent train control systems. German safety regulations (the EBO, the German federal rail safety regulator) requires PZB on all but very minor lines. All traction vehicles must be equipped with Indusi in Germany. [EBO §40. In exceptional cases, one may drive a traction vehicle without or with disturbed Indusi, but only up to a speed of 100 km/h.] Originally Indusi provided warnings and enforced braking only if the warning was not acknowledged (similar to traditional automatic train stop), but current developments provide more enforcement.

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 distant signal being passed shows "caution";500 Hz:maximum speed (V_max) of 65 km/h (40 mph) is enforced;2000 Hz:stop1000 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.

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. Depending on the type of train the locomotive was hauling, the system could be manually switched between three modes of operation: freight train, low speed and high speed passenger train. In each mode, the system calculated a different speed curve based on the maximum allowable speed and breaking characteristics of the train.

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.

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 exit 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 45 km/h when stopping after an active 1000 Hz inductor or to 25 km/h when stopping after an active 500 Hz inductor.

Overseas usage

In Ottawa, Canada OC Transpo's O-Train uses Indusi controls on its German-built Talents.

Similar accidents

Failure to control speed after passing signal at stop:

* Glenbrook train disaster
* Lindfield train disaster

ee also

* Train protection system
* Cab signalling

References