PZB or Indusi is an intermittent cab signalling system and train protection system used in Germany, Austria, Slovenia, Croatia, Romania, Israel and on one line in Canada.
Developed in Germany the historic short name Indusi was derived from German Induktive Zugsicherung ("inductive train protection"). Later generations of the system were named PZB short of German Punktförmige Zugbeeinflussung ("intermittent automatic train running control"[1]) as PZB/Indusi is a family of intermittent train control systems and it is a predecessor of the German Linienzugbeeinflussung (LZB, "continuous train protection") system. Originally Indusi provided warnings and enforced braking only if the warning was not acknowledged (similar to traditional automatic train stop) but current developments of PZB provide more enforcement.
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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 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.
Experiments with magnetic induction for a train protection system can be traced back as early as 1908. All of the early prototypes did require track-side electricity supply which was not available however in the widespread mechanical interlocking stations. Parallel investigations did look at optical recognition equipment (Optische Zugsicherung / OPSI) which was dumped however on the base of instability due to dirt and dust on the lenses.
Since 1931 the development concentrated on an inductive train protection system (INDUSI) that did not require electricity. In a parallel development Switzerland started to introduce the Integra-Signum system based on magnets since 1933 which is based on similar ideas. The original Indusi system was deployed since 1934 which however had only a train stop function (the 2000 Hz signal in later revisions). The system spread to Austria and countries of the historic Austro-Hungarian Empire which share a common root with Germany in terms of rail transport history during the German Customs Union.
Indusi prototypes had been developed in the 1930s but further deployment was inhibited at the end of war in 1945. The Deutsche Bundesbahn specified the modern Indusi system in 1954 and called it Indusi I 54.
Minor improvements in the 1960s led to the Indusi 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 braking characteristics of the train.
The original I 60 system proved insufficient in a number of situation so that it saw multiple revisions that finally led to the revised standard I 60R.
With the introduction of Linienzugbeeinflussung by Deutsche Bundesbahn the locomotives were equipped with a microprocessor-based LZB/I 80 train protection system since 1980 which was able to pick up the Indusi signals. The experience with this system led to the development of the Indusi I 60R system that 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.
The PZ80 is a result of the German division and the enforcement of the inner German border since 1967. The East-German Deutsche Reichsbahn wanted to gain independence of the I 60 supply by the West-German Siemens manufacturer and later the Romanian I 60 Icret that was based on I 60. The East-German manufacturer Geräte- und Reglerwerk Teltow was advised to develop a native intermittent train control. The PZ80 supports all Indusi 60 modes enhanced with a number of new modes including speed control in steps of 10 km/h, continuous braking curves and a restrictive mode. After the German reunification in 1990 the upcoming PZB90 system was able to pick up on the experiences of the PZ80 system.
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.
German safety regulations (the EBO, the German federal rail safety regulator) requires PZB on all but very minor lines. Since 1998 all traction vehicles must be equipped with Indusi in Germany - before that it was possible for trains without a protection system to use PZB-enabled lines up to a speed of 100 km/h.[2] The change of allowance guidelines of the EBO did require about 800 vehicles from the former Deutsche Reichsbahn to be either retrofitted or scrapped.
An Indusi I-60 system identical to the German one is equipped on all standard-gauge railroads in Romania. The Romanian rail regulator, AFER, requires all locomotives, EMUs and DMUs operating on public infrastructure to be equipped with Indusi systems.
In Ottawa, Canada, OC Transpo's O-Train uses Indusi controls on its German-built Talents.
Indusi is also installed in 10 Danish IC3 flexliner trains used on the Copenhagen - Hamburg line.
Failure to control speed after passing signal at stop:
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