PZB or Indusi is an intermittent cab signalling system and train protection system used in Germany, Austria, Slovenia, Croatia, Romania, Israel, Serbia, on two lines in Hungary, on the Tyne and Wear Metro in the United Kingdom, and formerly on the Trillium Line in Canada. Originally, Indusi provided warnings and enforced braking only if the warning was not acknowledged (similar to traditional automatic train stop). The later PZB systems provide more enforcement, relying on a train computer.