LZB

Introduction

LZB (Linienzugbeinflussung = train control system / cab signalling) is a continuous working train control system that provides full supervision for a train movement. The LZB system is designed by Siemens and was introduced in 1960/1970 in Germany on mostly the high speed lines.

signal visibility

If a train driver is running with 140 km/h he is going down the tracks with 38.88 meters per second. If there is 25 meters visibility he has 0.64 second to observe and react to a signal aspect outside. A trained train driver CAN do that, but it is a real challenge! Going with 160 km/h, (44.44 m/s) this observation time is 0.56 seconds. That's almost a blink of an eye.

high speed

In Germany the railway set a standard that above a speed of 160 km/h a train driver cannot humanely and reliably observe a signal aspect at such a speed.

Therefore a cab signalling system was designed that translates the outside signals to a set of indications in the train cab. The system was also designed to fully supervise the train speed and operate the train fully automatically. If a train does NOT have this full supervision cab signalling system, the maximum allowed speed of the train is 160 km/h.

principles of LZB

The LZB system consist of a train borne computer and a lineside computer next to LZB-computer in the signal box. With a special antenna-wire build in in the track, the LZB-computer and lineside computer can communicate with the train borne computer and vice versa. This goes via a system of simple data telegrams that are constantly send to the train. These data telegrams provides speed and locator information for the train borne computer. The train borne computer calculates the current maximum allowed speed (based on the train data, braking capability, length of the train and distance to the next speed reduction), the distance to the next speed reduction and the target speed. These three critical information items: maximum allowed speed, target distance and target speed is shown to the train driver and he can choose to let the train follow this data automatically or manually operate his train in such way to stay within these given data. After 40 years working, the system has been proven to be very reliable. Only very few irregularities have taken place.

train picks up LZB cab signal

For a train to run under cab signalling rules, the train must enter an entry point, marked by little LZB signs next to the track. The train driver may expect to be "picked up" by the cab signalling system when his train is equipped with the LZB system and it is operational and the track side system is operational and his whole train length is within the LZB area.

If this does NOT happen, the train may continue with his normal operation speed, but limited to 160 km/h.

If the train is picked up by the LZB system, the train driver will adhere to the cab signal ONLY and does not have to observe line side signals. Simply said: he must completely rely on the cab signalling and even ignore outside signal aspects. He still must be alert though and observe the line for irregularities and hazardous objects. LZB doesn't detect animals or trees on the line.