Linienzugbeeinflussung - Overview

Overview

In Germany, the standard distance from a distant signal to its home signal is 1,000 m. On a train with strong brakes, this is the braking distance from 160 km/h. In the 1960s Germany evaluated various options to increase speeds, including increasing the distance between distant and home signals, adding additional aspects, and cab signalling. Increasing the distance between the home and distant signals would decrease capacity. Adding an additional aspect would make the signals harder to recognize. In either case, changes to the conventional signals wouldn't solve the problem of the difficulty of seeing and reacting to the signals at higher speeds. To overcome all of these problems, Germany chose to develop continuous cab signalling.

The LZB cab signalling system was first demonstrated in 1965, enabling daily trains to the International Transport Exhibition in Munich to run at 200 km/h. The system was further developed through the 1970s, released on various lines in Germany in the early 1980s and in German, Spanish, and Austrian high-speed lines in the 1990s with trains running up to 300 km/h. Meanwhile, additional capabilities were added to the system.

LZB consists of equipment on the line as well as on the trains. A 30–40 km segment of track is controlled by a LZB control center. The control center computer receives information about occupied blocks from track circuits or axle counters and locked routes from interlockings. It is programmed with the track configuration including the location of points, turnouts, gradients, and curve speed limits. With this, it has sufficient information to calculate how far each train may proceed and at what speed.

The control center communicates with the train using two conductor cables that run between the tracks and are crossed every 100 m. The control center sends data packets, known as telegrams, to the vehicle which give its movement authority (how far it can proceed and at what speed) and the vehicle sends back data packets indicating its configuration, braking capabilities, speed, and position.

The train's on-board computer processes the packets and displays the following information to the driver:

• Current speed: locally derived from speed sensing equipment - shown with a standard speedometer
• Permitted speed: maximum allowed speed now - shown with a red line or triange on the outside of the speedometer
• Target speed: maximum speed at a certain distance - shown with LED numbers at the bottom of the speedometer
• Target distance: distance for target speed - shown with LED bars showing up to 4000 m, with numbers for longer distances

If there is a long distance free in front of the train the driver will see the target speed and permitted speed equal to the maximum line speed, with the distance showing the maximum distance, between 4 km and 13.2 km depending on the unit, train, and line.

As the train approaches a speed restriction, such as one for a curve or turnout, LZB will sound a buzzer and display the distance to and speed of the restriction. As the train continues the target distance will decrease. As the train nears the speed restriction the permitted speed will start to decrease, ending up at the target speed at the restriction. At that point the display will change to the next target.

The LZB system treats a red signal or the beginning of a block containing a train as a speed restriction of 0 speed. The driver will see the same sequence as approaching a speed restriction except the target speed is 0.

LZB includes Automatic Train Protection. If the driver exceeds the permitted speed plus a margin LZB will activate the buzzer and an overspeed light. If the driver fails to slow the train the LZB system can apply the brakes itself, bringing the train to a halt if necessary.

LZB also include an Automatic Train Operation system known as AFB (Automatische Fahr- und Bremssteuerung, automatic driving and braking control), which enables the driver to let the computer drive the train on auto-pilot, automatically driving at the maximum speed currently allowed by the LZB. In this mode, the driver only monitors the train and watches for unexpected obstacles on the tracks.

Finally, the LZB vehicle system includes the conventional Indusi (or PZB) train protection system for use on lines that aren't LZB equipped.