Linienzugbeeinflussung


Linienzugbeeinflussung is a cab signalling and train protection system used on selected German and Austrian railway lines as well as on the AVE and some commuter rail lines in Spain. The system was mandatory where trains were allowed to exceed speeds of in Germany and in Spain. It is also used on some slower railway and urban rapid transit lines to increase capacity. In German, the word Linienzugbeeinflussung translates to continuous train control, or more literally: linear train influencing. It is also occasionally called linienförmige Zugbeeinflussung.
LZB is deprecated, and is to be replaced with the European Train Control System between 2023 and 2030. It is referenced by European Union Agency for Railways as a Class B train protection system in National Train Control. Driving cars mostly have to replace classical control logic to ETCS Onboard Units with common Driver Machine Interface. Because high performance trains are often not scrapped or reused on second order lines, special Specific Transmission Modules for LZB were developed for further support of LZB installation.

Overview

In Germany the standard distance from a distant signal to its home signal is. 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, and cab signalling. Increasing the distance between the home and distant signals would decrease capacity. Adding another 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 these problems, Germany chose to develop continuous cab signalling.
The LZB cab signalling system was first demonstrated in 1965, enabling daily trains at the International Transport Exhibition in Munich to run at 200 km/h. The system was further developed throughout the 1970s, then released on various lines in Germany in the early 1980s and on German, Spanish, and Austrian high-speed lines in the 1990s with trains running up to. Meanwhile, additional capabilities were built into 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 centre. The control centre 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 centre communicates with the train using two conductor cables that run between the tracks and are crossed every 100 m. The control centre sends data packets, known as telegrams, to the vehicle which give it its movement authority 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 triangle 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 includes an Automatic Train Operation system known as AFB, 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 train protection system for use on lines not equipped with LZB.

History

Choice of cab signalling

In the 1960s, the German railways wanted to increase the speeds of some of their railway lines. One issue in doing so is signalling. German signals are placed too close to allow high-speed trains to stop between them, and signals may be difficult for train drivers to see at high speeds.
Germany uses distant signals placed before the main signal. Trains with conventional brakes, decelerating at, can stop from in that distance. Trains with strong brakes, usually including electromagnetic track brakes, decelerating at can stop from and are allowed to travel that speed. However, even with strong brakes and the same deceleration, a train travelling would require to stop, exceeding the signalling distance. Furthermore, as the energy dissipated at a given acceleration increases with speed, higher speeds may require lower decelerations to avoid overheating the brakes, further increasing the distance.
One possibility to increase speed would be to increase the distance between the main and distant signal. But, this would require longer blocks, which would decrease line capacity for slower trains. Another solution would be to introduce multiple aspect signalling. A train travelling at would see a "slow to 160" signal in the first block and then a stop signal in the 2nd block.
Introducing multi-aspect signalling would require substantial reworking for the existing lines, as additional distant signals would need to be added onto long blocks and the signals reworked on shorter ones. In addition, it wouldn't solve the other problem with high-speed operation, the difficulty of seeing signals as a train rushes past, especially in marginal conditions such as rain, snow, and fog.
Cab signalling solves these problems. For existing lines it can be added on top of the existing signalling system with little, if any, modifications to the existing system. Bringing the signals inside the cab makes it easy for the driver to see them. On top of these, the LZB cab signalling system has other advantages:
  • The driver is immediately aware of signalling changes.
  • * This allows a driver to stop slowing down if a signal at the end of a block improves, saving energy and time.
  • * It also allows the control centre to instantly signal stop in the case of dangerous conditions such as a derailment or avalanche.
  • The driver can electronically "see" a long distance down the track, allowing them to drive the train more smoothly.
  • A train following a slower train can "see" the slower train well in advance, coasting or using regenerative braking to slow and thereby save energy.
  • It can signal a variety of speeds.
  • It allows the track to be divided up into a large number of small blocks if necessary to increase capacity.
  • It enables a more capable Automatic Train Protection system.
  • It enables the AFB Automatic Train Operation system.
Given all of these advantages, in the 1960s, the German railways chose to go with LZB cab signalling instead of increasing the signal spacing or adding aspects.

Development

The first prototype system was developed by German Federal Railways in conjunction with Siemens and tested in 1963. It was installed in Class 103 locomotives and presented in 1965 with runs on trains to the International Exhibition in Munich. From this Siemens developed the LZB 100 system and introduced it on the Munich-Augsburg-Donauwörth and Hanover-Celle-Uelzen lines, all in Class 103 locomotives. The system was overlaid on the existing signal system. All trains would obey the standard signals, but LZB-equipped trains could run faster than normal as long as the track was clear ahead for a sufficient distance. LZB 100 could display up to in advance.
The original installations were all hard-wired logic. However, as the 1970s progressed Standard Elektrik Lorenz developed the computer-based LZB L72 central controllers and equipped other lines with them.
By the late 1970s, with the development of microprocessors, the 2-out-of-3 computers could be applied to on-board equipment. Siemens and SEL jointly developed the LZB 80 on-board system and equipped all locomotives and trains that travel over plus some heavy haul locomotives. By 1991, Germany replaced all LZB 100 equipment with LZB 80/L 72.
When Germany built its high-speed lines, beginning with the Fulda-Würzburg segment that started operation in 1988, it incorporated LZB into the lines. The lines were divided into blocks about long, but instead of having a signal for every block, there are only fixed signals at switches and stations, with approximately between them. If there was no train for the entire distance the entry signal would be green. If the first block was occupied it would be red as usual. Otherwise, if the first block was free and a LZB train approached the signal would be dark and the train would proceed on LZB indications alone.
The system has spread to other countries. The Spanish equipped their first high-speed line, operating at, with LZB. It opened in 1992 and connects Madrid, Cordoba, and Seville. In 1987 the Austrian railways introduced LZB into their systems, and with the 23 May 1993 timetable change introduced EuroCity trains running on a -long section of the Westbahn between Linz and Wels.
Siemens continued to develop the system, with "Computer Integrated Railroading", or "CIR ELKE", lineside equipment in 1999. This permitted shorter blocks and allowed speed restrictions for switches to start at the switch instead of at a block boundary. See [|CIR ELKE] below for details.