Linienzugbeeinflussung
Linienzugbeeinflussung (or LZB) 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. The German Linienzugbeeinflussung translates to "continuous train control", literally: "linear train influencing". It is also called "linienförmige Zugbeeinflussung". LZB is deprecated and will be replaced with European Train Control System (ETCS) between 2023 and  2030. It is referenced by European Union Agency for Railways (ERA) as a Class B "train protection system" in "National Train Control" (NTC). Driving cars mostly have to replace classical control logic to ETCS "Onboard Units" (OBU) with common "Driver Machine Interface" (DMI). Because high performance trains are often not scrapped or reused on second order lines, special "Specific Transmission Modules" (STM) 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 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 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 (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: 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 (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. 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 traveling would require to stop, exceeding the signalling distance. Furthermore, as 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 traveling 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: 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 (SEL) 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. Line equipment. Cable loops. The LZB control centre communicates with the train using conductor cable loops. Loops can be as  short as 50 meters long, as used at the entrance and exit to LZB controlled track, or as long as . Where the loops are longer than they are crossed every . At the crossing the signal phase angle is changed by 180° reducing electrical interference between the track and the train as well as long-distance radiation of the signal. The train detects this crossing and uses it to help determine its position. Longer loops are generally fed from the middle rather than an end. One disadvantage of very long loops is that any break in the cable will disable  LZB transmission for the entire section, up to . Thus, newer LZB installations, including all high-speed lines, break the cable loops into physical cables. Each cable is fed from a repeater, and all of the cables in a section will transmit the same information. LZB route centre (central controller). The core of the LZB route centre, or central controller, consists of a 2-of-3 computer system with two computers connected to the outputs and an extra for standby. Each computer has its own power supply and is in its own frame. All 3 computers receive and process inputs and interchange  their outputs and important intermediate results. If one disagrees it is disabled and the standby computer takes its place. The computers are programmed with fixed information from the route such as speed limits, gradients, and the location of block boundaries, switches, and signals. They are linked by LAN or cables to the interlocking system from which they receive indications of switch positions, signal indications, and track circuit or axle counter occupancy. Finally, the route center's computers communicates with controlled trains via the cable loops previously described. Vehicle equipment. The vehicle equipment in the original LZB80 designed consisted of: The  equipment in newer trains is similar, although the details may vary. For example, some vehicles use radar rather than accelerometers to aid in their odometry. The number of antennas may vary by vehicle. Finally, some newer vehicles use a full-screen computer generated "Man-machine interface" (MMI) display rather than the separate dials of the "Modular cab display" (MFA). Operation. Telegrams. LZB operates by exchanging telegrams between the central controller and the trains. The central controller transmits a "call telegram" using Frequency-shift keying (FSK) signalling at 1200 bits per second on a 36 kHz ± 0.4 kHz. The train  replies with a "response telegram" at 600 bits per second at 56 kHz ± 0.2 kHz. Call telegram format. Call telegrams are 83.5 bits long: One might note that there is no "train identification" field in the telegram. Instead, a train is identified by position. See Zones and Addressing for more details. Response telegram format. There are 4 types of response telegrams, each 41 bits long. The exact type of telegram a train sends depends on the "Group identity" in the call telegram. The other telegrams are used primarily when a train enters the LZB controlled section. They all start  with the same synchronization and start sequence and a "group identity" to identify the telegram type, and end with the CRC. Their data fields vary as follows: Entry into LZB, zones and addressing. Before entering an LZB controlled section the driver must enable the train by entering the required information on the Driver Input Unit and enabling LZB. When enabled the train will light a "B" light. A controlled section of track is divided into up to 127 zones, each long. The zones are consecutively numbered, counting up from 1 in one direction and down from 255 in the opposite . When a train enters a LZB controlled section of track, it will normally pass over a fixed loop that transmits a "change of section identification" (BKW) telegram. This telegram indicates to the train the section identification number as well as the starting zone, either 1 or 255. The train sends back an acknowledgement telegram. At that time the LZB indications are switched on, including the "Ü" light to indicate that LZB is running. From that point on the train's location is used to identify a train. When a train enters a new zone it sends a response telegram with  the "vehicle location acknowledgement" filed indicating that it has advanced into a new zone. The central controller will then use the new zone when addressing the train in the future. Thus a trains address will gradually increase or decrease, depending on its direction, as it travels along the track. A train identifies that it has entered a new zone by either detecting the cable transposition point in the cable or when it has traveled . A train can miss detecting up to 3 transposition points and still remain under LZB control. The procedure for entering LZB controlled track is repeated when  a train transitions from one controlled section to another. The train receives a new "change of section identification" telegram and gets a new address. Until the train knows its address it will ignore any telegrams received. Thus, if a train doesn't properly enter into the controlled section it won't be under LZB control until the next section. Speed signalling. The main task of LZB is signalling to the train the speed and distance it is allowed to travel. It does this by transmitting periodic call telegrams to each train one to five times per second, depending on the  number of trains present. Four fields in the call telegram are particularly relevant: The target speed and location are used to display the target speed and distance to the driver. The train's permitted speed is calculated using the trains braking curve, which can vary by train type, and the XG location, which is the distance from the start of the zone that is used to address the train. If the train is approaching a red signal or the beginning of an occupied block the location will match the location of the signal or block boundary. The on-board equipment  will calculate the permitted speed at any point so that the train, decelerating at the deceleration indicated by its braking curve, will stop by the stopping point. A train will have a parabolic braking curve as follows: where: Where a train is approaching a speed restriction the control center will transmit a packet with an XG location set to a point behind the speed restriction such that a train, decelerating based on its braking curve, will arrive at the correct speed at the start of the speed restriction. This, as well as deceleration to zero speed, is illustrated with the  green line in the "Permitted and supervised speed calculation" figure. The red line in the figure shows the "monitoring speed", which is the speed which, if exceeded, the train will automatically apply the emergency brakes. When running at constant speed this is above the permitted speed for transited emergency braking (until speed is reduced) or above the permitted speed for continuous emergency braking. When approaching a stopping point, the monitoring speed follows a braking curve similar to the permitted speed, but with a higher deceleration, that will bring it to zero at the stopping point. When approaching a speed restriction , the monitoring speed braking curve intersects the speed restriction point at above the constant speed. Deceleration rates are more conservative with LZB than with conventional German signalling. A typical passenger train braking curve might have a "permitted speed" deceleration of and a "monitoring speed" deceleration of 42% higher than the deceleration for the permitted speed, but lower than the required to stop from in used in conventional signaling. The ICE3, which has a full service braking deceleration of below , dropping to by , has a LZB target speed deceleration of only to , between , and at higher speeds. In between the permitted  speed and monitoring speed is a warning speed, normally above the permitted speed. If the train exceeds that speed LZB will flash the "G" light on the train's display and sound a horn. Leaving LZB. About before the end of the LZB controlled section the central controller will send a telegram to announce the end of LZB control. The train will flash the "ENDE" light which the driver must acknowledge within 10 seconds. The display will normally give the distance and target speed at the end of the controlled section, which will depend on the signal at that point . When the train reaches the end of LZB control the "Ü" and "ENDE" lights go off and the conventional Indusi (or PZB) system takes over automatic train protection. Special operating modes. Special conditions not covered by the full LZB system or failures can put LZB into one of the special operating modes. Crossover to opposite track. As a train approaches a crossover to a normally opposite direction track the display will flash the "E/40" light. The driver confirms the indication and the permitted speed drops following the braking curve to . When the crossover section is reached the displays are switched  off and the driver can proceed through the crossover at . Drive by sight signal. German signalling systems have a "drive by sight" signal that consists of 3 white lights forming a triangle with one light at the top. This signal, labeled "Zs 101", is placed with a fixed line side signal and, when lighted, permits the driver to pass a fixed red or defective signal and drive by sight to the end of the interlocking no faster than . When approaching such a signal in LZB territory the "E/40" light will be lit until before the signal, then the "E/40" will  go dark and "V40" will flash. The "V40" signal indicates the ability to drive by sight. Transmission failure. If data exchange is interrupted, the trains distance measurement system fails, or the train fails to detect 4 or more cable transposition points the LZB system will go into a failure state. It will light the "Stör" indicator and then flash "Ü". The driver must acknowledge the indications within 10 seconds. The driver must slow the train to no more than or lower; the exact speed depends on the backup signalling system in place. Extensions. CIR ELKE-I. CIR-ELKE is an  improvement on the basic LZB system. It uses the same physical interface and packets as standard LZB but upgrades its software, adding capabilities and modifying some procedures. It is designed to increase line capacity by up to 40% and to further shorten travel times. The name is an abbreviation of the English/German project title "Computer Integrated Railroading - Erhöhung der Leistungsfähigkeit im Kernnetz der Eisenbahn" (Computer Integrated Railroading - Increase Capacity in the Core Railway Network). Being an extension of LZB it is also called LZB-CIR-ELKE further abbreviated into LZB-CE. CIR-ELKE includes the following improvements: CIR  ELKE-II. The original LZB system was designed for permitted speeds up to and gradients up to 1.25%. The Cologne–Frankfurt high-speed rail line was designed for operation and has 4% gradients; thus, it needed a new version of LZB, and CIR ELKE-II was developed for this line. CIR ELKE-II has the following features: Malfunctions. The LZB system has been quite safe and reliable; so much so that there have been no collisions on LZB equipped lines because of the failure of the LZB system. However, there have been some malfunctions that could have potentially resulted in  accidents. They are: Equipped lines. DB (Germany). The following lines of Deutsche Bahn are equipped with LZB, allowing for speeds in excess of 160 km/h (providing the general suitability of the track): Note: "italics" indicate the physical location of an LZB control center. ÖBB (Austria). The West railway (Vienna–Salzburg) is equipped with LZB in three sections: United Kingdom. A modified version of LZB is installed on the Chiltern Mainline as Chiltern ATP. Non-mainline uses. In addition to mainline railways, versions of the LZB system are also used in suburban (S-Bahn) railways and subways. Dusseldorf, Duisburg, Krefeld , Mülheim an der Ruhr. Tunnels in the Düsseldorf and Duisburg Stadtbahn (light rail) systems, and some tunnels of the Essen Stadtbahn around the Mülheim an der Ruhr area are equipped with LZB. Vienna (Wien). With the exception of line 6, the entire Vienna U-Bahn is equipped with LZB since it was first built and includes the capability of automatic driving with the operator monitoring the train. Munich. The Munich U-Bahn was built with LZB control. During regular daytime operations the trains are automatically driven with the operator simply starting the train. Stationary signals remain dark during that time . In the evenings from 9:00 p.m. until end of service and on Sundays the operators drive the trains manually according to the stationary signals in order to remain in practice. There are plans to automate the placement and reversal of empty trains. The Munich S-Bahn uses LZB on its core mainline tunnel section (Stammstrecke). Nuremberg. The Nuremberg U-Bahn U3 line uses LZB for fully automatic (driverless) operation. The system was jointly developed by Siemens and VAG Nuremberg and is the first system where driverless trains and conventional trains share a section of line. The existing, conventionally driven U2  line trains shares a segment with the automatic U3 line trains. Currently, an employee still accompanies the automatically driven trains, but later the trains will travel unaccompanied. After several years of delays, the final three-month test run was successfully completed on April 20, 2008, and the operating licence granted on April 30, 2008. A few days later the driverless trains started operating with passengers, first on Sundays and public holidays, then weekdays at peak hours, and finally after the morning rush hour which has a tight sequence of U2 trains. The official opening ceremony for the U3 line was  held on June 14, 2008 in the presence of the Bavarian Prime Minister and Federal Minister of Transport, the regular operation began with the schedule change on 15 June 2008. The Nuremberg U-bahn plans to convert U2 to automatic operation in about a year. London. The Docklands Light Railway in east London uses the SelTrac technology which was derived from LZB to run automated trains. The trains are accompanied by an employee who closes the doors and signals the train to start, but then is mainly dedicated to customer service and ticket control. In case of failure the train  can be driven manually by the on train staff.