Signal box

from Wikipedia, the free encyclopedia
Mechanical signal box, type Jüdel 1910, 1990
Signal box Burgsinn Bbf , 1988
Signal box Bindlach , type Jüdel (2006)
Former central signal box of the Frankfurt (Main) Hbf train station

A signal box is a fixed railway system used by the railway to control railway operations. It is used to position route elements such as switches and track barriers , creates dependencies between route elements and signals and integrates level crossing safety systems into the safety logic. A track vacancy detection system can be connected to the signal box , which monitors the current occupancy status of the tracks. Where such is not present, an operator must look, the freedom of the tracks within railway stations and branch-off or crossovers check . If this is necessary, the interlocking must be in an elevated position so that the operator can see the entire route inspection area through the window.

Mechanical, electrical or electronic dependencies between these elements characterize the technical-historical development stages of the interlockings. The employees working in the signal box are the dispatchers , point attendants and train detectors .


Signal box in Schleusingen train station at the southern exit to Themar
Former mechanical equestrian signal box in Constance
Equestrian signal box from Constance, rebuilt as a museum at the Blumberg station of the Wutachtalbahn
"Standard signal box " in Ilmenau station (signal box south), built in 1881

The interdependencies of the interlockings and the route elements ensure a secure operation.

A signal can only be set to travel when all the equipment on the route is in the position required for the journey and is locked (fixed and monitored) in this state, as well as all track clearance reports in the route and slip-through report that vehicles are free (in In Austria, it is possible to “release” the signals for new systems, even if the track sections are occupied, subject to documentation - the slip path can always be occupied). The so-called signal dependency is established through this highest quality condition of the interlocking, the position of the signal . As long as the associated start signal is in the driving position, all devices forming the route are locked in the position required for driving. The specified route can only be triggered or resolved (changed) with auxiliary devices subject to documentation.

Signal boxes also use the route block to regulate subsequent and opposing train journeys on the open route . Trains follow each other at a “spatial distance”, also called block distance , counter-train journeys are excluded. The free series can in individual with block signals limited block sections or -strecken be divided.

Appropriate design of the technical equipment of the interlocking ensures that any errors that occur have an effect on the safe side. Signals must not move from the stop position to the drive position due to an error or change from a lower to a higher drive concept, switches must not be switched ( fail-safe behavior ).

The UIC Euro Interlocking project is developing an international standard for the planning of new railway interlockings.


Interlockings are differentiated according to the technology of control and security as follows:

Mechanical signal box

  • It is operated using switch, bolt, track barrier and signal levers, and in some cases also winches ( signal winches and barrier systems). Electromechanical devices are usually available for the station and route blocks. Crank mechanisms are a special form .
  • The mechanical power transmission to the outdoor facilities takes place using two different systems:
    • via wire pull cables, usually double wire pull cables, e.g. B. in Germany , Switzerland and other Central and Eastern European countries;
    • via rods ( Saxby system ), e.g. B. in France , Switzerland , Great Britain , USA . Mixed systems are possible and common. Typical for old British interlockings are rod lines for points and wire pull lines, usually single wire pull lines, for signals.
  • In the signal box, the dependencies are created by mechanical means. Due to the system, the check of the fulfillment of the conditions for the signal dependency only takes place punctually when setting routes.

Because of the limited distances to the outdoor facilities, mechanical interlockings must be set up within their control area; central interlockings for an entire train station can only be mechanically implemented under particularly favorable circumstances.

Electromechanical signal box

  • It is operated with small levers, rotary switches and individual pushbuttons.
  • The outdoor facilities (switches, track barriers, form signals) are electrically powered; Shape and light signals can be present as signals.
  • In the signal box, the dependencies are mainly created by mechanical means, which are, however, supplemented by electrical dependencies.
  • In contrast to mechanical interlockings, the dependencies and locks are not only checked once when a route is set, but are constantly monitored by the coupling circuit until the route is cleared. If this is interrupted while the start signal is showing a travel concept, it falls into the stop position. The regular signal stop is also triggered by interrupting the coupling circuit.

Mechanical and electromechanical interlockings are usually built high in order to maintain a compact building, to accommodate additional facilities such as tensioning or relay and battery rooms under the lever system and to give the operator as complete an overview as possible of his actuation area, in particular of the occupation to be able to visually determine the tracks. If the signal box operator is to take on other tasks such as supervision or ticket sales in the combined service , then a ground level service room is required.

Relay interlocking

  • It is operated with push buttons and / or pull buttons.
  • The operating and display elements are arranged in a control box , on a control table or control panel in such a way that their position corresponds schematically to that in reality. In some cases, it is also operated via computer workstations with a monitor, keyboard and mouse.
  • The outdoor facilities are controlled electrically throughout.
  • The production of the dependencies is done electrically through relay circuits, which led to the naming.

The operating distance, i.e. the distance between the relay room of the signal box and the element to be controlled, is limited to around 6.5 to 8.3 km in the systems common in German-speaking countries due to the transmission technology, depending on the type of cable used. By using remote control devices that increase the distance between the operating and relay systems, these distances can be increased to a multiple of these values.

Electronic signal box (ESTW)

  • The user is guided by a schematic graphic representation of the elements of the outdoor system on monitors, in larger systems also on projection walls (not common in Germany).
  • It is usually operated with the mouse, or alternatively with the keyboard. Older designs were operated using a graphics tablet or light pen (both of which are now technically obsolete).
  • The outdoor facilities are controlled electrically throughout (relay technology, today also power electronics).
  • The dependencies are created using software in redundant computer systems.

In Germany, relay interlockings and electronic interlockings are also called track diagram interlockings because they are operated with control elements that are arranged or displayed on a table , a control panel or on monitors in a schematic track diagram. Transmission technology for the control element from relay technology was largely used, making it possible to set distances of up to 6.5 km. Scheidt & Bachmann later introduced the data bus (based on CAN ), and in 2007 Bombardier introduced IP-based networks on the control level, which allow distances of up to 90 km via fiber optic cables if a separate power supply is available on the control element. Old technology is being replaced more and more by this.

With a few exceptions, new interlockings in Germany are built exclusively as electronic interlockings. Currently (2018) the electronic interlockings are being further developed into digital interlockings . In the future, train traffic in Germany is to be controlled by 280 digital interlockings.


The development of the signal boxes is closely linked with the history of the operating regulations in the respective countries, with the techniques for securing through route blocks , with the progressive operational requirements (e.g. with regard to train lengths and travel speeds), with the history of the signal systems and with progress in mechanics and electrical engineering, in particular for track vacancy reports and axle counters up to high-speed eddy current-resistant devices.

The railway signal boxes were essentially developed in the order of the designs given above.

Mechanical signal boxes

The mechanical signal box in Fridingen station (2018)

The first mechanical signal box was installed in 1843 (1841 according to other sources) at the Bricklayers' Arms Junction in England. The main developments were carried out by John Saxby in the years from 1855. The first mechanical interlockings in continental Europe were derived from English interlockings (e.g. rod lines instead of the later common wire pull lines, pivot point of the levers below the floor). In Germany, the first mechanical interlocking, from which points and signals could be remotely controlled and centrally secured, was put into operation by the English company Saxby & Farmer in Stettin in 1867 . The first signal box in Austria was in Rekawinkel in 1876, and in Switzerland in 1880 in Bern.

Carl Frischen succeeded in making an important invention in 1870 with the alternating current block field, which enabled reliable electrical transmission of information over long distances. Security systems in German-speaking countries soon used this technology both for securing journeys on the route ( route block ) and journeys in the station area ( station block ).

In the 19th century, the signal boxes (and also the signal systems ) differed from manufacturer to manufacturer. At the turn of the 20th century, standardized standard designs were introduced in the German states and Austria. In Germany this was the "Einheit" type, which was developed in Prussia between 1911 and 1915. In Austria, as early as 1880, the type 12SA was built according to standard drawings by several signal construction companies. From 1909 the signal box 5007 (according to the drawing number of the overall composition) was the new Austrian control box. Due to the large number of private railway companies, there were no standard types in Switzerland.

Electromechanical signal boxes

Towards the end of the 19th century, attempts were made to use electricity to drive points (but to continue to mechanically secure the dependencies between control elements). In 1894 the first electromechanical signal box was put into operation in Prerau in Moravia (today in the Czech Republic). The first electromechanical signal box in Germany went into operation in Berlin Westend in 1896 . The milestone in the development of the electromechanical signal box was the Siemens 1912 type, which became the basis for almost all electromechanical signal boxes in German-speaking countries.

Relay interlockings

In the thirties, the first attempts were made to build completely electric signal boxes in which all dependencies and locks were implemented with relay circuits. After previous designs from Ericsson in Sweden or Integra in Switzerland, the first track diagram signal boxes were finally built in the early 1950s. After the first types were implemented in free circuit, standardized relay groups were soon designed for recurring tasks (e.g. turnout, route, signal and block groups), which made the production and testing of interlocking systems easier. In the 1960s, the track plan signal boxes were finally constructed, in which each track element forms a single partial track and the interconnection is almost exclusively done with prefabricated and pluggable connections as spur cables according to the track plan and ring lines between groups of the same type.

Electronic signal boxes

In 1978 the first computer-based signal box went into operation in Gothenburg. The great advantage of electronic interlockings, free programming, had to be bought at the cost of complex hardware or software solutions that provide the necessary security against failures. While the other types are no longer being developed in Germany, the development of electronic interlockings continues in the direction of further centralization and new operating options. Lines of high-speed traffic must be supplied with information for line control or ETCS , which only electronic interlockings or track plan relay interlockings of the SpDrL60 or SpDrS600 types, which have been upgraded with so-called high-speed block assemblies.


At the end of 2019, 2557 signal boxes were in operation in the Deutsche Bahn network, including:

  • 642 mechanical signal boxes
  • 287 electromechanical signal boxes
  • 1197 relay interlockings
  • 351 electronic signal boxes
  • 80 other designs

While the number of mechanical, electromechanical and relay interlockings has decreased in recent years, the number of electronic interlockings has increased.

In 2014 there were still 3090 signal boxes in operation, which were divided as follows:

  • 839 mechanical interlockings (share of total stock: 27 percent)
  • 339 electromechanical interlockings (share of the total stock: 10 percent)
  • 1397 relay interlockings (share of total stock: 45 percent)
  • 424 electronic interlockings (share of total stock: 13 percent)
  • 91 other types of construction (including drainage and EOW interlockings) (share of total stock: five percent)

At the end of 2013, Deutsche Bahn said it had 3397 signal boxes, which were on average 47 years old. In around one third of the systems, the technical service life is far exceeded. In 2013, Deutsche Bahn operated a total of 130 different types of signal boxes.

In 2003, around 250,000 actuating units were installed in the Deutsche Bahn network. Around 80,000 of these were for turnouts and 170,000 for signals (including additional signals ). At the beginning of 2006, an average of 14 control units (signals, points, track barriers, etc.) were attached to a mechanical interlocking of Deutsche Bahn, an electromechanical interlocking 31, relay interlocking 77 and ESTW 236.

Building shapes

Branching point Kostheim Mainz-Kostheim at the Taunus Railway and the avoidance trajectory Mainz with interlocking (right) - Even modern interlocking with relay technology were favored built near the track: So operators can of interlocking systems in disorders of train detection systems by visual inspection of the affected railway facilities to Accelerate operations and discover irregularities on railway vehicles by observing trains

The classification of signal boxes according to the shape of the building, which is often used by outsiders, has little to do with the function and technology of the signal box, especially since this distinction is only used in old systems with mechanical or electromechanical control technology, which provides an overview of the railway systems supervised by the signal box for the purpose of checking the clearance Inspection "require. A distinction is made here:

  • Signal tower, also switch towers, which were erected on the side of a railway system and have a raised control room. In addition, this type of building enables additional facilities to be accommodated. In the case of mechanical interlockings, in particular, tensioning mechanisms can be accommodated in the tensioning room under the lever system, protected from the weather.
  • Bridge signal boxes , which have their control room in a bridge across the supervised railway systems (e.g. signal box Bingerbrück Kreuzbach ), and
  • Rider interlockings, the control room of which is raised lengthways between the railway systems.

In modern interlockings with relay technology or electronic designs, the track systems included in train and shunting routes are fully equipped with automatic track vacancy detection systems that make an overview of the track system from the window superfluous. If the interlocking operator is to take on other tasks, for example as a supervisor or ticket seller (“unified service”), the control room must be set up on the ground floor. This type of construction is often found in through stations, recognizable by the typical signal box front structures on the reception buildings.

Mechanical interlockings require a tensioning room under the control room ; if the height is not sufficient, this only contains deflection rollers and angle levers, which guide the rod and wire cables leading vertically downwards from the lever bank in a horizontal direction and out of the building. Instead, electrical interlockings require additional rooms for the safety switchgear as well as the power supply and emergency power systems. They can be located in the signal box itself (often under the control room), in an extension or in a separate building.

Remote position and remote control

As far made valid a place of business, if there is no signal box at the site of this operating point and the points and signals are connected to an interlocking an adjacent operating agency. Remote control is only possible within the control distance of a signal box (approx. 6.5 km). Remote control units are those that have their own, locally unmanned interlocking that is operated from another interlocking or an operations center using special remote control technology. Placed away is a signal box, when it is fully available and locally operated locally that used in regular operation control device, however, is at a different location, usually in the neighboring station.

In the case of electronic interlockings , in addition to the central components in the ESTW control center (ESTW-Z), there are also so-called remote control computers or so-called ESTW branch offices (ESTW-A) which are sent to the ESTW-Z with different forms of communication media are connected. In terms of their function, these ESTW-A are in most types of electronic interlockings not independent interlockings in the actual sense with their own security logic. Parts of the security logic are only integrated in the ESTW-A in some types / generations of electronic interlockings from Siemens. Nevertheless, it has become common practice among experts to speak of remote control by an ESTW-Z in the case of ESTW-A.


Signalman 1949
Track diagram setting table type GS II ( WSSB ) 1975
Dispatcher interlocking as a central interlocking

The operator of an interlocking is called a warden in Germany . A keeper who is responsible for executing the train journeys according to the schedule is called a dispatcher . Guards who are not dispatchers are called switch attendants . You operate your interlocking independently when maneuvering and take part in train journeys on behalf of the dispatcher. The facilities of the station block create the necessary technical dependencies .


Dispatcher interlocking

Signal boxes that are manned by a dispatcher are called dispatcher interlockings or command interlockings . They control and dispatch the train traffic in the local area of ​​a train station or another operating point. The dispatcher is the sole operator of the dispatcher interlocking in smaller interlockings. However, one or more point attendants can be assigned to him to operate the points in large mechanical and electromechanical signal boxes . In large relay interlockings , one or more guards can also support the dispatcher. However, a separate table is then usually provided for each operator. Classic command dependencies then exist for train journeys, comparable to electromechanical interlockings. The guards handle the shunting operations independently. The division into several dispatcher districts - also in the same building - is possible and common at large train stations and in lane plan signal boxes. As a rule, the operators then have the same priority and when driving between the operator areas they give each other consent. In the case of electronic interlockings , several operators, usually with equal rights, are the rule due to the size of the control areas.

In the area of ​​the former Deutsche Bundesbahn , dispatcher interlockings or command interlockings can usually be recognized by the short names attached to the outside of the interlocking building that end with a small "f". This is unusual in the area of ​​the Deutsche Reichsbahn , usually the capital letter "B" is placed in front of the signal box number. Other railways do not mark command signal boxes.

In the case of interlockings without automatic track vacancy reports (i.e. predominantly mechanical and electromechanical interlockings), the work areas of the dispatchers or point attendants were determined from which track areas can be viewed from the workplace in order to be able to check whether they are clear. To rationalize their work, track vacancy reports or vacancy flags were introduced. In the case of mechanical interlockings in particular, the controllable cable lengths also have a limiting effect.

Security signal box

In stations with mechanical or electromechanical signal boxes, the station area is often divided into signal box districts. In addition to a dispatcher interlocking, there are also one or more attendant interlockings that are operated by a switch attendant . Point attendants act independently when maneuvering , and on train journeys on the individual order of the dispatcher.

In Germany, guard interlockings can sometimes be identified by the small “w” in the abbreviation, which, however, can also mean the position of the interlocking in the direction of the compass (= west).

Command post

Often one wanted to relieve the dispatcher from setting the switches and signals as well as the shunting operations so that he could concentrate on his other tasks. In addition, as a contact person, he should be accommodated in the station building within easy reach. Therefore, in some cases, separate command posts were set up, from which the dispatcher could only give the orders for the formation of the train routes to the guard interlocking at the two ends of the station, but did not have to set any switches or signals.

Command posts were particularly widespread in southern Germany, Saxony and Austria. Command posts are rarely found in Germany, but in Austria they can still be found at most train stations that are equipped with older signal box technology.


Guard interlockings, which are used exclusively for shunting and are not involved in train journeys, are called shunting interlockings . You are e.g. B. to be found in large marshalling yards . A special form of the interlocking is the interlocking . Typically, there are no train routes on shunting interlockings .

Control box

A drainage interlocking is a special form of the marshalling interlocking that is responsible for the implementation of the drainage operation on a drainage mountain . Interlocking systems are also mainly to be found in large marshalling yards . The peculiarities of the process operation cause some fundamental differences to other interlocking systems. There is no signal dependency in the usual sense, the push-off signal can be set without a previously set route and switches are switched immediately before rolling cars - this is why high-speed drives with switching times of less than one second are used, especially on the distribution switches of the first and second series , while normal electrical switch drives are used Changeover times of two to six seconds. Sequence interlockings are available in every possible design; to relieve the operator, they can only be automated as relay or electronic interlockings.

Central signal box

Large dispatcher interlockings with special facilities and tasks are called central interlockings . Central interlockings set the points and signals in the local area, for example in a large train station and also often one or more remote or remote-controlled operating points - these are usually other (smaller) stations and junctions nearby .

Line signal box

The "Maf" signal box in Oberhausen Mathilde is a typical line signal box , 2015

A route interlocking is a form of central interlocking that is (predominantly) responsible for a route section (or a part of it) between two node stations and remotely or remotely controls the operating points on this section.


A node interlocking , like the route interlocking, is another common name for a central interlocking .


In Germany, signal boxes are marked as such on the outside of the signal box. To differentiate between the tasks of the signal boxes, letters were chosen from the former Prussia . Thereafter, this marking was introduced in all northern German administrative districts and finally widely at the former Deutsche Bundesbahn as well as in the northern half of the network of the former Deutsche Reichsbahn and in Thuringia .

Specifically in Germany, the first capital letter indicates the first letter of the station name (usually the place name). The following lower-case letter denotes the position of the signal box within a train station in the direction north ("n"), west ("w"), south ("s") and east ("o"). The function of an interlocking is indicated by the letters “f” for dispatcher - or “b” for command interlocking and “p”, “g” and “r” for belonging to a passenger, freight or marshalling yard. Because many places only have one dispatcher interlocking, the additional IDs are only used in larger train stations.

In Saxony and the southern German directorates, the signal boxes were simply numbered in the direction of the kilometers. The operational function was later identified by the code letters “B” for command interlocking or command station (dispatcher interlocking), “W” for guard interlocking and “R” for shunting interlocking (not involved in train journeys). In the DR network, central interlockings without dependent interlockings were usually called "B1".

In Austria (and therefore in most of the successor states of Austria-Hungary ) and in Switzerland, signal boxes within a train station are numbered according to the kilometering.

Operations center

An operations center (BZ) is by definition not a signal box, as no technical dependencies and fuses of the track are made in it. Instead, it serves primarily to guide and control rail operations , especially for large-scale dispatching far beyond the area of ​​the individual interlockings.

If the interlockings in the catchment area of ​​the operations center are appropriately "BZ-capable", the interlocking user interfaces can also be integrated in this in addition to the dispatching tasks. Electronic interlockings and newer relay interlockings are equally suitable for FC-capable equipment .

Training signal box

To train dispatchers and other signal box personnel, the railway administrations set up training signal boxes. The basics of technology are taught at the mechanical interlocking systems available there and operational disruptions are simulated on a fictitious railway line. Deutsche Bahn largely decommissioned these facilities. Only a few DB training centers (Berlin-Schöneweide, Regensburg and Magdeburg) therefore still have appropriate training facilities.

The town of Kornwestheim owns the historic and listed training signal box Kornwestheim. It was restored by a sponsoring association and started up again. As part of the training for new dispatchers, Deutsche Bahn discovered that many mechanical interlockings, some of them from the era of the regional railways, are still in operation. DB Netz is therefore training again in Kornwestheim (in addition to the interlocking simulations of electronic interlockings of the DB training centers).

The transport science institutes of RWTH Aachen University and TU Dresden each operate a signal laboratory for research purposes, to train students and to impart basic knowledge as part of further training to managers in the railway sector.

Museum signal boxes

Jüdel museum signal box in the north
Historic signal tower 1 from 1900, today a museum signal box in Schelklingen

In addition to the museum railways , some museum signal boxes have also been built in recent years, which are intended to bring the function of the safety technology of the railway closer to the interested public.

Such museum signal boxes are located in the German-speaking area, for example, in Hagen , Cologne-Dünnwald , Lehrte , Mühldorf , Rheine and at the Blumberg-Zollhaus station of the Wutachtalbahn .

A very large and worth seeing museum signal box is located in Berlin. It belongs to the Berliner Verkehrsbetriebe (BVG) and is located in the Berlin U-Bahn Museum . It is an old electromechanical signal box that has been replaced by a track plan signal box of the SpDrS-U type.

The historic training signal box of the Hamburg Federal Railway Directorate, housed in the former VT 137 137 railcar, is located in the Aumühle Railway Museum . It is demonstrated on visitor days.

In Switzerland, the Kerzers mechanical signal box is preserved as a museum.

In the Schwarzenberg Railway Museum, an electromechanical signal box of the Gaselan design will be kept operational as a museum and connecting railway signal box. It is open to the public on selected days.

In the station Děčín hlavní nádraží ( railway line Dresden – Děčín , Czech Republic ) the electromechanical signal box (DR design) from 1941 has been open to the public as a museum since 2003.

In Great Britain, the birthplace of interlockings, a number of mechanical interlockings are preserved as museums, including those in St Albans , North Weald and Crewe .


Web links

Commons : Signal boxes  - collection of images, videos and audio files
Wiktionary: Stellwerk  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. DB continues digitization offensive: In future, 280 digital interlockings will control train traffic in Germany. In: Deutsche Bahn, October 30, 2019, accessed on October 30, 2019 .
  2. ^ A b Christian Hager: Railway safety systems in Austria . tape 1 : Signal boxes . Verlag Pospischil, Vienna 1984, p. 20 .
  3. ^ Karl Oehler: Railway safety technology in Switzerland - The development of electrical equipment . Birkhäuser Verlag, Basel / Boston / Stuttgart 1981, ISBN 3-7643-1233-5 , p. 9 .
  4. Lexicon of all technology , entry "Signal boxes"
  5. Berlin signal boxes. Retrieved November 24, 2012 .
  6. a b Infrastructure status and development report 2019. (PDF) Performance and financing agreement II. In: Deutsche Bahn, April 2020, p. 134 f. , accessed on May 17, 2020 .
  7. Service and financing agreement: Infrastructure status and development report 2017. (PDF; 12.0 MiB) Chapter 2.4 “Development of the system inventory (ISK network)”, section “Development of the existing interlockings”, Figure 125: Development of the number of interlockings by design DB Netz AG. Deutsche Bahn AG, p. 141 , accessed on April 4, 2019 .
  8. Christian Schlesinger, Reinhold Böhmer: “Unjustly in the pillory” . In: Wirtschaftswoche . No. 48 , November 25, 2013, ISSN  0042-8582 , p. 54 (including title online ).
  9. Nikolaus Doll, Steffen Fründt, Ernst-August Ginten, Thomas Heuzeroth, Birger Nicolai, Andre Tauber and Daniel Wetzel: Bodenlos . In: Welt am Sonntag . No. 19 , May 12, 2013, ZDB -ID 1123516-0 , p. 13 (similar version online ).
  10. Dieter Fockenbrock, Thomas Tuma: “You have to fight on the railway” . In: Handelsblatt . No. 240 , December 14, 2013, ISSN  0017-7296 , p. 22 .
  11. Jörg Bormet: Requirements of the operator on the life cycle in route safety technology . In: signal + wire . tape 99 , no. 1 + 2 , 2007, ISSN  0037-4997 , p. 6-16 .
  12. Freiherr von Röll: Encyclopedia of the Railway System. Volume 10. Berlin, Vienna 1923, p. 318 ( switch tower ).
  13. website
  14. website