Relay interlocking

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Table of a track plan relay interlocking in Steinhausen station

A relay interlocking (also RSTW for short ) is a type of interlocking used to control railway operations , in which the safety-related dependencies are established entirely electrically using signal relays . In addition to electronic signal boxes, it belongs to the group of electrical signal boxes and is a track diagram signal box . Functions that are not relevant to safety can also be implemented with other relays as signal relays.


Cut-out of a control panel from a Sp Dr S 60 interlocking with a set train route

In contrast to the mechanical and electromechanical interlockings, the relay interlockings allow the setting of technically secured routes ( route ) not only for train journeys (train), but also for shunting (shunting routes ). The switches and other devices in the route no longer have to be individually brought into the correct position, but the switches required for a trip run, if they are not already in the required position, automatically in the required position when setting the route, with the motor starting staggered by the switch chain so as not to overload the power supply. After a train journey, the route is pulled either in the case of older designs as a whole, or in the case of newer designs in sections. Manual resolution as standard operation is only available in a few cases that cannot be controlled otherwise.

Message board of the Sp-Dr-S-60 signal box of the Trier Hbf train station with number control panel (front far right)

The setting range is shown as a schematic track diagram on a flat user interface . The operating status is displayed in the track diagram by means of different colored indicator lights. The operating elements, which are mostly pushbuttons (in the area of ​​the former DR often also pull buttons in the beginning ), are located in the track diagram at the point where the associated facilities are also located in the outdoor area.

In order to simplify the structure, the track diagram in German and many foreign systems consists of a lattice frame in which the illumination or button elements are inserted. The shape of the elements depends on the manufacturer, so WSSB and Thales (formerly Alcatel) have square table fields with an edge length of 40 millimeters, while Siemens have rectangular ones.

A control panel set up on the work table , a control box embedded in it or a control table slightly inclined towards the operator serve as the user interface . The track diagram desk is used for small to medium-sized systems . This can be operated while seated and enables written work to be carried out at the same workplace.

For a better overview, large interlockings use a vertical display and signaling board or partition, which is usually operated from the operator's workplace with the help of a track diagram desk. In this case, the display of the track diagram on the control table is greatly simplified, and individual operations such as switching points are rarely required using a number pre-selection device . In place of the buttons, there are button lamps on the message board , by their lighting up the operator can recognize the correct selection of the element to be operated. In addition, turnout and turnout group buttons are usually built into the message board at the lower edge. These buttons can be used to operate even if the number prefix fails.

The term push button interlocking ( Dr interlocking ) was established at the former Deutsche Bundesbahn . The former Deutsche Reichsbahn used the name Gleisbildstellwerk . Except for the fact that not all relay interlockings are push-button interlockings, the terminology differences have no meaning.

At the beginning of 2006, Deutsche Bahn operated 1830 relay interlockings with 141,231 actuating units. The types most widely used by DB in 2003 were Sp Dr S60 (543 units), Dr S2 (342 units) and GS II DR (251 units). Around 60 percent of the actuating units in the DB network were monitored and operated by relay interlockings.

The main advantages over mechanical and electromechanical interlockings include:

  • The overview of the outdoor facilities is comprehensive and makes scheduling easier
  • Due to the layout of the control elements, the operation is more intuitive than with a classic lever system, the learning effort for training the employees is lower
  • The operation via buttons does not require any heavy physical work, it is possible with a track diagram desk, a separate control and reporting device and, within certain limits, with a track diagram table while sitting
  • Due to the significantly longer travel distances, which are only limited by the wire resistance , a central relay interlocking can replace several conventional interlockings
  • Increased safety through automatic track vacancy detection systems and secured shunting routes
  • The operating sequence is accelerated by the automatic rotation of switches when setting the route and the general train-induced dismantling of routes, which, as partial routes, release the route elements that are no longer required shortly after the train has been cleared
  • Relay interlockings are suitable for remote control in connection with an automatic track vacancy detection system

Compared to electronic interlockings , the advantage of relay interlockings with basically the same distance between the indoor and outdoor systems is that the failure behavior of relay systems is more predictable and fault detection is better without costly aids. A fault in the indoor system can hardly lead to a total failure of the entire signal box. In addition, air conditioning of the technical rooms is usually not required.


It is operated using the two-button principle: To initiate an actuation process, two buttons that are logically related must be operated at the same time. This is to avoid accidental operations.

To set a route for a train or a shunting run and to get the signal moving , the start button and destination button are operated simultaneously. The start button is located at the beginning of the route. It is assigned to the signal that is to be set to travel. Depending on the type of interlocking, the destination button is located in the track into which the journey is to take place, or at the next signal at which the journey ends.

With most designs, the switches then automatically revert to the required position. As soon as all the requirements for the journey are met, i.e. the tracks are also free of other vehicles or route assignments, the route is determined and the main signal automatically switches to the driving position.

A process for which a large number of operator actions are required in mechanical and electromechanical interlockings is thus done here with the press of two buttons.



Even before the Second World War , mechanical and electromechanical interlockings were so technically mature that they could no longer be improved. That is why the development of a new type of interlocking was started, in which the operating elements are grouped together on a flat surface and the control and safety technology only works electrically.

Before the actual relay interlockings, types were developed from the electromechanical interlockings that only realized the dependencies required for security systems electrically, i.e. without a mechanical locking register . Often the mechanically moved contact axes of the electromechanical interlockings were still used, but now moved by electromagnets.

  • In Germany there were first attempts with so-called cartridge signal boxes during the 1930s . The track area belonging to the signal box was shown schematically with metal parts on a flat user interface. The electrically powered points were designed as levers with which they could be switched. These were integrated into the track diagram and indicated the respective position and thus the set route. The associated switches, including those for the signals, were in a kind of cartridge case that was inserted into the user interface. A start was made, but these signal boxes did not get beyond the experimental stage and were therefore of no importance.
  • In Switzerland, the Signum company built a single-row switch mechanism without mechanical dependencies in 1939 . The dependencies were also implemented using contact axes. Other such switch mechanisms followed in the 1940s and 1950s - see the following section.
  • In Austria, the OES company designed the "rotary axis signal box" in the years after the Second World War, whereby the "rotary axis" that controls many contacts can also be described as a "very long relay". The arrangement of the operating devices was solved in different ways: in some such interlockings push buttons or pull buttons were arranged in rows, in others on consoles roughly in the position of the switches and signals, in the last type already in a track diagram.
  • In North America, with the introduction of CTC (Centralized Traffic Control) in the 1930s, the first all-electric relay interlockings appeared.

Integra switch factories in Switzerland

The Swiss switch mechanisms from Integra are characterized by the following properties:

  • All interdependencies between the switches (turnouts and route signal switches and possibly block and barrier switches) are established electrically . This means that no locking rulers are required.
  • In general, at least the sections used by trains are equipped with track vacancy detection systems. Normally, therefore, no inspection by looking is necessary for setting and canceling a route (exception: shunting trips and route blocks with manual feedback).
  • Small lamps are used for all feedback (signal positions, isolation, blocking, route block, point monitoring, ...). With a few exceptions, these are built into a board with a track plan on the switchgear at the geographically correct location.
  • The route is selected using the track buttons assigned to the station tracks . These must be pressed in the first detent of the route signal switch. As a result, after checking the correct position of the switches, the release lock of the route signal switch is activated, so that it can be turned further. If the block conditions, the point monitoring and other conditions have been checked, the coupling current block, which only works when the switch is set, is also activated. Then both coupling current blocking cams can be overcome and the switch can be turned up to 90 °. The signal goes automatically to the driving aspect that the switch allows.

Track diagram signal boxes

In the next development step, there were essential innovations:

The operating elements are now push buttons or pull-cord buttons that are arranged on a flat user interface in a realistic representation of the track systems and signals where the device to be operated is located on site. Only electrical drives are used for the track equipment operated by the signal box (switches, track barriers ); changeable signals are always light signals. It was made possible to set up larger control areas, because the operator no longer has to check that the route is clear during the route inspection by looking ( visually ), as in mechanical and electromechanical interlockings, but instead an automatic track vacancy detection system is used.

Building of a track diagram interlocking with attached relay room

The interlocking now only works with circuits that are switched by relays; mechanical locking devices are completely absent. They are combined in functional groups, mounted on racks and housed in a special relay room, in smaller interlockings in a relay cabinet that is only accessible to technical maintenance personnel in order to prevent manipulation. The relays are controlled on the one hand by the operator by pressing the pushbuttons, on the other hand by the vehicles via the track switching means of the track vacancy detection system.

Types of construction in Germany

German Federal Railroad

A 50 km long section of the
high-speed line Hanover – Würzburg is controlled from the control room of the relay interlocking in the Burgsinn depot . (Photo from 1988)

During the Second World War, the development of relay interlockings largely came to a standstill. On October 18, 1948, Siemens & Halske ( Signalwerk Braunschweig ) handed over the first fully operational relay interlocking ("Dr I") to what was then the "Deutsche Reichsbahn im Vereinigte Wirtschaftsgebiet" ( German State Railroad in the United Economic Area) at Düsseldorf-Derendorf station, which was also used in other stations. u. a. in the Hamburg-Altona train station and in the area of ​​the remote control route from Nuremberg to Regensburg.

In addition to Siemens later expanded its Stuttgart-based company also C. Lorenz , the 1958 Standard Elektrik to Standard Elektrik Lorenz merged (SEL), relay interlocking for the German Federal Railways on the basis of more advanced signal to relay telecommunications relays . The abbreviation introduced by the Deutsche Bundesbahn to designate the design now distinguishes the manufacturers. The abbreviation “Dr S” stands for Siemens and “Dr L” for Lorenz (“Dr A” for AEG did not go beyond test installations). Early designs by Lorenz were called "Dr L 2" and "Dr L 3". They were followed by the "Dr L 20" and "Dr L 30" systems, and from 1963 "Sp Dr L 60". The rail systems division, later transport systems from Standard Elektrik Lorenz , later Alcatel SEL AG , has been part of the French Thales Group since 2007 as Thales Rail Signaling Solutions GmbH , and since 2011 as Thales Transportation Systems GmbH . The interlockings of both manufacturers differ among other things in the size and appearance of the operating and signaling elements, but initially also in their operation. With newer interlockings of the 1960s, the so-called track plan interlockings (see below), the operation has been standardized across companies.

The successor to the "Dr I" signal box was therefore called "Dr S" and is still in use in many train stations today. For smaller train stations, the manufacturer developed the "Dr S 2" signal box, which was built and used in larger numbers. Building on this, the "Dr S 3 (2)" was created for medium-sized stations.

When dividing the station into interlocking districts, in the early days one orientated itself largely on the stations realized with mechanical and electromechanical interlocking technology and built a command post with several guard interlockings in larger stations . The switch keepers maneuvered themselves independently in their districts, but they could only set train routes on the orders of the dispatcher in the command post . But soon they started building central signal boxes.

Right from the start, relay interlockings were built up modularly from standardized relay groups, each of which performs a specific function (e.g. controlling a signal or a turnout, or setting or canceling routes), is interchangeable within the same type and can be manufactured industrially. The display and control elements are also composed of standardized individual components. In the route-based interlockings, the connections between the individual relay groups are established by means of "jumper wiring" to be inserted on the construction site between solder lug distributors, which are usually arranged on the rear of the group, according to plans projected in individual cases on the basis of the respective basic circuits.

Since this is relatively time-consuming and complex, improvements were considered that led to the development of the track plan signal box. This means that each route element (switch, intersection, track section) represents its own partial route, controlled by an associated relay group. The relay groups are connected to each other by spur cables just like the individual elements in the real track system. The number of soldered connections to be made on the construction site drops dramatically. The interlocking automatically searches for the route via the spur cables for every route request and secures it. This means that it is not necessary to set up every route manually, there are no classic route groups, and every possible route can be set by the interlocking without additional switching effort. Only more complicated detours and auxiliary routes require greater operator effort.

Manufacturer-side differences are based on the number of lane veins (20 at Siemens - only extended with SpDrS600 -, 30 at Lorenz and WSSB) and the discrete cross-wiring that remains for setting exclusions between the routes. In contrast to this, with route-based interlockings, only those routes can be signaled that were provided in the project planning of the interlocking and that were largely built in freely. A relay interlocking with this technology is also called a track plan interlocking (abbreviation Sp ).

In the case of smaller systems, a lane-plan signal box is more complex than a route-based interlocking, which is why the route-based types Dr S 2 and GS II DR were rebuilt in small train stations even after the lane-plan signal boxes were introduced.

For the former Deutsche Bundesbahn, u. a. the track plan interlockings of the prototype designs "Sp Dr S 57" and "Sp Dr S 59" by Siemens as well as "Sp Dr L 20" by Standard Elektrik Lorenz have been developed, which are then built in large numbers into the designs "Sp Dr S 60" and " Sp Dr L 30 ”. In the course of an adaptation of the operation of the Lorenz signal boxes to the Sp Dr S 60 requested by the Federal Railroad, Lorenz developed the "Sp Dr L 60".

The first Sp Dr S 57 interlocking was in Kreiensen until 2011 . From around the end of the 1960s to the beginning of 1990, the series designs "Sp Dr S 60", "Sp Dr L 30" and "Sp Dr L 60" replaced many of the existing mechanical and electromechanical interlockings, and in some cases the first relay interlockings. The first signal box Sp Dr S 60 is in Sarstedt ; it is still in operation with a greatly reduced track plan.

At the end of the 1970s, Siemens developed the “Sp Dr S 600”, a successor with extended functionality, which was particularly advantageous in larger stations and on new lines, but was also used in medium-sized and small stations.

The C. Lorenz company, on the other hand, launched the "MC L 84", a simplified track plan interlocking system that was optimized with a reduced range of functions especially for the needs of small train stations. Here one signal and one turnout covered by it were connected in a common group, thus reducing the number of different switching groups to a minimum.

Signal boxes that had not yet reached the end of their useful life were occasionally reused in other places, e.g. B. the Dr S 2 signal box from Rethen (Leine) in Emmerke, until it was replaced there by a remote control computer from the Hildesheim electronic signal box. In stations with little freight traffic, the last relay interlockings were used again in a simplified design (Sp Dr S 60 V). There are no shunting signals (Hp0 / Sh1) there. Examples are Weetzen and Himmighausen .

By the end of 1981, 1500 track diagram interlockings with a total investment volume of 3.7 billion DM had been put into operation in the area of ​​the Deutsche Bundesbahn. The number of jobs in the signal boxes could be reduced by 13,000.

The Deutsche Bundesbahn also shortened the terms train route to "train route" and shunting route to "shunting route" in official documents . This is not common with other operators.

German Reichsbahn

In the early 1950s, the Deutsche Reichsbahn had the first track diagram interlockings built using relay technology.

The first of the "Design 0", built in 1951 in Wildau and Königs Wusterhausen (Kwm), still evidently came from the electromechanical signal box, for example DC voltages of 34 volts were used for monitoring and 136 volts for the control current.

The designs "GS I DR" (from 1950/1951), "GS II" (from 1958/1959), "GS II Sp 64" (from 1968/1969), "GS II A 68" (from 1968/1969) were used in series production. from 1968; signal box for operation in shunting yards) and "GS III Sp 68" (from 1974). With design I, the voltage levels still used today of 60 volts direct voltage for supplying the relay circuits and 380 volts three-phase alternating voltage as the control voltage were converted. While the signals in interlockings of type GS I DR are fed with a direct voltage of 60 volts, with signal lamps for 50, 40 or 30 volts being used depending on the distance to the point and the further adjustment of the lamp currents by means of resistors, they are used in all of the following types of construction supplied with 185 volts AC voltage. The adaptation to the flat-core filament lamps with 12 volts and 20 watts used here is carried out by a transformer in each lantern cover. These lanterns can be recognized from the outside by the greater height of the cover.

The GS II design exists in two versions: GS II DR for railways with passenger traffic with Hl signaling and GS II IB for industrial railways with simplified circuits. In this design, a turnout group contains devices for two turnouts. Both versions were exported to different countries with adapted signaling. There are four versions of the GS II Sp64 design:

  • GS II Sp64a for industrial railways
  • GS II Sp64b for the Deutsche Reichsbahn
  • GS II Sp64c for the Berlin subway
  • GS II Sp64d for export customers

Operation with pull-cord buttons was distinctive for older DR systems. These have the advantage that they cannot be accidentally operated, but the desk surface quickly tears off and becomes illegible. With the GS I design, for example, the switch switch was only triggered with a single button. Many GS II DR interlockings also originally had pull-cord buttons and have since been converted to push buttons, which is safe from a safety point of view due to the general two-button operation.

In the GS I design, there were no relay groups in the form that would later be used. The relays with open contacts, which can be seen as the origin of the VES magnetic switches from the time before the Second World War, are inserted from below into the rack inserts for three relays each. They are available as single, double and triple relays, with a triple relay completely occupying one rack insert. Relays that belong together are only housed close to each other, the entire wiring is implemented on the construction site in free switching.

With the GS II design, prefabricated relay groups and new, dust-protected relays in two sizes were introduced. In the large design, the normal, toggle, backup and block relays, in the small design, small and latching relays as well as flat relays, capacitors, transformers, delay and block inductor inserts.

A large relay corresponds to two small relays arranged one above the other. They can be plugged in on the back and are covered with a transparent cap, safe to touch and protected from dust. An unmistakable device in the form of a sheet metal plate with holes in which pins on the plug side of the relay engage, prevents the installation of incorrect relays.

For most applications, there are prefabricated relay groups with a tested internal circuit with standardized and identical dimensions, such as turnout, route main and additional groups, various signal groups and block groups for relay and automatic route blocks. Groups for free switching are used for switching cases that do not occur regularly and other applications such as key-dependent switches, adaptation to interlockings of other designs or non-standard applications such as connection relays for route storage. With these, all relay coil and contact connections are brought out to the solder lug distributors. Only the connections between the groups as well as to the operator station, to the outdoor system and to the power supply (for which there is a separate terminal strip) are made on the construction site with jumper wire. The relay groups of the track plan interlockings, especially in the GS II Sp 64, are externally similar, only with the exception of the block relays only small and latching relays are used. These relay groups are also covered on the back and the connections are made using plug strips and the associated plug-in room cables. In the GS III Sp 68 design, the relays in the form of the N3 / P3 relays have been reduced by half and packed more densely. The motor relay groups for the automatic track vacancy detection are a special case. They correspond in shape, size and connections to the principles of the respective interlocking design and contain six slots for motor relays as well as the phase selection transformers for the selection of the control phase and the associated auxiliary phase.

Soft self-running , route signal position (the start-finish operation is stored, and after the switches have passed in the correct position, the signal concerned is in the parking stand and can automatically by manual operation or by a simultaneously at the respective signal ending and specified traveling road in this state, be brought into the driving position), drive-through operation and partial routes have been possible since the GS II design and were also installed and used, especially in larger systems. As a matter of principle, these devices are always present in track plan signal boxes, but apart from the route signal setting, they are not always in operation. In the track plan signal boxes, each track element, i.e. each turnout and each track section, is its own partial route, which is immediately cleared and available for a new run. A new feature of the GS II Sp 64b design was the control switch-off , so that individual system parts can be withdrawn from operation. This replaces the auxiliary locks that were still necessary in the previous designs (in the form of sleeves to be inserted over the buttons).

In addition to the simple drive-through operation ("signal self-setting mode"), in which one and the same route is determined again and again after it is canceled, there is also a program self-setting mode from the GS II Sp 64b design . This enables the scheduled automatic change of different routes after a train journey has taken place, without the need for further operator action by the dispatcher.

Due to supply bottlenecks at the WSSB company, Soviet-style track diagram signal boxes were imported from 1976 onwards. These relay interlockings are known as EZMG interlockings (EZMG = Elektritscheskaja Zentralisazija malych stanzij Germanii = electrical central interlocking for small train stations in Germany). Due to their design, these signal boxes could only be used in small train stations. Most of the signal boxes of this type were therefore installed in the stations of the branch lines .

The last development by WSSB before 1990 was the GS III 80 design, also in several versions for different operating conditions. The relay groups have a smooth back, so that they can be installed back to back or in front of the wall to save space. As a result of political developments, only a few of them were built.

Many interlockings of the old types were modernized or expanded at the DR with elements of the track diagram interlocking technology, for example light signals were set up or electrical drives were installed for points far away.

Deutsche Bahn AG

Since around 1987, electronic interlockings have replaced relay interlockings at the Deutsche Bundes- und Reichsbahn and Deutsche Bahn AG. In spite of this, relay interlockings are still being built sporadically, since smaller operating points in particular can be equipped with them more cost-effectively than with electronic interlockings. In addition, relay interlockings have proven to be more flexible, especially when it comes to renovations. Only the offers for the latest generations SpDrL60 and SpDrS600 contain so-called high - speed block groups, which can provide approximation information about more than one block section, as required for line train control or ETCS .

Deutsche Bahn anticipates a technical service life of the operating system of 25 years for its relay interlockings. The indoor system has a lifespan of 40 years, for the outdoor system 50 years are expected. The service life in which operation is worthwhile from a technical and economic point of view is estimated at 50 years.

In the mid-2000s, the first relay interlockings were connected to the control centers . Special interfaces were developed for this. Relay interlockings from a certain technical functional standard can be connected to BZs.

At Deutsche Bahn, 1,329 relay interlockings are still in operation (as of 2017).

Types in Austria

In Austria there were fully electric signal boxes very early on.

The first pure relay interlockings were developed and produced in Austria by the Wiener Schwachstromwerke ( Siemens operated under this name in Austria at the time). These were also given the designation DrS but differ in details and operation from the German types, this is due to the different signal regulations.

In the first systems, the classic arrangement with a command center in the control room and two terminal interlockings was used, but later the command post was housed in the same building as a terminal interlocking (but technically it remained separate systems), and central interlockings were subsequently also built.

The Lorenz company was only active in Austria since the ITT Group took over the German SEL and the Austrian Südbahnwerke . In the beginning, ITT Austria therefore built an electromechanical interlocking with automatic route entry instead of the DrL interlocking that was widespread in Germany, the EM55 developed by the SBW (These differ from the ones made before the takeover in the size of the fields in the track diagram, since then the square Lorenz fields were used instead of the original large rectangular ones).

The track plan technique was also used in Austria. Both ITT and Siemens built signal boxes for ÖBB. But here, too, there are major differences to the German designs. In Austria only two types of fully equipped track plan signal boxes were installed, namely the SpDrL from ITT (which is based on the same prototypes as the German SpDrL20) and the SpDrS from Siemens.

Both designs have been improved and adapted over the years, so the first SpDrL with computer operation via the so-called video desk system from ITT was put into operation in Wolfurt. There was also a computer-operated SpDrS, one of which stood at Vienna's Südbahnhof until it was demolished .

However, since the costs for track plan interlockings in small train stations could quickly become very high and many of the functions were not required (e.g. the partial resolution of routes), a simplified track plan interlocking was developed in Austria that basically corresponds to a track plan interlocking does not have many functions (e.g. an automated route entry). They were built by a consortium made up of AEG and Siemens.

These signal boxes were externally recognizable by their very small table fields. The most important simplifications:

  • no automatic route entry (when you press the start and destination button, only the position of the switches is checked, but it is not automatically changed)
  • no shunting routes ( shunting signals could simply be set freely together with the corresponding group key)
  • Routes are always resolved as a whole
  • there is no way to control protection signals

In the last few years, many relay interlockings of the types SpDrL and SpDrS have been converted to operation via the uniform user interface EBO so that they can also be controlled from the BFZ. Those interlockings where this is not possible will be replaced step by step by ESTW.


  • Ferdinand Hein: Sp Dr 60 signal boxes operate, Part A , 3rd edition Jan. 2000, ISBN 3-9801093-0-5 .
  • Ferdinand Hein: Sp Dr 60 signal boxes operate, Part B , 4th edition Apr. 2000, ISBN 3-9801093-2-1 , both railway specialist publisher Heidelberg-Mainz.
  • Jürgen Ernst: The Sp Dr S60 signal box , Josef Keller Verlag, 1st edition 1975, ISBN 3-7808-0107-8 .
  • Erich Preuß: Stellwerke , transpress Verlag, Stuttgart, 2002, ISBN 3-613-71196-6
  • Author collective, led by Hans-Jürgen Arnold: Eisenbahnsicherungstechnik , VEB Verlag für Verkehrwesen Berlin, 1987 - 4th edition, ISBN 3-344-00152-3 .
  • Wolfgang Kusche: Gleisbildstellwerke , 1st edition, transpress VEB Verlag for Transport, Berlin, 1984.
  • Ludwig Wehner: The emergence of the track plan signal box SpDrL60. In: Signal + Draht , Volume 62, Issue 10 (1970) 182-186.
  • Ludwig Wehner: The circuit of the track plan interlocking SpDrL60. In: Signal + Draht, Volume 64f, (1972f) several episodes.

Web links

Individual evidence

  1. a b Jörg Bormet: Requirements of the operator on the life cycle in the route safety technology . In: signal + wire . tape 99 , no. 1 + 2 , 2007, ISSN  0037-4997 , p. 6-16 .
  2. ^ A b Michael Lübbers, Adem Varol: Integration of relay interlockings in the operation of control centers . In: signal + wire . tape 99 , no. 6 , 2007, ISSN  0037-4997 , p. 13-19 .
  3. ^ Karl Oehler: Railway safety technology in Switzerland - The development of electrical equipment . Birkhäuser Verlag, Basel, Boston, Stuttgart 1981, ISBN 3-7643-1233-5 , pp. 16-23.
  4. ^ Christian Hager: Railway Safety Systems in Austria, Volume 1: Signal boxes . Pospischil Verlag, Vienna 1984, pp. 29-39.
  5. When the relays moved into the signal boxes . In: DB Welt , October 2008 edition, p. 2.
  6. Horst Binnewies: The investment strategy of the German Federal Railroad in focus of the year 1982 . In: The Federal Railroad . Vol. 57, No. 11, 1981, ISSN  0007-5876 , pp. 875-881.
  7. Deutsche Bundesbahn: Operation and maintenance of interlocking systems of the regular form, part 4a track diagram interlocking (DrI interlocking) , 1951.
  8. ^ Deutsche Reichsbahn (Hrsg.): Service regulation DV 873 Th. 41 - Operating regulation for track diagram signal boxes . 1984.
  9. Jens Dinewitzer, Björn Zimmer: Strategy of the “partial renewal of signal boxes . In: signal + wire . tape 105 , no. 6 , 2013, ISSN  0037-4997 , p. 17-19 .
  10. Digital and good? In: DB World . No. 5 , May 2017, p. 4 f .