Securing train journeys

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In order to secure train journeys , the railway companies take various measures in order to safely operate train journeys within the framework of the technical requirements - track guidance and long braking distances . Special regulations apply to certain operating modes, such as maneuvering .


Essential for the operation of railways are their decisive system properties:

The track guidance leads to the need for movable track elements (e.g. switches ) and the low static friction to long braking distances , which often clearly exceed the range of vision.

In order to be able to carry out a safe operation, there must be hazards for train journeys that result from derailments

  • due to discontinuities in the route, e.g. B. on switches or broken rails , or
  • due to the excessive speed of the train,

or from collisions , namely

result, can be prevented.

Example of a deadlock on a single-track route between two train stations with two tracks each

In addition, there is the need to prevent overfill in order to prevent the so-called deadlock , in which the trains block each other.

Securing can basically take place technically (through dependencies in the operation of the systems, signals and trains) and non-technically through operational regulations (see also operating procedures ), which means greater responsibility for safety for people. The greater the risk potential (e.g. high speeds), the higher the proportion of technical security. In Germany today, rail operations without any technical security are only permitted on branch lines ( train control operation ), in shunting operations or in the event of technical faults.


Early days

Siemens pointer telegraph
The Royal Train arriving at Tattenham Corner for the Epsom Derby 1959. The front signal for the Royal Train can be seen on the front of the locomotive - the four white dots.

In the early days of operations, there were railways that tried to get by without safety systems. The railway operation was seen in the same way as the road traffic at that time: the locomotive drivers drove on sight and should, if necessary, agree on who might have to drive their train to a siding on single-track routes . Since trains were slower to brake due to their low-friction road surface and greater mass than road vehicles, this soon led to accidents (see, for example, the Suffolk railway accident , 1837). That is why signals were used. The first railway company to do this was the Liverpool and Manchester Railway . In the beginning there were colored flags during the day and corresponding lanterns in the dark. In addition, the locomotives were soon equipped with steam whistles.

The flags were subsequently replaced by shape signals that were developed from the optical telegraph . The railways were also equipped with electric telegraphs . A first model had been developed by Wilhelm Weber and Carl Friedrich Gauß as early as 1832 . The electric telegraph also made it possible to pre-announce incoming trains to the next and following operating points. The first to put Leipzig-Dresden Railway Company on the system in Germany, where her Taunus Railway , the Palatine railways and the Hessian Ludwig Railway , which the pointer telegraph of William Fardely began, and the Cologne-Minden Railway Company , the Rheinische Railway company , the Main-Neckar-Railway and the Main-Weser-Bahn , which used the pointer telegraph according to August Kramer , followed.

Another safeguard was the installation of bells , first in Germany on the Thuringian Railway in 1846.

The train itself also became a carrier of signals: the vehicle in front - usually the locomotive - received a defined peak signal , which was particularly important at night or to announce special trains. The last vehicle of the train has a train rear end in which the stationary staff could always check that the train in its entire length traveled by and not or more vehicles on the track, a left behind .

Modern train protection

While in Germany, until then widely driving in the time interval should safeguard train that was nationwide after 1870 driving in space distance and block system introduced. Also in Germany from 1871 with the "Railway Police Regulations" and in 1875 with the "Signal Ordinance" for the first time safety regulations were standardized and railway companies were introduced across the board. However, the railway system was a matter for the federal states of the German Reich . It took until after the First World War before the safety regulations and facilities could be standardized across Germany.

Originally, the night signs of the main and distant signals used the following color scheme:

  • white light: ride
  • green light: expect stop
  • red light: stop

It was not until 1907 that the colors still valid today were changed: red means “stop”, green means “drive”. This happened mainly because of the great danger of confusion with white light. Only the Royal Bavarian State Railways failed to make the switch, which then resulted in the major railway accident in Nannhofen, among other things .

Train rides in stations

In train stations there are switches and track closures that can derail trains if they are driven on in the wrong position. For every train journey, all points and track barriers must therefore be set correctly and held in their position until the train has passed them completely.

In the simplest case, these tasks are taken over by a company employee ( dispatcher or switch keeper ) who sets the switches and gives the trains driving orders. In shunting operations, this is partly done by the train drivers and shunters.

In the case of maximum permissible line speeds of 30 km / h or more, operations are normally secured by signal boxes. Among other things, these ensure that there are no incorrectly set points in the entry path. If signals are available, then these can only be set to "Travel" if all safety-related requirements for the train journey are met ( signal dependency ). In the event of technical malfunctions, it may be that the signal dependency cannot be established or that it has to be removed for troubleshooting and maintenance work. In this case, the dispatcher is responsible for ensuring that the route for a train is only released when all the equipment required for the journey is in the correct position. With some railway administrations, traffic may then only be handled at reduced speed.

In the area of ​​the switches, there is also the risk that vehicles from another track will penetrate the route of the train ( flanking ). In order to prevent this, turnouts that are not used are also held in a repelling (protective) position and adjacent signals (including shunting signals) in the “stop” or “no travel” position. This flank protection is also i. d. Usually ensured by internal dependencies in the signal box.

Hazards from railway vehicles standing in the route are classically checked by the route check , the apparent checking of the tracks for clearness "by looking" by the signal box operator or route attendants. In modern systems, this is done by track vacancy detection systems .

The interlocking logic (route logic) ensures that follow-up and oncoming journeys are excluded.

Before a journey is permitted, shunting operations that may endanger this journey may also have to be stopped. When trains are departing, attention must be paid to obstacles to the route and the correct position of the switches between the end of the train and the signal that allows travel.

If all these prerequisites are met, the train may be given the order to travel or the associated signal for travel can be set to travel.

Securing the trains on the route

Securing train journeys today is based on the principle of keeping distance. This states that a certain distance must be ensured between railway vehicles in order to prevent collisions.

Driving within sight

In shunting operations, driving is generally carried out on sight . In certain operating situations (e.g. faulty track vacancy detection system), you must drive on sight . The speed is adjusted by the train driver to the respective visibility conditions and must not exceed 40 km / h in Germany due to the long braking distances of trains.

As a rule, trams also run on sight.

Driving at a time interval

Establishing and maintaining a timetable promised a much safer operation. It soon became clear, however, that this procedure also led to accidents, since every major delay or technical malfunction contained the risk of a collision.

In America, driving was refined over time. With the so-called timetable-and-train-order procedure, a train may only follow the train ahead after a certain buffer time. This buffer time is so long (approx. 10 minutes) that the staff of the train ahead has enough time to warn the next train in the event of a malfunction. The warning is given by burning flares thrown into the track when the vehicle is slowing down, or by a flagman and popping capsules when a train has stalled. With this procedure, the last wagon of each train must be manned. For special trains or delays, there is a complex set of rules to enable unscheduled train journeys.

Driving in a fixed space

With the increasing number of trains and higher speeds, there was no further development of time-lag driving in Europe. Instead, driving at a fixed distance was introduced. The routes are divided into train sequence sections (also block sections) by stationary signals or with the aid of driver's cab signaling . In principle, one section is made available to one vehicle or train. This section and a protective route behind it ( slip path or danger point distance) must be free before the train receives approval to enter the section. The section must be closed to other vehicles from the time you give your driver's license until the train has finished its journey.

The information as to whether the section is free from other vehicles is therefore essential for safety when driving at a distance. In the early years of the railway, a track-free test was only possible through observation due to a lack of technical possibilities. Local employees can carry out a track clearance check by looking at an operating site . On the other hand, on the free route between the stations, due to the lack of an overview, only an indirect clear indication is possible by observing the end of the train.

This led to two fundamentally different technologies that can be used to secure train journeys in space:

  • Securing with routes: Here the track clearance test takes place immediately before the driver's license is issued
  • Securing with block information: In the past, the track vacancy check was carried out indirectly by observing the train closing; in Germany, since the 1950s, an automatic track vacancy detection system has been used in regular operation with modern block designs (self-block, automated relay block, automatic line block).

Traditionally z. In Germany, for example, journeys within operating points are secured using routes (see train journeys in stations ) and on the free route between operating points using block information. In other countries this distinction between train stations and free routes is partly unknown.

The capacity of a route is largely determined by the length of the block section and the security technology used. Especially on main lines, the free route is often divided into several block sections by means of block sections.

Train notification procedure

Train notification by phone (1928)

Main article: Train notification procedure

In operating procedures without technical security or in the case of simple technology, the information about the occupancy and driving on a block section is visually recorded and transmitted optically , by telegram or by telephone . On most railways, the trains therefore have end-of-train signals that mark the end of the train. This final train signal can then be recognized by the dispatcher of the next train sequence station and the section can be reported as free (feedback). This feedback takes place between the dispatchers involved in the journey with the prescribed choice of words. In this process, a major safety responsibility remains with humans.

Two essential inventions improved the train notification procedure significantly by transferring responsibility more to technical systems:

The block field is a system in which the train sequence points are made electrically dependent on one another in such a way that locks occur at one point that can only be lifted by another point or by the involvement of the train. This means that once a signal has shown the travel term, it can be put into the stop position, but can only be set to travel again when the train sequence point ahead has technically blocked the last train. Opposite journeys are excluded via a special permission field, which creates the corresponding dependency between the bounding stations of a single-track route. The system was later refined in such a way that blocking back is only possible after a train has actually passed by. Nevertheless, the operator must check whether the train is complete by observing the end-of-train signals, because some wagons may have come loose and pose a risk to the next train.

With the track circuit it was possible to use automatic track block systems. Track circuits initially caught on primarily in North America. In Germany, on the other hand, the first automatic line block systems were set up relatively late. Today there are also automatic track block systems that check the occupancy of the tracks with technical means ( track circuits or axle counters ) ( see also: Clearance of the tracks ). With these systems, not every train sequence point has to be staffed, so that the line capacity can be increased by shorter block sections.

The information about the journey / stop is usually passed on via stationary railway signals along the route. Systems have also been developed for high-speed traffic that transmit the information directly to the vehicle ( e.g. LZB , ETCS Level 2 ). Stationary signals can be dispensed with if only trains are running that are equipped with the associated transmission system. There are only boards along the route that mark the boundaries of the block sections. The block sections can be optimally adapted to the needs of trains of different speeds. The performance can be increased considerably by short block sections, but with conventional systems this is associated with a large technical and financial effort.

Driving with tension rods (tension rod systems)

The token is handed over to the train by the signal box staff

With a pull rod system, there is a unique object (pull rod, also known as " token ") for each section of a single-track line . Only those who are in their possession are allowed to enter the route. In Germany, for example, this system is still used today on the Kirnitzschtalbahn in the Saxon Elbe Sandstone Mountains and in Norway on the Oslo T-bane underground railway . The procedure in Oslo is only used for single-track operation in the eastern part of the network.

There were various options for allowing several trains to run one behind the other in the same direction in so-called follow - up train operations . When driving in a group, the first trains only travel with an order from the commanding officer and showing the staff, the last train in one direction receives the pull staff to hand it over to the counter train. With this method, trains in one direction run on sight or at intervals.

The English railways developed the electric staff system, in which several tension rods exist for one section of the route. These are inserted into pull rod devices at the adjacent train stations and are held in them. Only if the sum of the tension rods in both devices is the same as the number of tension rods can exactly one tension rod be removed, the others remain locked. However, such a system already requires a technical transfer of information between the train stations. The disadvantage is that the transfer of the bars, in particular from the track to the vehicle, only works at a relatively low speed.

Driving on command

In the case of single-track routes with trains in opposite directions, the departure of a train was made dependent on the arrival of the opposite train. If the entry into the common single-track section was not regulated with the tension rod system, it could be done on command.

Drive according to the intersection plan

With - typically single-track - interurban trams in the past, driving according to a so-called intersection plan was widespread . The internal timetable documents stipulate that, for example, course 1 must cross opposite course 2 in switch A and counter course 3 in switch B. The driver has to check the course board of the oncoming train in order to determine whether the correct train has been waited for or whether it is a delayed train and the train to be waited for is still following. In 2016, for example, driving according to the intersection plan can still be found on the Thuringian Forest Railway.

Driving in a moving distance

(Also driving on electronic sight or moving block )

The capacity of a route can be maximized and the technical equipment can be minimized if stationary block sections and their track vacancy detection systems are dispensed with. The trains then determine the location of their train end themselves and send it quasi-continuously to the next train. Taking into account its braking distance, this calculates the point from which the speed must be reduced. If the braking distance of the previous train is taken into account, then driving is referred to as the relative braking distance , otherwise driving in the absolute braking distance . A driving in relative braking distance risked rear-end collisions when the preceding vehicle train is stronger than predicted braked, for example by a collision. This violation of the basic principle of failure safety makes driving in the relative braking distance unsuitable in practice due to the safety requirements of railways. With ERTMS , the UIC has specified a Europe-wide uniform technical specification for driving with absolute braking distance and moving space distance ( ETCS Level 3 ).

It should be noted that traveling in a moving space only works if all trains involved are equipped with the appropriate technology. The position of the end of the train must be reliably determined using signals or a possible train separation recognized within a few seconds. In freight transport in particular, with its internationally interchangeable fleet of vehicles, there is currently no solution for checking the integrity of trains . An introduction, however, is conceivable for routes with specific traffic, such as special high-speed routes or (automatic) city high-speed railways. There, an integrity check is easier to implement due to the manageable number of vehicles or unnecessary if inseparable units are in operation. Driving in a moving spatial distance is already used in the first urban rapid transit systems.

Special procedures

Driving in one-train operation

The first railways only ran one train at a time on a single-track line. Some museum railways still operate according to this principle today.

A modern form of this mode of operation is the branch line block , which allows only one train to enter a track section secured to the outside. The branch line block is based in turn on the principle of driving in space.

Driving in rope operation

Trains on steep sections with a particularly steep longitudinal incline were attached to ropes in the area of ​​this section with detachable clamps; this mechanical coupling ensures the spacing. The transition between different ropes, if any, takes place using different safety principles.

Today this principle is still used in funiculars and individual underground railways ( e.g. MiniMetro Perugia, Dorfbahn Serfaus , Skymetro Zurich) as well as in people mover systems and mine railways ( e.g. in the Berchtesgaden salt mine ).

Driving in sections

Magnetic levitation trains of certain systems (for example Transrapid ) and individual railways, whose current is controlled on the track side and in sections, are protected against other train journeys within these control sections if all trains within this section run at the same speed. Securing at section boundaries, if any, is carried out using other security principles.

Today this principle is used, for example, in the Transrapid Shanghai .

Train control

The security procedures presented are based on the trains being guided by signals that are either on the track or transmitted directly to the driver's cab. However, if a train driver overlooks a signal, it can still lead to considerable hazards and serious accidents. Train control systems were developed to prevent such accidents.

According to the principles of control engineering , a distinction is made between positive and negative train control. In the case of a positive influence, a vehicle may only move with permission and must stop independently after the permission has expired. In the event of a negative influence, a vehicle can drive as long as and as soon as there is no prohibition. The attributes “positive” and “negative” are not to be equated with the technical evaluation. Historically, all punctual train control systems are of the "negative" type, but achieve a very high safety standard with relatively little effort. In the US , a modern system called Positive Train Control (PTC) is a big step forward; however, in marketing the control technology existing "positive" behavior is not in the foreground.

According to the operating principle of information transmission, a distinction is made between punctiform train control and quasi-continuous control (linear). In the case of punctual train control, information can only be transmitted to the locomotive at this point. In contrast, in the case of linear influencing, there is the possibility of information transmission permanently or over longer distances. As a result, systems that act punctiformly are not signal-technically safe due to the open-circuit principle. Missing or incorrectly ineffective route facilities are not noticed unless explicit countermeasures such as the balise announcement under ETCS are taken. Compared to an operation without train control, their use is a sensible, safety-enhancing measure, especially since point train control systems usually work concealed and in the background and apart from the vigilance control for restrictive travel terms and measures for the permitted pass-by signals indicating stopping, no operator intervention is required.

Line-shaped train influences enable the transition to the closed-circuit principle and thus to a signal-technically safe transmission through the continuous transmission.

In the new European Train Control System (ETCS) train control system , the operating mode ETCS Level 1 stands for punctiform and ETCS Level 2 for linear control.

The forerunner systems that are still widely used in Germany are known under the names PZB and LZB . With the PZB, track magnets that are attached to signals or in front of dangerous or slow driving areas influence the vehicle equipment of the traction vehicle: If a driver does not react when passing a signal that shows a restrictive signal aspect or drives past a stop sign, this will cause automatic braking of the train forced. The LZB system transmits the permissible speed and length of the existing travel permit through antenna cables ("line cables") laid in the center of the track. The system also enables the vehicle to be located by crossing the two line conductor strands in the center of the track and in the tab chamber of a rail. The reference variables that are displayed to the driver are generated from this information. This enables automatic driving, but people are still superior to linear train control in anticipatory driving.

The failure of the train control usually requires a speed reduction and possibly a double occupancy of the locomotive.

Railroad Crossing

See also


Web links

Individual evidence

  1. a b Maschek, Ulrich: Securing rail traffic, basics and planning of control and safety technology . 3rd, revised. u. exp. Edition Springer Fachmedien Wiesbaden, Wiesbaden 2015, ISBN 978-3-658-10757-4 .
  2. Jörn Pachl: System technology of rail traffic: plan, control and secure rail operations . 6th edition, Vieweg + Teubner 2011, p. 214. ISBN 978-3-8348-1428-9 , doi : 10.1007 / 978-3-8348-8307-0 .
  3. ^ Lionel Thomas Caswell Rolt : Red for Danger . Edition: London 1978, pp. 24-26, reports on near-accidents in this operating situation on English railways, even with double-track operation.
  4. Püschel, p. 7.
  5. a b Püschel, p. 8.
  6. a b c Püschel, p. 9.