Derailment (train)

from Wikipedia, the free encyclopedia

Derailed wheelset of a cogwheel vehicle
Derailment of the “Amstetten” locomotive in 1875. Cause: tire breakage due to material fatigue
Derailment on May 29, 1908 in Lübeck . Cause: Switch breakage when driving over
Intentional derailment of freight wagons at a track barrier in Ingolstadt Hbf
ICE 1 derailed after the ICE accident in Eschede . Cause: tire breakage due to
material fatigue
Rescue work after the railway accident in Santiago de Compostela . Cause: excessive speed
Derailment in Stuttgart . Cause: Overbuffering due to defective buffers

A derailment is a railway accident in which a rail vehicle leaves its track, the track , in an uncontrolled manner, which is also known as jumping off the rails . The opposite is the rerailing or railing, that is, the proper placement of a rail vehicle on the rail (s). In Germany, the derailment is one of the most dangerous events in rail operations .


The definition of the term derailment is not uniform in the German-speaking areas.

Definition of the Federal Railway Authority

For the railways of the Federal in Germany which defines the Federal Railway Authority (EBA): " A derailment is slipping or lifting a railway vehicle from the road, even if it themselves aufgleist again, or the two-lane running a railway vehicle ." A rail vehicle shall be so already derailed when the constant contact between the wheel flange and / or the running surface of the wheel to both rail heads has been lost, even if the target state (guidance of the wheel flange on the running edge of the rail heads) is then achieved again. The fact that lifting a wheel off the road is considered a derailment is due to the axle slide bearings that were common in the past. The bearing shell, which is usually only loosely inserted into the axle bearing housing, can slip out of its intended position when the load is removed and thus become inoperative.

The definition of the EBA corresponds to the definition of the UIC , which describes a vehicle as a "derailed vehicle" with this definition . Because in the regulations of the UIC ( AVV "General contract for the use of freight wagons" and RIC "Regolamento Internazionale delle Carrozze" ), a special examination of the rolling stock concerned is required in the case of a derailed vehicle.

Definition in Switzerland

The Swiss Federal Railways (SBB) and the Swiss Safety Investigation Board (SUST) use the following definition: " Derailment is the lifting of a wheel set or one of its wheels until the flange tops meet the running surface of the rails or the upper limit of additional track guidance devices and then leave the Rails. "

A distinction is made between ascending and climbing .

When climbing, the wheel flange rolls over an obstacle in the track area, which raises it to the height necessary for derailment. These are typically switch tongues that are not firmly attached to the stick rail or foreign objects that are trapped in grooved track .

When climbing, the frictional force between the rail and the wheel flange is so great that there is a friction fit between these parts. As a result, the wheel is pushed upwards during the rolling movement until the wheel flange tip is raised to the level of the running surface of the rail and is pushed across it by the tracking forces until the wheel falls on the other side of the rail.

Equation according to Nadal

The equation published in 1908 by François-Joseph Nadal , chief engineer of the Chemins de fer de l'État , describes the criteria that enable a wheel to climb. The process begins as soon as the vertical component of the frictional force between the flange and rail becomes greater than the contact force of the wheel. According to Nadal, the derailment coefficient can be calculated as follows:

where the parameters are used as follows:

Track guidance force across the track direction
Wheel contact force perpendicular to the rail
Wheel flange angle measured from the horizontal
Friction coefficient between the wheel flange and the rail


Unintentional derailment

Vehicle-related causes

Rail vehicles can derail if their speed is too high for the route geometry ( curve radius , superelevation , switch design , etc.) . Furthermore, can the error on the vehicle (for example, wheel and axle failure, Sollmaßabweichungen of the wheel flanges, broken axle and defects on bogies ) lead to derailment. Improper securing loads or exceedingly unbalanced load can freight cars from the track balancing .

Operator-related causes

A derailment can occur if, for example , the driver ignores signals , drives at excessive speed or starts off in the wrong direction (forwards or backwards). If the driver brakes in front of a track end with a buffer stop , derailment can also occur if the end of the track is run over. Vehicles can over- buffer and derail in the process when maneuvering , during operation and when driving on narrow curves . Here, the buffers of two vehicles slide one above the other or next to one another and lever the affected vehicles off the track.

Errors made by operators of the railway infrastructure , such as dispatchers and point attendants , can lead to derailments in the following cases, for example:

  • A switch is switched over while a rail vehicle drives over it. The process is called "driving in two lanes".
  • Improper behavior in the event of signal interference.
  • Communication, especially when maneuvering, is not clear.
  • A necessary command is not given or is given ambiguously.
  • The necessary requirements for allowing a train or shunting run were not met.
  • Unintentional lifting of the vehicle during loading and unloading (e.g. that the wagon is also lifted when unloading by a tilted container) and derailment when it is set down.
  • Driving over an obstacle , because the wheel "jumps" over the obstacle (also applies if the vehicle is then properly back on the track). Obstacles that are overlooked before vehicles are moved, if they get into a frog from the end of the turnout, will certainly lead to derailment because they tilt in the frog and push wheel sets running over them out of the track.
  • Braking and driving over a track end or end .

Incorrect operation of vehicles can promote technical derailments. For example, strong acceleration or braking on damaged track systems are often responsible for derailment. This means that several trains were able to run over the damage without any problems; only the additional dynamic forces triggered by acceleration / braking made the derailment possible.

Route-related causes

Derailed locomotive

The smooth running of rail vehicles is guaranteed by the correct track geometry. Therefore, any impermissible deviation in the position and condition of the tracks , including switches, can lead to derailment. Such deviations from the target geometry are:

  • Worn and broken rails;
  • Switch is not in the end position ( switch lock not locked);
  • Foreign bodies of any kind, also railway-related such as buffers , in the normal light space ;
  • People or animals on the track;
  • temperature- related track warping ;
  • Track gauge changes beyond the tolerance range;
  • Changes to the track axis beyond the tolerance range (e.g. due to undercuts or earthquakes ).

As a rule, however, it does not lead to a derailment if a switch is driven on but is in the wrong position. The switches are designed for this opening of the switch blades, but only a derailment of the run can be avoided, but not always damage to the blades, switch locks and transmission parts. If the speed is too high and if the affected turnout is mechanically locked, a derailment occurs because the tongues cannot follow the movement at all due to the locking or cannot follow the movement quickly enough because of the inertia. Due to the design, the approach does not work with high-speed turnouts and some other types of turnouts (e.g. with moving frogs), because incorrectly positioned frogs and drives for high-speed turnouts cannot be opened due to excessive holding force. In order to prevent derailments on points, the end position is checked when a route is set in the interlocking and the points are secured against switching.

On particularly dangerous places in the rail network (such as front rail bridges ) are guide rails as derailment protection mounted. These are additional rails on the inside or, if there is a lack of space in the track, on the outside, which guide derailed wheel sets and make it difficult to leave the track completely.

Intentional derailment

A derailment is intentionally brought about, but in practice avoided as much as possible in order to prevent further damage in the event of unintentional vehicle movements. This can either be stipulated in local guidelines for shunting and driving of trains (conceivable in downhill stations) or it is decided on a case-by-case basis depending on the specific situation. Decisions are preferred, as a result of which the kinetic energy is softly, i.e. gradually, withdrawn from the uncontrolled vehicle.

Derailment devices such as sand switches and track closures are part of the flank protection measures . They force a diversion or even derailment of vehicles that are making an impermissible movement.

The necessary derailment by lifting the rail vehicle using a lifting device or crane system for maintenance or repair purposes is not a dangerous event or incident in the sense of the above definitions.


Consequences for the superstructure after a freight train has traveled with a derailed wagon at Hofheim (Ried) station on the Darmstadt – Worms railway line : Destroyed sleepers can ensure that the affected area is declared impassable.

Sometimes vehicles with derailed axles are carried along in the train for many kilometers , primarily in freight transport , before the derailment is noticed. This generally causes major damage to the railway systems (track, cables, etc.).

The rail vehicle in question is severely braked as a result of a derailment. This usually leads to the vehicle tearing off from the train in front, while the vehicles behind are braked together with the derailed vehicle due to the automatic action of the railway brake by opening the main air line. As a rule, the front part of the train also brakes due to the main air duct opened as a result of the train separation. The more critical case is when the derailment goes unnoticed and the clutch does not break. The train can then continue for many kilometers until it reaches z. B. by jamming in switch areas to the actual accident, with the correspondingly serious consequences for passengers and property.

If derailed vehicles or lost cargo protrude into the siding, subsequent derailment of vehicles there can occur. Another consequence of derailments on electrified lines and train stations is damage to the overhead contact line systems, including the overhead line masts .

On-board sensors can be used for the rapid detection of derailments . The development of infrastructure monitoring devices is new, but so far only as a prototype . In both cases, the extent of the derailment can be reduced if it is recognized in good time and immediate countermeasures take effect.

Even seemingly harmless derailments can lead to structural damage to the vehicle. With every derailment, it must be assumed that the vehicle has been overloaded at certain points, for example if a wheel disc suddenly has to take up the entire load of the wagon axle (or even more). In addition, the load is often not taken at the angle for which the wheel disc is designed to take the load. This can lead to the two wheel disks no longer being parallel to each other after the derailment. The springs can also shift, so that they are no longer in the correct position or are no longer correctly guided. Therefore, even slightly derailed vehicles may not be put back into operation before a fitness test has been carried out. Without this, it is forbidden to continue operating vehicles that have been re-tracked (even if only one axle was derailed).

Likewise, the condition of the route and, if necessary, the overhead contact line system must be checked and, if necessary, repaired.

See also

Web links

Commons : Derailments  - collection of images, videos and audio files

Individual evidence

  1. ^ Jürgen Janicki: System Knowledge Railway . Berlin 2011. ISBN 978-3-9808002-6-6 , p. 187.
  2. derail. In: Duden. Retrieved September 22, 2019 .
  3. EBA instruction A 210000 Report , investigate and report dangerous incidents in railway operations , valid from January 1, 2000 (This instruction is also Appendix 1 to regulation DS 123.0180 of the Deutsche Bahn ).
  4. EUB general decree on reporting dangerous incidents in railway operations ( Memento of the original from March 5, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , valid from January 1, 2010. @1@ 2Template: Webachiv / IABot /
  5. Johannes Piringer, Johannes Stephanides: Relationship - wheel and rail: derailments considered closer . What is a derailment?, P. 3 ( [PDF]).
  6. a b Swiss Safety Investigation Board SUST (Ed.): Final report of the Swiss Safety Investigation Board SAE on the derailment of a Eurocity train from March 22, 2017 in Lucerne (LU) . 1.11.6 Definition of derailment, p. 40 .
  7. Attila Miluczky: The laws of the running gear of tried and tested multi-articulated low-floor light rail cars . 3.2 The criteria for a vehicle derailment, p. 100 ( [PDF]).