Aspect Indication
R Y/R Stop
fR Y/fR Stop and proceed
Y/G Proceed (at limited speed)
G Proceed
fG G/G Proceed through
Table 2.1: Aspects of main signals and their indication
In this work, we are only interested in stopping and moving trains, ignoring speed limitations. Disregarding the signalling variants of stopping and proceeding the aspects has been reduced to the stop and proceed aspects. Table2.2denotes the aspects used throughout this thesis.
Aspect Indication
R Stop
G Proceed
Table 2.2: Aspects
2.4 Safety
In this section the safety properties of the railway network are described as well as how it is enforced to ensure the safety of passengers and trains. These properties is a set of requirements to the system that needs to be maintained at all time. Furthermore, safety approaches are introduced, which are different kinds of implementations to maintain these safety properties.
16 Domain Description
2.4.1 Safety Properties
In the previous sections we have introduced the elements to construct a working railway network. The interaction between all these objects constitute the safety of the train operations. These interactions needs to follow a set of rules to fulfil the basic safety requirements, namely [4]:
• Trains/shunt movements must not collide.
• Trains/shunt movements must not derail.
• Train/shunt movements must not collide with vehicles or humans crossing the railway at authorised crossings.
• Protect railway employees from trains.
For this thesis we do not consider shunting movements, level crossings and railway employees. Therefore the basic safety requirements can be reduced to the following subset of the basic safety requirements:
• Trains must not collide.
• Trains must not derail.
Henceforth, any reference to the basic safety requirements will be to the above subset.
In the following sections it will be explained how the events of collision and derailing can occur, and later how to avoid them.
2.4.1.1 Collision
A collision is an unintended contact between trains. Combining trains is an example of intended contact between trains. High speed collisions, on the other hand, are likely to have catastrophic consequences.
We consider any situation where two or more trains occupy the same track section a collision. This situation will not necessarily result in a collision, but the potential is there and that is enough for it to be considered a collision.
2.4 Safety 17
2.4.1.2 Derailing
Derailment can be caused by many things. Broken rails, traversing curves at too high speed, as a result of collision, travelling beyond the end of line, hitting obstacles, travelling on unlocked points and so on.
Many of these situations are out of the scope for this project. In fact, they can be reduced to travelling on unlocked points. Figure2.8show situations that can result in a derailing on a points section.
Train Train
Train Train
A B C D
Figure 2.8: Possibility of derailing
Train
Train Train Train
A B C D
Figure 2.9: No derailing
2.4.2 Safety Approaches
Banedanmark uses two methods of securing train movements:
Route based The entire intended path of a train movement is locked for use by a single train only. The route is not released until the train has reached the end of the route. This principle is used by Banedanmark at stations.
Block based The railway is divided into blocks. When a train enters a block, no other train is allowed to enter that block, until the first train is out of the block again. This principle is used by Banedanmark on the open line.
18 Domain Description
2.4.2.1 Train Route
A train route is a secured path from one point4 (called the start point) to another (called the end point) in a railway network. These points are normally signals [10].
The following describes the concepts associated with train routes.
Safety overlap The safety overlap is an extension of a train route, intended to provide additional clear track in case the train fails to stop at the end point, e.g. the driver misjudges the braking distance.
Conflicting train routes Train routes are considered conflicting if they share points in their paths, incl. the safety overlap. Conflicting train routes are mutually exclusive and may not be locked at the same time. However, it is possible to extend a route with another by replacing the safety overlap with another route.
Flank protection Flank protection is protecting a train route from conflicting movements. The interlocking system achieves this first and foremost, by not allowing conflicting routes. This protects against train movements, but not against roll away vehicles. Therefore, further measures are taken, such as locking points, that are not part of the route, into positions that direct traffic away from the route in question
Locking train route A train route can be locked manually by pressing buttons on the operator’s panel or automatically when the system detects an approaching train.
A train route can be locked if the track sections, that constitutes the route, are all clear, the points sections on the route are locked in proper position and the desired route is not in conflict with any other currently locked route.
A train route stays locked until it is released. The objects, which were part of the released train route, can then be used to form new train routes.
4This does not refer to points sections.