Method for releasing overlaps in a railway signaling system

Abstract

A method for clearing an overlap in a railway signaling system, the system comprising a signaling interlock, trackside processing equipment and at least one signal, the overlap being a section of railway track located beyond the signal in the direction of train movement, characterized in that the method comprises: configuring both the interlocking and the track processing equipment to treat the overlap as an individual overlap route, such that a train requires a movement authorization to proceed onto that route, wherein the method further comprises the step of configuring the track processing equipment with: a first route leading to the signal, with an authorization end near the signal and a danger point beyond the signal, and the overlap route that only includes the overlap section with an authorization end at or near the sign and a hazard point at the end of the overlap.

Description

Method for releasing overlaps in a railway signaling system This invention relates to a method for releasing an overlay in a railway signaling system and changing an overlay to an alternative overlay in a railway signaling system. Background Figure 1 shows a simplified generic track layout, in which trains can approach from the right-hand side, as shown, along either of the two parallel track lines, with the intention, for example, of stopping at Platform A on the upper line, or at Platform B on the lower line. Beyond the platforms, points P1 can be selectively directed to pass a train over the lower line to join the upper line. The presence of a train over a particular section of track is determined by the use of track circuits, as is well known in the art, with the track circuits being labeled T1 to T6 on the upper line and T11 to T14 on the lower line. As experts in the field will observe, railway system architectures can generally be divided into two types: "conventional signaling," which is based on transmitting information to the train via signals on the track, and "communication-based signaling," such as ETCS (European Train Control System), which is part of ERTMS (European Rail Traffic Management System). These will be analyzed separately below. Figure 1 shows three sets of signals on the track: S11 and S21, located before the platforms and transmitting signaling information to trains on the upper and lower lines, respectively; S13 and S23, located at the platform exit and transmitting signaling information to trains on the upper and lower lines, respectively; and S15, located on the upper line some distance beyond the platform.If all trains use communication-based signaling, the presence of these signals is not strictly necessary, but the general concept of operation is similar enough to describe the present invention. In conventional signaling (i.e., without ETCS), if a line signal authorizes a train to proceed to the next signal, which is red, a safety margin beyond the red signal is normally established and blocked for the train in case it overshoots the red signal. This safety margin is often called an "overlap." No other train may use the overlap section of track until it is demonstrated that the train for which it has been established no longer needs the overlap. This is often achieved by timing the occupation of the track loop leading to the red signal (the "stop track loop") to allow sufficient time for the train, for which the overlap has been established, to reach a stopped position (and not have overshooted the red signal within the overlap). The timer is calculated based on the length of the track loop and is typically on the order of 30 to 60 seconds. In the case of communications-based signaling (e.g., ETCS Level 2), a movement authorization (MA) is sent to a train by trackside processing equipment (TPE, i.e., a radio block center (RBC) in the case of ETCS) that is compatible with the established routes and proceed indications provided by a signal interlocking system. The TPE is configured with track data that provides details about signal positions, track circuits, routes, overlaps, and so on. The interlocking system is expected to provide a proceed indication to the TPE for each route from a route entry point (i.e., a signal) when it is safe for an approaching train to enter the route. Traditionally, each route would be from one signal to the next. In the example in Figure 1, there is only one route from each signal shown to the next signal, but in more complex designs, there could be several possible routes from a single signal. A movement authorization will typically define a position beyond which the train should not travel (i.e., an "end of authorization" (EoA) in ETCS) and a safety boundary beyond which the train must be prevented from leaving (i.e., a "supervised location" in ETCS, the position of which can be specified in the movement authorization by defining a danger point). Due to the precautionary (i.e., safety-critical) nature of the train protection system, it will not allow the train to approach the supervised location too closely because it must always be possible to stop the train even if it makes an unexpected movement. A movement authorization to a red signal can typically define an EoA at the signal and a danger point (DP) at the end of the overlap, giving the train the greatest available safety margin. This is shown schematically in Figure 2. In this case, a train would be expected to stop as it approaches the signal and not proceed directly to the EoA. The required stopping position at a platform, Platform A as shown, for example, would not normally require the driver to proceed to the EoA. In ETCS, it is known that there is a facility where overlap information can be sent to a train with the MA (Management Authority) that defines a temporary overlap limit, an overlap timer, and the train's position where the timing should begin, for example, the start of the relevant track circuit. This overlap information can be sent with a shorter hazard point, for example, placed at the point of obstruction (FP), i.e., the point on the track beyond which a train would physically impede the movement of another train on a different track, for converging tracks. The train's protection system will initially use a monitored location at the end of the overlap. When the timer expires, the protection system on the train will shorten the monitored location to the hazard point. This should only happen once the train is stationary because the timer will be similar to the one used for the track.The track interlock will also run a timer and allow the overlap to be released when it finishes. This arrangement is shown schematically in Figure 3. During normal operation, as routes are established ahead of a train, the movement authorization is replaced by a new, extended authorization that allows the train to proceed further along the track. For example, as shown schematically in Figure 4, MA1 is replaced by MA2, with a new associated authorization end EoA2 and danger point DP2, when an authorization to proceed is given by interlocking for signal S11. For any signaling system, if a clearance to proceed that has been given to a train is subsequently removed (for example, the signal controller may decide to allow another train to proceed first), then the route or routes beyond that signal are held in a blocked state for that train until it is demonstrated that the train will not use them. This form of blocking is often referred to as "approach blocking." Depending on the signaling system and operational requirements, this test can be carried out in different ways. However, a common feature is the use of a timer that allows sufficient time for the driver to observe that the clearance for the train has changed and to bring the train to a stop without entering the route from the replaced signal. This timer is typically on the order of 3 or 4 minutes. One known feature in ETCS is the so-called "cooperative shortening of a movement authorization." ETCS provides a feature where trackside equipment can send a message to a train requesting a shortening of the movement authorization (MA). The train protection system will calculate new braking profiles to determine whether the train can stop before the shortest MA limit and respond to the trackside to accept or reject the shortening request. If the train accepts the shortening request, this allows the trackside protection equipment to inform the interlocking that the route or routes beyond the replaced signal no longer need to be held for the train. An example is shown schematically in Figure 5, where a movement authorization MA1 could be shortened from S5 to S1 (i.e., MA2) to allow another train to proceed from S3. As a general previous technique, one can mention document EP1752355, which describes a common system architecture with a bidirectional interface between a signaling interlock and track processing equipment. EP 2216230 A1 document discloses a method for releasing a route after route cancellation by means of an interlock. However, in certain circumstances, it may be desirable to implement the ability to release a signal overlap when no forward route is established from the corresponding signal and the overlap is no longer required for an approaching train. As mentioned earlier, this can be achieved using a conventional timer based on the occupancy of the signal stop track; however, it is convenient to provide improved performance for an ETCS-equipped train by releasing the overlap, when it is no longer required, without waiting for the timer to expire. It has been suggested that the TPE (an RBC in this case) inform the interlocking system when a train is stationary on the stop track and the movement authorization has been withdrawn. However, the functionality of an RBC to inform an interlocking system of a stationary train is not the functionality of conventional ETCS, and its existence is not known. An objective of the present invention is to provide an alternative method by which the overlap release operation could be achieved using the existing TPE functionality. This objective is achieved by effectively treating the overlap as a single path. A second requirement is the ability to switch from an overlap to an alternative track section. This operation would be carried out, for example, when a train is not immediately approaching the danger signal, the currently established overlap is blocking a path for another train, and an alternative overlap is available. Another objective of the present invention, similarly resolved, is to provide a method for enabling this capability. According to a first aspect of the present invention, a method is provided for clearing an overlap in a railway signaling system, the system comprising a signaling interlock, track friction equipment, and at least one signal, the overlap being a section of railway track located beyond the signal in the direction of train movement, the method comprising: configuring both the interlocking and the track processing equipment to treat the overlap as an individual overlap route, such that a train requires a movement authorization to proceed onto that route, wherein the method further comprises the step of configuring the track processing equipment with: a first route leading to the signal, with an authorization end near the signal and a danger point beyond the signal, and the overlap route that only includes the overlap section with an authorization end at or near the sign and a hazard point at the end of the overlap. According to a second aspect of the present invention, a method is provided for changing one overlay to an alternative overlay in a railway signaling system, the system comprising a signaling interlock and trackside equipment, comprising the steps of: a) request the use of the alternative overlay; b) determine, at the interlock, whether the conditions are suitable for the overlap to change, c) if so, use the trackside processing equipment to provide an override of the interlock, and release the overlap using a method in accordance with the first aspect, and d) change the overlay to the alternative overlay. The invention will now be described with reference to the accompanying drawings, in which: Figure 1 schematically shows a simplified generic track design; Figure 2 schematically shows a movement authorization granted for the design of Figure 1; Figure 3 schematically shows an overlay for the design of Figure 1; Figure 4 schematically shows a new movement authorization for the design in Figure 1; Figure 5 schematically shows an example of shortening the cooperative movement authorization for a modified design, so that overlaps do not conflict with other movements; Figure 6 schematically shows a track layout exemplifying an overlap release method according to an embodiment of the present invention; and Figure 7 schematically shows a track design that exemplifies a method of overlap change according to the present invention. A first embodiment of the present invention is shown schematically in Figure 6, using for ease of use the same track design as in Figure 1. The signaling interlock is configured as follows: - a non-overlapping route to each signal where the overlap will be released, i.e., to S13 and also to S23; - a 'route' from these signals (i.e., from S13 and from S23) to the end of the overlay to be released (in addition to any normal routes configured from that signal); - a 'proceed' indication for the overlap provided to the TPE whenever the overlap is available for use by an approaching train, and the route to the associated signal is established but no other forward route from that signal is established. The TPE is configured with the following: - a route leading to each signal where the overlap is to be released (i.e., S13 and S23) with an EoA at, or near, the signal and a hazard point at the obstruction point, a short distance beyond the signal. It should be noted that although there is no overlap for this route, there will be, for this particular design, a short section of railway track to the obstruction point that will not require any other train. - A 'route' from these signals (S13 and S23) that only includes overlap with an EoA at or near the signal, i.e., the shortest possible distance (e.g., around 1 m) beyond, and a hazard point at the end of the overlap. It should be noted that, depending on the system, the EoA may or may not be in the same location as the preceding route. The train should be able to handle either scenario. - an indication to the interlock that indicates whether the overlay can be released or not. When the interlocking provides a proceed indication to the TPE for the route leading to S13 (i.e., from signal S11), the TPE sends a move authorization (MA1) to the train with EoA1 at the signal and a danger point DP1 a short distance further on, at obstruction point FP. When the interlocking provides a 'proceed' indication for the overlap, the TPE sends a new move authorization (MA2) with an EoA2 similar to EoA1, but with a danger point DP2 at the end of the overlap. Therefore, it can be seen that the overlap is configured in both the interlock and the TPE as a separate "path" with conventional interaction between them to establish a "progress" for the TPE. When the interlocking receives a request to release the overlap, it removes the 'proceed' indication for the overlap from the TPE. The TPE then sends a request to shorten the movement authorization to the approaching train, specifying the end of the authorization and the MA1 danger point again (i.e., EoA1 and DP1). If the train accepts the shortening request (for example, because it has already stopped), then the TPE can signal the interlocking that the overlap can be released. If the train rejects the shortening request, the overlap is not released until, for example, a longer conventional time limit has expired. If the train is stationary when the request is received, then the reduction in movement authorization should not cause the train any problems, and the request would be accepted.If the train is not on its final approach profile to the stop position, it should also be able to adjust its profile to accept the reduction in movement authorization. However, as the train approaches the stop position, a sudden backward movement of the hazard point could cause a potential breach of the emergency braking profile, and the train would reject the request for shortening. Assuming the train accepts the shortening request, the TPE will provide an approach block override to the interlocking that allows the release of the overlapping path. The request to release an overlap could originate from the signal controller and be used only when necessary. However, it would also be possible for the overlap release to be triggered automatically using a timer in the interlocking system, based on the occupancy of the track circuit leading to signal S13. The difference in this case is that the timer only needs to be set long enough for the train to have likely stopped, not to have come to a complete stop as was the case in the prior art—i.e., no longer being safety-critical. This is expected to reduce the timer used to trigger the overlap release by more than 10 seconds, which is significant in terms of railway operations. Another embodiment of the present invention, relating to a method of changing overlays, is indicated in more detail with reference to Figure 7. Changing an overlay is a common feature of conventional signaling (at least in the UK), and if the signaling has been configured to provide this feature, it will be permitted under certain conditions: primarily that the approaching train is sufficiently far from the signal so that it cannot enter the overlay during the time that the relevant points (shown as P2A and P2B) are moving, as described below. The ability to change an overlay can be seen as an extension of the ability to release an overlay. If the interlocking system considers the conditions suitable for changing an overlay—that is, the train is not immediately approaching the signal—then it can request the release of the currently established overlay.This should not cause any problems for any ETCS train, which should accept the small reduction in its movement authorization. The TPE then provides an approach block override to the interlocking, which can then select an alternative override. Based on the previous technique, the TPE is expected to indicate to the interlocking system that the next train approaching a signal is an ETCS-controlled train. Therefore, the TPE's involvement in releasing and changing an overlay can be conditional within the interlocking system on the next train being indicated as an ETCS train. If the next train is not indicated as an ETCS train, either because it is not an ETCS train or because its movement authorization has not yet reached that signal, the interlocking system can change the overlay according to conventional rules. A possible sequence of events according to this realization could be: 1) The signal controller establishes the route for a first train to signal S13, including the overlap beyond points P1, called "Overlap 1"; 2) As described above, the RBC initially issues a movement authorization MA1 up to the signal, which includes EoA1 and DP1. It should be noted that DP1 in this case is configured to be at the divergence point for alternative paths through points P2A; 3) The interlocking provides a proceed indication to the RBC for Overlap 1 and the RBC extends the move authorization for the first train sending MA2, which includes EoA2 and DP2; 4) The signal controller, for example, may then wish to allow a second train to proceed from signal S23. If "Overlap 2" from signal S13 is available and does not conflict with other movements, the signal controller may request that the overlap be moved, or 'switched', away from the path of the second train from S23; 5) The interlocking system verifies that the approaching train is not too close to the signal. Then, as described above, the interlocking system removes the proceed indication for Overlap 1 from the RBC. This causes the RBC to issue a request to shorten the movement clearance back to EoA1 and DP1 (i.e., essentially back to MA1). 6) Since the first train is known to be a certain distance from signal S13, it is expected that the train will accept the shortening request, allowing the RBC to signal the interlocking system that Overlay 1 can be released; 7) The interlocking system releases Overlay 1 and moves points P2A and P2B to the reverse position. (A note on terminology: conventionally, points P2A and P2B are numbered 'A' and 'B' because they always move together and cannot be controlled independently; additionally, the points have a 'normal' position and a 'reverse' position, with diagrams normally showing them in the normal position); 8) Once points P2A and P2B have been locked and detected in their required reverse position, the interlocking can provide a forward indication for Overlap 2 to the RBC. This allows the RBC to again extend the movement authorization for the first train, this time by sending MA3, including EoA3 and DP3. EoA3 can be set to the same location as EoA2; and 9) After completing the process of changing the overlap, the interlocking will then allow the signal controller to establish the route for the second train from signal S23. It should be noted that in stage 6, the interlock maintains the block on Overlay 1 until the RBC indicates that it can be released. If, for any reason, the train decides it cannot accept the shortened movement authorization request, or does not respond, Overlay 1 will remain blocked for the first train, and the switch will not be permitted. In this case, the interlock is expected to wait a defined time for a release from the RBC, after which the interlock will cancel the request to switch the overlay and reset the advance indication for Overlay 1 to the RBC. The embodiments described above are only illustrative, and experts in the field will come to know other possibilities and alternatives within the scope of the invention.

Claims

1. A method for clearing an overlap in a railway signaling system, the system comprising a signaling interlock, track processing equipment, and at least one signal, the overlap being a section of railway track located beyond the signal in the direction of train movement, characterized in that the method comprises: configuring both the interlock and the track processing equipment to treat the overlap as an individual overlap route, such that a train requires movement clearance to proceed to that route, wherein the method further comprises the step of configuring the track processing equipment with: a first route leading to the signal, with an clearance end near the signal and a danger point beyond the signal,and the overlap route comprising only the overlap section with an authorization end at or near the signal and a danger point at the end of the overlap.

2. A method according to claim 1, comprising the step of configuring the interlock with: a route without an overlap to the signal, and the overlap route being from the signal to the end of the overlap.

3. A method according to any preceding claim, comprising the step of configuring the interlock with: a forward indication for the overlap route, and providing the forward indication to the trackside processing equipment if the overlap is available for use by an approaching train.

4. A method according to claim 3, wherein if the interlock receives a request to release the overlap,The interlocking removes the advance indication for the overlap from the track processing equipment.

5. A method according to claim 4 when dependent on claim 3, wherein, after removing the advance indication, the track processing equipment sends a request to shorten the movement authorization to an approaching train, specifying the end of the authorization and the hazard point associated with the first route.

6. A method according to claim 5, wherein, after the request is sent, if the train accepts the request to shorten, the track processing equipment signals the interlocking that the overlap can be released.

7. A method according to any of claims 4 to 6, wherein the request to release the overlap is sent by a signal controller.

8. A method according to any of claims 4 to 6,wherein the request to release the overlap is automatically generated by the interlock, based on the track circuit occupancy time in a section of railway track leading to the signal.

9. A method for changing an overlap to an alternative overlap in a railway signaling system, the system comprising a signaling interlock and trackside equipment, comprising the steps of: a) requesting the use of the alternative overlap; b) determining, at the interlock, whether the conditions are suitable for changing the overlap; c) if so, using the trackside processing equipment to provide an override of the interlock, and releasing the overlap using a method according to any preceding claim; and d) changing the overlap to the alternative overlap.

10. A method according to claim 9, wherein in step a),The request is sent by a signal controller.

11. A method according to any of claims 9 and 10, wherein in step d), authorization is provided to the processing equipment on the track to use the alternative overlay.

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