The initiative to find a way of moving trains more quickly when a signalling or power failure occurs has reached the stage whereby a demonstration of the concept took place recently at the Hitchin ENIF (ETCS National Integration Facility) test control site and on a test train using the Hertford Loop test track.
The COMPASS – DMWS (Degraded Mode Working System) has been reported on in Rail Engineer for the past two years, with a full description of the intended system given in issue 155 (September 2017).
If a signal section becomes failed because of loss of power, points failure, level crossing malfunction, track circuit or axle counter failure, interlocking fault, cable theft et al, then trains will stop and people have to be got to site to assess the problem, take remedial measures (such as clipping points) and instigate temporary block working.
This all takes time and the ensuing delay can be frustrating for passengers and costly in terms of penalty (Section 8) payments. If a way can be found to speed things up by remotely assessing the on-site situation, fulfil some proving checks and issue drivers with cautionary movement instructions, then trains can be instructed to move and a general win-win situation emerges.
The DMWS concept is to independently ascertain the train’s position using a combination of GPS and TD-Net (the national train describer data base) to ensure, not only geographic location, but also which track the train is on.
The system will then prove the position of points or the status of level crossings using a local PLC (programmable logic controller) linked to sensors, which would be interrogated by a radio message either from GSM-R or the public mobile service. This local interrogation equipment is known as an IDR unit (Inhibit, Detect and Repeat).
Once satisfied that the route ahead is clear and proven, the signaller will instigate DMWS working, issuing instructions to the driver by means of the SMS messaging service that will be displayed in the cab either on a screen or the GSM-R radio. The text-based instruction can be confirmed by a voice call if need be.
All of this replicates the present temporary block working routines, but is capable of taking place much quicker.
Hitchin control room
The Hertford Loop test track uses the Down line either side of Watton at Stone station, with the off-peak hourly service trains using the Up line in both directions. The test track has a limit of around two miles either side of the station and the whole of the test section is viewed and controlled from a screen in the ENIF test centre (initially established for the ERTMS proving trials) at Hitchin. The demonstration DMWS screen also shows the Up line and the progression of the service trains. Stop boards are placed at each end of the test section.
Once the test train has accessed the section and been ‘shut inside’, all movements of the train are controlled from Hitchin. These can be normal signalling, ETCS operation or DMWS operation. Although plain line, artificial points and a level crossing were inserted into the section using real equipment in the training facilities at Walsall, thus creating the failure conditions that might be experienced on the real railway. The view of these elements could be seen at Hitchin via a CCTV link operating over public mobile 3G networks.
DMWS is aimed at significant signalling equipment failures and, should such a failure occur, the signaller can set up a DMWS zone to manage trains through the failed area. A basic form of the system, the track-only version, will allow the signaller to interrogate the IDR for confirmation of points and/or level crossing status, whence a verbal authority can then be given to trains in the form of an Emergency Special Working instruction.
The alternative ‘full track-train’ system allows the signaller to set up a DMWS zone between designated signals. The zone will be shown in green on the signaller’s screen, whence the signaller can set up an Authority to Move (AtM) shown as a black and white hashing, each time a train is to proceed through the zone. An interchange of data messages then takes place between signaller and driver culminating in the driver accepting the AtM and its end location, whereupon the route setting goes solid white. The train movement is then detected by GPS, since a track circuit or axle counter problem may be the cause of the failure.
At the end of the zone, the driver will normally encounter a green signal, whence a white arrow appears on the DMWS screen to show that the driver has accepted normal working. As with temporary block working, a train within a DMWS section is limited to 50mph. Part of DMWS will mean the suppression of TPWS loops within the zone, to avoid the driver having to stop and manually isolate the on-board TPWS equipment.
As it is entirely possible that the DMWS section will be long and cover several normal signals, the system must be capable of accommodating more than one train in the section, in which case the AtM for a second train may only be a partway authority. The AtM would be progressively advanced as the first train proceeds through the section.
Once the failure has been rectified, it will be necessary for all trains to have exited the DMWS section before the signaller restores the signalling to its primary control system. To try and do this whilst a train is still in section could create unnecessary confusion and possibly impinge on safety movements.
The Class 313 EMU used for conducting the earlier ERTMS trials has been adapted for other test purposes including DMWS. In one cab is a graphical display showing the DMWS instructions, whilst, in the other cab, the GSM-R radio has been adapted to display the same information. An article in issue 117 (March 2014) described how the Siemens radio product had considerably more processing power than that needed for voice calls and could be adapted for other purposes. DMWS is just one of them.
Each DMWS train-borne unit consists of GSM-R and public mobile modems, a satellite navigation chipset and a processor to drive the display. The Siemens cab radio used in the demonstration (one of the latest mark 4 radios) also provided the GPS feed as well as the modems and connections to both the GPS and GSM-R antennae.
Two banks of TV screens had been set up, showing pictures of the line ahead and behind, the commands and instructions as viewed on the DMWS cab unit and the display on the GSM-R cab radio. This gave a good view of what was going on without the need to cram into the limited cab space.
When standing at the entry signal to the failed area, the procedures for instigating DMWS operation can be seen quite clearly. A panel within the screen shows the train description, the signal the train is standing at and the signal to which the train may proceed. With the Hitchin controller having selected the section for DMWS working, the system offers an AtM to move from xxxx signal to yyyy signal. Providing this is in line with expectations, the driver accepts the offer and the authorised AtM is then shown on the screen.
Once the train is underway, the signals that may be passed under the authority of the DMWS are updated and a countdown informs the distance remaining to the end of the AtM.
Exceeding the AtM limit was also demonstrated. With the train going past the designated end-point signal, an audible alert immediately sounded and a flashing STOP message was displayed. The driver reacted to that and a voice call was then made with the signaller to regularise the situation.
There will be those who challenge whether the system is safe but, in truth, it is only replicating the paper-based system that already exists. Also, the principle of giving movement authorities by a screen-based message was established when RETB systems were introduced several decades ago. With DMWS, positional information is available which RETB never had, together with detection of authority exceedance.
To assure point detection and lock position will require verification from the IDR equipment, which implies a standby power facility is needed for interrogation of the points should the main signalling power supply fail. The level crossing assurance is aimed mainly at four-barrier crossings with CCTV supervision, but it is also compatible with the obstacle-detector crossings now being introduced. Barrier position and warning-light sequences will need to be proved. The situation with AHBs (automatic half-barrier level crossings) is less certain, as these are usually independent of the signalling system.
It is considered that DMWS should be capable of achieving SIL2 status, which is probably better than the present manual procedure.
Supplying the Kit and the Business Case
As explained in the September 2017 article, Network Rail conducted a three-part development programme. 15 companies received an invitation to undertake a feasibility study of which five accepted. From these, two companies proceeded to build a simulator following which Altran was selected to produce the demonstration system and equipment. Co-operation with Siemens was needed for the adaptation of the GSM-R radio screen display.
It must be emphasised that the kit as seen was not a prototype, but a system demonstrator to show the concept, which represents the end of the development phase. That said, the demonstrator used a real train with real infrastructure assets communicating through the live GSM-R and public mobile networks.
The value and practicality of DMWS has now to be evaluated, including the logistics of deploying on a wider scale. Each IDR unit is stated as being capable of interrogating up to eight pieces of infrastructure in the immediate locality. Even with this, it is recognised that several thousand units would be needed for full nationwide deployment, which would not be practical or cost effective. A calculation will therefore take place to pick out the places where disruption and capacity is the most critical and a business case will be produced on the basis of the reduction in Section 8 delay payments.
A new tender will hopefully be produced early in 2019 for a start to be made in CP6.
Thanks to Chris Fulford, the Network Rail Lead Engineer for the project, and to Ken Greenwood and Susanna Holden-White from Altran for arranging the demonstration and explaining the procedures.
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