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Wednesday, August 17, 2022

Cambrian trail signals new era

The UK has at last joined the ERTMS club. With its partial commissioning of the Cambrian line, Britain has reached a milestone in the future of rail signalling. Eventually, ERTMS (or more correctly ETCS – European Train Control System) will be the natural choice for all resignalling projects. It is a small beginning but an important step.

RETB alternative

The Cambrian route from Shrewsbury to Aberystwyth and Pwllheli was resignalled in the 1980s using the RETB (Radio Electronic Token Block) system. With its equipment ageing, an upgrade similar to what has been achieved in Scotland (see Issue 66 April 2010) was a possibility but a trial site to test out ERTMS (European Rail Traffic Management System) had to be identified. The Cambrian was seen as ideal, being sufficiently self-contained that only a small number of traction units needed to be equipped with the on-train kit. It could also test out the various interfaces that would be needed with existing pieces of railway infrastructure. As such, valuable experience could be gained before rolling the system out to busier lines.

The ERTMS concept has been described before in the rail engineer, with its component parts of ETCS, GSM-R (the radio bearer) and ETML (the still-to-be-developed traffic management layer). The three levels of ERTMS have also been previously described –

L1: the standardised bolt-on ATP

L2: a complete train control system using radio but retaining some lineside infrastructure

L3: a total radio-based solution but needing much more research before it becomes a practical reality.

It is thus the Level 2 application for which the Cambrian is the test bed.

Project scope

The heart of the Cambrian ETCS is a new control centre at Machynlleth, close to the Arriva Trains Wales depot. Purpose built, it contains the control and equipment rooms, a simulator, as well as various maintenance areas and facilities. Being close to the depot, this allows easy testing of train-mounted equipment to ensure units leave for operational service with everything working.

The ETCS equipment has been designed and supplied by Ansaldo STS using the latest software, version 2.3.0d. The GSM-R radio infrastructure is supplied by Nortel as part of the nationwide roll-out. Very few of the RETB radio towers have been used as GSM-R is in the 880MHz band, requiring many more masts and different coverage planning. Trains are fitted with Siemens mobile radios as part of the national contract.

The first section from Pwllheli to Harlech was commissioned on the 28th October and a publicity day was arranged on 16th November to show how the system works. The remainder of the route will be brought into service some time during the spring of 2011, the date being somewhat dependent on how well this initial stage fairs. So far, the performance has exceeded expectations.

ETCS in operation

Those familiar with new signalling control centres will recognise the similarity to the VDU control screens at Machynlleth. Routes are set and trains proceed across the screens in the normal way. However, the means by which this information is received and distributed is totally different. The line is segmented into block sections, these being from one passing loop to the next, except where a manually controlled level crossing is encountered, in which case the block section is limited to that point. A duplicated Radio Block Centre (RBC) manages the control of these block sections and supervises the issue of ‘movement authorities’.

There are no conventional signals but lineside signs mark the block section position for the driver. Once a route is set by clicking on the entrance and exit point with a conventional mouse, the system will determine whether this is safe – in other words, there are no other trains in that section – and then the movement authority will be given to the train. This is transmitted via the GSM-R system using the FTN fibre and transmission network, the radio MSCs at either Stoke or Didcot, and the various radio base stations along the route. The movement authority is little more than a data message displayed on the driver’s screen.

Cambrian trial signals new control centre
Inside the new control centre at Machynlleth

However, once the train moves, its speed and positional information is constantly sent to the RBC so that speed supervision can be monitored. This happens every ½ second. Movement is determined by periodic Eurobalises located in the track as well as the train odometer that increments from the balise position. The balises therefore act as reference markers. Should the train be exceeding the permitted speed or not decelerate sufficiently to stop at the end of the movement authority, the brakes will be automatically applied.

Since this ETCS trial is aimed at testing out the full system, a number of facilities are enabled that were not possible with RETB operation. The most significant is loop operation. The ‘stored energy’ train-activated points have been replaced by clamp locks. This will enable all loops to become bi-directional; the points can also be much higher speed. At stations, this is not too significant but where the loop is in open country and trains are not booked to pass, this will give a useful time saving.

Applying temporary speed restrictions is made easy with ETCS. The location details are built in at the control centre – these then become part of the movement authority and the required speed is made visible to the driver. Should he/she forget the restriction then the brakes are applied. Train completeness is achieved by the use of axle counters which count in and out at each block section.

Level crossings

The Cambrian route features all types of level crossing and the monitoring of these was a constant problem with RETB. AHB, AOCL, UWC and full-barrier CCTV control are all encountered. The first three exist as before but the signaller has much more control over train speed if he suspects that things have gone wrong. CCTV crossings remain remotely operated by direct signaller action but these are linked to block sections. Once the barriers are lowered and the TV picture shows the crossing to be clear then the movement authority can be given.

A quirk of the Harlech-Pwllheli section is the flat rail crossing with the Welsh Highland Railway at Porthmadog. This requires the WHR to control its train movements by ground frame for which a release is required from the ETCS system. The signaller has to judge what time he has available – usually allowing 15 minutes – during which time no movement authorities are allowed. No doubt once the WHR trains run to Porthmadog on a regular basis, both parties will get better at the procedures and the time slot will reduce.

Cambrian trial signals Harlech train
A train heads towards Harlech past a block section marker

Rolling stock

The line’s Arriva Trains Wales passenger fleet consists of 24 Class 158 two-car DMUs. All these are now fitted with ETCS and GSM-R cab equipment. This has been quite a challenge as the cab of a 158 is small and the RETB equipment has to be maintained in service for the time being. Retro-fitting rolling stock is an expensive business and it has cost around £350,000 to equip each two-car unit. The fleet becomes captive to the line and it is unlikely that any other units will be deployed until new trains are purchased. Since the latest European Directive requires all new rolling stock to be fitted, equipping the trains will not be a future problem.

Also fitted are three Class 37 diesel locomotives (actually Class 97 as they are part of the engineering fleet) and these will be used for test and engineering purposes. More challenging is what to do about steam specials. No immediate solution is in sight but the vision is to have most of the equipment mounted in the support coach with just a remotely linked driver’s panel on the footplate. Funding for this development is awaited so a steam enthusiast benefactor would be welcomed.

Training and support

The introduction of a new system like ETCS requires a whole new training regime for signallers, drivers and technicians. Simulators to mirror both the signalling control consoles and the driver’s train equipment have been procured and installed at the Machynlleth centre. Not only do these permit normal day-to-day operational training but faults can be inserted that give experience on how to deal with problems that might occur when in service. Technician training, including the use of diagnostics, is also carried out at the centre.

The trial in perspective

This project has had a long gestation period but Network Rail and the suppliers have sensibly taken their time to get the technology right. The only problem identified so far has been the visibility of driver display panels in some lighting conditions and a redesign is being progressed. The Cambrian line is a relative backwater and would not normally justify the expenditure that has been outlaid. However, that is to the line’s advantage and a much improved train service will result. At present this is every two hours but, with an extended loop at Welshpool and improved layout at Dovey Junction, one train every hour will be possible.

The trial will give valuable operational experience on what ETCS can offer, help test the capacity of the GSM-R radio to carry both ETCS data and voice traffic, as well as giving an insight into the problems of retro-fitting rolling stock. What it won’t do is confirm the capacity of ETCS to handle intensive rail traffic on busy main lines and in dense suburban areas, but it will give an indication of system capability.

The first section’s commissioning has brought benefits to the Cambrian in terms of public exposure. Full conversion to ETCS operation will bring many more with greater operational flexibility delivering better services and, hopefully, increased passenger numbers. Spring time in mid-Wales could look very rosy.


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