Network Rail’s strategy to control the whole UK network from 12 Rail Operating Centres (ROCs) will require existing signalling centres using SSI (solid state interlocking) technology to be ‘re-controlled’. Writes Ian Mitchell

The interlockings will remain in place and become remotely controlled from the new ROC.

DeltaRail has led the way in developing the remote interface (RIF) technology to achieve this and the first application has now been commissioned in Scotland.

From PSB to ROC Edinburgh is unique amongst the 12 ROCs in that the building was originally a power signal box (PSB) opened in 1977 with a large entrance exit control panel controlling relay interlockings along the East Coast main line from the England-Scotland border through the City of Edinburgh and over the Forth Bridge into Fife. Its second life began in 2006 as part of a major capacity improvement project for Edinburgh Waverley station – the interlockings in the station area were replaced with SSI and a new operating floor with VDU workstations replaced the panel.

The signalling control system technology chosen for this critical project was an Integrated Electronic Control Centre (IECC) supplied by DeltaRail – a decision driven by the requirement to provide automatic route-setting (ARS) to maximise performance over the new layout, and to be capable of interfacing to the existing relay interlockings which were retained outside the central Edinburgh area.

The seven IECC workstations installed at Edinburgh were designed with spare capacity which is being taken up by a number of extensions of the area of control:

  • Airdrie to Bathgate re-opening (2010); Polmont signalbox re-control (2012);
  • Millerhill signalbox re-control (2012);
  • Borders railway re-opening (planned for 2015)

Network Rail’s new operating strategy has resulted in Edinburgh being designated as the ROC for the East and North of Scotland – the key internal links between Scotland’s seven cities – Edinburgh, Glasgow, Aberdeen, Dundee, Inverness, Perth and Stirling. The other Scottish ROC is the West of Scotland Signalling Centre which will cover the Glasgow suburban services and trains to Ayrshire and the West Coast main line to England.

The first step towards realising the operating strategy is for Edinburgh ROC to take over the signalling on the Edinburgh-Glasgow route via Falkirk. This is taking place as part of the Edinburgh Glasgow Improvement Project (EGIP) – a £650m investment to electrify and upgrade the route. The Glasgow end of the route has been controlled from the Cowlairs signalling centre, an SSI installation with a panel, since 1998. At 15 years old, this was clearly an installation with a lot of life remaining, so re-control rather than re- signalling was the preferred option although this wasn’t a straightforward task.

The callenge of controlling SSI

SSI, as conceived by British Rail in the 1980s, was based on a distributed system architecture with electronic interlockings in the control centre, and interfaced with lineside signalling equipment via trackside functional modules (TFMs) distributed along the trackside. The communications protocols allowed the interlockings to be remote from the TFMs but assumed they would be in the same building as the control system – a panel or IECC.

In hardware terms, it would be possible to plug the serial data link from the interlocking into a modem and send the information over Network Rail’s fixed telecommunications network to a remote control centre. However, this would not be compliant with CENELEC (le Comité européen de normalisation électrotechnique – the European Committee for Electrotechnical Standardisation) standards for safety related communications. There is a risk that data transmitted in this way could be changed through accidental or deliberate misrouting or interference without being detected, resulting in false indications
to the signaller or incorrect controls to the interlocking.

One solution would be to stick with the SSI architecture and relocate the interlockings to the ROC. This was done when Leeds PSB was re-controlled to York IECC in 2002. The five Leeds North West SSIs controlling the lines to Bradford, Ilkley and Skipton were ‘moved’ – in fact new interlocking cubicles were provided at York, and only the SSI processor modules were moved on the commissioning weekend. However, this approach incurs significant installation, test and commissioning costs and, as ever-larger areas are controlled from the ROCs, there is a limit to the number of interlockings that can be easily accommodated, and a certain nervousness in concentrating so much critical equipment in one location.

The alternative approach is to develop a remote interface (RIF) to be installed alongside the SSIs at the old signalling centre, which then communicates with the ROC using a modern protocol that is fully compliant with the CENELEC standards for safety related communications. DeltaRail has developed this capability for the new generation IECC Scalable signalling control system, and the Cowlairs re-control project provided an ideal opportunity to offer this solution and get it through the product acceptance process.

IECC Scalable

The original IECC system architecture remained in production (with numerous hardware and software upgrades over the years) until 2011. In 2012 DeltaRail introduced IECC Scalable, with a highly successful pilot installation. This replaced the original IECC at Swindon B signalling centre on the Western route (issue 92, June 2012) prior to the relocking and recontrol of this area to Thames Valley Signalling Centre (TVSC). IECC Scalable delivers proven functionality on industry standard blade hardware achieving a very compact, cost effective and future proof solution that is being applied in a wide variety of projects.

The installation at TVSC has been extended and now controls the Paddington-Heathrow end of the Great Western main line and, at the other end of the scale of application complexity, IECC Scalable workstations can now be seen in a mechanical signalbox at Harrogate and controlling the modular signalling between Ely and Norwich.

The key architectural innovation in IECC Scalable is the use of IBM’s MQTT messaging technology as the information path between the subsystems that implement various functions within the system. The benefit from this is that MQTT messaging is a widely used IT industry standard that enables exchange of information with a wide range of systems and supports extensions to functionality, for example future interfacing to ERTMS and Traffic Management systems. It also allows any component of the system to be deployed remotely from the others, with the messaging enabling communication over any IP-based transmission media.

For re-control of an SSI, the interlocking interface component can be deployed in an IECC Scalable RIF alongside the interlockings. The RIF then communicates locally with the SSI interlockings using the legacy NR/SP/ SIG/17503 protocol, and to the main IECC Scalable system at the ROC via the messaging over a suitable communications link.

The Safety Case for IECC Scalable has to demonstrate that safety related functions of the signalling control system (up to SIL2 in CENELEC terms) can be depended upon, taking into account the use of the MQTT messaging software (which is commercial off the shelf without a railway safety case) and to allow the possibility of communications over an open communications network.

The solution was to treat the messaging as part of the communications network, and to provide a software safety adaptor between the message broker and each module that implements SIL-rated functionality. The software within the adaptor implements a set of defences that allow messages to be checked against the various threats to communications – all in accordance with the requirements of CENELEC BS EN 50159:2010 ‘Safety Related Communications in Transmission Systems’.

Signaller workstations

While the use of the IECC Scalable RIF was the main innovation for the Cowlairs recontrol, there were a number of other interesting features of the project. Whilst it is technically possible to control the whole of the Cowlairs area from a single IECC Scalable workstation, the ergonomics study for the project suggested that the workload at peak periods would be excessive for one signaller. Provision of a second workstation would also provide sufficient capacity for the future re-control or re-signalling of the remaining signalbox areas between Edinburgh and Glasgow (Greenhill Junction, Carmuirs East and Grangemouth Junction).

The chosen solution was to provide two workstations on the IECC Scalable system – a primary workstation, capable of controlling all of the former Cowlairs PSB area and a secondary workstation to control the main Edinburgh- Glasgow line only.

During day shifts, both workstations are manned with the secondary workstation controlling the Edinburgh-Glasgow line and the primary workstation the rest of the controlled area (the Springburn to Cumbernauld line).

At night time, the secondary workstation is unmanned, and the primary workstation controls the whole area. The two workstations are located side by side on linked desks with hard wired controls, such as the ‘emergency signals on’ facility, located between the two where they can be easily reached from either position.

To allow the supervision of such a large area, each workstation has two rows of screens. The upper row displays non-controllable overviews that provide a permanent display of the entire area for monitoring purposes. The lower row shows detailed views which the signaller selects as required for manual route setting or other controls. Of course, ARS is provided as a standard feature of IECC, so only a few trains require manual route setting.

Project delivery

As well as the IECC Scalable supply, DeltaRail’s scope of work for the project included updating the SSI data to work with a VDU-based control system and ARS. The Cowlairs area includes an early implementation of axle counters using co-operative reset which was retained after the re-control, and this required some further changes to SSI data to make it compatible with the standard IECC axle counter controls and indications.

Inevitably, the project was a little more complicated than a straight re-control. The first stage of EGIP electrification is the Cumbernauld line, with an enhanced service to be provided in time for the 2014 Commonwealth Games by extension of the existing Glasgow Queen Street Low Level service that terminates at Springburn. This requires some track remodelling in an area where the existing SSI was full to capacity, and so the project required the number of SSIs to be increased from 5 to 6. DeltaRail undertook the initial split of interlocking data and then handed over to Atkins which was the signalling contractor for the remodelling work.

Provision of a robust IP networking solution between Cowlairs and Edinburgh was an essential element to delivering the IECC Scalable RIF, and fortunately Network Rail in Scotland has been somewhat of a pioneer in this regard (issue 72, October 2010), building a wide area IP network using gigabit Ethernet optical links over spare fibres in the cables installed for the main fixed telecommunications voice network. A ring topology for the network provides alternative paths allowing data to be rerouted if any links are damaged or fail.

The initial use of this approach was for remote condition monitoring and long line public address systems, but it was equally suitable for the IECC Scalable RIF application, with access points available at Cowlairs and Edinburgh.

As part of the product acceptance testing for the IECC Scalable RIF, testing was undertaken to ensure the capacity and propagation times delivered by the network was adequate to achieve reliable operation – as expected the relatively modest data rate required was easily achieved.


The re-control of Cowlairs to Edinburgh was successfully commissioned on 7 October 2013, and the IECC Scalable RIF performed faultlessly throughout the three month trial period required to achieve full product acceptance. DeltaRail has provided post-commissioning support with regular reviews which focused largely on optimising the ARS performance in the area.

Further minor updates are programmed for 2014 as electrification and remodelling continue, and DeltaRail is looking forward to further work in Scotland to fill in the gap between Cowlairs and Edinburgh as the EGIP project progresses.

The approved IECC Scalable RIF now means that any SSI signalling centre can be recontrolled to a ROC with minimum change to the existing equipment – and this includes sites that use the next generation SSI-compatible interlockings Westlock and Smartlock. The IECC Scalable RIF will be equally applicable to projects requiring re-control of relay-based signalling systems, and DeltaRail is looking forward to winning a contract where this version can be demonstrated and approved.

The ease with which re-control can be delivered will allow a step-up in the pace of migration to the ROCs, enabling Network Rail to realise the benefits of reduced operational expenditure and improved performance earlier than anticipated.