Signalling systems have to be safe, reliable, maintainable, sustainable, and cost effective. While electronic solid-state interlockings have been used for over 30 years, there are still many relay and mechanical-based systems in place. To deliver the additional capacity required for tomorrow’s railway, new ways of controlling train movements using the best technology available are needed, from signalling control systems to signal equipment, train detection and interlockings.

With over 1.6 billion passenger journeys a year recorded by the Office of Rail and Road (ORR), the highest recorded figure since the series began, and with continued growth of 4 per cent per annum anticipated, there is an urgent need for solutions that will deliver future demand, help improve reliability and capacity, and reduce delays to benefit passengers.

Atkins, with its extensive team of railway professionals and links to other industries and the UK supply chain, is ideally placed to develop and introduce future signalling systems. As an independent integrator, they can search and use/adapt the best products in the world, building signalling systems today that enable the digital railway of tomorrow. Atkins prides itself on being able to provide a signalling system service using the best technology available, rather than supplying a pre-determined catalogue of parts.

The Atkins signalling and telecoms (S&T) design teams have the capacity to undertake all control and communications work from outline feasibility studies to scheme and detailed design.

They provide installation, testing and commissioning on full-scale remodelling programmes, as well as for smaller projects together with technical investigation work. Over 200 Institution of Railway Signal Engineers (IRSE) licensed signalling design engineers deliver a range of services from feasibility to detailed design for major and minor mainline, together with metro, railway projects.

Supplementing the signalling design capability, there are qualified and experienced installers, testers and technical specialists who can work on all major equipment and technologies for projects of any scale. This wealth of knowledge and experience is available to advise on the next generation of control systems and to ensure that the lessons learned from the past are used to engineer the future.

Independent clean sheet

Atkins is employing new digital technology and delivery methods to re-engineer the whole signalling system so that future rail services can be delivered and maintained with greater whole asset life efficiencies.

It is clear that Network Rail’s future signalling strategy will centre on ERTMS, with its benefits of increased capacity and lower running costs. However, the whole network and the fleet of rolling stock cannot be upgraded overnight. Asset managers may have assets that have reached the end of their life and which need to be replaced based upon their condition. It’s also important that the industry feeds the supply chain with a steady supply of work.

What is required are methods of replacing redundant assets with conventional, lower-cost fixed-block signalling which is ERTMS-ready and can be easily upgraded to gain the full benefits when the rolling stock becomes available. While continuing to offer traditional technologies and delivery methods, Atkins has worked in partnership to meet Network Rail’s future needs to deploy new technology, using proven products from other industries, which can be applied and used on the railway now.

In 2012, Atkins looked at the signalling requirements of the future with a clean sheet of paper. By adopting modern software techniques with progressive assurance ‘in-built’ and standards aligned to the right technologies, Atkins believes that it is possible to implement signalling systems on complex railways with a greater level of confidence than has previously been experienced. High levels of automated testing can save time to commission projects, while reducing the amount of scarce resource required and the associated risks.

In consultation with its main customer, Network Rail, Atkins determined that the future signalling asset base should be based on electronic PLCs (Programmable Logic Controller) using ladder logic, reliable, self-diagnostic, maintenance-free, self-assuring in design, capable of using open system TCP/IP communications, scalable, flexible, future proof and cost-effective. It must also limit the need for workers to go out on track – both for installation and maintenance.

By building on experience in other sectors such as nuclear and defence, which deploy similar technologies and delivery methods, Atkins is combining the expertise of its signalling engineers with the latest technology and new ways of working. This is aimed at creating integrated future signalling systems to deliver the digital railway services for tomorrow, with the best products available in the world. These systems are now being trialled and approved for industry roll out.

Interlockings and standards

The heart of any signalling system is the interlocking of signalling assets with one another, preventing conflicting or unsafe train movement. Interlockings were introduced in the UK following the Regulation of Railways Act of 1889 and range from the earliest mechanical variants, through a variety of electro-mechanical and electrical relay interlocking, up to modern automated electronic systems. Interlockings are the ‘brain’ for communication between the signaller and the infrastructure, translating the signaller’s commands into the safe control of signal and point-operating equipment.

At the start of CP5, electronic-based interlockings only accounted for approximately 40 per cent of the British network by size, with the remaining 60 per cent either relay or mechanical. Within the last few years, relay interlockings were still being specified for schemes, as the industry capacity for electronic systems could not keep up with the demand. On the telecoms side of S&T, relay-based switching systems were phased out 25 years ago and there have been impressive reliability and maintenance cost-savings as a result. Electronic control systems and IP-based communications systems are now found in all industries, and with the digital rail programme to provide more capacity at less cost, there is now the opportunity to provide signalling, interlocking and systems using such technology.

Signalling principles and standards have evolved around hard-wired relay logic, so the obvious way of programming a PLC is to convert the relay logic into PLC code. This, however, causes problems as relay circuits have evolved to compensate for relay behavioural characteristics, and therefore principles and standards have evolved around relay circuit characteristics. In order to programme a PLC correctly and efficiently, a system requirement specification has to be created using a formal method (in accordance with EN 50128, the standard for software-based signalling) before coding the PLC and proving it is safe.

The standards that apply to future signalling systems by Atkins are the European EN5012x family, including EN50126, EN50128 and EN50129. EN 50126 covers the specification and demonstration of reliability, availability, maintainability and safety (RAMS). EN 50128, addresses requirements capture, software design, implementation and testing while EN 50129 describes in detail what action and documentation has to be provided for the purpose of preparing a safety case.

Hardware and software

Within its future signalling systems offer, Atkins evaluated a number of interlocking products against the required criteria before deciding to adopt Alstom’s ElectroLogIXS technology. This is used extensively around the world and has a good reputation for reliability. It can be configured in a number of ways, so it could control a level crossing, an object controller for a signal or set of points, or a very complex layout.

The other advantage of selecting ElectroLogIXS was that it provided Atkins with a blank canvas for the bespoke software which has been created in-house. This resulted in Atkins being able to ensure its solution complies with signalling principles, rather than having to adapt other software systems. This also means that, in the event of future modifications or enhancements being required, the expertise and coding is with Atkins, so they will be able to support the system throughout its lifetime.

Some electronic interlocking systems in the past have used serial processing, which has resulted in signallers taking longer to set routes compared to a relay interlocking. Atkins has made sure this is not the case with ElectroLogIXS.

Critical electrical signalling control equipment must be housed in a secure, weatherproof environment, with the housings provided at regular intervals along the trackside. Historically, these have been provided in various forms, ranging from small apparatus housings containing minimal equipment through to large expensive buildings in the form of relay rooms and relocatable equipment buildings (REB).

Relay rooms and REBs were required because the geographical or relay interlockings were large. When the first, smaller electronic interlockings were introduced, REBs continued to be implemented to provide security and the correct environmental conditions. Maintainers preferred REBs as they provide a safe, warm and dry environment to fault and maintain equipment. All this comes at a cost, not only to install, but also to maintain and repair the building throughout the life of the asset.

Modern electronic systems and interlockings are now very reliable, small and require no maintenance. They can be networked to a central control and be self-diagnosing, so a maintainer can be told exactly which component to replace in the (rare) event of a failure, or even a non-service- effecting failure. This is the approach Atkins has taken and it has established that the ElectroLogIXS technology can be housed in standard inexpensive location cases, with no expensive environmental equipment. The tail cables to the equipment allow the location cases to be sited near access points in positions of safety. What, only a few years ago, would have required a room full of relays can now be provided by a single electronic card.

Care needs to be taken so that commercial-off-the-shelf equipment, such as power supplies, can operate in location cases, but the telecoms industry has proved electronic equipment doesn’t always need a building. Just observe all the green street cabinets that are used by BT to deliver high speed broadband into most homes. What would a town / village look like with an REB on every other street? Not to think of the costs involved.

Safety integrity level and electromagnetic compatibility

An appropriate safety integrity level (SIL) is required for any item of equipment with a safety role and it is this that differentiates a normal industrial PLC from one used in a signalling interlocking system.

Future signalling systems by Atkins Crewe Test Facility [online]

Unfortunately, SIL is often misunderstood. SILs relate to specific safety functions and not overall reliability. Some procurement specifications specify that a system or piece of equipment meets a particular SIL, without assessing if it is needed at all, when maybe only one or two functions within the overall system actually need a SIL. A system with high reliability may well be safe, but a system with a high SIL may have low reliability.

It has been known for some specifiers to require a SIL level for quality or reliability, rather than safety, reasons. This fails to recognise that SIL relates only to safety-related systems and their safety functions. If not assessed correctly, it can result in systems being delivered that do not meet the true performance requirements and have higher than expected whole-life costs.

For its new portfolio of future signalling systems technologies, Atkins has used its expertise to make sure only the right components have been assessed for the correct SIL, but not overlooking the EN 50126 reliability requirements.

The ElectroLogIXS interlocking has been assessed as compliant to SIL4 and has undergone rigorous testing for both AC and DC immunisation, in some of the worst locations on the network for such interference. ElectroLogIXS has been successfully used in countries with far higher lightening damage risk and ranges of temperature and humidity.

Chilworth level crossing

Atkins builds strong relationships with trusted partners, from technology suppliers to small and medium-sized enterprises. This enables Atkins’ solutions the flexibility to deliver bespoke and best practice technologies from across the supply chain. Atkins has looked at all the components of the signalling system to see what can be improved upon, and one example is the level crossing barrier.

Historically, railway level crossing barriers have been of railway propriety designs, operated from low voltages. Atkins has worked with Newgate (Newark) Limited to develop a new railway level crossing barrier machine, based on Newgate’s experience in the traffic barrier and gate industry.

This has resulted in a design which is rated at 110V and therefore requires smaller diameter cables and power supplies. The first installation and trial of the new barrier machine controlled from a small ElectroLogIXS interlocking will be at Chilworth level crossing on the Wessex route later in 2016. This is a manually controlled barrier crossing with train signalling protection. The Atkins installation will trial a number of new products, including a new 110V AC power system from GE.

Rail Engineer looks forward to inspecting and reviewing the installation and to hear more about future signalling systems by Atkins.