At nearly £15 billion, Crossrail is Europe’s largest current construction project. It will provide faster, more frequent main-line trains right into the heart of London, linking Heathrow directly with the City and Canary Wharf, connecting towns in the East and the West to central London, and delivering faster cross-city journeys between stations like Paddington, Liverpool Street, Whitechapel and Stratford.

The new route will pass through 37 stations and run 118 kilometres from Maidenhead and Heathrow in the west, through two new 21 kilometre tunnels beneath central London, out to Shenfield in the east and Abbey Wood in the south-east. A fleet of new trains will operate a 24 train per hour service between Paddington and Liverpool Street, with 12 trains per hour running to Stratford and Canary Wharf.

Communications-based system

To enable this high-frequency operation, Crossrail Limited (CRL) created a detailed performance specification for the central section. This will be delivered under the Signalling and Control System Contract (C620). Outside that central section, trains will operate over existing Network Rail tracks and infrastructure, and under the control of Network Rail signalling and control systems.

To the west of Paddington, this will be on Great Western main line (GWML), and it is planned that trains will operate under European Train Control System (ETCS) control.

To the east of the Pudding Mill Lane portal (where Crossrail trains heading eastward emerge from the central section tunnels), signalling will be controlled by the existing Network Rail interlocking at Liverpool Street. However, between Pudding Mill Lane and Stratford, Crossrail trains will interoperate with non-Crossrail trains bound for the existing Liverpool Street station platforms.

Throughout the central section, trains will be driven and controlled automatically by a communication-based train control (CBTC) system in moving-block automatic train operation (ATO) mode, allowing them to operate closer together and to run with precise speed control and stopping accuracy, all the more important because the underground platforms will be fitted with platform screen doors with which the train must align accurately when it stops.

CBTC systems are usually found on metro systems because they enable shorter headways and so higher capacities, particularly where stations are close together – this is one of the key advantages of moving block.

Combined approach

The contract was awarded in November 2012 to a consortium of Siemens and Invensys Rail. Between them, the two companies offered a combination of proven technology and delivery experience to the project. Of course, following the company’s acquisition in May 2013, Invensys Rail is now an integral part of Siemens Rail Automation which retains responsibility for the ‘conventional’ signalling scope of the C620 contract.

There are no conventional lineside signals in the central section because the CBTC provides in-cab signalling to the driver, but axle counter train detection, points control and route- setting will be managed by the company’s latest-generation WESTRACE interlocking.

The interlocking will interface with the Trainguard CBTC and with the automatic train supervision (ATS) systems (both of which are also within the scope of the C620 contract) at a new control centre which is being constructed at Ilford in Essex. In the control room, operators will oversee the running of the railway, and will have a large digital ‘Line Wide Overview Display’ in addition to their operator workstations.

Detailed analysis is underway to design the display layouts, both at the control centre and the driver’s display in the cab, ensuring that data is displayed in a clear format, that critical data is easily identifiable, and that operators are not overloaded with lower-priority messages.

Comprehensive engineering

Although the signalling and control system is just one small part of the final railway, it will be one of the last to complete in 2018, and so has a significant importance to overall completion and hand-over to passenger service. To minimise delivery risk, the system will use existing, proven products, systems and sub-systems and will avoid new development as far as possible – although inevitably, as with every railway, the signalling and control system has to be tailored to the specific requirements of layout and functionality. In addition, new interfaces between the Siemens Trainguard MT system and the WESTRACE interlocking will be developed.

A comprehensive systems-engineering approach is being employed on the project to assure delivery and to make sure validation and verification evidence is established from the outset. The company is currently developing the formal System Requirement Specification, to relate the functionality of the final system to the requirements of the client, and to provide linked requirement tracing through to subsystem design level.

The client’s approach has been unique and technically knowledgeable. The specification is thorough and comprehensive, and generally functionality-based rather than overly prescriptive. This gives the delivery contractor leeway in its approach to system design and engineering, although this must always be fully supported by comprehensive safety assurance and compliance with relevant standards. This approach is to some extent the product of an unusual contract. Based on the Institute of Civil Engineering’s NEC (New Engineering Contract) form of contract, it has a ‘pain-share, gain-share’ mechanism. It is a target cost contract, but if the contractor spends less than the target or identifies a cost-saving, the benefits are shared with the client, so it is in both parties interests to deliver optimum value-for-money.

Complex interfaces

The signalling and control system has a significant number of complex interfaces especially with the new Crossrail rolling stock. To enable a smooth transition of trains from Network Rail operation in the outer sections to CBTC in the central section, interfaces will be developed at the service control level and at the interlocking level – these interfaces with Network Rail being seen as key to delivering an integrated, tested and validated railway.

Another key interface is with the platform screen door (PSD) system. This will be the first delivery of PSDs in the UK since London Underground’s Jubilee Line extension project, and technology has progressed significantly since then. The Crossrail system will provide new functionality which automatically inhibits a platform door from opening if the corresponding train door is identified as faulty by the train management system, and vice versa if a platform door is faulty. The signalling and control system provides the high-integrity data link between the train and the PSDs to ensure that they are only opened at the right time – when a train is stationary in the platform.

Recognising the complexity of these interfaces, the client awarded the signalling and control system relatively early in the project – the new tunnels are still being bored, and some of the stations are still in their civil engineering phase. This early engagement allows the interface details with partnering contracts to be agreed at an early stage, particularly with civil engineering contractors and Network Rail.

Completion and hand-over in 2018 may seem a long way off, but there is a huge amount of work to do before then. Siemens’ teams in Chippenham, Braunschweig and London are already progressing well with design and systems engineering and over the next five years, the company will be tackling the challenges of integrating all these complex systems to ensure that this, London’s newest railway, and Europe’s biggest construction project, is delivered successfully.

Article by Frank Foley, senior project engineer, Siemens Rail Automation