Tunnelling for the £15 billion railway was completed last May with the final two TBMs, Elizabeth and Victoria, being decommissioned. The task of fitting out the tunnels and stations, installing track, OHLE and signalling is now well under way.

Crossrail was invented to increase capacity for east-west journeys, relieving the Central and Jubilee lines as well as providing wider connectivity along the Shenfield – Liverpool Street – Central London – Paddington – Heathrow – Reading axis. The Sponsors’ Agreement was signed in 2008 committing Transport for London and the Department for Transport (TfL and DfT) to finance the scheme, with contributions from Network Rail, Heathrow Airport, Canary Wharf Group, City of London and London business. Crossrail Ltd developed the specifications, designed and is implementing the construction of the new railway through central London. On completion it will hand over the infrastructure management for the new section to Rail for London (RfL), a subsidiary of TfL. The signalling and communications contractor is Siemens. However, as regards the signalling systems on the train, Siemens is sub-contracted to train builder Bombardier. MTR Crossrail is the company holding the concession from TfL to run the trains.

Rail Engineer was invited to meet Siv Bhamra, Crossrail railway systems and commissioning director, to hear about the challenges of providing the signalling, control and communications systems.

Crossrail consists of three sections. The Central Operating Section (COS) runs from a point between Portobello Jcn and Westbourne Park in the west, and Abbey Wood in south- east London, and from Stepney Green Jcn to Pudding Mill Lane Jcn. This is all new railway and signalling for which Communications Based Train Control (CBTC) moving block signalling is to be deployed.

08 Liverpool Street station [online]

At the western end, Crossrail trains join the Great Western main line (GWML) and operate under the supervision of ETCS level 2 as an overlay to existing lineside signalling to Airport Jn and Heathrow terminals. For trains continuing along the GWML to Maidenhead/Reading, conventional signalling with Automatic Warning System (AWS) / Train Protection Warning System (TPWS) will be used west of Airport Jn.

In the east, Crossrail meets the Great Eastern Main line, joining into the ‘electric’ lines shared to Shenfield, also using lineside signalling fitted with AWS/TPWS.

The depots which will look after the new Bombardier-manufactured trains will be at Old Oak Common and Ilford.

Opening strategy

Crossrail will be commissioned into service on a staged basis. Stage 0 took place in May 2015 with the ‘TfL Rail’ brand taking over the existing Class 315 service between Liverpool Street main line (dubbed ‘high level’) and Shenfield.

Stage 1 in 2017 sees the introduction of the new 145 km/h (90 mph) Class 345 Bombardier Aventra trains. The units are powered by 25kV AC but there is space for third rail power equipment for possible extension of services further into Kent. The production run for this stage will consist of seven cars per train, each with three doors per side to help meet dwell times, as the platforms at Liverpool Street and elsewhere are not long enough for the final nine-car fixed formation. Platform lengthening to the standard 240 metres is under way at various stations with selective door opening provided for those stations which cannot be extended.

Stage 2 in 2018 sees Crossrail replace the Heathrow Connect service between Paddington high level and Heathrow Airport with a four trains per hour (tph) service using the nine-car Class 345.

Stage 3 takes place at the end of 2018 when trains start running on the COS from Paddington low level to Abbey Wood. Stage four in 2019 sees the opening of the Stepney Green Jct to Pudding Mill lane section, providing a through service from Paddington low level to Shenfield. In Stage 5 at the end of 2019, the final link at Westbourne Park opens to facilitate the full Crossrail service.

00 Crossrail Train Protection Dec 2019 [online]

The need for CBTC

The planned throughput of trains per hour from central London is:

  • 2 tph to Reading
  • 4 tph to Maidenhead
  • 4 tph Heathrow
  • 10 tph to Hayes and Harlington
  • 14 tph turning back at Westbourne Park

The total of 24 tph through the central section could potentially become 30 tph. At the east end there is a 50:50 split at Stepney Green Jcn:

  • 12 tph to Shenfield
  • 12 tph to Abbey Wood

The specification is for 110 second headways with 60 second dwell times at Paddington and Liverpool Street, putting trains 50 seconds apart. Independent modelling showed that this can only be achieved using a moving block signalling system. It was considered that developing ETCS Level 3 in the timescales was too risky, whilst GSM-R is a 2G system that might not be sufficiently capable. Thus CBTC was chosen for the COS.

However, the Crossrail route comes under the European interoperability regulations and hence a derogation has been secured from the Command Control and Signalling Technical Specification for Interoperability (TSI). The derogation will include a commitment to migrate to ETCS Level 3 when there is sufficient confidence that a mature product can deliver the specification of the sponsors.

Siemens Trainguard mass transit system

Trainguard MT is new to the UK but has been successfully used in Beijing and Copenhagen. The schedule compiler, timetable processor, Trainguard MT units and Westrace interlockings in the route control centre (RCC) at Romford are linked to the Airlink central system router which is hard wired to a lineside Ethernet radio bus installed along the COS. Access points (AP) exchange data with the train-borne equipment using a 2.2 GHz standard Wi-Fi signal.

On board the train, automatic train operation (ATO) drives the train and automatic train protection (ATP) ensures that the movement authority is not exceeded. ATP movement authority is updated every 0.4 seconds and ATP position reporting is also every 0.4 seconds. ATO receives target arrival time for next station, updated every five seconds. ATO recalculates and drives to the most energy-efficient profile whilst meeting next station arrival time subject to movement authority.

Every effort is being made to achieve a reliable CBTC system. However, secondary train detection in the COS is provided by axle counters, which cover the use of engineering plant and failure of the CBTC train. This allows the signaller to move failed trains safely. A failure of an axle counter will not impact on the normal service if all trains are running with healthy CBTC.

Platform screen doors, supplied by Knorr- Bremse, will be provided in the underground stations for ventilation strategy and to keep heat in tunnels and out of stations so the latter don’t need to be air-conditioned. Platform screen doors and train doors are opened and closed at the same time, synchronised and controlled by the signalling system. Above each platform door will be a customer information screen.

Auto-reverse

A new facility called ‘auto reverse’ is being provided at Westbourne Park (no station) for turning the 14 trains per hour in the reversing sidings. The driver selects ‘auto reverse’ on leaving Paddington station and walks back through the train, obviating the need for drivers to ‘step-up’. By the time the train gets back to Paddington (about a mile) the driver should be in the other cab ready to form the next eastbound departure.

The facility has the capability to turn round a full 30 tph service. There is just time for the driver to walk back through the train whilst in the reversing siding but doing so on departure at Paddington gives that extra time that will also help recover from perturbation.

tfl-image---crossrail-train-exterior_22822209920_o [online]

Auto reverse (AR) is not provided on Network Rail infrastructure. There will also be the possibility to use AR into and out of the stabling sidings at Abbey Wood so the driver will be at the correct end of the train to finish a shift or, when coming on duty, to start a new run westwards. Service trains will, however, normally reverse in the station. AR may also be used at Custom House and anywhere using crossovers in the central section.

Signalling west

Network Rail is carrying out significant preparatory works on both west and east legs of what will become the Crossrail route, funded by DfT within an investment budget of £2.3 billion. There is a major track layout reconfiguration at Heathrow Airport Jcn to provide full grade separation of trains to/ from the airport line (issue 124, February 2015). Other works include a dive-under at Acton and turnback facilities at Maidenhead. Old Oak Common is the main Crossrail depot with 33 sidings and has its own conventional signalling system. The depot is being built by Bombardier.

In a relock exercise between Paddington and Heathrow Airport Jcn, new Alstom Smartlock interlockings, with sufficient capacity to embrace the significant layout changes required to accommodate Crossrail, were introduced in 2011 replacing the previous SSIs.

At Westbourne Park the transition between CBTC and ETCS will take place on the move up to 50mph. If a westbound transition to ETCS level 2 should fail, multiple aspect signalling will still be in place (ETCS is initially provided on GWML as an overlay) enabling Crossrail trains to run on conventional signalling using AWS/TPWS under ‘NTC ‘(National Train Control).

For train builders, delivering compatibility between legacy TPWS and ETCS is challenging. However, UNISIG, the industrial consortium created to develop the ERTMS/ETCS technical specifications, has issued an interface specification for a unit they call a Specific Transmission Module (STM).

The purpose of the STM is to manage the interface between national train protection systems and ETCS to provide seamless train operation. In 2014, Mors Smitt was awarded a contract by Bombardier Rail Control Solutions to install TPWS+STM on the fleet of class

345 Aventra EMUs, providing TPWS/AWS functionality outlined in the latest GE/RT8075 group standard with the STM functionality defined in UNISIG standards.

The need for an ETCS ‘Plan B’

A number of potential risk factors exist in delivering ETCS in the area between Paddington and the Heathrow tunnel portal, including engineering resources, limited delivery experience of ETCS in UK, complexity of rail infrastructure in the area, and modifications to accommodate the new Class 800/801 trains for the InterCity Express Programme (IEP). Accordingly, ‘Plan B’ is being progressed under a £3 million contract awarded to Amey to provide Enhanced TPWS.

On the face of it, Class 345 trains could run on GWML using standard TPWS which is already provided, but the issues are complex. The route between Paddington and Heathrow is also equipped with Great Western Automatic Train Protection (GW-ATP). On the approach to every stop signal, ATP monitors the train speed profile in relation to line speed and movement authority, sounding a warning to the driver and applying the brakes if there is a digression. As there is no TPWS between Heathrow Portal and the Heathrow terminals, only Class 332 and 360 trains equipped with GW-ATP operate to Heathrow. The Heathrow Connect Class 360 service is to be replaced by a Crossrail Class 345 service. As this latter short section of route is relatively straightforward there is confidence that ETCS will be delivered on this stretch in time for the start of Crossrail services. ETCS takes train protection to a new level, continuously monitoring train speed.

The existing standard TPWS between Paddington and Heathrow Airport Junction deploys Train Stop System (TSS) loops and Overspeed Sensor System (OSS) loops at selected signals, generally those protecting junctions, to mitigate Signal Passed at Danger (SPAD) risk.

However, for the purposes of the regulation, TPWS is considered a ‘train protection system’ only if it is not reasonably practical to install an ATP or ETCS system, as standard TPWS provides a lower level of protection. For the new Crossrail service, as it could be considered reasonable to provide ETCS to operate at every stop signal, it is considered non-compliant with the Railway Safety Regulations 1999 (RSR99) if this service operates with TPWS.

As the Paddington route already has ATP, and ETCS is ‘Plan A’ for Crossrail, it is apparent that existing standard TPWS would not comply with RSR99, not to mention the sensitivities in relation to the disasters at Ladbroke Grove and Southall.

Significant option analysis work has been undertaken for Network Rail to establish the way forward. Fitting GW-ATP to Class 345 trains was discounted early on due to additional costs, and risk to timescales for entry into service.

Enhanced TPWS

Following extensive review, evaluation and quantification of the levels of safety offered by Enhanced TPWS, it has been found to be commensurate with that of GW-ATP/TPWS for the proposed mix of services and rolling stock. The Enhanced TPWS project will add TSS loops at stop signals currently not fitted with TPWS (generally signals on plain line sections, thus mitigating the risk of a rear-end collision), and OSS loops designed to stop a Class 345 train short of a conflict, generally within the overlap for the signal.

Additional OSS loops will also be provided on approaches to buffer stops so as to afford an increased level of speed monitoring at these locations. All other TPWS-protected trains operating over Enhanced TPWS will have a significant benefit from the increased TPWS provision. Trains that have GW-ATP will continue to be operated and protected with GW-ATP until they are upgraded to ETCS.

Subsequent to consultation with the interested and affected parties, an application has been made to the Office of Rail and Road (ORR) for exemption to RSR99 for the interim period until ETCS is commissioned, for which a decision is awaited at the time of writing.

Signalling east

Track remodelling works are being carried out at Pudding Mill Lane where the COS joins the Great Eastern Main Line (GEML), Ilford (depot location), Chadwell Heath (turn back siding), Brentwood (turn back crossover) and Shenfield.

At the latter a new bay Platform 6 is being built on the Down side. Currently, Down trains for Southend Victoria cross over from the Down main to gain Platform 5, thereby blocking the path of metro trains, and then take the GEML dive-under at the country end of the station. The new track layout will allow Southend trains to cross from the Down main into Platform 4 for the dive-under without conflicting with Crossrail trains using Platforms 5 and 6.

A relock exercise will see 12 SSIs replaced with higher capacity Alstom Smartlock interlockings, which will provide the additional interlocking capacity to support the Crossrail changes.

12 Romford ROC Crossrail RCC [online]

Transition between CBTC and conventional signalling with AWS/TPWS will, for the most part, be made whilst stationary in Stratford station. There are three overlay signals in each direction. The human factors are under close scrutiny and, as drivers will be busy with station duties, the changeover will be automated, the driver only having to acknowledge the mode change and observe signal aspects before setting off along the GEML. The project team are keen to avoid a SPAD trap.

Route Control Centre (RCC)

A new RCC is being created on the second floor of Network Rail’s Romford Rail Operating Centre (ROC). The signalling overview screen is along one wall, with CCTV monitoring along the opposite side. Other functions include SCADA, OHL and tunnel ventilation controls. The MTR Crossrail train operator will have a presence.

The RCC signaller interface is Siemens VICOS, with the overview screen displaying the whole of the Crossrail route. However, the signaller can, of course, only signal trains on the COS. Signalling controls for the west and east sections are located at Thames Valley Signalling Centre and Liverpool Street IECC respectively.

The COS junctions are controlled by Westrace MkII interlockings and simple automatic route setting will be used. A rule-based suggestions screen will give the signaller options in the event of an incident. The signaller can change minimum dwell times at stations and trip times which all go through the train regulation system to ensure even interval spacing of trains in the COS and right time presentation to Network Rail. This data is passed to the train and the ATO calculates optimum speed profile and maximum acceleration, and will coast as long as possible before braking.

At Abbey Wood there will be a simple interface with the Network Rail signalling system for the transfer of engineering trains.

RSSB (Rail Safety & Standards Board) has been engaged to prepare operating rules for the COS, which will need to reflect the special characteristics of the central section whilst maintaining consistency with relevant national rules where possible.

Siemens also holds the contract for communications networks including SCADA, CCTV, radio systems, and public address.

A backup control centre will be available in a separate building should anything happen to the Romford facility.

Integration testing

The new trains are currently being manufactured at Derby. In the spring of 2016, the first trains off the production line will be taken to RIDC at Melton Mowbray (Network Rail’s Railway Innovation Development Centre – formerly the Old Dalby test track). Single train testing will be done to prove all the train systems including the transitions and wayside systems. Design work is complete for a Thameslink-style integration laboratory based in London to test all the software including the wayside signalling and GWML and GEML interfaces.

And finally, in late 2017, the section of route between Canary Wharf and Abbey Wood will be able to be used for extensive live testing of the CBTC systems with multiple trains.

Thanks to Siv Bhamra and Jonathan Osgood from Crossrail, and to the Network Rail Crossrail programme, for help in the preparation of this article.