Crossrail in London is currently Europe’s largest infrastructure project, running from Reading and Heathrow in the west, through 42km of new tunnels under London to Shenfield and Abbey Wood in the east. The line will consist of 10 new and 30 upgraded stations and will be known as the Elizabeth line when services in the tunnels begin in December 2018. It will be fully integrated with London’s existing main line and underground rail network and will carry an estimated 200 million passengers per year, with up to 24 trains per hour in each direction, which may rise to 30 trains per hour later.

The new Bombardier Class 345 Elizabeth line trains will be the first trains in the UK capable of transitioning from a mainline signalling system to a high-capacity metro-type signalling system and then back again. In the tunnels, the trains will use communications-based train control (CBTC) and on the surface sections the trains will use conventional signalling, along with the additional overlay of European Train Control System (ETCS) Level 2 on the Heathrow Spur – the 8.6 kilometres of railway infrastructure linking Heathrow Airport to the Great Western main line (GWML). This will be extended all the way to Paddington by December 2019.

Christmas 2017 saw a key milestone achieved, with the signalling immediately to the west of Paddington upgraded to allow trains to connect to and from the existing GWML at line speed. This will help to improve reliability and connect the new Crossrail tunnels and the new depot to the GWML.

The signalling arrangements for Crossrail are complicated and were described in issue 135 (January 2016). CBTC is required to deliver the planned throughput of 24 trains per hour in each direction through the central section under London. This will consist of 110-second headways with 60 second dwell times at Paddington and Liverpool Street, with trains only 50 seconds apart.

Such intense throughput of trains can only be achieved using a moving block signalling system and it was determined that developing ETCS Level 3 in the timescales of Crossrail was too risky. CBTC was therefore chosen for the central section signalling, using the Siemens Trainguard mass transit system product as used in Beijing and Copenhagen. Radio access points will exchange data with the train-borne equipment using Wi-Fi technology rather than the GSM-R that is used in ERTMS.

Signalling west

Network Rail needed to deliver significant works both west and east of the new Crossrail tunnels to get trains in and out of the central section efficiently, and this forms a contractual agreement between Crossrail and Network Rail Infrastructure Limited in terms of delivering the throughput of trains.

The works included a major track layout reconfiguration at Heathrow Airport junction, to provide full grade separation of trains to/from the airport line, along with a dive-under at Acton and turnback facilities at Maidenhead.

Old Oak Common is the main Crossrail depot with 33 sidings, and this will have its own brand-new ElectroLogIXS signalling system provided by Atkins. This is a separate contract and workstream, but will be another first deployment and a complex interface which the Paddington programme has had to manage.

New Alstom Smartlock interlockings were introduced in 2011, between Paddington and Heathrow Airport junction, to replace the 13 previous SSIs (solid-state interlockings). These were provided with sufficient capacity to enable the significant layout changes required by both the Crossrail programme and future ETCS requirements.

At Westbourne Park, the transition between CBTC and ETCS will take place with trains moving at up to 50mph. ETCS level 2 will be provided on GWML as an overlay, so multiple aspect signalling will still be in place, enabling Crossrail trains to run on conventional signalling using AWS/TPWS as a fall-back should the ETCS system fail.

As well as being the most complicated stretch of the GWML and the need to interface to both CBTC and ETCS, signalling arrangements were further complicated as the existing interlocking systems in the Old Oak Common Paddington Approach area included a number of unconventional protection arrangements. These were provided, in the wake of the Ladbroke Grove accident in 1999, to minimise the risk of signals passed at danger still further.

The Western Region is also uniquely fitted with Automatic Train Protection (ATP) manufactured by ACEC of Charleroi Belgium, which enforces obedience to signals by helping control a train’s speed profile.

In November 2016, new high-resolution IECC Scalable workstations were provided by Resonate at the Thames Valley signalling centre. The new screens provide greater flexibility to the signallers’ displays as well as moving the control systems onto a modern hardware platform. The upgrade was also preparation for the introduction of the upcoming traffic management system trial, which will further help operate the railway during times of perturbation.

On Christmas Eve December 2017, the Network Rail Crossrail programme undertook what is believed to be the single largest and most complex data signalling upgrade in history. After an integrated programme of works with all disciplines staged over six years and three years of data rewriting, new signal interlocking data was uploaded for all of the 500 signal routes in the three-mile approach to London Paddington. The scope involved 13 equivalent SSI interlockings, with the complete replacement of five equivalent SSI interlockings with brand new data to modern standards, together with amending eight further equivalent SSI interlocking data sets.

It’s all in the data

The data rewrite involved considerable preplanning, which commenced in the late summer of 2012, with people sitting down for the first time to think how they would complete the activity within the Crossrail programme requirements. 2014 saw the specification finalised with the methodology and timing in place, and work to actually rewrite the data began in the second half of 2015. There were complex parallel design stages required which all had to be planned to achieve the same timeframe.

The entire project had to lock down the operational layout of the railway two and half years out. It had to take into account significant track layout changes in order to connect the Crossrail tunnels onto the GWML and electrify all of Paddington station’s platforms. The signalling in the Paddington area will have to interface to ETCS level 2, CBTC, ACEC ATP, TPWS and Atkins ElectroLogIXS, so it was essential that a documented solid data set foundation, which was fully understood, was in place.

A collaborative, united programme was vital and a scope alignment meeting was held every two weeks involving the key parties. These were Alstom for the conventional interlocking signalling, Atkins for the new signalling data, and Resonate for the control system data. This took place for over two years, ensuring all aspects of the programme remained in line, enabling best practise to be identified and shared openly, and allowing the project to speak with one voice. This scope-alignment process will be used for future projects of a similar nature.

Ricardo Rail has provided the validation and verification project safety assessment for the works undertaken so far, and over the next few months further safety assessments will be undertaken before all the technical interfaces between systems are brought fully into use. The interfaces have been tested and are available but disconnected. At the moment, signalling moves into the Crossrail depot and central sections have been disconnected, pending verification testing, and will not be brought fully into use until all the safety actions required by the assessors have been closed out.

GSM-R replaces Cab Secure Radio

GSM-R has been installed and commissioned in the Heathrow tunnels. A big project in its own right, and a task undertaken by ADComms, assisted for radio frequency design by its own new subsidiary AIB Wireless, this was successfully delivered in the same timescale as the Paddington upgrade. It will replace the last operational Cab Secure Radio system in the country, still in use between Paddington and Heathrow.

The Heathrow GSM-R installation has been designed from the outset to meet the capacity, coverage and availability requirements required for both ETCS and conventional voice operation. GSM-R propagation in the Heathrow tunnels is predominantly by new radiating cable (otherwise known as “leaky feeder”), but with antennas used at the tunnel portal and in the stations.

GSM-R coverage has also been provided in the emergency access shafts to the tunnels, so that communication is available to rail staff in the event of an emergency train evacuation. The Class 345s are equipped with a portable GSM-R handset in each cab for this purpose.

As GSM-R is essential for ETCS operation, the Heathrow tunnels installation has been designed to offer a high level of availability, with duplication of GSM-R base stations, fibre-fed repeaters used to ‘boost’ the signal along the tunnels and the optical master units which connect between the base stations and repeaters. This is so GSM-R will continue to operate even if there is failure of an item of active equipment.

GSM-R is also being upgraded between Paddington and Airport junction, with the replacement of six existing base stations to provide enhanced capacity and reliability for ETCS. This includes the addition of a new base station to the east of Ealing Broadway, providing an improved level of radio coverage for ETCS. A contract for this work has yet to be awarded.

Whilst the ETCS Level 2 operation will initially use circuit-switched data connectivity, the upgraded GSM-R trackside system will enable an easy migration to packet-switched data ETCS in the future.

Collaborative working

A new smart-tracking tool was used for the first time, which provided an open and collaborative information stream between all the contractual parties involved in the signalling programme. This allowed shared access to real time progress reporting of all activities, with everyone – including all the different parties in the same organisation and all the organisations involved in the programme – having visibility of the same accurate information and a consistent messaging format to update one another.

Taking this step provided confidence that things were progressing as planned and, if they were not, it gave the opportunity to amend plans and resources for any sequential activity.

The final connection

In addition to these signalling works, Network Rail’s Crossrail programme successfully completed the final connection between the national rail network and the Crossrail tunnels over the festive period, linking east and west for the first time.

More than 6,400 metres of new track has been installed in the Old Oak Common Paddington Approach (OOCPA) area, to connect the tunnels and the new Crossrail depot at Old Oak Common to the existing rail infrastructure.

The Network Rail and Carillion-led team installed the final piece of track near Westbourne on 17 December, connecting Brunel’s historic Great Western main line to the new Crossrail tunnel system beneath London.

With all of the Crossrail track in place, the team worked round the clock over the Christmas blockade (146,000 hours across a 10-day period) to install more than 4.5km of complex wire runs between Old Oak Common and Paddington to electrify the new lines connecting to the Crossrail tunnels and the Crossrail depot to the network. This included the electrification of Paddington’s Platform 2, the final platform to receive its OLE.

In addition, all of the platform extensions were completed, with the exception of Ealing Broadway’s Platform 1, in preparation for the launch of TfL Rail services in May.

Fourway installed more than 100 cameras for the new Crossrail Driver-Only Operation (DOO) system in conjunction with stations contractor Vinci.

Piled foundations for the new passenger footbridge and station building at Acton Main Line and Hayes & Harlington were completed, and the final high voltage cable pull at Westbourne Park was undertaken. This completes the physical traction power works required to provide power from the Kensal Green feeder station to the Crossrail tunnels. This will be the secondary (back-up) feed for the tunnels.

The portal outside Paddington is the final of the three portals to be connected to the Crossrail tunnels and puts the project on track to meet Key Output 2 in June 2018, when all of the infrastructure between the three tunnel portals and surface railway at Plumstead, Pudding Mill Lane and Westbourne Park must be complete.

Passengers in the Thames Valley start using the connection in Dec 2019 and will be able to catch new Elizabeth line trains all the way through central London without having to change onto the Underground at Paddington, making it quicker and easier to get to a range of destinations across London and the South East.


Crossrail West milestones

  • Late 2012 – preplanning commences for December 2017 signalling data upgrade at Paddington.
  • Summer 2014 – Paddington data upgrade specification, programme and methodology in place.
  • September 2015 – work starts on rewriting data for Old Oak and Paddington areas.
  • December 2015 – commissioning of major upgrades and remodelling of Heathrow to Paddington.
  • Easter 2016 – commissioning of major upgrades at Maidenhead Station.
  • November 2016 – new high resolution IECC Scalable work stations provided by Resonate at the Thames Valley Signalling Centre.
  • December 2016 – commissioning of largest multidisciplinary railway upgrade across Reading to Paddington area and introduction of new ETCS system for the first time. This stage established the foundation and interlocking interfaces for December 2017 data changes.
  • April 2017 – ETCS train-protection signalling system operational between Paddington and Heathrow. Testing with Network Rail Class 313 ETCS fitted unit commenced.
  • June 2017 – first Elizabeth line train runs in service on the Liverpool Street to Shenfield route (Crossrail East).
  • December 2017 – commissioning of final stage of Crossrail West signalling, introducing brand new signalling data for the Old Oak and Paddington area.
  • January 2018 – first stage in enabling HS2 construction works.
  • May 2018 – Elizabeth line trains scheduled to commence between Paddington and Heathrow.
  • September 2018 – all Network Rail rail infrastructure for Crossrail complete.
  • December 2018 – passenger services commence from Paddington to Abbey Wood, using the central section tunnels.
  • December 2019 – Elizabeth line fully open for 24 trains per hour. Services commence to Maidenhead, Reading and through the tunnels to Shenfield.

This article was written by Paul Darlington.


Read more: London Bridge – The Final Countdown, Christmas 2017