London’s Crossrail scheme, like so many other major infrastructure projects around the world, has been under discussion for decades. Following several failed attempts to get the green light for the project during the 1980s and 1990s, it was eventually put to one side and safeguarded.

However, due to the continued overcrowding and congestion of the London Underground network, the government was prompted to once again examine the feasibility of the rail link. Hence Cross London Rail Links Ltd (CLRL) was formed, two years ago, as a partnership between the Strategic Rail Authority (SRA) and Transport for London (TfL), in order to define, develop and promote the scheme.

CLRL is currently developing the plans for the high capacity regional metro, its aims are to ensure that the system’s alignment is acceptable to all, that it is constructable, and capable of increasing passenger capacity into and within the central area of London.

It is intended to prepare a hybrid Bill to submit to the UK Parliament in November 2004. It is hoped that Royal Assent will be received in December 2006, with construction starting soon afterwards.

Route alignment

Crossrail forms two staggered projects: Crossrail 1 and Crossrail 2. The preferred route for Crossrail Line 1 (Figure 1) runs from Kingston and Heathrow in the West through to Ebbsfleet and Shenfield in the East. Crossrail Line 2 is a scheme to link south-west London with north-east London, which will be addressed later.

The central section of the Crossrail alignment comprises the largest tunnelling project ever envisaged under central London, with up to 24km of bored tunnels (shown in red).

The speakers from CLRL explained that the selection of the alignment through the central area has been a careful process, to avoid clashing with the vast amounts of pre-existing underground infrastructure and piled foundations under the city.

Central section

The depth of the twin-tube 6m internal diameter running tunnels will be similar to those of London Underground’s Central Line, at 20m to 30m deep. A total of twenty tunnel drives are proposed, and TBMs will be launched in pairs from the eastern and western portals, and from an intermediate shaft near Liverpool Street.

Two machines will also be launched from the Isle of Dogs station box. According to the preliminary construction schedule, the stations’ primary lining would be complete before the TBMs arrive, so that they can be moved along the platform length before being relaunched on the next section.

Open-faced machines will be used in the western part of the alignment, where the tunnels will be constructed mainly in London Clay, and employ an expanded reinforced concrete lining. In the east, dual-mode EPBMs, with a reinforced concrete bolted lining, are likely to be used, where the geology is more challenging; through the Lambeth Group and the underlying Thanet Sands.

The basic design for stations along the central route include a 245m long platform and two ticket halls, one situated at either end of the platform. There will be no standard method of construction for all the stations, each will be addressed individually. Some are currently planned as box constructions, with others adopting sprayed concrete linings.

Project funding

The total cost for the project, including contingencies, is estimated at £10bn (US$14.5bn) at 2002 prices. It would be possible to phase the work to spread the financial burden but this would reduce the benefit-cost ratio. This is because the central section would not be able to deliver the full benefits until the outer sections have been completed.

Whilst 75% to 80% of the total cost is for the construction of the central section beneath London, there are major benefits for the areas at the outer ends of the links. By providing extra capacity the scheme will decrease congestion on other routes into the capital and assist in the regeneration of several areas by improving accessibility.

Two five-car units will be linked to initially form 200m long ten-car trains, expanding to 12-car trains, and with up to 24 trains per hour in each direction at peak time the system will be able to handle up to 50,000 passengers per hour.

Design and safety issues

It is intended to use proven technology for both constructing and running the railway in order to provide certainty that the project can be delivered as planned. Much of the system’s design is at an early stage but much work has been done on the fire loadings for the design.

The design fire loading is 7MW, but this has been reconsidered due to the connection to Heathrow that will increase the number of passengers with large amounts of luggage. The as the fuel provided by passengers luggage is a most serious consideration in assessing fire loading.

All stretches between emergency shafts or stations are less than 1,000m and a 1m wide evacuation walkway will be provided at train floor level throughout the tunnels. A further walkway for intervention access will be provided at track level.

The way forward

Given the importance and cost of the project, the government is now entering an evaluation period to assess the CLRL proposals. Once the evaluation is complete and a comprehensive funding package agreed, the government intends to promote the Bill, which will seek powers for the project’s go-ahead.

Related Files
Fig 1 – Map of London, showing the proposed Crossrail route alignment