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Crossing the river from a different angle

While the Jubilee Line extension misses deadlines and runs vastly over budget, a more modest railway extension, which also improves public transport in South and East London and provides a new river crossing, is within budget and looks set to open on time.

 

The 4.2km Docklands Light Railway extension from the Isle of Dogs to Greenwich and Lewisham, due to open in spring 2000, is costing only £200 million compared with a likely £3 billion outturn for the JLE. Though a much more limited scheme, it promises to deliver valuable benefits to local people, commuters and - not least - the DLR itself.

 

The DLR expects to lose passengers to the Jubilee Line, but the cross-Thames extension allows it to recoup by attracting peop le travell ing to work at Canary Wharf and elsewhere, many of whom at present reluctantly drive through the congestiondogged Blackwall Tunnel. The extension leaves the existing DLR tracks just north of Mudchute, descending from the existing embankment to a new Mudchute station in a cutting. Then it runs in a cut-and-cover tunnel under Millwall Park to a new underground Island Gardens station just north of the existing terminus. From there twin bored tunnels take it to a new underground station, Cutty Sark, in Greenwich town centre; then on to a point 100m east of Greenwich Railtrack station, under which it rises on a 6 per cent gradient to its own, shorter platforms alongside.

 

Leaving Greenwich, a viaduct takes the extension, crossing the serpentine Deptford Creek no fewer than five times, to an elevated station straddling the A2 trunk road at Deptford Broadway. Descending from the viaduct, it runs for a short stretch in the existing concrete channel of the River Ravensbourne; while - reversing 1960s canalisation - the river meanders through a relandscaped and extended Brookmill Park.

 

The extension calls at one more station, Elverson Road, before following the Ravensbourne to Lewisham, where it tunnels under Connex’s Bexleyheath branch platforms and tracks to arrive at its terminus between the existing rail and bus stations. In a pioneering private finance venture which preceded the official PFI, a consortium called CGL (City, Greenwich, Lewisham) won a 24-year concession to finance, build and maintain the extension. Payments depend partly on CGL’s management, partly on passengers carried. CGL, which comprises original DLR builders Mowlem with Hyder, London Electricity, and Mitsui, then appointed LRG contractors (Mowlem + Mitsui-Nishimatsu) to construct the line.

 

Work started in October 1996; the line is due to open early in 2000. With luck, it might even open at the end of 1999.

 

Near r ight, top : model of Lewisham DLR station, designed like all stations on the line by W S Atkins Consultants. After passing under the Bexleyheath Line embankment, the tracks emerge from under the DLR station’s upper concourse (top left of picture). The island platform continues under the canopy of the lower concourse (bottom right) which connects directly with bus stops, but unfortunately does not shelter them.

 

Far right, top : model of the new Mudchute station, where the extension emerges from the tunnel. East Ferry Road has been diverted to make way for this.

 

Near right, middle : model of the new Island Gardens station, north across Manchester Road from the existing elevated station. The concourse (near right) has vents from the tunnel under the Thames on its roof; the platforms lie under a reinstated section of Millwall Park; top left are vents from the cut-and-cover tunnel to Mudchute. Like Cutty Sark, the new Island Gardens is a ‘section 12’ station: because it is underground, both platforms and concourse must be staffed.

 

Far right, middle : south of Elverson Road station, the tracks will run in the canalised bed of the Ravensbourne (right of picture) while the river takes a new route (left of picture).

 

DRAWINGS

 

Top: elevation of Deptford Bridge station which, after the viaduct has squeezed through and over Lewisham College’s Deptford campus, straddles the busy A2 trunk road.

 

Near r ight : cross-section of Deptford Bridge station, showing canopies over platforms.

 

Far right : canopy at Greenwich DLR station, which is alongside North Kent Line platforms. Variants of this canopy design by W S Atkins Consultants appear at other surface stations on the extension.

 

Far left, top: a photo taken last December shows the 60mlong concrete box which accommodates the three-storey underground Cutty Sark station, the cost of which is being met by grants from local organisations and commercial development on the surface. A controversial scheme, backed by English Partnerships but opposed by EH and local conservationists, includes a crescent-shaped open-air shopping street with DLR lifts and escalators opening into it, and entrances into Creek Road and Greenwich Church Street.

 

Far left, bottom: from Greenwich Station to Deptford Bridge the railway is carried on a cantilevered viaduct with 22 spans of prestressed post-tensioned in-situ concrete.

 

The blue steelwork is temporary bracing.

 

Middle: in contrast to the high-tech methods used under the Thames, the short tunnel under platforms 3 and 4 at Railtrack’s Lewisham station comprises an open-ended concrete box in what was Tesco’s overflow car park (top right in picture) which was then jacked through the embankment behind a tunnelling frame through which workers excavated the ground metre by metre: the method Brunel used in the first Thames tunnel at Rotherhithe. The station site is in the foreground.

 

Near left: test bores to the foundations of the listed Greenwich Railtrack station suggested them to be not as deep as original drawings indicated, so LRG provide extra support during excavation of the cut-and-cover tunnel alongside the 1840 building. The tracks rise on a 4.7 per cent gradient in a concrete trough (left of picture) to DLR platforms alongside Railtrack’s.

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