Cost of Docklands road tops 340m pounds: Geological difficulty and noise controls have pushed the tunnel bill way over estimate. Christian Wolmar reports

A fleet of black taxis yesterday became the first vehicles to drive on the most expensive stretch of road in Britain, a 1.1-mile tunnel linking Docklands with the rest of London.

The construction of the Limehouse Link cost about pounds 260m but with pounds 15m for the land and about extra pounds 70m for rehousing 600 families whose three blocks had to be demolished to make way for the road, the eventual bill will be about pounds 345m.

The run through by the taxis was part of a publicity campaign by the London Docklands Development Corporation to highlight the near completion of the road, which the corporation feels is as important to the regeneration of Docklands as the Jubilee Line tube extension, the fate of which is in the balance.

The corporation's chief engineer, Bob Blyth, confidently predicts the link will open on schedule on 17 May 1993. It will then complete a through route of seven miles called the Docklands Highways which will be an alternative to the overstretched A13 for traffic travelling in and out of the City, although Mr Blyth says: 'About 70 per cent of the traffic will be for journeys starting or ending in Docklands.'

The link dips steeply from The Highway underneath Limehouse Basin, towards the Isle of Dogs which it reaches north of Canary Wharf. Work on the twin tunnels started in November 1989.

The high cost is a result of the difficult terrain of the site for road building and the choice of a route that minimised community disruption and maximised the potential for development on top of the tunnel, which is capable of withstanding buildings of up to six floors. A straighter alignment would have reduced the length and therefore the construction cost by a third but it would have involved more demolition including a school. Using the 'cut and cover' way of building the road, which reduced the levels of noise and dust, also increased the price.

Mr Blyth said: 'It is no coincidence that there are no tube lines in this area. The geology is very difficult, with sand and gravel and a shifting water table caused by the proximity to the Thames. It was never going to be a cheap job.'

The original contract price of the road was pounds 171m but this increased to pounds 260m with inflation, contingencies and a series of claims by the contractors because of delays in handing over some land, unforeseen problems with soil conditions and stricter than expected noise abatement requirements from Tower Hamlets Council. Rather than allow these claims to delay completion, the corporation agreed to pay more to guarantee that the road would open on schedule.

At one time, construction of the road was held up for three days by Tower Hamlets' environmental health department because noise was affecting a new housing development on Limehouse Basin.

Mr Blyth said: 'We had to double-glaze the houses. We had never expected that those flats would start selling before we had completed the work but for some reason they did and the residents complained.' Piling had to be restricted, sometimes to just 35 minutes per day. Unusually, all future claims by the contractor have been bought out by the corporation, which ensures the final price will be between pounds 257m and pounds 263m.

The corporation argues that the Limehouse Link is not really the most expensive road built in Britain. It claims that on a cost per metre basis, and allowing for inflation, the pounds 5.1m Hyde Park underpass project in the early Sixties was slightly more expensive.

The cost of the link has been met by the Department of the Environment, which is responsible for the regeneration of Docklands and therefore is additional to the Department of Transport's spending of just over pounds 2bn this year. The average price of new road was about pounds 1.76m per lane-mile in 1990/91, the last year for which figures were available, but tunnels are much more expensive.

Outside London, a typical scheme, such as the 6.6-mile stage of the western-northern relief road in Manchester cost pounds 85.9m or pounds 13m per mile, and the infamous Twyford Down extension in Hampshire will cost just over pounds 50m for 3.7 miles of six-lane motorway. In London, a scheme to add a carriageway and build an underpass on the North Circular Road at the Chingford road junction, which covers just over a mile and a half, will cost pounds 140m.

(Photograph omitted)