The plan involves building a series of double-decker tunnels 40 to 50 metres below ground from the edge of London into the centre, where massive car parks would accommodate the vehicles and people would take lifts to the surface or directly onto public transport.
As the tunnels would allow motorists to bypass London's inner suburbs, the tunnels would be free-flowing, enabling very rapid journeys into the centre from where people could walk or take public transport. It is estimated that traffic on key routes could be reduced by a fifth.
The idea is the brainchild of an Imperial College Research Fellow, Gabriel Khoury, who first drew up the plans five years ago and has now received support from a number of major companies, including British Telecom, four engineering consultants and three contractors.
So far preliminary work has cost pounds 600,000 and the team has obtained government support for part of the second stage of studies which will cost another pounds 600,000.
Only one section of the tunnels, a route from the end of the M4 motorway in west London to Blackfriars bridge, has been fully costed at an estimated pounds 2.3bn including financing costs. Because the tunnels would be so deep under London, Dr Khoury says they would not affect the foundations or other existing services such as the utilities and the Tube system.
Dr Khoury says that the main benefit, apart from reducing journey times, would be in regenerating the inner city: "The idea is not to allow a lot of extra traffic into London, but to improve the environment which is increasingly important in determining where companies locate their offices."
Finance would be obtained from the private sector, with some government support, and the roads, called London Expressways, would be tolled. Preliminary calculations suggest that tolls of around 40p-70p per mile would be needed to finance the tunnels, depending on the level of public-sector support.
Government support would be justified on the basis of the wider environmental and transport benefits from the scheme.
Dr Khoury dismissed the suggestion that the whole idea was merely a harebrained scheme emanating from the lofty towers of academe: "This plan could be realised within the early years of the next decade. In Britain we are behind in our thinking on this compared with other countries. There is no insuperable barrier."
He said that in Boston, some elevated motorways had already been replaced by underground roads and the consequent benefits to the environment had been tremendous. He said: "In Boston they want to put 18 per cent of the strategic traffic underground." He cited similar plans in Paris, Tokyo, Singapore and Stockholm.
The transport minister Steven Norris said yesterday that he was interested in the idea as complementary to rail schemes such as Crossrail and the Chelsea to Hackney Underground line. He said: "I am prepared to take this scheme forward step by step, but if it proves unworkable we will not support it. We are prepared to make a modest contribution to the research costs."
t Green Transport Week, a week-long series of events around the country, was launched in Leeds yesterday by the Secretary of State for Transport, Sir George Young.
The week, the fourth time the event has been organised by the Environmental Transport Association, is an attempt to draw attention to the impact that transport has on the environment and demonstrate ways of reducing car dependence. Churchgoers will be asked to give their cars a day of rest on Sunday next week and churches around Britain will be urged to "operate in a more environmentally responsible way". Friends of the Earth is running a "Cars cost the earth" campaign, several towns are running car-free days and children will be encourage to walk to school.
The National Trust is creating a working group on transport which will try to reduce car use to its properties by 40 per cent and will be opening Priory Park, in Bath, where no car park provision is being made.