Hammersmith Flyunder? Boris Johnson wants to send London's traffic underground

Days after hosting an awards event where the prize for best conceptual design went to a proposal for cyclists to be sent underground, Mayor of London Boris Johnson has outlined plans for several road tunnels in the capital that would free up space at ground level for people on foot or on bikes.

But with huge costs involved and a leading academic saying five years ago that hugely expensive infrastructure such as urban motorways is a “relic” that belongs to a bygone age, will Mr Johnson’s dreams become reality?

Well, the mayor certainly seems to think so, although he will have vacated City Hall long before any of the five schemes he has outlined come close to seeing the light of day, if they ever do.

For now, he has given the go-ahead for feasibility studies to be conducted on five proposed tunnels, among more than 70 locations identified in the capital that it is believed could benefit from such schemes.

While the word “tunnel” is replaced at times by “fly-under” or “decking,” the purpose in each case is essentially the same – to divert traffic beneath the surface.

The proposed projects are said to be in line with London’s 2050 Infrastructure Plan, and have also been recommended by the mayor’s Roads Task Force.

According to a press release from Mr Johnson’s office, they would be “aimed at reducing congestion, creating new public spaces and encouraging more people to walk and cycle,” and would also “unlock growth and make the capital a more attractive place to live and work.”

He made the announcement during a trip to Boston, Massachusetts, where he saw first-hand how the replacement of the six-lane Central Artery by an eight-lane underground road had helped regenerate parts of the city the elevated road previously ran through, as well as reducing traffic jams.

The five proposed schemes announced today are:

A mini tunnel at the A13 in Barking Riverside – By creating a new tunnel for the A13, a huge amount of land could potentially be opened up for future development whilst reconnecting the Borough of Barking with the new Barking Riverside development, which is the location for just under 11,000 new homes

Decking of the A3 in Tolworth - By decking over the A3, severance would be reduced and the area adjacent to the proposed Crossrail 2 station would be connected with the rest of the Borough, providing additional land for new homes

A fly-under at the A316 at Chalkers Corner - A small fly-under would reduce severance and radically improve facilities for cyclists and pedestrians and remove a major pinch point for traffic along the A316

A fly-under at the A4 in Hammersmith - By replacing the existing viaduct with a new tunnel, the town centre would be reconnected with the River Thames, creating new opportunities for development and open space

Decking or a mini-tunnel at the A406 in New Southgate - By building over this junction on the North Circular, land would be unlocked for new homes and connect the area around the proposed Crossrail 2 station.

Mr Johnson, who says the infrastructure is needed to help London cope with its forecast population growth, said: “Rebuilding some of our complex and aging road network underneath our city would not only provide additional capacity for traffic, but it would also unlock surface space and reduce the impact of noise and pollution.

“I am inspired by what the ambitious people of Boston have achieved here at the Big Dig, both in terms of reducing congestion and how they have dramatically improved the quality of life on the surface.

“In London we face similar challenges on our roads, but this could also be a fantastic opportunity to better shape our city and support economic growth.”

What wasn’t mentioned, however, was the potential cost of installing road tunnels at the locations in question might be – but if the experience of Boston, not to mention projects closer to home in London and elsewhere is anything to go by, it could be eye-watering.

The city’s Central Artery-Tunnel Project – nicknamed locally the Big Dig – is held up as the biggest, and the most complex, road infrastructure project ever carried out in the US. The 3.5-mile road, completed in 2007, ended up costing $20 billion.

That dwarfs the sum spent on what remains the most expensive road tunnelling project carried out in the UK, the Limehouse Link close to Canary Wharf in London’s Docklands, which was on the route of last July’s Tour de France as Stage 3 headed into the heart of the capital.

Opened in 1993 following seven years of construction work, the 1.1 mile tunnel cost £293 million at the time.

For cost per mile it remains far and away the most expensive stretch of road in Britain, with the project made more complicated by the fact that the route had to avoid other tunnels, take the docks and River Thames into account, and also incorporates a junction.

Speaking to BBC News in 2011, Sir Peter Hall, Bartlett professor of planning at University College London, said: "It was almost insane. But Margaret Thatcher would stop at nothing to get the Isle of Dogs developed.”

The same year saw the opening of two other road projects completed at huge cost.

One is the £692 million M74 extension in Glasgow – described by Professor Hall as a “relic” of a time when transport planners viewed urban motorways as the future; the other, the 1.2-mile Hindhead Tunnels that carry the A3 under the Devil’s Punchbowl beauty spot in Surrey and cost £300 million.

The mayor’s 2050 Infrastructure Plan, however, includes two projects that in all likelihood would make their cost look insignificant – an inner orbital ring road, or two cross-city tunnels.

His office says that they “could enable more efficient and reliable vehicle movement,” as well as reducing congestion in the centre of the city by 20 per cent “and free up space on the surface which could support the creation of 170,000 additional jobs.”

With parts of Inner and Central London having some of the lowest levels of car ownership and use anywhere in the country, some will query whether spending what will be vast sums on money on such infrastructure is the best use of public money.

Equally, others would say that it is a price worth paying if it provides subterranean routes that take heavy vehicles off the surface and make the city above more pleasant – and safer – for cyclists and pedestrians alike.