Tunnel renaissance: Why cities are hiding roads down in the ground

From Dublin to Sydney, there's a worldwide trend for burying roads – and even Boris wants a Hammersmith 'flyunder'. Christopher Beanland digs out the reasons

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In JG Ballard's biting satire Concrete Island, architect Robert Maitland ploughs his Jaguar off the M4 and wakes up trapped within a tangle of slip roads. The novel was published in 1973, when motorways were all the rage. But that dystopian vision of chunky flyovers and tangled roads in the sky is disappearing, as cities around the world are electing to hide roads down in the ground.

Boston's "Big Dig" megaproject took 20 years to put the city's main elevated freeway in a tunnel, and now Seattle is doing exactly the same. Hamburg is also sending its roads underground, and it wants to go even further and get rid of all cars from the centre of the city in 20 years. Meanwhile, Sydney has built a brand new road tunnel right under the centre of town. But it doesn't come cheap – Boston's tunnel was over budget by 200 per cent, coming in at an eye-watering £10bn. Melbourne wanted to spend about the same on a controversial road tunnel of its own, but that idea has recently been dumped. Dublin's Port Tunnel looks like a snip in comparison, at £500m.

In Britain there is a precedent. The famous post-war planner Patrick Abercrombie suggested road tunnels under Bath and London. The inner ring road in Leeds goes underneath the General Infirmary and there's a shopping centre plonked on top of the A1 tunnel through Hatfield. Birmingham has just upgraded its Queensway tunnel, and has aspirations to extend it, turning greedy dual carriageway into subterranean phantom. Boris Johnson has got the tunnelling bug, too. London's City Hall announced plans for road tunnels under Tolworth in south-west London, and Barking. The geriatric Hammersmith (aka Jammersmith) flyover could be replaced by a "flyunder".

"This drive to bury the roads that divide communities throughout London – and create town centres fit for a civilised 21st century – is very exciting," says Allan Baird, the director of Studio B+W, one of the nine architects masterplanning the Hammersmith tunnel.

The architect Nigel Lea, of Conran & Partners, wants to sink the A12 in east London below ground: "Victoria Park is the new 'Central Park' for Londoners and developing over the A12 would tie the new international and cultural quarters at Stratford into the fabric of the city." The zaniest London scheme of all is a £30bn plan to build an entire underground ring road.

Tunnels remove noise and pollution; they give us space. Conspiracy theorists might spy an ulterior motive, though. When the motorways were built above ground in all these cities in the 1950s, land was cheap and urban living was seen as second-best. Now neither is true, and the space freed up for blocks of flats will make a fortune for a lucky few. (If the artists' impressions are to be believed, there will also be attractive new public parks for the rest of us.)

"In principle, tunnels offer the enticing prospect of truly separating motorists from cyclists and pedestrians – a holy grail for many cities and one answer to the problem of air quality and noise above ground," says David Bizley, the RAC's chief engineer. "But the reality might be somewhat different. Is it not the case that in many of our cities, especially London, the sub-surface environment is almost as congested as our roads are above ground?"

Other questions remain: should we be investing in infrastructure for cars instead of railways and cycle lanes? And if you build more roads don't they just fill with more cars? One thing's for sure – when we constructed thrusting elevated roads in the sky, such as London's Westway and Manchester's Mancunian Way, they were an emblem of pride and prestige; a symbol of the car's primacy. Now we're hiding roads under our feet, it seems like we're a bit embarrassed; like we want them out of sight, and out of mind.