The A3 at Tolworth could be moved underground to free up land for development, the Mayor of London has said.

Boris Johnson said sinking the key traffic artery into a tunnel would also improve the environment at the junction, currently one of the borough's pollution hotspots.

He made the announcement during a visit to Boston, Massachussetts, where a major interstate highway was sunk underground in a years-long project called the Big Dig.

City Hall claimed that decking over the A3 would reduce "severance" - the separation of communities by transport infrastructure and traffic - and provide new land for homes.

Mr Johnson 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."

Mr Johnson's press team could not say how the scheme would reduce pollution, but said the Boston project had done so.

A concept drawing shows the proposed tunnel would extend from the roundabout at Tolworth Tower to beyond Princes Avenue to the west.

Princes Avenue appears to continue across the A3 towards the train line, and into the former government land owned by Tesco, itself subject to major redevelopment proposals.

A smaller road would be built on top of the tunnel, according to the image.

Tolworth and Hook Rise councillor Vicki Harris said it was difficult to analyse the "airy-fairy" proposals at such an early stage, but questioned how drivers would leave the A3 at the Tolworth roundabout if it was decked over.

Green parliamentary candidate Clare Keogh said: "It could potentially address the problem of pollution. It would be worth the investment if the issues in the area are considered properly."

But visions of a transformed Tolworth extend beyond the A3.

Ms Keogh said the Greens backed the creation of a community garden along the Broadway, while council leader Kevin Davis said he believed taking Broadway traffic underground could free up even more land.

He added: "There are three places in Kingston where I think an opportunity like this could be explored, Kington town centre, replacing the current relief road, Tolworth, under the Broadway to the A3 and at Hook on the A243 to Malden Rushett."

Plans to move part of Kingston town centre's one way system underground were considered during the council's mini-Holland cycle scheme bid, but rejected over the cost, said to be in the region of £50m.

Surrey Comet:

This view will disappear in the vision set out by the Mayor of London

Labour candidate Lee Godfrey said: "I would be concerned about potential costs and disruption to local residents while the tunnel was being built, but as long as these issues are addressed and local residents are fully consulted, I think this is an idea worth exploring."

Conservative candidate James Berry said: "If plans for the space created on top of the A3 included community facilities and affordable housing, the project would be a very positive step."

The Tolworth junction, currently a traffic hotspot and easily congested, is one of five locations across the capital which could be sunk into an underground tunnel.

The others are the A4 in Hammersmith, the A13 in Barking Riverside, the A316 at Chalkers Corner and the A406 in New Southgate.

Transport for London will draw up more detailed plans, including around funding, with Kingston Council before reporting back to Mr Johnson in May.

The Big Dig saw I-93, an elevated highway running through the heart of Boston, replaced by a tunnel and two new bridges.

The Boston Globe reported the scheme freed up 300 acres of land and reduced "horrific" traffic jams - and the associated pollution.

But the final bill, including interest, will come to some $24bn, the newspaper said, instead of the $12bn to $14bn that was envisaged.