Proposals to get more traffic underground also aimed at regenerating areas near major roads and improving air quality

Two major road tunnels across London could significantly ease congestion, the capital’s mayor, Boris Johnson, has said as he unveiled proposals to send more traffic underground..

Transport for London (TfL) could also seek to ease traffic flow more locally with smaller “flyunders” and mini-tunnels.

The mayor said the first tunnel, the Northern Cross City Corridor, could be opened in 20 years and be funded by toll charges.

The 18km tunnel would run from west to east linking the A40 at Park Royal to the A12 at Hackney Wick. A second 25km tunnel could be developed to the south from the A4 in Chiswick to the A13 in Beckton. The tunnels could cut congestion in central London by 20%, Johnson claimed.

TfL planners will now carry out detailed feasibility studies into the two routes, which have superseded Johnson’s previous vision for an orbital tunnel, although that is said to remain an option.

City planners are also examining nine potential sites for smaller tunnels and flyunders, which would move stretches of busy roads underground and create new space on the surface for parks or homes. By removing the physical barrier to pedestrians, the flyunders would be expected to regenerate the surrounding area. Possible locations include parts of the A13 in Barking and the A3 in Tolworth.

With the capital’s population forecast to grow almost 20% to 10.3 million by 2030, Johnson and TfL are also considering revising road charging to manage traffic. Goods traffic in particular could face new restrictions, include bans or higher charges on freight vehicles at certain times of day.

Johnson said: “London is booming and, as our great capital thrives, our ambitions for the veins and arteries that keep our city alive must grow with it.

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“Around eight of every 10 journeys in London are made using our roads – whether by car, taxi, motorbike, bus, cycle, foot or freight – which is why it is vital that we think big. We must deliver long-term solutions that will not just make the most of the space we have for road users but bring environmental and amenity improvements to local areas.”

Johnson said he was proud of the “congestion-busting measures” that had been introduced during his term in office. The mayor’s idea of an ultra-low emission zone is due to be implemented in 2020, but he admitted “we need to go further” to improve air quality and cut traffic.

He added: “By pushing forward strategic initiatives we are outlining today, we will lay the foundation for the next wave of improvements to everyone’s experience of the road network across the city.”

The major road tunnels are based on the strategies pursued in Stockholm and Boston, although the latter’s “Big Dig” proved difficult, costly and controversial. The success of flyunders in transforming parts of cities such as Madrid, where its inner ring road was partially buried, may make the smaller projects more viable. TfL believes a 1.3km tunnel at Barking could create a new neighbourhood of 5,000 homes in a blighted area, and that either tolls or the housing could make the project pay for itself.