Parks could replace congestion on London's busiest roads if recommendations by a special taskforce set up by the Mayor of London are acted on.
The Roads Task Force report published yesterday recommends large sections of the A406, known as the North and South Circulars be re-routed into tunnels underground while the space on top is reserved for cyclists, pedestrians and in some places, leisure.
On one stretch, near Brent Cross shopping centre, the task force suggests "a flyunder" with a park on top. The South Circular meanwhile should be almost completely buried to make the area more residential.
Other roads such as the A12 and the A4 should also benefit from roofs and tunnels, extra trees and a more attractive public realm, as part of a proposed £30bn investment over two decades.
The report authors think any changes could be subsidised by raising venture capital from new properties whose values would rise as a result of the improvements. Tolls could also be used, especially in new tunnels.
They also recommend an increase of 20mph speed limits across the capital.
Mayor of London, Boris Johnson said he welcomed the report and its "bold approach."
"For this great city to retain its global pre-eminence, it is essential we continue to invest and have the courage and vision to develop and drive forward innovative solutions.
"This is a fantastic contribution and I look forward to working with partners, including those represented on the RTF, in taking many of these ideas forward."
Currently 80 per cent of all trips made by people and 90 per cent of all goods moved in London every day are on roads and population growth in the capital is set to rise by 1.7m to ten million by 2031.
Infrastructure director at London First and a RTF member David Leam, said: "On rail, London is planning for future growth with bold projects like Crossrail 2.
"We now need to be similarly visionary for London's roads. With road congestion in London costing the UK economy £4bn a year, we need a radical new plan to keep London moving, including new road links and tunnels.
"Only in this way can we create the world class public spaces and revitalised high streets that will ensure London remains a globally competitive and attractive city."
The RTF is an independent body set up by Johnson in July 2012 and London boroughs motoring organisations and cycling groups were among those consulted.