New roads needed in the South East of England could create "another M25", an environmental group has warned.
Transport 2000 says the M25 "generated car-dependent sprawl"
Transport 2000 says the roads could lead to a new orbital road outside the M25 - and turn the region into "the Los Angeles of Europe".
New roads are likely to be built to cope with expanded or new airports and thousands of new homes set to be built.
But Transport 2000 says the new roads would encourage even more housing, transport, traffic and roads.
'Chill down the spine'
The group's director Stephen Joseph said: "This is not just an environmentalist's bad dream but a real possibility that should send a chill down the spine of all those who live in this corner of England."
The South East is stumbling towards a nightmare future of chronic overheating and over-development
Report author Jonathan Bray
The report, published on Friday, says there could be a third more traffic on the South East's roads by 2016.
Earlier this year the government announced plans to build hundreds of thousands of new homes in Ashford in Kent, the Thames Gateway, Milton Keynes and the London-Stansted-Cambridge corridor.
New roads around the housing would be essential to the scheme, set to be completed by 2031.
And the government is due to announce later this year which scheme it prefers to cope with the growth of air travel in the south, with expansion of Gatwick or Stansted or a new airport at Cliffe in Kent under consideration.
'Future of concrete and tyres'
Transport 2000 says any of the schemes would bring a doubling of air travel by 2020, with raised passenger numbers making new or bigger roads around the airports essential.
The report says Los Angeles-style roads could be on the way
The group also predicts a 45% increase in tonnage through sea ports in the South East by 2016.
The report was written by transport consultant Jonathan Bray.
He said: "As the M25 generated car-dependent sprawl and transformed the region, so an outer M25 would amplify and extend the damage.
"It would also stimulate and facilitate wider plans for huge growth
in ports, airports, traffic and housing.
"Overall, the South East is stumbling towards a nightmare future of chronic overheating and over-development.
"The cumulative impact of the numerous disparate pseudo-strategies for housing and transport will mean a future of concrete and tyres: a future more like Los Angeles than the garden of England."