Motorists across England will be allowed to drive on motorway hard shoulders in a bid to ease congestion on the busiest roads, the transport secretary announced today.
Following a successful trial in Birmingham, Ruth Kelly confirmed the government is now looking at which other motorways could benefit from extra lane capacity.
Critics claim the policy risks drivers' safety, as it potentially impedes emergency services' access to the motorway.
Liberal Democrat transport spokesman Norman Baker said: "It confuses the purpose of a hard shoulder, which we have been told for decades exists for safety reasons. Now it will become partly pay-if-you-want, partly share-if-you-want and partly for emergency vehicles."
But Ms Kelly maintained the trial on the M4 around Birmingham had shown safety is not compromised by opening the hard shoulder to regular traffic, with the motorway closely monitored by CCTV.
Specific sites have not yet been chosen, but the M1, M6 and M62 are likely to benefit.
The hard shoulder could also be opened on parts of the M27 around Southampton, M4/M5 near Bristol and parts of the M23, M20, M3 and M4 connecting the M25.
Ms Kelly said the scheme would bring "real improvements" for drivers affected by congested roads and would be a "win-win" for motorists.
But she accepted criticisms that the extra capacity must be managed effectively to prevent it simply filling up.
"There is a compelling argument for car-share or charged lanes, which have been used for some time in the US," she said.
Ms Kelly continued: "In order to get maximum benefit, access to car-share lanes is limited to vehicles carrying passengers, or single drivers willing to pay a toll. I intend to explore the possibility for taking a similar approach here where we are adding new capacity."
The government has also announced extra funding to help towns and cities develop localised congestion schemes, including road pricing and congestion charging.
The Liberal Democrats have dismissed the policy as a "complete dog's dinner".
Mr Baker argued the government should be focusing on introducing a national road pricing scheme which could replace road taxes.
"Instead of investing properly in our public transport system and shifting to fairer and greener taxation, Ruth Kelly is dodging the issue and produced this total mess of a proposal," he said.