Motorists will be allowed to drive on the hard shoulder of motorways during busy times, Transport Secretary Ruth Kelly has said.
Drivers move across to use the hard shoulder of the M42
The "extra lane" scheme will be rolled out on the M6 near Birmingham following a successful trial on the nearby M42.
It aims to ease rush-hour bottlenecks, and could be extended to other motorways in the future.
Sensors detect traffic build-up, which trigger signs asking drivers to slow down and spread out.
During the trial, a 50mph speed limit was imposed while the "extra lanes" were in operation.
The report on the M42 trial has shown a reduction in journey times north by up to 25% and a drop in the average accident rate from 5.2 per month to 1.5.
The report also found there had been a drop in pollution around the M42, with fuel consumption down by 4% and vehicle emissions down by 10%.
But Tony Bosworth, from Friends of the Earth (FoE), disagreed there were environmental benefits: "It's effectively motorway widening on the cheap.
"We believe it's simply going to encourage more drivers and cause an increase in carbon dioxide."
Nowhere to stop
Ms Kelly said "extra lanes" would be introduced on the M6 between junctions 4 and 5 near the Birmingham NEC arena, and junctions 8 and 10A between the M5 link and the M54 motorway junction.
The expansion will cost £150m and is due to be completed by 2011.
The government is also launching a feasibility study to consider including the M1, M25, M4 and M20 in the future.
The Royal Society for the Prevention of Accidents (RoSPA) said it had reservations about the changes when they were first introduced on the M42, near Birmingham.
Kevin Clinton, from RoSPA, said: "We were concerned that if the hard shoulder is used as a running lane, if there was a major crash it may take the emergency services longer to get there.
"Or when someone breaks down, they may not be able to get their vehicle out of the running lane."
But Graham Bowskill, from the Highways Agency, told the BBC that the hard shoulder would not be opened to traffic if there was a broken down vehicle on it.
"We do actually have cameras that are constantly monitoring to see whether there are any parked vehicles," Mr Bowskill said.
"At the same time, we've built additional safety features into the scheme.
"There are emergency refuges approximately every 500 metres along this section of motorway and that's where people can park safely if they break down."
Ms Kelly said the M42 trial had been "really impressive", adding: "People get from their front door to their place of work in a much more reliable time frame.
"The safety fears that some people have haven't materialised at all and, not only that, it's good for the economy and the environment too."
Rebecca Lush Blum, from the Campaign for Better Transport, said the success of the M42 trial in cutting congestion showed motorway widening schemes were "very hard to justify".
"But managing traffic is not enough - we need to reduce it," she said.
"In allowing for increased traffic levels, active traffic management ignores the real, pressing problem of too much traffic and rising C02 levels."
Paul Watters, head of roads policy at the AA, said the M42 trial appeared to be working well although it had so far not been tested by a major incident.
"It's a much more comfortable experience [for drivers]. They travel slower, but get to their journey destination quicker," he said.
Mr Watters said his organisation backed the expansion if it was done "for the right reasons and in the right manner".
"We wouldn't support just taking the hard shoulder away."
And he added: "There is a risk that rolling it out nationally there could be skimping which would be counter-productive and even dangerous."
The use of variable speed limits will be introduced on the M40 between junctions 16 and 3A and where it joins the M42 south of Birmingham.
Variable speed limits currently in operation on the M42 will be extended north to junction 9.
Geoff Dossetter, from the Freight Transport Association, said lorry drivers wanted to see motorways widened and new roads built, but the hard shoulder scheme was "a sensible way of making the most of the roads network that we already have".
"It has made an important contribution to improving journey time reliability for commercial vehicle operators," Mr Dossetter added.
"Replicating the scheme elsewhere - and quickly - clearly makes sense."
ACTIVE TRAFFIC MANAGEMENT SYSTEM
1 Computer-controlled sensors in road detect increased traffic and feed data back to control centre
2 Mandatory speed limit imposed to protect queuing traffic and smooth flows
3 Information signs warn or advise drivers of hazards/lane use
4 Overhead signal indicates when hard shoulder is open to traffic
5 Hard shoulder to be used for travel between consecutive junctions
6 Broken-down vehicles use emergency refuge areas to ensure hard shoulder remains clear
7 Controllers use CCTV and sensors to monitor hard shoulder for obstructions/debris and can manually override ATM system
Other safety improvements include highly visible roadside emergency phones (8) located behind safety barriers, and lighting (9) at more frequent intervals along entire stretch of motorway