Traffic chaos after two fatal crashes on the M4 has prompted the Welsh Assembly Government to put a date on the possible opening of a relief road.
On Monday, there was heavy congestion in the Newport area after the motorway was closed for eight hours following a head-on collision in which five died.
Transport Minister Ieuan Wyn Jones said the road would run from Magor to Castleton, and could open in 2013.
But environmentalists said they would oppose the plans on several grounds.
Over 100,000 vehicles a day travel on the M4 in the Newport area.
Plans for a relief road have been on the drawing board for 15 years.
Speaking in the Senedd on Wednesday, the deputy first minister told AMs that two recent crashes had caused grid lock to the south Wales corridor.
Last month, there were 10-mile tailbacks during rush hour when the motorway was closed after a lorry driver died in a crash at Tredegar Park.
Mr Jones told BBC Wales: "There will be a business case looked at this year, and if that is a robust business case then there's a possibility of a business inquiry in 2009 then hopefully we could start the work in 2010, with an anticipated completion date of 2013."
The relief road would run for 14 miles (22.5km) from Magor to Castleton.
Part of it could cross the Gwent Levels, an area renowned for wildlife.
Neil Crumpton, from Friends of the Earth Cymru, said they would oppose the plans even if the road was built across a brownfield site.
He said: "It's not a good example to set internationally in terms of climate protection or conservation protection."
Following the crash on Monday, Patrick Long from the Newport and Gwent Chamber of Commerce, Enterprise and Industry said the economy of the area had been affected by the traffic congestion.
He said: "It's [the relief road] been spoken about before.
"Certainly we'd like to see it but there's nothing definite come out yet, and it seems to be all talk at the moment."