Plans for a 14-mile road to ease congestion on the M4 around Newport in south Wales have been announced.
The road, between junctions 23 and 29, is expected to cost at least £350m and is likely to be tolled, but faces opposition from environmental groups.
Economic Transport Minister Andrew Davies said work on the road, through the former Llanwern steelmaking site, could start in the next five years.
It is part of the assembly government's 15-year transport plan.
Setting out the assembly government's transport priorities for the next 15 years, Mr Davies also announced plans for a twice-daily air link between Swansea and Cardiff and RAF Valley on Anglesey.
The service will start in 2006 "subject to a number of consents and approvals", said Mr Davies.
Several new road schemes have also been announced - the most controversial of which was a relief road for the M4 at Newport, around the traffic blackspot known as Brynglas Tunnels.
The 14-mile section would run between Magor and Castleton, with work scheduled to start within the next five years.
Mr Davies said: "The proposed route, through the former Llanwern steelmaking site, will deliver the lowest possible long-term environmental impact, consistent with our economic and social objectives."
Mike Farmer, of the Road Haulage Association, said he was "delighted" plans for a relief road had been announced but said it was "about time, too".
"We have a major route into Wales, which is not fulfilling the purpose of getting traffic in and out of Wales, and we need something to be done."
But Mr Farmer said he was "slightly less ecstatic" at the prospect of the road being tolled, saying it added to the cost for freight travel.
"Paying on the bridge then a toll road is almost rubbing salt into the wound", he said.
The route of the new M4, alongside the existing motorway
Environmental campaigners oppose the building of the relief road as part of it will cross the Gwent Levels - an area of unspoiled wetlands.
It features several Sites of Special Scientific Interest and provides habitat for otters, birds, and rare plants and insects.
Friends of the Earth Cymru and Gwent Wildlife Trust have both questioned the economic benefits of a new road.
They believe money should be spent on helping people find alternative forms of transport.
Neil Crumpton, of Friends of the Earth Cymru, said: "The new road would create a massive increase in traffic and car-dependency in south Wales when there could be more mixed spending between road and rail.
"That could move the lorries without increasing long-distance commuting, the shopping trips and the leisure trips that would undoubtedly be created, which would put congestion further along the network in Cardiff and the Valleys."
Port Talbot distributor £95m
Rhondda Fach relief road £69m
Bargoed by-pass £27m
A497 in Gwynedd £17m
Ammanford distributor £7m
Swansea park-and-ride £4m
Mr Crumpton said his organisation preferred an option of widening the M4 around Newport to three lanes, including the Brynglas Tunnels.
He estimated a £200m saving could be made to be spent on improving public transport.
But road traffic expert Dr Anthony Beresford, of Cardiff Business School, told BBC Wales a toll road around Newport would be "a white elephant for 20 hours a day".
"The feature of the area here is the flow is very tidal. You get peak travel which is bunching into the two hours in the morning and the two hours in the evening.
"Outside those four hours I think people will find the toll road very unattractive becaue the original route around Newport will still be quite good," said Dr Beresford.
"I think we will have a toll road that will be a white elephant for 20 hours a day."
Tuesday's announcement also set out further spending to improve road links throughout Wales, including the A55, A550 and A495 in north east Wales to create better access to Holyhead.
10 million drivers used the M6 toll in its first eight months
Further work on the A465 Heads of the Valleys road will be brought forward, and bypasses will be built on the A40 west of St Clears in Carmarthenshire.
Spending was also announced for the Rhondda Fach relief road, the Ceredigion link road, the Port Talbot distributor road and the A497 in Gwynedd.
Plaid Cymru transport spokeswoman Janet Davies AM called the M4 toll road a short term solution.
She said: "Andrew Davies himself said only last year that evidence shows that building more or bigger roads eventually increases the usage of the roads. Building the M4 relief road will only store up problems for the future."
"Instead we need a national transport network, which must be environmentally sustainable. "
Liberal Democrats transport spokesman Jenny Randerson AM said more information was needed as to whether the M4 toll road was necessary.
"These proposals must not mean a double tax on Wales," she said.
"Paying twice to get in will encourage no-one to come across the Severn Bridge, either for business or for pleasure.
"There are also questions to be answered about what happens further along the M4. The risk is that by relieving congestion at the Brynglas Tunnels, the jams will just move two or three junctions along."
Conservative AM for South Wales East William Graham said he had been campaigning for a M4 relief road for a number of years.
He said: "I am saddened that the road network will not be ready in time for the Ryder Cup. This is a unique opportunity, with world-wide attention focussed upon Newport, to generate investment and economic growth."
A M4 toll road would follow in the wake of the M6 toll motorway north of Birmingham, which opened a year ago this week.
The RAC Foundation said the experience of the 27-mile route had been been "overwhelmingly positive", with less congestion on the old M6 and also a significant reduction in journey times.
But the Foundation said that while it has been popular with car drivers - who pay £3 - lorry operators have been reluctant to pay the tolls.
Lorry tolls have now been cut from £10 to £6 -- but the Foundation said that even this appears to have made little difference.