A serious crash involving a tanker, a van and several cars has closed the westbound carriageway of the M4 in Cardiff.
The tanker hit the central reservation halfway between junction 32 for Coryton and junction 33, Cardiff West, at about 17:50 GMT on Monday.
The motorway is closed between junctions 32 and 33 and one lane has also been closed on the eastbound carriageway.
There are long queues in both directions and a diversion has been set up at junction 30.
The Welsh Ambulance Service said it sent two rapid rapid response vehicles, one ambulance and a doctor.
An air ambulance cannot be called in due to the weather conditions.
This map shows the section of the M4 that is frequently congested, and that would be bypassed if plans for a 14-mile relief road went ahead.
The Welsh government has long pushed for a relief road in this area. Plans were shelved in 2009 after the projected cost of the project rose to £1 billion.
The Welsh Government have refused to comment on reports that the UK Government will soon announce plans to back a new M4 relief road around Newport.
In a statement they said that they "do not comment on speculation."
Sustrans Cymru - an organisation that promotes greener transport - has condemned the potential M4 Toll as "poor value for money".
A spokesman said that a "more cost effective way to reduce congestion would be to invest in shifting these journeys to public transport."
"The Welsh Government acknowledges that 40% of journeys on this stretch of the M4 are local trips of under 20 miles," he added.
The prospect of a new toll road relieving pressure on the M4 has reportedly been welcomed by motoring groups.
A spokesman for the AA, while welcoming a relief road, said that charging a toll on the road would “double the injury” for drivers as many would already have paid £6.20 to cross the Severn Bridge.
The government is reportedly planning to agree to a new toll road on the M4 in South Wales, but this is part of a multibillion-pound scheme of road upgrades in the UK.
According to the Times, the other upgrades include:
- A1 between Newcastle and Berwick-Upon-Tweed to be converted to a dual carriageway
- Widening of the A47 in Norfolk
- A303 to be turned into a continuous dual-carriageway
It will become the second toll road in Britain - following the M6 in Staffordshire - and will run between junctions 23 and 29 of the M4 to relieve congestion on the outskirts of Newport.
The newspaper reports that the Chancellor will agree to guarantee loans for the building of the M4 relief road, but the devolved Welsh government will meet the cost - expected to be around £830 million.
This cost will be recouped at least partly through tolls. While the price of tolls is not known, the longer M6 Toll currently charges £5.50 for a car and £11 for a lorry on weekdays.