Drivers on the M4 have been facing long delays amid heavy Good Friday travel after a gas tanker fire closed the motorway in both directions.
The lorry caught fire on the eastbound carriageway of the motorway between Junction 18 Bath to Junction 17 Chippenham.
An estimated 6.6 million people in the UK were believed to be planning a trip involving an overnight stay over the Easter weekend.
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.