The M5 near Bristol southbound has reopened after a car transporter overturned, blocking all three carriageways.
Traffic was diverted off the motorway at Junction 18A and onto the A4 Portway after the accident on Wednesday.
An Avon and Somerset police spokesman confirmed an ambulance had been called as it was thought the driver may have suffered injuries.
One lane was temporarily reopened then closed again, near Junction 20.
A Highways Agency spokesman said the lane had been opened at 1745 GMT to allow through trapped traffic which was stuck between Junctions 18 and 20.
The lane was reclosed 30 minutes later but traffic built up through the rush hour on the A38 and A370 roads south of Bristol.
Then at 1900 GMT another accident on the A370 at Brockley blocked the road. The road had partially reopened by 2115 GMT but traffic was slow moving.
Several drivers called BBC Radio Bristol throughout the evening, reporting very lengthy journey times including three-and-a-half hours from Cribbs Causeway to Cleeve - a distance of about 10 miles.
On Monday the M5 was also closed when a lorry overturned and crossed the central reservation, north of Bristol.
On that occasion the vehicle crashed between junction 15 and 14 at Tytherington and the motorway was shut for several hours.