Drivers face long delays after a section of the M4 motorway was closed due to a crash.
Traffic was temporarily held between J17 for Chippenham and J18 for Bath and Tormarton.
Emergency services and traffic officers are on the scene where a vehicle has overturned.
Motorists are being warned of delays of 30 minutes or more with congestion stretching one mile and traffic continuing to build in the area.
National Highways South West is warning people to "allow extra time" for their journeys.