The A34 southbound between the A303 and the junction with the M3, is completely backed up this afternoon.
The traffic backs up to the Winnall Roundabout, the cause being the end of Boomtowm Festival which ran over the weekend.
There are currently delays of around 50 minutes, the traffic is not expected to clear until late this evening.
Drivers are advised to avoid the area and take an alternative route.