One driver, who did not want to be named, said he was stuck at the front of the queue for four hours before being turned around by police.
“People were getting out of their cars and walking their dogs. We’ve been turned around and are now back past the Gordano turn off,” he said.
Abbi King, from Bridgwater in Somerset, left the town at 12:30 GMT to drive to Northampton and is still stuck in traffic.
“We got past the Clevedon turn-off but there were no signs telling us to leave the motorway before that. The signs were still saying 50mph.
“It was only when I looked at my phone to see where we were that I saw all the red lines on the map,” she said.