Drivers have been warned not to break the law by going the wrong way on the M5 to avoid long queues.
Highways England said it had seen "traffic driving the wrong way into Avonmouth" following an accident northbound between J18 and J17 earlier.
It said in a tweet: "This is illegal. You are putting yourselves, our roadworkers and other road users at great risk."
Traffic that was being held has now been released, a spokesperson said.