Traffic had been temporarily stopped as the lane was blocked on the M4 exit slip road.
Three vehicles have been involved in a collision blocking lanes on the roundabout.
Delays are likely with traffic already queuing back.
While police are working to clear the stretch of road between J23 and J24 after the top of a tanker split and kerosene spilt onto the carriageway - we've been hearing from people stuck in the gridlock.
Richard Pennock took this video while stranded in the gridlock for more than 4 hours.
He saw people getting out of their cars and chatting to one another, some he spotted even exchanging numbers.
Max Bristow left his home in Cullompton at 08:30 this morning (6 January) to get on a flight back to university in America from Heathrow.
But after travelling for 30 minutes, he became stuck in traffic for over 3 hours.
Ian Le Sueur sent us these videos showing the slow moving traffic inching along the carriageways.
Delays are expected despite the reopening of the Southbound lanes.
Did you get stuck? Send your photos or videos if safe to do so, to email@example.com
A failure in traffic light systems has caused traffic chaos for people heading home in Bristol.Read the full story ›
A man has died following a serious two-car crash on the A4 Bath road near the Sylvan Way traffic lights in Sea Mills.
The road remains closed in both directions between Hotwells and Shirehampton due to this and a second incident near the Bridge Valley Road. Diversions are in place.
TRAFFIC UPDATE: The A4 Portway remains closed in both directions in Sea Mills, Bristol due to a serious accident between Riverleaze and A4162 Sylvan Way.
The accident happened at around 6:20 this morning.
Plans to ease congestion in Bath have been given early support by the Government.
A new 'park and rail' station in Bathampton - with a large car park - will ease traffic in and out of the east of the city.
Plans also include a road linking the new station to the A36 - bypassing the city.
Bristol Mayor George Ferguson says he wants to see the popular Make Sunday Special scheme extended to other parts of the city. At present part of the city centre is closed to traffic once a month to host entertainment and boost trade
The Alliance of British Drivers say Bristol is the worst city in the UK for motorists.Read the full story ›
Three were injured in a crash between a car and a lorry just before 3am. The road has now reopened between junctions 22 and 23.
There are still delays on the M5 southbound.
Bristol is the worst city in the country for motorists. That's according to the Alliance of British Drivers who've made a video showing what they say are the main problems facing car users.
A recent report found that on average, commuters in Bristol spend 84 hours a year stuck in traffic. And business leaders have told ITV news that the situation is now so bad, it's hitting the city's economy.