The M3 has reopened hours after being closed because of “potential hazardous material” on the road.
Thousands of motorists were caught in long queues on the motorway and surrounding roads.
Police said a bomb disposal team had been at the scene of the closure between junctions nine and 11 at Winchester.
The motorway was closed in both directions from about 04:00 BST, but fully reopened at about 15:30.
Hampshire Constabulary said officers were working with fire crews and the Ministry of Defence’s Explosive Ordnance Disposal (EOD) team to establish what the material on the road was.
It has not yet given any further details.
Motorists trapped by the initial motorway closure were able to leave the M3 by 07:00, said Highways England.
At midday, queues on the M3 eastbound were three miles long and westbound they were two miles long as drivers waited to leave the motorway, it said.
It tweeted to warn football fans travelling to the Southampton match against Manchester United of the “heavy traffic”.
United fan Paul Hibbert was travelling to the match with friends, but decided to leave the coach and make the one-and-a-half-mile final leg of journey to Winchester station by foot, walking along the hard shoulder to junction nine.
The 53-year-old, from Manchester, described it as “chaos” and said: “We are walking up the hard shoulder, people here are driving up the hard shoulder.”
Hampshire County Council’s travel information provider Romanse said Winchester city centre and all routes in were gridlocked at lunchtime on Saturday.
Cyclist Simon Read said he had to abandon his bike ride.
“I got to a bridge down a little track, and there was a policeman who told me I couldn’t go that way.
“As I went back down the track I could see there was a lot of police and emergency services personnel and then I saw the bomb disposal unit, with what looked like a robot at the back of it.”
BBC reporter Toby Wadey at the scene
It’s absolute chaos on the roads. Motorists are switching off their engines and getting out of their cars.
It took me three hours to travel 10 miles. I’ve since abandoned a trip from Basingstoke to Bournemouth.
We were diverted off the M3 at the Winnall roundabout.
It took more than an hour just to get round the roundabout with people switching lanes and stopping in yellow junction boxes.
When I returned to an empty M3 northbound, the scene on the other side of the carriageway consisted of miles of queues, with thousands of motorists stranded.
Motorists took to social media to express their frustration.
@neeshy_ tweeted: “Part of the M3 is closed. I’m going to be late. And I’ve just spilled hot coffee on myself. Shaping up to be a brilliant day”
Jim Hall said: “Stuck at Winchester Services M3 South, if the roads been closed since 4am why did they let us on if no way of getting off.”
Other have shared pictures of the scene, including one showing a man walking his dog on the hard shoulder and another showing a handstand on the carriageway.
George Vitelis, who was stranded at Winchester service station, said: “It’s quite a strange situation – there are babies having their diapers changed next to the M3, guys playing golf, people having picnics.
“The sun is shining, the weather is warm, I’m quite happy here to be honest.”