The A31 through the New Forest was closed for around 12 hours on Friday evening after a van left the carriageway.
Emergency services closed the road between Ringwood and the M27 whilst one person was rescued from the vehicle after being trapped.
Eastbound traffic was diverted off the dual carriageway at Stoney Cross and re-entered at Cadnam via Forest Road.
Some motorists reported being stuck on Friday evening for over four hours following the incident around 4pm.
One driver told Bournemouth One: “I set off towards Southampton to meet friends knowing there was an incident but reports on the radio said there were only 20 minutes of delays, so we carried on instead of taking a diversion.
“We joined the road at 5pm and didn’t leave till after 9pm.
“We were checking emergency services websites and social media but there was no information regarding the road closure, which is why more and more people continued to join the road.”
The road reopened at 3.30am Saturday.
Hampshire emergency services have been contacted for more details.