A woman was left fighting for her life and another person was badly hurt in the crash on the M275.
The accident left the road closed for more than four hours.
Police said the woman had sustained life-threatening head and face injuries in the accident near the Rudmore flyover on the northbound carriageway.
'Lessons to learn'
A spokeswoman said the woman's hatchback was broken down and facing the wrong way in the third lane of the M275 when it was hit by a Mercedes van.
The woman was taken to the Queen Alexandra Hospital in Cosham after the accident at 0620 BST.
City council road chiefs thanked motorists for their co-operation during the tailbacks, which saw the first use of Portsmouth's new emergency traffic plan.
The plan was drawn up by traffic and emergency planning officers to try to prevent gridlock for people getting out of Portsmouth if one of the city's major roads were to be closed.
Charles Stunell, the council's head of traffic, said: "There are lessons to learn from what happened today, and we have already held a debrief with the police to make some amendments and revisions to the plan.
"We appreciate that some motorists coming into Portsmouth continued to face lengthy delays but our efforts to get rush-hour traffic out of the city generally worked pretty well.
"The plan aims to avoid the gridlock we had last November when there was a fatal accident on the M275.
"On that occasion, Portsmouth froze - today the traffic moved very slowly, but it did keep moving."
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