A four-vehicle accident caused delays on the A19 south of Hartlepool this morning.
The southbound carriageway was partially blocked at the junction with the A689.
One lane was closed while police dealt with the incident, which involved two cars, a van and a mini-bus.
Traffic was queuing back to Elwick.
An eyewitness described seeing a white van which appeared to have collided with the central reservation.
"There were a couple of other cars that looked as if they had been caught up in it," she said.
"There were two ambulances and two police cars blocking off one of the lanes, and a third ambulance making its way through the traffic, which was backed up to the Windmill pub."
The North East Ambulance Service transported four patients to the University Hospital of North Tees in Stockton.
A Cleveland Police spokeswoman said there were not believed to have been any serious injuries.