Four horses caused a closure on the A19 after they got loose from a field near Hartlepool.
The incident happened on the southbound carriageway, when the animals began to head north towards traffic.
One of the horses was hit before the road could be closed off, but was not badly injured.
Cleveland Police closed off the route while the animals were rounded up and put onto grazing land.
The incident happened at around 2.30pm near the A689 turn off at Wolviston.