The A23 was closed for almost ten hours on Tuesday evening (December 18) after two separate collisions, Sussex Police has confirmed.
Officers were originally called to a collision in lane three of the A23 Brighton Road just north of Hickstead, at 7.18pm on Tuesday (December 18).
There were no injuries reported from this collision, police said.
While officers were dealing with the incident another car collided with the police car, according to police, which was stationary with blue lights active.
A police spokesman said the driver of this vehicle suffered serious leg injuries and was taken to the Royal Sussex County Hospital.
The road was reopened at 5am on Wednesday (December 19).
If anyone witnessed the collision please report online or call 101 quoting Operation Cheltenham.