A man was killed after his car left the A470, collided with a tree and rolled down an embankment.
The southbound carriageway at Abercynon was closed after the accident at 6.20am on Tuesday creating huge traffic delays in the area.
The carriageway was reopened at 2pm after being closed between Abercynon and Nantgarw with a diversion through Caerphilly County Borough.
The incident happened just past the Pontypridd turn-off towards Rhydyfelin.
South Wales Police said the driver killed in the crash was the only person in the car.