A 47-year-old man is in critical condition in hospital after an accident on the A470.
Police were called to the west bound off slip before Abercynon shortly after 18:30 on 4 January.
A silver Ford Fiesta was involved in a collision and left the carriageway.
Police say the driver of the car is in a critical condition at The University of Wales Hospital in Cardiff.
Anyone who may have witnessed the collision or who was travelling along the road around the time of the incident is asked to call 101.
A main road through Cardiff city centre will reopen once Australia v Fiji has kicked off at the Millennium Stadium after a lorry overturned on the A470 caused long traffic delays into the city.
The A470 near Coryton remains closed northbound as emergency services work to remove the lorry from the road.
It's understood the vehicle was carrying chemicals but there was no spillage or contamination.
Emergency services have closed the A470 near Coryton in both directions after a lorry overturned on the road.
It happened just after 11:00 BST.
Police warned of traffic delays following the incident and has advised drivers to take an alternative route.
Cardiff city centre is braced for a busy day on the roads and railways as the Millennium Stadium hosts Australia and Fiji in the latest World Cup pool match.
No-one is believed to be injured after a lorry overturned on the A470 near Cardiff this morning.
The accident near the Coryton interchange caused heavy delays in the area. The northbound slip road is still believed to be closed.
Emergency services are advising drivers to take an alternative route after a lorry overturned on the A470.
It happened just before 11:00 BST on the A470 northbound near the Coryton interchange. Police say the slip road is closed and diversions are in place.
Heavy traffic is expected across much of the city this afternoon as Australia take on Fiji in the World Cup at the Millennium Stadium.
One lane is closed and there is queueing traffic after an accident on the A470 at A4054 Coedpenmaen Road / A4223 / Bridge Street / Ynysangharad Road (Bridge Street Interchange).
One lane is closed and there is queueing traffic because of emergency repairs on the A470 Northern Avenue inbound before Ty'n-Y-Parc Road (Whitchurch High School). There is congestion on the M4 to J32 A470 / A4054 (Coryton Interchange).
There's queueing traffic because the road is blocked after a car fire on the A470 Northbound between Abercynon Roundabout and Abercanaid Roundabout.
One lane is closed and there's queueing traffic for three miles after an accident and recovery work on the A470 Northbound near the B4275 (AberCynon South)
There's congestion to the A4054 (Bridge Street Interchange).
The A470 has re-opened after earlier accident investigation work between A4059 / A472 (Abercynon Roundabout) and A4060 (Abercanaid Roundabout).