One person is critically ill in hospital following a two-vehicle collision on the A48.
A Ford Fiesta car collided with a Ford Transit van near a section of the road known as The Tumble at around 6.40pm on Wednesday evening.
The road was closed both ways between the Culverhouse Cross roundabout and the Downs junction for nearly twelve hours.
Three people were taken to hospital - with one person suffering injuries which are described as life threatening.
A South Wales Police spokesperson said: "The circumstances surrounding the collision remain under investigation."
The road reopened at around 6.30am on Thursday morning.

Vueling withdraws winter flights to Aicante this winter
Playground in Barry forced to close after fire damages equipment
Campaigners Take Fight for Fairer Pathways in Welsh Women’s Football to Parliament
Vale Councillor Gwyn John Launches His First Novel at Llantwit Major Book Signing
Pink poppy display commences with celebration of life
Former Barry office block converted into new homes for people at risk of homelessness
Welsh Government publishes independent report on Level 4 intervention at Cardiff and Vale UHB
Three CoastSnap stations set to be installed along the Glamorgan Heritage Coast
Daffodil Runner statue installed at Marie Curie Hospice in Penarth
Woman Dies After Incident in Leckwith as Police Investigation Continues
Vale entrepreneur wins national Innovate UK award for sustainable construction technology
Cardiff Airport retains top accessibility rating as regulator reports record demand for assistance
Open Doors event to showcase hidden world of Glamorgan Archives
New details have emerged of a new tree-lined public square that will replace a traffic dominated junction
Dyffryn Gardens’ Edwardian rose garden blooms again after decade-long restoration
Barry’s Own Daniel White to Walk 190 Miles Back to Where His Round Table Story Began
1,300 people attend Flying Start Family Fun Day
Dispersal order put in place to tackle anti-social behaviour
Interim Chief Executive Appointed at Cardiff and Vale University Health Board
Cardiff Theatre Marks 50 Years of Service for Long‑Standing Staff Member