Four women were seriously injured after the car they were travelling hit the safety barrier and rolled over onto a grass verge on the M8 in Glasgow.
The crash, involving a red Suzuki Swift, happened on the westbound carriageway opposite the Fort Shopping Centre at about 18:50 on Friday.
The 66-year-old driver and three passengers, aged 67, 59 and 56, were taken to hospital.
Police said the motorway was extremely busy at the time.
They have appealed for witnesses to come forward.
The driver and two of the passengers were taken to Glasgow Royal Infirmary.
The third passenger, the 56-year-old woman, was taken to the Queen Elizabeth University Hospital.
One lane of the motorway was closed for several hours as investigations were carried out.
PC Thomas Lynch said: "This was an incident which has left four women with serious injuries.
"Police officers are carrying out inquiries to piece together the exact circumstances of the incident and would appeal to anybody who may have seen the car prior to the crash taking place to come forward.
"The M8 would have been extremely busy at that time of night, with people heading home from work or perhaps going to and from the Glasgow Fort Shopping Centre.
"We would ask anyone with any information to contact the road policing complex via 101."