Police have identified the body found on the M20 as a 32-year-old woman from Kent.
A man arrested on suspicion of murder remains in custody, Kent Police said on Thursday afternoon.
Officers discovered the body on the London-bound carriageway near Ashford at 6.05pm on Tuesday. The road was closed between junctions 9 and 10 for nearly 24 hours while the scene was investigated.
Police officers search by junction 9 on the northbound carriageway of the M20 in Kent (Gareth Fuller/PA)
Officers initially appealed for the driver of a silver Nissan Qashqai to come forward and a man handed himself in at a police station on Wednesday evening.
The incident caused hours of delays with between six and seven miles of queues stretching back to junction 11 and a diversion was in place.
The road reopened shortly before 3pm on Wednesday.
The London-bound carriageway of the M20 was closed for nearly 24 hours after the incident (Gareth Fuller/PA
An accountant from Ashford told Press Association of his shock at the scene he saw while driving on to the coastbound stretch of motorway at about 6.20pm on Tuesday while emergency services were on the opposite side of the road.
The 21-year-old, who asked not to be named, said: “As I entered the motorway I expected to see a crash, when I suddenly realised that it wasn’t and unfortunately it appeared to be a body lying in the central lane with police and ambulance staff around it.
“Because of the torches being shone by police (I could see) it appeared that the body had been struck by vehicles.
“It was very shocking. It is not a sight I would want anyone to witness.
“My condolences are with the family of the deceased.”
Police are still appealing for drivers who were on the road at the time to check their vehicles for signs of a collision, and for anyone with dash cam footage or who saw the Nissan Qashqai with the registration KY15 WWX at the time of the incident to come forward.