The northbound M1 has reopened between junctions 15 and 18 in Northamptonshire after being closed for much of the day following the discovery of a body this morning.
The motorway was reopened at around 1pm by Highways England, although motorists are warned to expect some delays as diverted and queuing traffic clears.
Northamptonshire Police said that the incident was reported to them at about 2am by a lorry driver.
East Midlands Ambulance Service medics and a volunteer doctor attended the scene but the man had already passed away. Detective Sergeant Tony Hopkins of Northamptonshire Police said the injuries caused were 'catastrophic'.
Det Sgt Hopkins said: “We received a call at 2.09am from a lorry driver who believed he’d hit a man. We received several similar calls soon after from motorists heading northbound reporting they had hit a body in the road.
“Police arrived on the scene within 15 minutes. We were able to confirm we had a deceased person on the road between junction 16 and 17.
“We have not been able to identify the man or how he came to be on the motorway this morning.
“We understand that this is an unlit stretch of road in the early hours of the morning, but we are appealing for any witnesses who might have seen a man walking by the road at that time and particularly from anyone with a dashcam.”
Caught between roadworks and the concrete barrier of the motorway, the body was “traveled over several times” by motorists who police say were unlikely to have been able to avoid him.
Anyone with information can call Northamptonshire Police on 101 or 03000 111222 if out the county.