The A1(M) was closed for around six hours in both directions between junction 35 and 36 this morning (April 27).
The incident was initially reported as a crash but police have now confirmed a 73-year-old man fell from the bridge before being hit by a car.
Motorists faced delays of up to an hour as both carriageways were closed.
A statement from South Yorkshire Police said: "At about 5.10am we received a call from a member of the public reporting concerns for the safety of a man on the bridge over the A1(M) at Junction 36.
"The man fell from the bridge and has sadly died. Yorkshire Ambulance Service were also at the scene. The man’s family has been informed and are being supported by specially trained officers.
"The A1M was closed in both directions between Junction 35 and Junction 37 while emergency services continued to work at the scene. The bridge, the junction between Warmsworth Road, High Road and the A1M, was also closed.
"The roads have now reopened due to emergency service crews finishing their work at the scene.
"The investigating officers wish to thank motorists for their patience while this important work was carried out.
"We are appealing for anyone who saw the man in the moments before the collision, or saw the collision itself, to contact us. We are particularly interested in speaking to anyone who may have captured dash-cam footage of the incident or of any vehicles involved. Anyone with any information which could assist the investigation is asked to call us on 101.
"Please quote incident number 95 of the 27 April when passing information."
The road reopened at around 11am.
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