Detective Constable Ian Smollet, 35, stepped out of a vehicle on the hard shoulder of the M8 outside Edinburgh when he was hit by a passing truck yesterday.
He was taken to the city's Royal Infirmary where he died last night.
Police Scotland offered their sympathies to the family of Mr Smollet, from Livingston, West Lothian.
The accident involving a Leyland DAF tanker happened between junctions two and three on the westbound carriageway.
There were traffic delays as investigators examined the scene following the collision at around 3.40pm.
Chief Superintendent Gill Imery said: "It is with the deepest regret I can confirm that Detective Constable Ian Smollet, who served in the Lothians and Scottish Borders Division, has died following Thursday's collision on the M8.
"Our sympathies are with his family, friends and colleagues at this very difficult time.
"Road policing officers are continuing their investigation and I would urge any members of the public who witnessed the collision or who believe they can assist with this inquiry to contact police immediately."