The incident happened between 2.40 pm and 2.45 pm yesterday on the northbound carriageway of the M90, between junction 2 for Halbeath and junction 3 for Kelty.
Police are now calling for witnesses or for drivers with dashcam footage to come forward to help in the investigation.
Officers say that after a minor altercation between the driver of a white Ford Transit van and a silver Vauxhall Astra near junction 2, the occupants of a silver Astra sped ahead and stopped on the hard shoulder just prior to junction 3, where a male occupant threw an item at the passing transit van smashing the windscreen.
Both vehicles exited the motorway at junction 3 and travelled down Cocklaw Street, Kelty before the Astra was lost to sight.
Inspector Cameron from Cowdenbeath Police Station said: "Fortunately no one was injured as a result of this reckless act however as you can imagine the consequences could have been very different.
"I am appealing for anyone who can help us identify the individuals involved or who has any information relevant to this investigation, particularly any drivers who were in the area and have dash cam footage, to contact the police immediately.
"Those with information can contact Police Scotland via 101 quoting incident number 1896 of 01 September 2020.
"Alternatively, reports can be made anonymously to Crimestoppers on 0800 555 111."