The incident happened at about 10:00 on Tuesday on the M9, near junction four and Linlithgow Loch, heading towards Edinburgh.
A white BMW one series was damaged by a male passenger in a white van.
Sgt Andrew McGhee said: "We're appealing for anyone who might have witnessed this incident to please contact us."
A man struck the windscreen of a moving car while hanging out the window of a van on a busy motorway.