A white Ford Transit van was travelling on the Thorndike Road in Gainsborough when it is believed a brick was thrown from the bridge overhead causing the windscreen of the van to shatter.
The incident occurred on the 17th June at around 07.40am.
Police spokesman Jemma Peacock said: “Perhaps there was malicious intent, or perhaps it was just a prank that went too far.
“Either way this could have resulted in a fatal collision. Could the person/s who threw this brick live with themselves if that had been the case? We are determined to find out who did this hence this public appeal for information.”
Police would like any witnesses, or anyone with information to call 101 with incident reference number 63 of the 17th June.