The motorway was briefly closed on one side, delaying traffic heading into the capital, as police followed up reports that rocks had been dropped from the bridge.
The closure was effective between junctions 18 and 19 of the motorway, which was fully open again by 8am.
But further investigation revealed that an object thrown or dropped from a bridge could not have been the cause of the initial alert, police said.
“A motorist called us because his rear window was not smashed, but completely cracked. It happened as he drove under a motorway bridge,” duty officer Henrik Brix said.
Closer examination of the vehicle proved this could not have been caused by a dropped rock, Brix said.
“It's not physically possible. It is a near-vertical rear windscreen, and you can't throw a stone from a bridge and hit that type of rear windscreen on a motorway,” he said.
The impact was likely caused by a stone thrown up by a car travelling on the opposite side of the motorway, according to the officer's assessment.
“We have looked into this matter and have lifted the road closure,” Copenhagen Police tweeted early on Friday in regard to the incident.
Vi har undersøgt forholdet og ophæver afspærringen #politidk
— Københavns Politi (@KobenhavnPoliti) September 20, 2019