The vehicle struck the overpass at Treeswoodhead around 2.50pm on Wednesday, causing rubble and bricks to fall onto the carriageways.
This prompted a police response and saw a full road closure so that structural engineers could assess the damage.
The northbound section of the road reopened shortly after the incident, but the southbound section remained closed for over seven hours while inspections took place.
No injuries have been reported and the police are trying to trace the vehicle.
Sergeant Brian Simpson said: “This vehicle has been travelling south when it, or its load, has collided with the underside of the bridge.
“This has caused damage to the structure and caused debris to fall, with other motorists having to take evasive action.
“The vehicle may have been carrying a high sided load but will have felt the contact with the bridge. It is imperative that we trace this vehicle and the driver.
“I’d ask anyone who was on the A77 yesterday afternoon travelling south, or who saw what happened, to provide any relevant dash-cam footage or information as soon as possible.”
Police Scotland has appealed to the public for information. To supply information, you can contact the police by phone via 101 and quote incident number 1748 of 7 January 2026.