Emergency services were called to the crash at the railway bridge on the Kaitangata Highway, 1km east of Balclutha, at 4.45pm.
Constable Logan Dickie, of Balclutha, said the stock truck and trailer was travelling towards Stirling when the driver realised the bridge's 3.5m height tolerance ''at the last moment''.
The truck was damaged but driveable, the trailer was shorn off the deck, and the Holden Commodore travelling behind was unable to avoid it, Const Dickie said at the scene yesterday.
A Toyota Surf travelling in the opposite direction, from Stirling, was also unable to avoid the wreckage and was damaged.
A 30-year-old Macraes Flat man driving the truck was uninjured, as were two Stirling people and their two dogs in the Toyota.
A Stirling woman driving the Holden Commodore and her young son were taken to Clutha Health First for a check-up, police said.
Acting Senior Sergeant Craig Dinnissen said drivers often underestimated the height of their truck when driving under the bridge.
''It's a timely reminder for truck drivers to ensure they fit within restrictions, to reduce the possibility of this carnage happening again.''
