While police dealt with the crash, following which four people were taken to hospital with minor to moderate injuries, they tried to allow traffic to pass using a single lane.
However, that was intermittent as they investigated the crash and removed the cars.
By the time the four crashed vehicles were cleared from the bridge, and it was reopened, traffic had banked up each end by about 2.5km.
Compounding the problem was the closure, because of high flows, of the twin bridges at Kurow on SH82, which could have been used as a detour.
The crash happened about 11.20am when three cars halted behind a logging truck stopped for road works, reducing traffic to one lane at the northern end of the bridge, where two trees had crashed into its piers. One vehicle failed to stop, causing a chain-reaction with the three other vehicles.
Senior Sergeant Tony Woodbridge said police were still investigating why the vehicle did not stop in time.
He suspected it could have been because they were looking at the floodwater coming down the river.
Police from Waimate, an ambulance from Waimate and the Glenavy Fire Brigade were called to the crash. There were 10 people in the four cars.
One group was travelling to a funeral in Timaru and were transported there by police.
