Constable Pete Reed, of Wanaka said road conditions at the time were not a factor.
The driver had told him he swerved left as another car approached from the south, travelling uphill towards the Haast Pass, and his vehicle had hit the side of the culvert.
The car had travelled on and had smashed a road sign before coming to rest close in under a cliff face, Const Reed said.
Emergency services from Makarora, Lake Hawea, and Wanaka attended the accident, which is the third near the Haast Pass in the past five days.