Traffic was disrupted but the road remained open. The road was cleared using a crane by late afternoon.
Police at the scene said the driver "was very lucky".
The truck was stopped by the barrier, with a steep drop below.
A Horizons Regional Council road safety co-ordinator is warning drivers to take car because of "summer ice" on roads.
Glenda Leitao said rain on dry roads could be as slippery as ice. "Rain is fantastic news for our region at the moment and we would like to see more of it," Mrs Leitao said.
"But these kinds of showers can pose a hazard for drivers following long, dry spells.
"Dust, dirt, oil and a multitude of other material builds up on the road surface. When it rains after being dry for so long, this greasy cocktail can make the road surface extremely slippery.
"Nicknamed summer ice, it is similar to driving on black ice in winter. Because drivers can't see it, it can lead to potentially deadly situations - particularly if drivers aren't aware and don't adjust their driving to suit the conditions."
Mrs Leitao said the greatest risk to drivers was just after the onset of rain but it could affect the road surface for hours.
"I encourage anyone driving in the rain or on damp roads after a long dry spell to reduce their speed, take extra care on curves, increase their following distances, and be sure to check tyre tread and air pressure.
"Properly inflated tyres with good tread depth are a must for safe travel, but even more so in slippery conditions," she said.
