The impact of the trucks colliding forced the safety truck up the bank, where it rolled and landed back on the road on its side.
"There were two occupants in the roading truck. They were pretty much okay, I think. The driver may have lost a tooth," he said.
The driver of the logging truck was not hurt in the crash. The safety truck's two occupants suffered minor injuries. One was transported by ambulance to Matamata Medical Centre and the other to Waikato Hospital for assessment.
Eric Heurea, a contractor with Downer, was across the road from the crash when it happened.
"It was loud. The safety truck just flew up that hill and came down on its side."
He said it was frightening to see an accident that close-up. He had feared for the lives of the workers in the truck when it flipped and was surprised when they had climbed from the vehicle with only minor injuries.
"It's not really something I want to remember anymore ... just seeing that cab [flip]. It was the driver I was worried about. It took awhile for him to move. He must have been knocked out a bit," he said.
Mr Heurea immediately ran up the road to alert oncoming cars to the incident and wave them down, while his roading colleagues had helped the occupants of the truck.
The incident was the most recent in a string of crashes on the Kaimais.
Mr Colley said drivers needed to pay more attention when driving the route.
"This is a bloody delicate piece of road. And whenever we get rain, something is going to happen.
"Most of the time, it's driver error. When you drive up here in the wet, you've got to be cautious. People have just got to take care when it rains up here, it's as simple as that - and they don't," he said.
While the trucks and debris were cleared from the road, the slow vehicle lane remained closed but traffic was still able to travel in both directions.
Derek Dumbar, regional director of the Road Transport Forum, said the Kaimai Range was a known black spot.
"It's a danger spot. They're policing it every day and we still have accidents.
"The wet weather - it's just one of the problems with the Kaimais. It's the nature of the beast. We are going over a mountain range that does get a lot of rain. And the more vehicles we're putting over there, the more crashes we are going to have," he said.
Tauranga City councillor Murray Guy said the use of signage trucks had reached epidemic proportions and was part of a trend in which the over-use of safety warnings had led to motorists becoming blase about road works.
"The proliferation of safety concerns that we are enveloping ourselves in has reached epidemic proportions."
He cited the road works on Route J to Bethlehem where he said traffic had been reduced to a virtual standstill through lanes delineated by road cones, yet hazard trucks were still being used.
Cr Guy said no one denied the need to have a safe working environment on roads, but the hazard trucks were sometimes a hazard in themselves by reducing visibility and distracting motorists.
He questioned their use for roadside grass mowing operations on the highway between Maungatapu Roundabout and Baypark.
"Obviously they are valid in some circumstances."