Bevin described what it was like getting the call.
"It'll be the police comms ringing us and straight away you know it's going to be an awfully long day. We're always prepared for that phone call and if it's in the day time it's relatively easy, we've got resources and staff on hand," he said.
"More often than not though, when it happens at night time when you're fast asleep and the phone goes off, you're up and at 'em and into the car and off you go to the scene."
He said it was usually three or four hours' work at a time.
Bevin said before getting to the scene, it's about "15 minutes of mayhem".
"A lot of people describing what's happening and the resources that are required. So you get a bit of a mental picture of what to expect at the scene."
He says crash investigators let the emergency services do their jobs before they get stuck in.
Bevin said there were some scenes he wished he could unsee.
"Most traumatic for everyone involved would be especially young babies run over tragically on driveways," he said.
"It's always a big thing to deal with."
He said it was difficult to pinpoint the most common cause of crashes.
"We might get a spate of motorbike crashes, we might have a series of high-speed collisions where people have been under the influence of alcohol or drugs," he said.
Bevin said the crash unit had tried to plot statistically when they could expect to have a crash based on their data over the previous years.
"But really they still just happen ..."
Many happen because people have made one simple mistake, he says. Bevin copes with his own trauma by venting to his colleagues and his family.
He said he was quite tough on his two teenage sons getting behind the wheel.
"I am a little bit overly cautious with my own children and the fact they want to drive, they're at that age now, and they equally know if they do muck up they're going to be answering to dad."
In April alone, Bevin was called to 26 serious car crashes.
The focus for this year's Road Safety Week, run by road safety charity Brake, is on seatbelts and distractions.
Spokeswoman Caroline Perry said about a third of people killed on the roads were not wearing a seatbelt.
"That's the simplest thing that you can do to reduce your risk of death and serious injury in a crash," she said.
Mobile phone use while behind the wheel was a factor in about 11 per cent of crashes — but she believed it was a lot more than that.
"We all find it difficult to tear ourselves away from our smart phones but when we're at the wheel, we have to be 100 per cent focused on the task of driving."
NZ's road toll
134 people have died this year as of May 4 compared to 127 at the same time last year.
40 females have died compared to 29 at the same time last year, and 94 males have died (98.)
118 fatal crashes (116).
38 fatalities so far for over 60-year-olds. More than any other age group. This compares to 18 deaths among those aged 20-24 and 30 aged 25 to 39.
41 deaths in March, the worst month this year. January had 36 deaths.
For a video report see nzherald.co.nzCarla Penman
