The grim reaper face of road safety ads watched in horror as the filming of the ads became all too real for a stunt driver in one of the graphic car smashes.

David Austin, the grim bearded face of the New Zealand Transport Agency safety campaign, said ambulance services had to help the driver of a Nissan Primera damaged during filming.

The ads were filmed in April last year at the intersection of Te Atatu, Totara and Tawa Rds.

"The weather was dodgy for most of the shoot. We got rained on, on several occasions and only just had enough light left to do the final car crash," writes Austin on his website.

One of the crashes didn't quite go according to plan. "He [the driver] needed oxygen afterwards," says Austin, of Papatoetoe. "There were a few close calls."

Transport Agency spokesman Andrew Knackstedt said no one was injured during the filming, but confirmed that one of the drivers received medical attention at the site before being taken to hospital.

"Following the crash [involving the Primera] one of the drivers was shaken up and appeared groggy," he said. "He was assessed by safety and ambulance staff, given oxygen as a precaution on site, and taken to hospital for observation as a further precaution. The driver was observed and released."

Knackstedt said both vehicles were stunt vehicles, modified with cameras and features such as roll cages. Both drivers were harnessed and were wearing crash helmets.

Knackstedt said the incident illustrated the reason the campaign was important: "Crashes at intersections have the potential to hurt people. This was a carefully planned crash, carried out at very low speeds, in a highly controlled environment, with drivers fully harnessed and wearing crash helmets - and even with all of those precautions in place, one of the drivers was still shaken up."

He said the response to the ad was "overwhelmingly positive".

Austin said that when he first read the script for the ads he didn't realise they would have such an impact on viewers.

"I never thought for a second it would creep people out like it does," he wrote.

"Hopefully the ads' message well and truly gets across too. It certainly works for me.

"The script called for an odd looking man with pasty skin wearing a black suit and to me it seemed to be a bizarre cross between a game show host and the grim reaper."