ACC has been buying former police radar equipment in a clandestine plan to thwart speeding motorists who use radar detectors.
The old radars, which have been renamed "drones", have been mounted to power poles at up to 70 sites nationally, and are intended to fool motorists with detectors in their cars into thinking police are nearby.
Five drones have also been bought by school bus companies to slow motorists down around children, and another six have been requested.
Official estimates from the past decade put the number of motorists with radar detectors at about one in 10.
The radars are renamed by a Wellington company, which buys them from police and sells them on.
They are used as part of a project between ACC's Road Safety Action Planning Group, police, the New Zealand Transport Agency and councils.
Representatives from the Dunedin City, Central Otago, Queenstown Lakes and Clutha councils approached last night had not heard of the scheme.
However, Clutha Mayor Juno Hayes welcomed the move.
"It would be a good idea if it cuts the road toll."
The scheme has been under way for about a year, and about $7000 has been invested so far.
ACC buys the drones for about $150, before passing them on to NZTA, local authorities and others, for distribution.
Injury prevention manager Phil Wright yesterday said 10 drones were initially trialled in Canterbury for six months before they were moved to the North Island.
While there had been no plan to keep the project secret, the department had been happy for it to remain under wraps, he said.
"We haven't tried to keep it a secret but we didn't tell anyone, as we thought it would be best if, when a signal went off, motorists didn't assume it was part of this programme."
In the last financial year, ACC processed more than $80 million in injury claims from crashes where speed was a factor, he said.
Mr Wright said the radar idea had followed a proposal by former transport minister Harry Duynhoven to ban radar detectors.
"[Radar detectors] are sold to people who are the more hardcore speedsters. They are an essential element in a boy-racer car.
"They are banned in Australia. Even if they were banned here, there is a couple of years' leeway for retailers.
"We thought `What can we do in the meantime?'."
Current Minister Stephen Joyce's office said yesterday he was still awaiting advice from officials on the proposed radar-detector ban.
The retired police radar units are bought by ACC from Wellington company Emergency Vehicle Systems.
It was revealed in July that police had begun removing radars from vehicles throughout the country, as part of a "replacement programme" to reduce costs.
ACC refused to discuss the location of its drones.
Pukekohe resident Bob Prangnell discovered three of the devices when his radar detector started going off, despite there being no police cars in sight.
"They're all within 10 miles of my house. I drive those roads reasonably often and something was always giving off a radar when there were no police around ... One day I slowed down and had a look around and saw these things and took some photos."