NZTA suspects the remaining 52 "ambulances" belong to motorists looking for an easy way to save some cash - in fact, about over $200 every year.
NZTA spokesman Andrew Knackstedt said the agency is regularly being made aware of drivers registering their vehicles as ambulances.
As ambulances are exempt for ACC levies, the registration fee for a non-commercial ambulance is $52.11, compared with $282.55 for a petrol-powered passenger car.
Mr Knackstedt said this has been an ongoing issue throughout the country for several years.
"People like to try it on from time to time. Basically, they're routing ACC.
"The numbers aren't huge on a national scale, but it's the principle of the thing.
"ACC isn't getting the money, which means people aren't being adequately covered when it comes to motor accidents."
In 2011, NZTA found more than 1300 motorists nationwide had incorrectly registered their vehicles as non-commercial ambulances.
Seven of those vehicles, the Times-Age reported at the time, were in Wairarapa.
"If they're in a crash situation and their vehicle is registered incorrectly, their insurance won't cover them," said Mr Knackstedt.
Masterton traffic sergeant Chris Megaw said police regularly come across vehicles incorrectly registered as Exempt Class A - which are identifiable by the "A" in the corner of their registration sticker.
Other Class A vehicles include commercial passenger taxis, rental cars, and fire brigade, licensed goods or recovery service vehicles.
"When we ask them why, they usually tell us the car was handed down to them and they've got no idea," said Mr Megaw. These drivers are issued with a ticket for incorrect registration and $150 fine.
Mr Megaw said people do not realise the importance of paying ACC levies when opting for a lower registration fee. "If you're in a crash, your ACC levy covers the ambulance, police and fire call outs to the scene."
Mr Knackstedt said anyone operating a motor vehicle for which a lower licence fee has been paid can be fined up to $1000.
