The cameras installed at two highway spots and one local road, ran until November 23.
No one is being ticketed; to do that requires the law to be changed, which is likely to be next year.
The trial of the limits of the new technology comes ahead of Waka Kotahi taking over the camera network from police, and renewing and expanding it.
The results would take four months to analyse, the agency said.
“Waka Kotahi trialled safety cameras to get a better understanding of how many people drive while using their mobile phones and don’t wear their seatbelts,” it said.
The phone offence rate was three times the seatbelt rate - 1.58 per cent of motorists, versus 0.5 per cent.
In total, 12 million vehicles were caught on camera.
“All images taken were deleted within 48 hours, with a small number of anonymised images kept for reporting purposes,” the agency said.
Internal documents showed the agency expected the new cameras to triple the number of drivers caught, increasing from 1 million to 3 million offences a year before levelling off.
The agency’s director of land transport, Kane Patena, said driver distraction contributed to almost 8 per cent of fatal crashes, while 90 people a year died in smashes because they did not wear a seatbelt.
“However, the scale of actual distracted driving and seatbelt non-compliance in general is mostly anecdotal,” he said.
“The purpose of this trial is twofold - to test the camera technology and ensure that it is capable of detecting offences, and to build on the evidence base to help us better understand the scale of illegal mobile phone use and non-wearing of seatbelts.
“Better evidence on these issues will help shape new initiatives to encourage people to make safer choices while driving.”
The cameras were able to detect any driver whose hands were not both on the steering wheel.