A snap survey has busted 3.5 per cent of Auckland motorists - more than one in every 30 - using mobile phones while driving on a 100km/h stretch of the Southern Motorway.

The survey caught 671 drivers touching their phones in seven and a quarter hours under the East Tāmaki Rd overbridge - more than 10 times the 60 mobile phone driving offences a day recorded by police in the year to March nationwide.

Some motorists were photographed with other distractions, including dogs sitting on drivers' laps and another driver eating salad.

The findings have sparked warnings from road safety advocates and a call for motorists who break the law to have their phones permanently confiscated.

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Australian company One Task used specially developed cameras to conduct the survey between 8.45am and 4pm on Tuesday May 29, outside peak traffic times on a fine day when it said traffic was "flowing with speed".

Some of those snapped just had their phones in their laps (35 per cent) or were touching their phones in sockets near the dashboard (2 per cent) - but 63 per cent were holding them in their hands.

"Some of the images are quite compelling - people with both hands off the wheel and eating salad and stuff at 100km/h," said One Task project manager Alex McCredie.

"Some of the images are quite compelling - people with both hands off the wheel," says One Task's Alex McCredie. Photo / One Task

"On average a motorist was seen touching a phone every 39 seconds."

Road safety analyst Clive Matthew-Wilson said using mobile phones now caused more road deaths than speeding.

"Only 15 per cent of the road toll involves speed [only]. American studies show 28 per cent of road deaths involve cellphones, so it is a far greater risk," he said.

Other major factors in NZ road deaths from 2014-2018 were alcohol and drugs plus speed (15 per cent) and alcohol and drugs alone (14 per cent).

Road policing operations manager Inspector Peter McKennie said NZ police did not use fixed cameras to catch drivers using mobile phones.

"Police officers detect mobile phone infringements in New Zealand - cameras are not used to detect mobile phone offences," he said.

"Sometimes officers may use hand-held cameras to help detect these offences."

Traffic offences for using mobile phones peaked at 28,901 (averaging 79 a day) in 2016, but have declined to 23,490 (60.5 a day) in the latest year to March, possibly because dedicated traffic police numbers have been cut by 111, including 71 in Auckland.

McCredie said One Task was bidding in a tender by the New South Wales Government for cameras to detect mobile phone offences, but his company was struggling to even get meetings with officials in other Australian states.

"We reached out to the NZ Transport Agency. They seemed interested," he said.

"But I think without any mandate from the politicians and from the Minister for Transport, I don't think it's going to go anywhere."

NZ Transport Agency spokesman Andrew Knackstedt said the maximum penalty for using a mobile phone while driving was $1000.

He said a Ministry of Transport survey at 52 sites around New Zealand in 2014 found that 2.6 per cent of drivers were using mobile phones.

Inspector McKennie said most mobile phone offences were detected in low speed zones and when there was congestion and gridlock, such as at traffic lights.

"In 100km/h zones there tend to be fewer mobile phone infringements detected," he said.

"However, still far too many people flout the law. It takes just a second for the environment and conditions to change, and drivers need to ensure that nothing is causing them distraction that could cause harm to others."

He said Police "continually monitor developments in technology in other jurisdictions and use this information to help make future decisions".

One Task surveys actually found a lower proportion of drivers using mobile phones in Auckland than in any Australian state capital except Perth (3.2 per cent).

The highest proportion detected was 7.1 per cent in one part of Melbourne.

NZ Automobile Association road safety spokesman Dylan Thomsen said an AA survey found 15 per cent of AA members admitted to using mobile phones illegally. But the AA supported the ban on drivers using mobile phones and was interested in One Task's technology.

"It's absolutely worth looking at because we know that we have a serious problem with people using their phones on the roads," he said.

Matthew-Wilson said fines were unfair on poorer people and the best way to stop drivers using their phones would be to confiscate the devices.

"First offence, you lose the phone. Second offence, you lose the phone and the mobile number," he said.

"That affects the richest person and the poorest person equally and it would have a profound effect on people's behaviour."

A spokesman for Associate Transport Minister Julie Anne Genter said Genter was unavailable to comment and officials would be best placed to answer questions.

Numbers using mobile phones

Melbourne (location 1): 7.1 per cent
Melbourne (location 2): 4.7 per cent
Brisbane: 4.5 per cent
Adelaide: 4.4 per cent
Sydney: 4.2 per cent
Auckland: 3.5 per cent
Perth: 3.2 per cent

- Source: One Task