It should have been a commuter's worst nightmare: a rush-hour power cut blacking out traffic lights across Auckland.

But reports of a free-flowing commute during Monday's massive evening outage have prompted questions over whether so many signals are needed at all.

Sarah Lilburn filmed traffic flow outside her apartment on Union St in central Auckland at 4.50pm.

Her footage shows traffic flowing freely through the busy intersection with Wellington St and on to the Northern Motorway.

A comparison video taken at the same time the next day showed vehicles edging through the junction and long queues of traffic waiting to enter the motorway.

Lilburn thought the unusual circumstances on Monday made drivers more courteous and patient.

"Normally there is a lot of beeping during rush hour but there was none during that time," she said.

"You could see some people hesitating longer than they needed to, but the people behind them didn't beep because they seemed to understand."

Radio Live host James Coleman said there were no delays during his drive to work during the evening peak hour.

"Traffic flowed beautifully, it was absolutely amazing."

He said drivers appeared to be more careful and alert when navigating uncontrolled intersections, and thought traffic lights sent them into "autopilot" mode.

"I think people approach intersections with a little bit more care knowing there's an unpredictability about people's behaviour."

Coleman called for a traffic light-free day to be trialled in Auckland but acknowledged issues around pedestrian and cycle safety.

There were no crashes or major incidents reported during the outage, which cut power to 50,000 homes from just before 5pm.

Auckland city road policing inspector Gavin Macdonald said delays at some major intersections were eased by officers directing traffic.

"I think drivers realised if they didn't behave themselves, they would probably get gridlocked or prosecuted," he said.

Most traffic lights are installed, monitored and maintained by local authorities.

Last year cyclist Matt Hancock complained about encountering 14 sets of lights during his 5.5km commute from Ellerslie to Newmarket - averaging one every 390m.

The Herald on Sunday counted the lights on other major routes, and found commuters from Panmure and New Lynn struck traffic lights every 550m on average.

Auckland City Council network performance manager Karen Hay said drivers generally behaved more cautiously during a blackout, but would eventually take more risks if those circumstances became regular.

Traffic signals were a last-resort for vehicle control and were only used after a review of traffic demand, crash rates, and pedestrian and cycle safety, she said.

Alternatives included roundabouts, which allowed more free-flowing traffic, but sometimes led to long delays on side roads.

Hay said traffic light phasing - how quickly the sequence is completed and how sets interact with each other - were set by a software programme and adjusted by road sensors according to demand.

An advantage of signals over roundabouts was that lights could be overridden from two control rooms, a regional traffic management unit and an Auckland City Council unit.

AA motoring affairs general manager Mike Noon said there had been cases where removing lights had improved traffic flow and safety.

"But what happens is you have situations were you just can't get into the traffic, and you get big delays," he said.

"Are we going to get away from having traffic lights? No. We need them."