An over height warning system was working when a digger "well above" the cut-off 4.57 metre height hit the Penrose motorway overpass, NZTA said.

Nearly half of Automobile Association members in Auckland have considered changing where they live or work to avoid traffic jams.

Association infrastructure spokesman Barney Irvine said the survey of its members showed "just how much anxiety is out there" over Auckland's transport network.

Auckland desperately needed a better managed transport system, as shown by Monday's chaotic motorway digger accidents, Irvine said.

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A digger on a truck trailer crashed into an overbridge on the southern motorway's southbound lanes at Penrose on Monday afternoon, causing a massive traffic jam. Just hours earlier another digger fell off its trailer causing traffic to back up on the north western motorway.

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Auckland's AA Members had seen "congestion get steadily worse in recent years, they're worried that their quality of life is being eroded, and they don't see anyone stepping up to address it", Irvine said.

NZTA On Monday afternoon a toppled digger blocked Auckland's southern motorway at Penrose, backing up traffic for more than 10 kilometres.

A better alert system was needed so Auckland drivers could drive around motorway incidents.

"There is very little 'give' in the network, as soon as the motorway encounters something like this the whole system is impacted," Irvine said.

Almost daily, traffic incidents cause delays on Auckland motorways - the Penrose digger incident alone caused hours of traffic chaos, backing-up at least 10 kilometres on the southern motorway.

BEVAN READ / FAIRFAX NZ On Monday morning, a fallen digger ground traffic to a halt along Auckland's North Western Motorway,

The New Zealand Transport Agency (NZTA) said the Penrose digger was at least 20 centimetres over the 4.25 metre cut-off height for the overpass.

An over-height warning system stationed hundreds of metres upstream from the overbridge was working, the NZTA said.

The AA wanted local and central government to launch a focused and sustained campaign on Auckland congestion.

Better incident response, a congestion taskforce, small-scale anti-congestion measures and more park-and-ride facilities were needed, the AA said.

Research cited by the group showed traffic congestion was costing Auckland more than $1 billion per year.

NZTA spokeswoman Sarah Azam said despite increasing pressure, Auckland motorway average travel times remained steady during the morning travel peak and had eased in some places during the afternoon peak.

The agency was "putting a lot of effort into improving travel information" while motorway projects at key choke points continued or were soon to begin, Azam said.

Auckland Transport, which controls non-motorway roading and bus and train networks, said it agreed with some of the AA survey's findings.

"The report highlights key issues of unprecedented population growth and the challenges of managing that after many years of under investment. . . major infrastructure work needs to be accelerated . . . the continued expansion of public transport [is] critical to getting more private vehicles off the road," agency spokesman Mark Hannan said.

AT was working to "optimise" several Auckland roads by synchronising traffic lights, removing minor hazards and making sure roads were operating efficiently, Hannan said.