Because Auckland's population grew from 1,373,000 in 2006 to 1,507,600 in 2012, there was an increase overall in VKT during that period of 4 per cent. But because of the individual drop in car use, previous modelling predictions may have overestimated future road needs. Mr Arbury says this "may mean the need for some projects is delayed".
In a previous guise as head guru on his influential Transport Blog, Mr Arbury used to plug away at this message. Now, as poacher turned gamekeeper, he's got a captive audience of the politicians and the bureaucrats at the heart of the decision-making process.
Back in 2011, wearing his blogger hat, Mr Arbury revealed a confidential Beca Infrastructure report to the NZ Transport Agency noting a decline in both traffic loadings and volume on the harbour bridge since 2005, reversing the steady growth in average traffic recorded from 1960 to 2005.
Using NZTA figures, Mr Arbury calculated bridge traffic had declined 4.8 per cent between 2007 and 2011. Nationwide, motorway traffic volumes peaked around 2003, after a steady climb since records began in 1989.
As far as the bridge is concerned, the runaway success of the Northern Busway played a significant part in reducing vehicle usage.
This growth in public transport use was not just a North Shore phenomenon. Mr Arbury notes that between 2007 and 2013, public transport boardings across Auckland had increased from 52.4 million to more than 70 million. Some of this was because of population growth, but not all. Per capita boardings increased from 38 to 46 a year. Not enough for transport chairman Mike Lee, who says "we need to do a whole lot better", but a sign that, increasingly, Aucklanders are seeking out alternatives to car travel.
Mr Arbury says the Auckland and New Zealand trends "are broadly similar to those observed across a wide variety of developed world countries. In the USA for example, the total distance driven has remained approximately the same since 2004, with per capita distance driven reducing to 1996 levels."
He says the trends since 2004 "break a decades-long increase in both total and per capita distance driven". It's a change that predates the global financial crisis, and has persisted during the subsequent economic recovery.
He points to a similar "flat-lining" of vehicle use over the past decade in Australia, France, Britain, Sweden and Japan, "even though the population in most of those countries has continued to grow".
A combination of factors is credited for the change, including the global recession, higher fuel prices, improved public transport, off-putting traffic congestion, and population drift into higher-density living in brownfield and inner-city sites. New social patterns and preferences also play a part, with fewer young people acquiring driver's licences, concerns for the environment, and e-commerce and social media resulting in less need for travel.
Mr Arbury says that in the past, transport infrastructure investment was based on assumed traffic increases on an annual basis. Planners can no longer assume this.
Which opens up many possibilities.
On his blog, Mr Arbury tended to be talking to the converted. He now has a wider audience of decision-makers. One hopes they delve into this report, and consider its possibilities.
For those looking for budgetary cuts, crossing off a $5 billion second harbour crossing would be a tempting place to start.
