Another article has highlighted that Auckland’s traffic volumes aren’t growing anymore – rather stagnating and even falling slightly:
More Aucklanders are leaving their cars at home for the commute to work as high petrol prices bite.
New figures show almost 900 fewer cars a week travelled over the Auckland Harbour Bridge this year compared with last year.
The drop corresponds with a fall in petrol sales in the city and an increase in public transport patronage.
NZTA figures show 1,684,601 cars crossed the bridge in the year to December, 44,545 fewer than last year.
Figures provided by New Zealand-owned petrol retailer Gull from local authority levies on petrol sales in the Auckland region showed 19 million fewer litres of petrol were sold in the year to June – a two per cent drop on the previous year.
The change in volumes over the harbour bridge is very slight (and the above article is wrong with its yearly total as around 160,000 vehicles cross the bridge a day, meaning you’d get to 1.6 million in just over a week, not in a whole year) but the change in petrol sales is perhaps most interesting, highlighting a reduction in driving throughout Auckland, not just a shifting of traffic away from some roads and towards others.
This isn’t just an Auckland phenomenon either, with a more enlightened than average traffic engineer in the USA pointing out that traffic projections may need to be fundamentally changed from how things have been done in the past. He notes:
I’m working on a traffic study where the reviewing agencies asked us to prepare 20 year forecasts in addition to looking at the build out year. Typically, we look at data trendlines on nearby roads and throughout the county to determine a “typical growth rate” for traffic in the area. This has historically been an annual growth rate of 1 to 3%. This often leads us to factoring traffic up 50% or more over 20 years and then layering on the traffic from the proposed development. Factoring existing traffic volumes up approximately 50% is also how traffic forecasts are often prepared for road design projects.
I’m strongly reconsidering this approach. Consider Figure 1 below from the Federal Highway Administration’s Office of Highway Policy Information website. From 1986 to 2006, traffic on all of our highways did fit the model of growing by about 2 to 3% a year (or 50% to 60% over the 20 years). But since 2005, we’ve had a significant drop in traffic and the trendline sure makes it look like traffic growth has plateaued.
Here’s that figure one:Further analysis from the famous “Texas Transport Institute Urban Mobility Report” highlights that congestion has remained roughly the same over the past decade, once again reversing a long-term trend of ever-worsening congestion: Mike Spack, who wrote the blog post, makes the obvious – but incredibly important – conclusion from the above data (and a pile of other data he quotes in his post:
Based on national and local trends, my conclusion is that it is very reasonable to think traffic growth has plateaued. The punchline for traffic impact studies: the “no-build” traffic forecasts should be the same as the existing traffic volumes. We don’t need to do opening day forecasts and 20 year forecasts because they can reasonably be expected to be similar.
And given our huge budget shortfalls, this should also mean a policy of fixing the infrastructure we have. NOT expanding our transportation system to add capacity.
There are some excellent points made in the comments too. This one in particular is very relevant to our debates here in Auckland:
As always, this can be tied back to money. As long as outside funding sources (e.g. state, federal) continue to reward agencies with inflated no-build volumes, there is little benefit to agencies for projecting more realistic no-build volumes.
In addition, many agencies rely on inflated no-build volumes to justify the “need” for a project as required by federal environmental documents.
I suspect that the cost-benefit ratios of most of our proposed roading projects would plummet if we shifted to a “no growth” assumption for traffic volumes. Most projects derive their ‘benefits’ from projecting how utterly terrible things will be 20-30 years down the track if the project in question isn’t built (the increased ‘no-build’ volumes), then highlighting how the project in question will ensure that scenario does not occur. If things aren’t going to get worse in the future, when it comes to congestion and car volumes, then the justification for so many projects just disappears.