Along with keeping a close eye on public transport patronage, I also like track what is happening with traffic volumes. The NZTA release traffic volumes for a handful of sites on the state highway network on a monthly basis and release a much larger number of sites on an annual basis.
We frequently talk about how traffic in general hasn’t really be growing for some time and in the past we have tended to just look at the Harbour Bridge data but with this post I’m expanding it to other sites that are monitored monthly. These are:
- ALPURT (Orewa to Silverdale)
- The Harbour Bridge
- SH1 at Panama Rd
- SH20 between Puhinui and Massey Rd
- SH1 at Drury
- SH1 at Bombay
So what’s happening with traffic volumes?
With the exception of SH20 volumes are flat and not really doing anything. The reason SH20 is increasing is likely to be primarily due to the recent extensions and upgrades the route has had including the motorway connections at Manukau, the upgrade across the Manukau Harbour and the extension through to Maioro St. I would expect that growth to continue for a while, especially after Waterview is completed. To help show this further the graph below is indexed to when the SH20 numbers first became available in Feb 10 based of the 12 month rolling average. It quite dramatically shows the growth being seen on SH20 and to a lesser extent on ALPURT compared to the other sites on SH1.
For the sites on SH1 in particular it is important to remember that this represents a discontinuity with past trends. Here are some of the annual traffic volumes for a few locations around the motorway network which shows just how much the trends have been changing in the last decade or so after previously having reliable growth year on year.