Like with public transport patronage, I keep a close eye on what are happening with traffic volumes on the motorways thanks to the monthly data released by the NZTA. The data doesn’t cover the entire motorway network but it does cover a number of key locations on it that can help to give an indication of what’s happening. I think the picture painted by these figures is extremely interesting. The sites we get monthly data for are:
- ALPURT (the Orewa to Puhoi toll road)
- Harbour Bridge
- Upper Harbour Bridge
- SH16 between Royal Rd and Hobsonville Rd
- SH1 at Panama Rd
- SH20 between Puhinui Rd and Massey Rd
- SH1 at Drury
- SH1 at Bombay
Excluding Wellsford, here are the six sites that we have the most data for
There are a couple of things interesting going on here. At most sites the traffic volumes continue to remain fairly flat and in the case of the Harbour Bridge the annual figure remains lower than it was over a decade ago. Another interesting trend with the Harbour Bridge is that the annual figure is now bouncing up and down between 150k – 160k per day (it peaked in 2006 at 169k). However you see a clear change in the SH20 site. This isn’t surprising as in recent years there have been significant extensions and changes to that motorway including the opening of the Mt Roskill extension in May 2009 followed by the Manukau extension to SH1 and Manukau Harbour Crossing duplication in August 2010.
The changes can be shown even clearer by indexing them to Feb 2010 which is the earliest the SH20 data is available from.
You will also notice that ALPURT has shown growth. Unfortunately what isn’t clear is if this is a result of total traffic volumes along the route growing or people becoming more comfortable with paying for the toll road and so a higher percentage of people choosing it over the free route. The NZTA previously to recorded vehicle volumes at Hatfields Beach would have allowed that comparison but stopped doing that at the start of last year when they handed the road over to Auckland Transport.
As mentioned, the graphs above don’t include all of the collection sites reported on, the ones missing being on SH1 North of Wellsford, on the Upper Harbour Bridge and on SH16 between Royal Rd and Hobsonville. I haven’t graphed them due to how low the traffic volumes are in the case of Wellsford and how little data there is for the other two (only two years worth). In saying that the data that is available is quite interesting in its own right.
SH1 North of Wellsford – Traffic volumes are very seasonal peaking over summer but overall they have been in decline since monthly figures began in September 07. This is quite important as we often get told that the reason behind the Puhoi to Wellsford motorway is to unlock Northlands economy. Both the SH20 and Upper Harbour Bridge sites are interesting as the annual figures show traffic volumes on those sections had been flat since 2003. The volumes over the Upper Harbour Bridge only started increasing again in 2008 after the Upper Harbour section of SH18 was completed while the SH20 site only started increasing in 2011 after the Westgate to Hobsonville section of SH18 was completed.
To me these figures show a couple of key trends. The motorways not widened or extended have shown little to no growth and in some cases volumes remain below what they were in the mid 2000′s. In the places where we have built motorways, vehicle numbers have been increasing. To me what this effectively points out is that changes traffic volumes are really just a reflection of what we’ve invested in, or in other words a case of build it and they will come. That might sound logical (and it is) but it also highlights the opportunity we have to determine just how much traffic is on our roads in the future. Build more roads like the current plans suggest and we’ll get more traffic.
Of course the opposite is true too, remove roads and traffic disappears with it. This has been shown quite well in Seoul, Korea where since 2002, 15 expressways have been demolished and more are planned. The most famous of which was in Cheonggyecheon where they removed an elevated expressway and ground level roads carrying over 150,000 vehicles per day and restored the original stream making a wonderful urban park in the process.
It went from this:
And the outcome was even more impressive:
- Traffic volumes dropped while bus and subway usage rose
- There were increases in fish, birds and insects in the area.
- Temperatures decreased and are on average 3.6% lower than other parts of Seoul.
- It became a centre for cultural and economic activity.
- And perhaps most interesting to the NZTA/AT, traffic speeds on other roads increased which is an example of Braess’s paradox
Now I’m not suggesting that we tear any existing roads down but more just highlighting that we have the ability to shape the city how we want it. If we don’t want traffic volumes to increase in the future that we should start by not building a heap more roads.