Admin’s post the other day about Peak Traffic got me thinking about what some of our state highways would look like if we graphed their traffic volumes. Luckily the NZTA have published state highway volumes from between 1975 and 2010 which makes this fairly easy to do (although there are some gaps in the data which is a little annoying).
I have picked four points around the city to look at, they aren’t nessessarily the busiest parts but ones with a decent amount of data so that we can see some trends. The four places I picked are the Harbour Bridge, Northcote Rd to Tristram Ave, the SH16 causeway between Waterview and Rosebank/Pataki and the Newmarket Viaduct. Petrol Prices are often quoted as having an impact on traffic volumes so I have also added in the inflation adjusted price of petrol for the same timeframe thanks to the Ministry of Economic Development who publish it quarterly.
If you recall these two graphs, the first from the US and the second from the UK (thanks Patrick) both show traffic peaking and declining slightly over the last 4-5 years.
So who do the four spots I looked at compare?
As you can see they look very similar but interestingly all four of these lines flattened off in the early 2000’s so even earlier than the overseas ones. The only line to still have had some growth recently was Tristram to Northcote which had capacity added at the same time the busway was built but that seems to have flattened out again. That growth also hasn’t flowed onto the Harbour Bridge so is most likely a result of more local traffic using the motorway which means some of the local roads like Wairau Rd should hopefully have seen a similar reduction in traffic.
Petrol would definitely had a bit of an impact in recent years however it is worth noting that even in 2003 when petrol had come back down after a spike that vehicle numbers remained flat. Even things like the improvements to the capacity of CMJ don’t seem to have had an impact on the number of people travelling across the Newmarket Viaduct (with the exception of the periods of construction in the early 2000’s and recently with the bridge replacement).
Based on what we can see it would be interesting to see what the projections were for projects like the CMJ upgrade, if they are relying on the same long term increases that we saw before then there is a good chance the expected benefits of them won’t be fully realised.