The other day I put together a post that pointed out how traffic volumes over the Harbour Bridge have actually been falling over the past few years – which really calls into question why we are thinking about spending around $5 billion on another harbour crossing. In fact, if you look at the sections of the Northern Motorway that have had the least traffic growth over the past five years, you come up with exactly the section of motorway that’s proposed for duplication under the additional harbour crossing scheme: It’s also quite interesting to analyse these numbers (taken from here) for the Southern Motorway, once again with the sections of road where traffic has declined highlighted in yellow: It’s interesting to see that along much of the “core” part of the state highway network, the inner part of the southern motorway between spaghetti junction and Mt Wellington, traffic has declined over the past five years. Most of the increase has occurred in the outer parts of the network, as well as an interesting spike around Mt Wellington interchange (perhaps the result of Sylvia Park shopping centre?)
Here’s a graph of the change in traffic volumes over the five years: Looking at the average volumes also gives us an interesting overview of how the Southern Motorway works – with the section between Khyber Pass and Gillies Ave being the busiest section of road in New Zealand: The inner section of the southern motorway carries very high volumes in both directions, due to the large employment areas of Penrose & East Tamaki acting as a counterpoint to CBD-bound traffic – so you see volumes along this section of motorway similar to the Harbour Bridge. I also suspect we see quite a lot of inter-peak flows, I’ll make a comparison to the Northwest Motorway (which is very peaked) over the next few days.
Overall though, it’s fairly obvious that not only is it the Harbour Bridge where traffic growth has stalled over the past few years. Aside from some exceptions, and a bit of growth in the outer areas where development has occurred, most volumes along the southern motorway have either declined or only very marginally increased.