One of the many reasons why I oppose an additional road crossing of the Waitemata Harbour (along with the insane price tag and the horrific environmental effects) is that I simply don’t think it’s necessary. Let’s take a look at monthly averaged daily traffic flows across the Harbour Bridge over the past few years – thanks to this excellent data from NZTA: The gaps in the data (it would be really nice having the earlier months in 2007 in particular) limit comparison to some extent, particularly as 2008 was an incredibly unusual year for traffic volumes (it’s when petrol prices skyrocketed through $2 a litre for the first time). However, overall it seems the general trend has been downwards over the past few years.
Looking at annualised average daily traffic counts, you get the same story – once again thanks to NZTA’s great data: There are a number of potential reasons for such a change: less general travel between the isthmus and the North Shore might be the result of greater employment on the Shore, higher petrol prices discouraging travel, a static economy also discouraging travel and so forth. The other reason could be a shift in people from cars onto public transport – thanks to the Northern Busway, which just happened to open in early 2008.
Looking at peak time flows of people over the harbour bridge, it would seem that the number of people crossing at peak times has continued to increase over the past few years – mainly through a big upswing in bus usage: From looking at the graphs above it seems pretty clear that the Northern Busway has got people out of their cars and onto the bus. While general travel between the North Shore and the isthmus has continued to increase, this hasn’t led to more cars crossing the bridge – instead we have actually seen a fairly significant decline since 2006/2007, just before the Northern Busway opened.
These statistics tell me that it’s not a simple inevitability to expect traffic volumes to increase in the future – in fact they’ve been doing quite the opposite in recent years. While the number of people crossing the bridge seems likely to increase, as our population grows, there’s no reason why that has to require more general traffic lanes, if what’s happened over the past few years is anything to go by. Plus of course, if we need to cater for many more people between Akoranga and the city centre, we could always build a railway line for half the price of the road option.
Looking at traffic flows along all parts of the Northern Motorway over the past five years, it is interesting to note that the area with the least increase (Esmonde Road to Fanshawe Street) is exactly the same area of the motorway proposed for effective duplication with the additional crossing: