We spend a lot of money each year trying to “fix” congestion in Auckland and across New Zealand. In fact, it seems that the bulk of transport spending in this country has “fixing congestion” as its ultimate aim – which is a little odd as research from the USA shows that the most congested cities are the cities with the highest levels of economic productivity. But even if we decide that traffic congestion is a bad thing, the next question that comes into my mind is “how bad?”
What level of impact does congestion have on the functioning of Auckland? To what extent would Auckland’s economic performance be improved by the reduction or elimination of congestion? What does “uncongested” actually mean? If traffic congestion ‘costs’ us a particular amount each year, what is the comparison with – empty roads?
A research paper prepared for NZTA helpfully attempts to answer a lot of these questions and to structure a much better informed debate over the true cost of congestion – particularly in Auckland. A lot of this debate, as the paper notes, comes down to definitions – what is congestion?
The purpose of this research was to develop improved approaches to assessing the costs of urban traffic congestion and to make corresponding estimates of the costs of congestion in Auckland (New Zealand).
Various definitions of congestion were reviewed and it was found that the concept of congestion is surprisingly ill-defined. A definition commonly used by economists treats all interactions between vehicles as congestion, while a common engineering definition is based on levels of service and recognises congestion only when the road is operating near or in excess of capacity. A definition of congestion based on the road capacity (ie the maximum sustainable flow) was adopted. The costs of congestion on this basis are derived from the difference between the observed travel times and estimated travel times when the road is operating at capacity.
It is interesting to look at this ‘definitions’ issue in more detail to gain an understanding of what congestion actually is. I find the debate between the economist’s definition and the engineer’s definition – as noted above – pretty fascinating because the economist’s definition potentially leads to the construction of more roadspace (as the threshold for congestion is lower) whereas most transport economists would probably feel more nervous about building additional road capacity than traffic engineers would.
I actually agree with the engineering definition because building a transport system to ensure that no vehicles impact on others is just plain stupid and impossible, while the real impact of congestion beyond a certain level is a reduction in the efficiency of the system – that is once you pass an optimal level the number of people/vehicles that can pass across a certain point begins to reduce. As the research paper notes, at zero speed there is zero flow. This is shown in the graph below:It’s only the bottom half of the graph above (speeds lower than about 42 kph) which actually indicates congestion in my opinion – where the efficiency of the network is reduced because it has become completely overloaded. The research paper takes the same viewpoint.
Applied to Auckland, we actually find that the current speeds on parts of the network analysed are pretty damn close to the most efficient (i.e. maximum flow) speeds – as shown below:Using this information, the pieces of the puzzle about how much congestion really costs Auckland can start to be put together:I’m not entirely sure how relevant the “schedule delay cost” is to working out the economic impact of congestion on Auckland, because it seems like these trips were still taken in an efficient way just not necessarily at the most desirable time. But in any case, using a reasonable definition of congestion highlights that while $250 million a year is quite a bit of money, it’s perhaps a bit less than is often spouted (that $1 billion a year figure which apparently comes from a 1992 survey that unsurprisingly looked at comparison to free-flow (i.e. empty motorways) traffic.
What would be really helpful is to get an idea of where this $250 million of congestion impact happens and who it happens to. If it’s largely impacting on people in far flung suburbs who would just sleep in if their commute was a bit shorter, then I don’t think Auckland’s likely to benefit too much from eliminating/reducing it. However, if the impact is on commercial vehicles (trades vans, couriers, time-sensitive deliveries etc.) then there might be a benefit from reducing congestion.
So overall, I think what I take away from this research is a couple of things: firstly, that congestion is probably not as bad as we had thought if we use a more sensible definition. And secondly, that perhaps we still don’t really know much about the linkage between congestion and Auckland’s actual economic performance. While nobody likes being stuck in traffic jams, for some reason we seem happy to throw billions of dollars a year at trying to fix this problem without even working out whether it’s a problem in the first place, how bad a problem it is or even whether what we’re doing is making things better or worse. To me that seems pretty reckless and dumb.