As I blogged about a few days ago, I am reading the book “Still Stuck in Traffic: Coping with Peak-Hour Traffic Congestion” by Anthony Downs. This book is probably the most in depth look at the causes, and potential solutions to, traffic congestion that I have ever come across. It is also an extremely comprehensive look at the concept of “induced traffic demand“, which I think is generally ignored when making important transport related decisions in New Zealand. One of the main points of Downs’s book is that building additional transport capacity (whether it is extra roads or extra public transport) is unlikely to fix peak hour congestion – because of induced demand – but may still bring benefits.
Focusing first on the results of adding road capacity, here’s how Downs explains how that approach is unlikely to “fix” congestion:
“…once heavy peak-hour congestion has appeared in key parts of a region’s road network, building new roads or expanding existing ones there does not reduce the intensity of such congestion much in the long run. Once commuters realise the capacity of specific roads has been increased, they will quickly shift their routes, timing and modes of travel by moving to those roads during peak periods, thereby filling up the expanded capacity.
…the resulting triple convergence will soon bring congestion back to its maximum levels during peak periods. True, because of greater road capacity, peak periods of congestion may be shorter, and more drivers can use the roads during those periods – which are the most convenient times for their travel. Moreover, the overall mobility of the region is increased because more vehicles can use the expanded roads during peak hours and off-peak hours. So expanding existing road capacity does produce significant benefits, even if it does not end or greatly reduce peak-period commuting.
However, if the metropolitan area as a whole is growing rapidly, the traffic added by growth will soon overfill the newly built capacity, and periods of maximum congestion will go back to their prior length. Also, the added travel capacity may help persuade more people and firms to move into the region, or it may cause more residents already living there to buy and use automotive vehicles.”
So in the shorter run, there would appear to be transport benefits from widening roads, despite induced demand. If we take the widening of State Highway 16 as an example of a transport project that is very much likely to ‘suffer’ from triple-convergence, while the widening of that motorway will definitely not eliminate (or necessarily even reduce) the severity of congestion along it at peak hour, it is likely to shorten the duration of that peak hour – as more people who previously avoided the worst of the congestion by travelling should the “shoulder peak” periods will switch to travelling at peak time. This might be more convenient for them, and it might free up the road during those shoulder-peak periods. So there are some benefits in the shorter term.
However, in the longer term, widening SH16 is likely to encourage further development along the corridor served by the motorway (a process certainly likely to be helped by huge planned developments around the end of SH16). This development, plus a potential mode shift away from public transport and towards driving, appears likely to ‘eat up’ most of the gains from the SH16 widening project referred to in my previous paragraph. So in the longer-term, it really does seem exceedingly likely that the SH16 widening project will be a complete and utter waste of $800 million. That’s half a CBD Rail Tunnel.
So how about public transport? One of the things that slightly frustrates me about Downs’s book is how quickly he writes off public transport as a solution for most places because he says that urban densities are far too low for it to be viable. While it is true that many US cities do have extremely low urban densities (far lower than Auckland), my understanding of Paul Mees‘s books, particularly in relation to the network effect – as well as seeing how successful public transport has been over the past 10-20 years in very low density Australian cities like Perth and Brisbane – is that public transport can be quite successful and popular in relatively low density suburbia, as long as you’re smart about how you provide it. Putting that issue aside though, what Downs says about the effects of expanding public transport capacity is quite similar to what he says about expanding road capacity – in terms of effects (or lack thereof) on congestion:
“…expanding transit capacity rarely reduces existing roadway traffic congestion that has reached high levels of intensity. This conclusion may seem counterintuitive. If all the expressways leading into a major downtown are jammed every day during peak periods, it seems reasonable to assume that building an extensive fixed rail system on separate rights-of-way also serving the downtown will divert thousands of commuters off the roads, thereby relieving congestion.
In fact, such extensive systems have been built since 1950 in San Francisco, Washington DC and Atlanta. But peak-hour congestion did not decline in any of these regions; in fact, it got worse. Because of the principle of triple convergence, any initial improvement in speed on the expressways caused by such diversions to the new transit system did not last. In the short run, all the auto-driving commuters who shifted from expressways to the new rail systems were replaced on those expressways by other auto-driving commuters who had formerly traveled on other routes or at other times or on other modes. In the long run, the expanded overall capacity of each region’s transportation network – including more highways built in the same time periods – helped encourage more people and firms to locate in those regions. The resulting “induced demand” for travel soaked up all the additional capacity of all types in each region. This outcome was certainly not caused primarily by transit expansion. But neither did that expansion succeed in reducing rising roadway congestion in any perceptible way.
True, the expanded transit systems surely increased travel choices, thereby producing benefits for those who used them. And they enabled more people to travel during peak hours on transit and roads combined, thereby benefiting many auto-driving commuters too. But they did not reduce the intensity of peak-hour traffic congestion.”
This is a particularly interesting point actually, that just as triple convergence ‘eats up’ many of the benefits gained from adding roading capacity, it also eats up many of the benefits to road users of adding transit capacity. So perhaps just as it’s really debatable to say that the Waterview Connection will produce $2.6 billion of time savings benefits, it’s also debatable that 85% of the benefits of the Onehunga Line are really benefits that will be enjoyed by road users through reduced congestion at peak times. Of course, that’s not to say there are no benefits of expanding transit capacity – in fact I would hugely argue the opposite (and so does Downs, to be fair) – just that it’s unlikely that adding transit capacity will reduce the intensity of peak hour traffic congestion.
So if all these things don’t reduce the intensity of peak-hour congestion, what would? Well quite a lot of Downs’s book is dedicated to answering that question – and in short it is all about measures that can ‘spread the load’, ways in which more people can be encouraged to shift from travelling at peak times to travelling at off-peak times. It would appear as though the most effective way of doing that is through road-pricing: putting a price on road capacity that relates to the demand for it. Effectively, if you charge a high enough rate on congested roads at peak times a certain percentage of people will choose to travel somewhere else, at some other time or via some other mode: effectively a “triple divergence”.
Of course road pricing has its problems too, particularly in terms of social equity (to generalise, it will be the poor who are priced off the roads to create enough room for the rich to drive). Another issue is that unless you can come up with some sort of state of the art pricing system that covers every single road, pricing motorways is likely to result in traffic spreading to local roads – not exactly a desired outcome. Ultimately, it does seem as though there are two ways of dealing with the typical “big city” situation of too many cars and not enough peak hour transport capacity: you either price enough people off the road to free up that capacity, or you live with a certain level of congestion.
Which brings me to the question of whether we should actually even try to “fix” peak hour congestion. Or more widely, whether reducing congestion is actually what transport policy should be about. Road pricing, whilst potentially quite effective, does appear to be inequitable and works in three ways (diverging times, routes and modes) – only one of which (diverging modes) may necessarily be a gain at an overall level. By that I mean the disadvantages of forcing people to travel outside the peak period may actually outweigh the disadvantages of congestion – clearly that seems to be the case at the moment as people choose to travel at peak time even though they know they’re going to suffer from congestion (perhaps they have to work set hours, perhaps the benefits to the economy as a whole of having most people work the same hours is worth the congestion issue). Furthermore, as I already noted, spreading traffic away from major roads and onto local roads is likely to degrade the urban environment quite significantly, hardly the kind of outcome we would want. Putting people off driving altogether, by encouraging modeshift, or eliminating ‘unnecessary’ trips (and in the longer run encouraging more intensive urban forms) appears to me as the only real, long-lasting, benefit of road pricing.
So perhaps we’re asking the wrong question here. Perhaps the question shouldn’t be “how do we fix congestion?” Perhaps it should be “how can our transport system improve accessibility, making it easier for people to get around?” In a wider sense, I also think that we should also be concerned about questions like “how can we make our transport system more sustainable” and “how can our transport system help create a better Auckland”, but in a simple sense, it really does seem as though improving accessibility, rather than ‘fixing congestion’ needs to be the primary aim.
And there is a significant difference between the two. While building a new railway line might not fix congestion on the surrounding roads, it does provide potential capacity for 6 lanes worth of traffic in each direction to get where they want to go, at peak time, and be relatively unaffected by unexpected delays. In my mind, that is a huge transport improvement, even if all the people it “takes off the road” are quickly replaced through triple convergence. By contrast, although there may be benefits gained by doubling the width of a motorway – in that more people are able to travel at the time they want to – if all those people are stuck in congestion all you’ve really achieved is a situation where more people are sitting in traffic, not really a transport improvement in my mind.
Ultimately, I don’t know if it’s really possible, or even desirable, to try to “fix congestion”. The main tool for achieving such an outcome – road pricing – is potentially more trouble than it’s worth. But that doesn’t mean there’s no point in trying to improve out transport system, we just need to understand the reason we’re doing it: to improve accessibility, not to fix congestion.