The fear associated with even temporary reductions in road capacity in Auckland is often so extreme that this report from Joe Cortright in City Observatory, Why Carmaggedon never comes (Seattle edition), is worth drawing to everyone’s attention. It takes the example of the closure for demolition of the Alaskan Way, a 3.5km, double stacked, 6-lane, fugly as, harbour-severing, 1940s fly-over in Seattle, to illustrate a well observed feature of city traffic. One that appears so counterintuitive to so many that even our engineering experts commonly disbelieve it: To reduce congestion in a mature driving city; remove traffic lanes, even whole routes.
Above is the PM rush with whole flyover closed, but none of big replacements for it yet open. Not only is congestion not worse without this huge capacity removed, but it actually appears to be better. It’s worth reading the whole short article, but here’s what Cortright say about this:
So what’s going on here? Arguably, our mental model of traffic is just wrong. We tend to think of traffic volumes, and trip-making generally as inexorable forces of nature. The diurnal flow of 100,000 vehicles a day on an urban freeway the Alaskan Way viaduct is just as regular and predictable as the tides. What this misses is that there’s a deep behavioral basis to travel. Human beings will shift their behavior in response to changing circumstances. If road capacity is impaired, many people can decide not to travel, change when they travel, change where they travel, or even change their mode of travel. The fact that Carmageddon almost never comes is powerful evidence of induced demand: people travel on roadways because the capacity is available for their trips, when when the capacity goes away, so does much of the trip making.
We are in the middle of a real time example of this in Auckland too, a decent chunk of Albert St is severely restrict due to CRL works. I’m told it is currently carrying 1/10 of the volumes it used to around 2400 thousand movements a day, whereas it was previously 24,000. Where are those other vehicle trips, on the parallel streets? Well we know the buses are because we moved them there, which must have increased the traffic on both Queen and Hobson in particular, right, plus the rest of that traffic?:
Well it’s kinda nowhere, or rather somewhere, as overall volumes in the city are apparently pretty much the same, but surrounding the restricted street, and in particular in parallel to it, it’s arguably better. Both Queen and Hobson/Nelson (considered here to be one huge street with a block sized median) appear to be improved by this.
Traffic is not, as it appears the kids are taught in Traffic Engineering 101, an immovable force of nature that must accommodated or we will face the end of times, but rather a human creation, therefore with all the maddening human characteristics we should expect. In particular, drivers, unlike sewage, have agency, and if slowed annoyingly or blocked entirely, seem to be able to make other plans, drive elsewhere, drive at a different time, not drive at all…? Sewage however, can only follow the laws of gravity and if one route is barred will flow down the next available one, ad infinitum.
Traffic is not sewage. Perhaps the whole liquid language applied to traffic is at fault here? Perhaps we really ought to stop talking about traffic flow? Cortright:
If we visualize travel demand as an fixed, irreducible quantity, it’s easy to imagine that there will be carmaggedon when a major link of the transportation system goes away. But in the face of changed transportation system, people change their behavior. And while we tend to believe that most people have no choice and when and where they travel, the truth is many people do, and that they respond quickly to changes in the transportation system. Its a corollary of induced demand: when we build new capacity in urban roadways, traffic grows quickly to fill it, resulting in more travel and continuing traffic jams. What we have here is “reduced demand”–when we cut the supply of urban road space, traffic volumes fall.
‘Reduced demand’ as the corollary of induced demand, or should that be reduced supply? Anyway this phenomena really seems to be suggesting that an important amount of driving in our cities occurs simply because it can. Prevent it, and it goes away. I don’t think is the case in vastly crowded cities without mature road or alternative transit or active networks, but in cities like Seattle or Auckland with very high vehicle ownership numbers, complete driving networks, and at least some transit and bike lane systems, it appears an important amount of journeys on enough routes are entirely dispensable, all but valueless, discretionary. In these places, I propose, it’s so easy to jump in a car, facing very little marginal cost at all, either in time or money, that, what the hell, I may as well do it.
We perhaps have overshot, suppling nearly everyone with friction free car access and stacks of overbuilt driving infrastructure (evidenced by falling average car occupancy numbers; now 1.1) that the marginal value of the next trip maybe below zero?
Driving in first world cities is, as the economists have it in their typically clunky wording; an underpriced good.
To me this means it is likely that so much is wrong in our approach to our streets:
- We likely overvalue vehicle trips in economic calculations (it turns out they are easily abandoned)
- We make gods of tools like traffic modelling (these should only inform, but never determine decisions)
- We misconceive the very nature of traffic itself (we ignore driver agency)
Most of all we fail to see streets properly at all; they really are mutable public space that we can do all sorts of things with, if only we would allow ourselves the freedom from servitude to the seemingly unchangeable god of traffic. And all its high priests and their mumbo-jumbo methodologies.
This is a hugely liberating set of conclusions, because we know the economic and social value of walkable cities, and we know the huge economic and environmental costs that vehicle traffic imposes… So do we have the courage and imagination to move away from the barren 20th century ideology of traffic uber alles?