| Yesterday I was virtually thumbing through the Daily Journal of Commerce, reading about the ongoing discussions over the fate of the Columbia River Crossing, drawn in by the headline, "Could Columbia River Crossing increase congestion?" I know the answer to that is very possibly yes, and to its credit the DJC takes the time to report on major players in the CRC discussion who feel the same way: The Bicycle Transportation Alliance, in fact, doesn’t endorse any of the width options under review. The nonprofit organization says there’s insufficient evidence to convince it that a new bridge wouldn’t create “induced demand.”
That is, as something becomes increasingly available – in this case, traffic lanes – the demand for it will increase at a proportional rate.
Metro councilors say they are concerned that more lanes may equal more demand, and that more demand may equal more congestion.
More lane miles can, in fact, create more congestion, Metro Council President David Bragdon said. One example: Atlanta. According to Forbes, it’s one of the fastest growing cities in the U.S., but also one of the most congested.
Portland does not want to become another Atlanta, Bragdon said.
So Metro is calling for an independent analysis of induced demand. Councilors say they perceive the two states’ highway departments as reluctant to study or release that information.
As I said, kudos to DJC for even bringing it up; maybe it's happened in articles appearing in The O or the Trib, but I haven't seen it. However,in the end the limitations of space and the need for brevity in general reporting make the article into just another he-said/she-said on the question of congestion. And in this case, that's a painful omission because I think most folks, upon being told that adding capacity increases congestion, initially balk at such a concept. How is that logically possible? Without that explanation, the likelihood that anyone will be enlightened by the article is slim. Coincidentally, this past week I also got the Februrary edition of Scientific American magazine. Now I'm not a big science geek at all, particularly as things get more technical and gadget-y in the prose. But we bought a bunch of subscriptions with our expiring Delta miles, and the options were limited, so I got a year of SA. In this month's, serendipitously, is an article precisely explaining why adding capacity can actually make things MORE congested, not less. Head down below the fold for a review. {Head down, I said!} |
Linda Baker coincidentally hails from Portland, and I'm trying to see if I can get her for comment specifically on the connection between her article and the CRC. Here's why BTA and Metro follow the line from President David Bragdon's campaign, "Building highways to fight congestion is like having sex to fight pregnancy": Conventional traffic engineering assumes that given no increase in vehicles, more roads mean less congestion. So when planners in Seoul tore down a six-lane highway a few years ago and replaced it with a five-mile-long park, many transportation professionals were surprised to learn that the city’s traffic flow had actually improved, instead of worsening. “People were freaking out,” recalls Anna Nagurney, a researcher at the University of Massachusetts Amherst, who studies computer and transportation networks. “It was like an inverse of Braess’s paradox.”
The brainchild of mathematician Dietrich Braess of Ruhr University Bochum in Germany, the eponymous paradox unfolds as an abstraction: it states that in a network in which all the moving entities rationally seek the most efficient route, adding extra capacity can actually reduce the network’s overall efficiency. The Seoul project inverts this dynamic: closing a highway—that is, reducing network capacity—improves the system’s effectiveness.
Although Braess’s paradox was first identified in the 1960s and is rooted in 1920s economic theory, the concept never gained traction in the automobile-oriented U.S. But in the 21st century, economic and environmental problems are bringing new scrutiny to the idea that limiting spaces for cars may move more people more efficiently. A key to this counterintuitive approach to traffic design lies in manipulating the inherent self-interest of all drivers. Self-interest is the key here. Even this article doesn't quite get at the sociology involved to understand the phenomenon. If you look at traffic flow as the aggregate of tens or hundreds of thousands of individual route and driving pattern choices, each choice is likely to come as the result of the evaulation of self-interest: quickest time, least time spent stopped or under forced speed limitation, non-highway preference or highway preference, etc. It's seemingly always the uber-efficient Germans who do the most brilliant traffic network research; in addition to the Braess paradox they also are the proponents of bubble theory, that flow efficiency is like the flow of bubbles, and how the bubbles move create ripple effects such that a single disruption of flow can cascade back far behind the initial disturbance. A real world example of both these principles is one you're probably familiar with around the Northwest: the timed on-ramp lights. I often wonder how many people get why it's done; maybe I'm being an elitist prick and it's obvious. But it took bubble theory to really nail down why it was worth doing, and it boils down to self-interest. In a purely self-interested pattern, most drivers will follow one of two damaging choices: either they'll attempt to get on and get merged into the moving flow as quickly as possible, even if it's one behind the other; or they'll react cautiously and merge as slowly as seems braveable, often abruptly at the last opportunity. You can imagine what both choices do to flow. With either a rush of entering cars or a single car moving slowly and/or abruptly, it forces an overload of adjustments by vehicles already on the highway--namely, they brake or shift lanes to accomodate the new entrants. This braking activity then cascades in a wave behind itself, and you have the beginnings of a stall, otherwise known as a traffic jam. Most often they don't develop, but it's also kinda like hurricanes--eventually a seed will take root and develop under the right conditions. So to correct for the self interest, the metered entrance of cars into the highway flow restricts the pace at which drivers enter the stream. When the impact of new vehicles is regularized, traffic can accomodate it easily and smoothly. But it only happens when drivers sacrifice their self-interest, if even for a few moments. Another example? Traffic circles. Traditional intersections, particularly four way stops, are sometimes crazy "no you, garcon" affairs (or alternately "I'm going, who gives a crap about what you're doing" affairs), which can make them dangerous. When everybody pursues their best interest, those collisions of interest make for actual collisions! A traffic circle forces a couple of things: a yield to traffic in the circle, and a natural slowing of speed coupled with exiting choices in sequence rather than simultaneously. In other words, you can go right, then if you keep moving you can go "straight," then left, and then even a complete U-turn. U-turns in traditional intersections can be terribly dangerous, and many people will turn left and then into a parking lot or driveway to turn around. With a circle, it's almost TOO easy. But it only works when some self-interest is taken out of the picture. Whew! That was a lot of examples and explanations of a single concept. But I think it's important to drive home the concept that the free market of driving choices is an unhealthy system for transportation networks, when in fact reducing options through tight management can make things flow more efficiently and smoothly, not less. And that brings us round to the CRC. Until the public has a rationale to understand why more lanes equals more congestion, they're going to reject the hypothesis as stupid and counterintuitive. It's counterintuitive all right, but it ain't stupid. On the other hand, it's not a very complex phenomenon at root, either. I just wish there was a term for it! The “price of anarchy” is a measure of the inefficiency caused by selfish drivers. Analyzing a commute from Harvard Square to Boston Common, the researchers found that the price can be high—selfish drivers typically waste 30 percent more time than they would under “socially optimal” conditions. Oh hey, thanks Linda. The price of anarchy, indeed. Twelve lanes? It'd be anarchy! Two other notes: deeper into the article Baker talks about the movement in Europe to remove much of the signage, on the principle that the signs force co-dependency on signage to make drivers alert. In other words, it's only worth noticing if the sign tells you so. Without warnings, you have to pay attention, don't you? So people must, so folks are safer because drivers are more alert. I recall reading about this in The Atlantic a couple of years ago. The other thing is that I can't elucidate from the article...because the link to page 2 of the online version is broken. I've sent a twix to the webmaster; hopefully it can be restored and you can at least go read it there. |
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