Tuesday, July 15, 2014

Helsinki's 'mobility on demand' system and the travel-time landscape

I've got a lot on my plate so I'm just going to take a very quick pass at this. I may try to get back to it later.

There are a lot of good things in the proposal outlined in this Guardian article (via Marginal Revolution), but, as with most transportation articles, there is a bit that troubles me, both because these plans have a way of bringing out the inner ddulite in people and because generalizing from Helsinki is a tricky proposition.

I don't have time to dig into these questions in any depth but I did want to mention a way of thinking about the problems I find useful. For any geographic location and set of transportation options, you can overlay on the map something that looks a bit like a fitness landscape where instead of fitness the variable corresponding to each point on the map is the expected time to travel to that point from the origin.

For pedestrians, the landscape is more or less conical with irregularities caused by obstructions (highways, mountains, bodies of water). The sides of the cone slope up quite rapidly making all but relatively short trips prohibitive.

With automobiles, the slope becomes much more gradual but the landscape becomes much more rugged. A destination five miles away (actual, not driving, distance) can take longer to reach than one thirty miles away if the first has to be reached via surface streets and the second lies along a major highway. (I found numerous examples of this in LA using Google Maps.) Furthermore, the shape of this landscape changes dramatically with traffic levels.

The really rugged landscape comes with mass transit, particularly when you leave some of the more geographically compact cities in the Northeast. (According to Wikipedia "About one in every three users of mass transit in the United States and two-thirds of the nation's rail riders live in New York City and its suburbs." That level of use combined with a highly compact population makes for a unique transportation environment.) This is true for buses, trains and airplanes, but since most people who fly can also get access to cars and taxis, the effect is somewhat mitigated for high end travelers. For those who have to depend on buses and metro lines and who can't walk long distances, the differences can become startling.

I'm sure other people have been using this landscape approach but it doesn't seem to show up in many discussions of the topic. Personally, I find it a remarkably useful way to think about these problems, particularly when talking about food deserts and other areas where transportation and questions of inequality overlap.

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