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Induced travel

3 o'clock, January 23, 2003

When I left California I regretted leaving many things behind, but car madness was not one of them. Which is too bad, because it turns out I didn't leave it behind after all.

So I was pleased to see this Seattle Times article. Some researchers have confirmed something I've always suspected: Once your roads are already at capacity, building more roads will not shorten anyone's morning commute.

When the new, wider Interstate 90 bridge across Lake Washington and Mercer Island opened in 1989, state transportation engineers anticipated it would carry more traffic.

What actually happened took them completely by surprise.

Within weeks, daily volume on the new freeway shot up more than 50 percent, exceeding all projections. But traffic on Highway 520, the other bridge across the lake, dipped only slightly, again confounding the experts.

Almost overnight, total cross-lake traffic jumped 20 percent.

Why?

Most transportation experts now agree that building or widening urban highways attracts some traffic that wouldn't be there otherwise. They call it "induced travel" — an increase in traffic that's generated not by growth or other demographic forces but by expansion of the road system itself.

I also discovered a much more detailed economic model from the UK's Department for Transport that I'll have to have a look at.

If I understand the argument correctly, it's really just straightfoward supply-and-demand.

  • The average driver is only willing to spend so much time in traffic.
  • As the “supply” of roads goes up, this tends to drive the “price”, the amount of time it takes to get from point A to point B, down —
  • —but that in turn causes “demand,” the number of people who find driving from point A to point B feasible, up —
  • — pushing the “price” back up to its original level.

Simple, right? Almost makes me wonder why so many conservatives don't seem to get it, but I expect there are other reasons.

Not like any of this is going to stop the voters of King Countyfrom demanding additional lanes for the SR 520 floating bridge, or get them to understand that the purpose of mass transit is to have mass transit, not to make life easier for the people who refuse to abandon their cars.

But at least I can look forward to saying “I told you so.”

Footnote: I suspect that this also explains why — with the exception of LA's Interstate 10, which is possessed by the Devil — we never quite achieve the permanent traffic jam envisioned by Gene Wolfe's “Bluesberry Jam”, Pat Cadigan's Synners, and probably plenty of more famous SF stories I can't think of at the moment, even though it only takes one additional car to push a supersaturated road system over into gridlock: if it starts to happen regularly, people will give up driving, taking the additional car off the road and dropping the system back into its earlier equilibrium, where traffic is still able to move — however slowly.

Comments

Read that article from the Seattle Weekly, and not at all surprised to see Atlanta mentioned there. My town's fast becoming the LA of the South, only we don't have an ocean blocking growth on one side. We've also got the same "build it and they will drive on it" arguments going on here. There was a new highway proposal (called the Northern Arc, or the Perimeter Around the Perimeter) that would've added many more miles of highway. Got shot down, first by ethics violations, and then a change of governorship. Our mass transit is also widely considered humorous.

I, however, have cleverly decided to live a mere five miles from where I work. Go me!

—— Jon, 4:34 PM, Thursday, January 23, 2003

Public transportation is one of the battlefield s upon which we engage in class warfare. In the two big cities in which I've lived, only the poorest and most disenfranchised take public transportation. Public transportation is considered wellare, and those with influence would rather stew in traffic than pay for the transportation of those who clean their houses.

—— Greg van Eekhout, 6:46 PM, Thursday, January 23, 2003

Guess I should use that Preview feature more. Either that or live with my tyops and tortured grammar.

—— Greg van Eekhout, 6:47 PM, Thursday, January 23, 2003

Greg, 'tyops' sounds vaguely like the name of a moderator in some online S&M forum. (Or worse, the prison guard on a sadistic prison planet, sort of like the Australia of the future).

Dave, i'm increasingly convinced that there is a certain amount of intellectual dishonesty coming from some public conservatives, in that they will happily use economics to support their positions but ignore economics when it doesn't support them.

But i've also become convinced that economics, for the average conservative who hasn't been specifically schooled in it, functions a little bit like religion: the market outcome is always good, in their mind. Regardless of what that outcome is. I had one particularly frustating argument with a guy (who, incidentally, had started the argument by making fun of people who said that Amazon was overvalued, because the entire notion of being overvalued is a no-op, because 'value' is determined by the market) who insisted that the market simply cannot, ever, produce a suboptimal outcome; I wish I'd had then the economic training I have now, as I couldn't come up with a good rebuttal then (and think I can today).

It also seems to me that there's a certain amount of projection involved in economic predictions of people who approach economics this way: as if they are operating under the syllogism I think [x] is good. The market always produces good results. The market will therefore produce [x]. The prevelance of this 'logic' makes it extremely difficult to swallow economic predictions from politicians, and even more difficult to swallow economic predictions from random conservative activists.

How does this apply in the case of traffic? Well, if the market always produces the 'optimum' result, then clearly the people who are complaining about traffic have misguided impressions of what is optimum, right?

Note the frustrating part of this: without challenging the notion that the market always produces the optimum result, it's impossible to argue your way out of that particular corner.

—— aphrael, 9:48 PM, Thursday, January 23, 2003

You've heard the one about the University of Chicago economics professor and student walking across the campus, right?

Student: Look, professor, there's a ten-dollar bill on the ground!

Professor: Can't be. If there was, someone would have picked it up by now.

The thing about market economics, in its extreme form, is that it's nondisprovable. If everyone is a rational actor with full information, working to maximize his or her utility, then whatever we see must, by definition, be the best of all possible worlds.

This is a good argument if you're trying to get a free-market ideologue to quit complaining. It's a bad argument if a free-market ideologue is using it to justify the status quo. :)

—— David Moles, 10:14 AM, Friday, January 24, 2003

Ahh, the assumptions of economics. The things which make free-market economics a model rather than an actual description are that (a) people aren't completely rational; (b) people rarely have full information (in part because of the costs of obtaining full information).

I think there are also situations where the optimal individual response to changing market conditions constitutes the least optimal group response if every individual in the group takes it: a good example is farmers who respond to falling farm prices by increasing production. (A similar rationale can be used to explain why working-hour laws are a good thing).

But usually this argument, in my experience, involves a free-market ideologue who is using the market to justify the current situation and argue that any attempt to change anything is communist interfering with the working of the market and should be avoided at all costs.

—— aphrael, 10:46 AM, Friday, January 24, 2003

There's only one answer to an argument like that.

—— David Moles, 1:35 PM, Friday, January 24, 2003

If someone would propose a mass transit plan in Seattle that actually made sense... ah but we're dreaming. Seattle (and Washington state) make my mind hurt when it comes to this stuff.

The class thing about mass transit is bunk when it comes to Seattle mass transit. The only option for most is the bus. I don't take the bus because it would take me two hours to get to work and two hours back (not an exaggeration). I drive the same in 25-35 minutes depending on traffic.

The city of Seattle only has 500,000 people in it. The burbs have a population of 2,000,000. For a mass transit system to have any positive effect it needs to take the burbs into account. I've yet to hear one that does.

—— Scott Janssens, 1:53 PM, Friday, January 24, 2003

Hey, I'd like nothing better than a high-speed rail system taking in all of King, Snohomish, and Pierce counties — lines down the center of I-5, I-405/SR-518, I-90, SR-99, SR-520, SR-167 and SR- 509 with stops every two or three exits would do for a start — but nobody's going to bite off the multi-billion-dollar price tag for a system like that all in one chunk.

—— David Moles, 2:39 PM, Friday, January 24, 2003

They don't have to build it all in one chunk. But they do have to start in the right place, and the U-district to Seatac is not the right place. Ok, that's speculation, but I don't see how it possibly could be.

Because you can't afford to do the right thing is no reason to waste money on an ineffectial (read wrong) thing.

—— Scott Janssens, 4:22 PM, Friday, January 24, 2003