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Okay then figure out another term to explain why bumping Katy Freeway up to 28 lanes is not going to fix Houston's traffic problem. The real explanation is mor

Okay then figure out another term to explain why bumping Katy Freeway up to 28 lanes is not going to fix Houston's traffic problem. The real explanation is more subtle which is that sure, you can just keep adding freeway until there's no traffic, but it's actually bad to have monster 30+ lane highways running through the middle of your cities.

toast0 4y ago
It's not a cute name, but you can't measure actual demand when you're at capacity --- maybe hidden demand, unmeasured/unmeasurable demand. But population growth is often ignored too --- if your metro is growing rapidly, and your road expansion project takes several years and traffic 'is the same' after construction, that's actually a successful project; if the expansion didn't happen, traffic would most likely be much worse. Think of a webserver with a 100M link; if it's at capacity all day long, you know you should upgrade the link, but should you add a second link so you get 2x100M, or does it need 1G or 10G or more? Hard to say. If your 100M link is only at capacity for a few minutes or even an hour a day, adding another link is likely to be enough. Of course, network capacity is easier to add than road capacity.
- ethanbond 4y ago
  I understand all this, the only bit relevant to the point is “network capacity is easier to add than road capacity.” That is why people disparagingly call unmet demand for roads “induced demand,” because it makes it clear it will be very difficult to just more-roadway your way to low traffic.
  - toast0 4y ago
    Ok, the problem with the nomenclature is it sounds like the demand for trips just magically appear when the road does. If you don't want to satisfy the demand for trips with additional road capacity, that's fine; additional road capacity is expensive, but then so are most forms of additional trip capacity, but using a misleading term to defend the choice is not a great way to do it. You probably wouldn't be happy saying we shouldn't build additional housing in (wherever is housing capacity limited) because it will just induce demand for housing and it will still be capacity limited. Certainly, you'd need to build a lot of housing in San Francisco or New York or lots of metros to satisfy the unmet demand for housing and unless/until you build enough, housing will still be a congested resource, but there's no inducement; same thing with roads. At some point, if you're not going to build housing and you're not going to build transportation (whether that's roads or rails or bike paths or flying carpets or whatever), you need to have a real coming to terms of this metro is full and how do we manage its population in a reasonable and fair manner.

toast0 4y ago

It's not a cute name, but you can't measure actual demand when you're at capacity --- maybe hidden demand, unmeasured/unmeasurable demand. But population growth is often ignored too --- if your metro is growing rapidly, and your road expansion project takes several years and traffic 'is the same' after construction, that's actually a successful project; if the expansion didn't happen, traffic would most likely be much worse. Think of a webserver with a 100M link; if it's at capacity all day long, you know you should upgrade the link, but should you add a second link so you get 2x100M, or does it need 1G or 10G or more? Hard to say. If your 100M link is only at capacity for a few minutes or even an hour a day, adding another link is likely to be enough. Of course, network capacity is easier to add than road capacity.

ethanbond 4y ago
I understand all this, the only bit relevant to the point is “network capacity is easier to add than road capacity.” That is why people disparagingly call unmet demand for roads “induced demand,” because it makes it clear it will be very difficult to just more-roadway your way to low traffic.
- toast0 4y ago
  Ok, the problem with the nomenclature is it sounds like the demand for trips just magically appear when the road does. If you don't want to satisfy the demand for trips with additional road capacity, that's fine; additional road capacity is expensive, but then so are most forms of additional trip capacity, but using a misleading term to defend the choice is not a great way to do it. You probably wouldn't be happy saying we shouldn't build additional housing in (wherever is housing capacity limited) because it will just induce demand for housing and it will still be capacity limited. Certainly, you'd need to build a lot of housing in San Francisco or New York or lots of metros to satisfy the unmet demand for housing and unless/until you build enough, housing will still be a congested resource, but there's no inducement; same thing with roads. At some point, if you're not going to build housing and you're not going to build transportation (whether that's roads or rails or bike paths or flying carpets or whatever), you need to have a real coming to terms of this metro is full and how do we manage its population in a reasonable and fair manner.