“Does Induced Demand Apply to Bike Lanes?” and Other Questions
What happens when you expand a congested road?
There are actually two different effects that get lumped together under the heading "induced demand."
Effect 1: In the near term, expanding a road causes drivers to alter their travel patterns to use it more.
Effect 2: In the medium to long term, expanding a major road will alter the pattern of development in a city or region, which itself induces more driving.
... if widening a highway allows people to do things they find valuable that they couldn't do before, like choose from a wider pool of jobs, see more friends, or access more recreational activities, isn't that a good thing? Even if the highway does end up congested again at its higher capacity limit? Isn't the additional travel its users are doing improving their wellbeing?
If you want to make the case that increasing the supply of roads is truly a waste of resources (hint: it is), you need to contend with this argument. To do so, you need to understand the other induced demand effect, the one that truly is (mostly) unique to road building.
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When you build a new road or expand a congested one, in the short term it makes some destinations less costly (that is, time consuming or onerous) to reach for some people, while in theory not making any destinations harder to reach than they were before. And that would be the case, if the destinations themselves stayed put. But they don't.
Over time, development in the places that are now better served by road becomes more profitable and attractive. A lot more people are interested in buying a house that's 30 minutes from a major downtown than are interested in buying one that's 50 minutes away. So when you shorten the trip, newly-marketable development follows the new roads. This is especially true with expanding or building new freeways in a growing city: whether we add lanes near downtown or out in the 'burbs, shortening the commute time from the exurbs is a boon to land speculators and builders in those outlying areas.
Meanwhile, the value of close-in locations is depressed, because the competitive advantage of being close to the city has just become a little less. So over time, less development happens in these places, there's less of a market for infill, and in the most depressed neighborhoods, buildings might even be abandoned or demolished.
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Because cars are the fastest widely-available means of getting around we have, it's road building, and essentially only road building in our present-day context, that induces the large-scale changes to our cities that force us to drive ever farther. ... It would be far cheaper to build and live in cities where the people and things we care about are simply nearby to begin with.