The Demand-Induced Supply Fallacy and Why Fire Trucks Matter

In the midst of other things, I had forgotten that I gave a “24 hour challenge” that, unfortunately, only one person took me up on, and even that one was late. This is what happens when you have a mind that is constantly thinking of many different yet related things and you don’t write a note to remind yourself to stay on track. So, thanks Big Daddy for being brave enough to be the only one to venture a guess at the challenge.

The question was: “Moving cars quickly is an underlying purpose for wide streets, but can anyone tell me what the most significant reason for our wider-than-needed streets is?” (Read the entire post)

The answer that Big Daddy gave was “The [drivers] and their zig zagging, foot stomping, hair raising commuting events … are the reason for those wide streets, not to mention those rounded corners.”

Essentially, this answer reflects an interesting, but probably not uncommon, misconception that drivers have demanded such a road design, thus it was built. This may work in the marketplace to a certain extent, where a Furby craze will induce stores to devote entire isles to annoying little electronic creatures (the demand-induced supply model), but not when it comes to roads and other similar public investments. In the case of such large-scale public infrastructure investments, Shoeless Joe Jackson, as portrayed in Field of Dreams, had a perfect understanding of how things work: “If you build it, they will come.” More specifically, if we design streets to support wild driving, then wild driving will occur, but if we prevent “zig zagging, foot stomping, hair raising commuting events” by making it obviously unsafe for drivers to behave in such a manner (narrower streets, wide-turn corners, on-street parking), then streets will become much less unruly.

Incidentally, this concept of “supply-induced demand” also applies to suburban housing. We tend to think that we have so much suburban housing because that is what we the people want. In fact, we have an abundance of suburbia because that is what some people want, and that “some” includes politicians, developers, bankers, and, yes, planners. The demand for urban or inner-ring suburban housing is currently at around 51%, according to Chris Nelson, a premier housing demand researcher, meaning that the majority of people actually prefer to be closer to the city and all of its amenities and culture, not further away. Yet, we keep building the majority of our new housing as far from the city as possible while neglecting our decaying cities. Do we really think demand is inducing supply here?

Actually, the answer to my question above is so obscure that almost nobody outside of planning circles (and a good portion of this group has no clue) will have ever thought of it. The biggest reason why suburban streets are wider than urban streets (and why urban streets are under constant pressure to widen, to the outrage of their inhabitants) is because of fire department rules that changed several decades ago. The reason these rules changed: longer fire trucks. Fire chiefs wanted to make sure that new municipalities were built to support such beastly machines, so they began to “strongly suggest” (with political backing, making it a virtual requirement) that new suburban streets be wide enough for a fire truck to do a complete 180 degree turn in order to get back out of the neighborhood in which it was needed. Now, besides the ridiculousness of needing such a long fire truck (its length was meant to support longer ladders) in low-density neighborhoods where the tallest building is perhaps 3 stories, this is actually a reasonable request because suburban neighborhoods are built to impede through traffic. If the fire truck wants to get out of such a neighborhood, it must turn around and go back the way it came. But the pressure to widen urban neighborhood streets doesn’t make a whole heck of a lot of sense, because urban streets are laid in a grid pattern, meaning that the fire truck would need to simply make 3 right or left turns to get back to where it came from. The urban areas that have the tallest buildings to support the need for longer fire trucks already have the street structure to handle the vehicles without needing to widen, and the suburban areas do not need such long trucks, and therefore do not need the wider streets. This, of course, is to say nothing about the inefficiencies of suburban street patterns, which I have already addressed before.