Induced Demand: The principle that, because of pent-up demand, traffic expands to
fill capacity as new roads are built or existing ones expanded.
Christopher M. DiPrima’s excellent op-ed published by the NMA a few weeks ago, Vision Zero’s War on Arterials Has Been a Failure, #596, generated a response from member Sherman Johnson of Maryland who delved further into induced demand. That created an opportunity to ask Chris, who has an advanced degree in city planning, to respond to Sherman’s concerns.
The exchange is quite enlightening. As Chris subsequently noted, “Induced demand has become incredibly important to local (and in some cases, national) transportation policy in the 21st century, and I agree that it deserves an in-depth treatment. All too often, people interpret it to mean that “new roads make their own traffic,” and the reality is that the relationship is not so simple.
Let’s let Sherman and Chris help us navigate the issue, starting with Sherman’s reaction to the aforementioned NMA newsletter:
I’m also in full agreement, with one exception—DiPrima wrote:
“Coupled with a simplistic and incomplete understanding of induced demand (the idea that providing more capacity creates more traffic), these advocates believe that by reducing capacity, they can take sufficient vehicles off the road to improve safety.”
Induced demand is not an ‘idea’, sadly, it is very real. There is nothing complicated about it. It has been exhibited over and over again. There are countless examples all across America—my ‘backyard’ being one.
Parts of Frederick County Maryland are beautiful—they remind me of the unglaciated area of Wisconsin, up around Ontario—but it is being destroyed. The D.C. (and Baltimore) area continues to attract major employers, and that means more people. Most of those people look for someplace that they can afford and still be able to commute to work. As access to FredCo (northwest of D.C.) has been made easier—relative to other D.C. suburbs and exurbs anyway—people have chosen to locate here. That means our schools are ridiculously overcrowded. Many kids are forced to attend classes in “portables” (trailers) that are much less secure than a school building. Prime farmland is paved over for eternity; our property taxes increase (because development never pays for itself), and our quality of life continues to spiral downward.
I-270 is the artery that feeds the malignant ‘residential sprawl’ tumor. Widening 270 would guarantee that it would get much worse.
That aside, even developers must admit that we cannot continue to widen our way out of traffic congestion indefinitely. More highway capacity means more housing developments and more cars on the road (induced demand). The newly widened highway quickly becomes a linear parking lot again.
Eventually we run out of right-of-way. Many of our area roads are at that point now. Then what? Governor Hogan’s latest initiative calls for condemning a lot of private property—bulldozing homes and buildings, building sound barriers in what’s left of people’s back yards— and taking parkland to further widen I-495 (the Beltway) as well as I-270—all the way up to I-70 in Frederick.
One is reminded of the definition of insanity, ‘To keep doing the same thing over and over while expecting a different result each time.’
It’s time to stop and take a deep breath.
Continuing to widen highways, to the point where eminent domain must be used to kick people out of their homes is clearly not a good solution. Some urban areas are simply impacted. They are beyond any reasonable population limit. The only solution I can think of is to encourage large employers (public and private) to locate elsewhere. Maybe some form of tax incentives could be used? It’s a big country, and much of it is economically depressed and actively looking for growth—why not spread those businesses around?
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We debated including Chris’ response here. It is detailed enough—and trust us, worth the wait—that we felt it best to publish it in a second installment next week. Knowing how engaged both he and Sherman are on an issue that affects the daily driving of so many of us, we wouldn’t be surprised if the thoughtful discussion will trigger the demand for additional NMA E-Newsletters on induced demand.