Are Traffic Problems Population Problems?

A while ago, someone asked me what we could do to solve traffic problems. I was feeling flippant, so I said: “Birth control.”

I was reminded of this in a recent flurry of articles about overpopulation (here, for example), something that was broached again with the sordidly surreal “octuplets” case.

But in the U.S., at least, not all the news is bad, as reported by the New York Times:

“And besides, they say, the birth rate in the United States is barely at the level needed to replace the population. Total fertility rate, which predicts the number of children an average woman will have in her lifetime, reached 2.1, considered replacement level, in 2006, but it was the first time it had been that high since 1971. A small percentage of large families, they say, is not enough to tip the balance.”

Given that we’ve added roughly 100 million people since 1968, one does have to wonder, however, about the link between a growing population (via births or immigration) and consistently rising travel times (NB: traffic is far down on my list of “things to be worried about by a growing population”). But looking at some research by Steven Polzin, at the University of South Florida, this relationship is not as simple as it might seem.

The first thing to note, as in the slide below, is that while population has been on the rise, it is far outpaced by “vehicle miles traveled.” It’s not just how many people we have, it’s how much they’re driving.

And while it is inherently true that larger families consume more resources, including miles traveled, there is something of an “economy of travel” as household size increases. Most interesting, though, for travel demographers is the increasing number of single-person households, as in the slide below.

Also of interest is the issue of rising income, and the decreasing cost of travel.

And there’s the people who didn’t have cars who increasingly seem to have one.

Polzin himself does not put population at the top of causal factors for the increase in VMT (and thus, relatedly, congestion); but instead, “trip frequency.”

It goes without saying that population plays some role in contributing to congestion. But what is arguably more critical is a number of demographic changes in the population itself, including the way it has chosen to live (non-walkable neighborhoods in far-flung suburbs, meaning more trips and longer trips — a trend that Richard Florida suggests may have reached its zenith in the current economic meltdown), declining walk-to-work and walk-to-school shares, increasing numbers of cars per household, higher shares of licensed teenage drivers, declining carpool participation rates, under-priced car travel, declining transit funding, etc. etc.

For an example of how things can be done differently, we can look no further than NYC, where a recent study found that between 2003 and 2007, even as the city continued to grow (economically and population-wise), vehicle traffic actually dropped. Granted, the subway cars have felt more crowded since the introduction of the Metrocard, but unlike vehicular traffic, an absolutely packed train travels at essentially the same speed as an empty one.

This entry was posted on Monday, February 16th, 2009 at 10:36 am and is filed under Congestion, Etc.. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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Traffic Tom Vanderbilt

How We Drive is the companion blog to Tom Vanderbilt’s New York Times bestselling book, Traffic: Why We Drive the Way We Do (and What It Says About Us), published by Alfred A. Knopf in the U.S. and Canada, Penguin in the U.K, and in languages other than English by a number of other fine publishers worldwide.

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April 9, 2008.
California Office of Traffic Safety Summit
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May 19, 2009
University of Minnesota Center for Transportation Studies
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June 23, 2009
Driving Assessment 2009
Big Sky, Montana

June 26, 2009
PRI World Congress
Rotterdam, The Netherlands

June 27, 2009
Day of Architecture
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July 13, 2009
Association of Transportation Safety Information Professionals (ATSIP)
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Governors Highway Safety Association Annual Meeting
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October 21, 2009
California State University-San Bernardino, Leonard Transportation Center
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Yale University
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Yale University School of Architecture
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University of Delaware
Delaware Center for Transportation

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International Bridge, Tunnel and Turnpike Association (Organization Management Workshop)
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Edmonton Traffic Safety Conference
Edmonton, Canada

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Canadian Association of Road Safety Professionals
Niagara Falls, Ontario

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Fondo de Prevención Vial
Bogotá, Colombia

Tuesday, August 31
Royal Automobile Club
Perth, Australia

Wednesday, September 1
Australasian Road Safety Conference
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Wednesday, September 22

Wisconsin Department of Transportation’s
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Wednesday, October 20
Rutgers University
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Tuesday, March 8, 2011
Ontario Injury Prevention Resource Centre
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Monday, May 2
Idaho Public Driver Education Conference
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California Association of Cities
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Sunday, August 21, 2011
American Association of Motor Vehicle Administrators
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Wednesday, October 26, 2011
Attitudes: Iniciativa Social de Audi
Madrid, Spain

April 16, 2012
Institute for Sensible Transport Seminar
Gardens Theatre, QUT
Brisbane, Australia

April 17, 2012
Institute for Sensible Transport Seminar
Centennial Plaza, Sydney
Sydney, Australia

April 19, 2012
Institute for Sensible Transport Seminar
Melbourne Town Hall
Melbourne, Australia

January 30, 2013
University of Minnesota City Engineers Association Meeting
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January 31, 2013
Metropolis and Mobile Life
School of Architecture, University of Toronto

February 22, 2013
ISL Engineering
Edmonton, Canada

March 1, 2013
Australian Road Summit
Melbourne, Australia

May 8, 2013
New York State Association of
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Rochester, NY

August 18, 2013 “Ingenuity” Conference
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September 26, 2013
TransComm 2013
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Officials’ Subcommittee on Transportation
Grand Rapids MI



February 2009

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