Tools of the Trade: Practice‚ Measuring‚ and Models – Page 2

Are Induced-Travel Studies Inducing Bad Investments?

Robert Cervero

Mark Hansen's 1995 ACCESS article presented compelling evidence on induced travel demand. Titled “Do New Highways Generate Traffic?” it drew on eighteen years’ worth of data for fourteen California metropolitan areas and concluded that added road capacity unleashes new travel. The article showed that added trips quickly fill up an improved roadway, bringing it back to its original congested condition. On average, Hansen found, every ten percent increase in road capacity spurred a nine percent increase in traffic volumes within three or four years. That is, around nine-tenths of added road capacity was absorbed by new trips.

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2017-05-30T22:47:55+00:00Categories: ACCESS 22, Spring 2003|Tags: Congestion, Tools of the Trade: Practice‚ Measuring‚ and Models|

The Path to Discrete-Choice Models

Daniel L. McFadden

The research I’d like to describe was initiated in response to the travel models that were available in 1970. At that time, the dominant tool for urban transportation planning was the gravity model. I thought it was just too coarse to yield sensitive predictions of travelers’ choices among modes. Besides, because it was nonbehavioral, it was a poor ﬁt for those of us brought up on economic theory. Before recounting the exploratory path that led to discrete-choice models, I should ﬁrst say something about gravity models.

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2022-10-03T20:36:02+00:00Categories: ACCESS 20, Spring 2002|Tags: Tools of the Trade: Practice‚ Measuring‚ and Models|

Roughly Right or Precisely Wrong

Donald Shoup

How far is it from San Diego to San Francisco? An estimate of 632.125 miles is precise—but not accurate. An estimate of somewhere between 400 and 500 miles is less precise but more accurate because the correct answer is 460 miles. Nevertheless, if you had no idea how far it is from San Diego to San Francisco, whom would you believe: someone who confidently says 632.125 miles, or someone who tentatively says somewhere between 400 and 500 miles? Probably the first, because precision implies certainty. Although reporting estimates with extreme precision indicates conﬁdence in their accuracy, transportation engineers and urban planners often use precise numbers to report uncertain estimates. To illustrate this practice, I will draw on two manuals published by the Institute of Transportation Engineers (ITE)— Parking Generation and Trip Generation. These manuals have enormous practical consequences for transportation and land use. Urban planners rely on parking generation rates to establish off-street parking requirements, and transportation planners rely on trip generation rates to predict traffic effects of proposed developments. Many transportation models also incorporate trip generation rates. Yet a close look at the data shows that unwarranted trust in these precise but uncertain estimates of travel behavior can lead to bad transportation, parking, and land-use policies.

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2017-05-30T23:10:23+00:00Categories: ACCESS 20, Spring 2002|Tags: Tools of the Trade: Practice‚ Measuring‚ and Models|

A New CAFÉ

Charles Lave

Over the past six months, a National Academy of Sciences panel has been working intensively on a congressionally mandated evaluation of federal regulations on fuel economy in cars. The panel concluded that significant, cost-effective, safety-enhancing improvements were possible. Its report received extensive peer review and was published under the aegis of the National Research Council in a report titled “Effectiveness and Impact of Corporate Average Fuel Economy (CAFE ) Standards.” I was a member of that panel and in the following two essays, I want to review of some of the issues raised in its deliberations. The analytic material comes from the panel’s report; the opinions are my own.

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2017-05-30T23:15:09+00:00Categories: ACCESS 19, Fall 2001|Tags: Environment, Planning History, Tools of the Trade: Practice‚ Measuring‚ and Models|

THE ACCESS ALMANAC: Census Undercount

Paul Ong

The decennial census is America’s single most important effort to collect data on its population, and yet the count always comes up short. Over the years, the counts have been getting somewhat better, although it’s still nearly impossible to include everyone. Estimates of the uncounted population declined steadily from 5.4 percent in 1940 to 1.2 percent in 1980, then increased to 1.8 percent in 1990. Preliminary estimates for 2000 range from 0.96 to 1.4 percent. One troubling aspect of the undercount is the sizable variation among groups—what’s called the “differential undercount,” because groups are undercounted differently. Preliminary estimates for the 2000 census show undercount rates for minorities that are several times higher than rates for non-Hispanic whites—three times higher for African Americans, four times higher for Hispanics, and seven times higher for American Indians on reservations. Undercount rates also vary by region, level of urbanization, and home ownership.

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2017-05-31T21:26:13+00:00Categories: ACCESS 18, Spring 2001|Tags: Equity in Transportation, Tools of the Trade: Practice‚ Measuring‚ and Models|

An Eye on the Fast Lane: Making Freeways Work

Pravin Varaiya

Before leaving for work you can check the weather from the newspaper, radio, or TV report. You can just look at the sky and make your own guess. But you can’t determine much about current traffic conditions. TV and radio traffic reports provide only a summary (“traffic is running smoothly this morning”) and spotty coverage of incidents (“an accident in the second lane has been cleared”). If you are unexpectedly stalled in traffic, your frustration and anxiety mount. You don’t know how long you’ll be stuck or whether you should use your cell phone to cancel your appointment.

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2017-05-31T21:28:12+00:00Categories: ACCESS 16, Spring 2000|Tags: Technology & Innovation, Tools of the Trade: Practice‚ Measuring‚ and Models|

Simulating Highway and Transit Effects

John Landis

Transportation investments and land developments are opposite sides of the same coin. Urban historians and planners have long recognized the power of highway and transit investments to shape metropolitan development patterns. Likewise, transportation planners have long realized the importance of development densities and patterns in shaping the demand for transportation facilities and services. While these relationships may be clear in hindsight, they’re usually cryptic in foresight.

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2017-05-31T21:39:43+00:00Categories: ACCESS 12, Spring 1998|Tags: Tools of the Trade: Practice‚ Measuring‚ and Models|

THE ACCESS ALMANAC: The Pedigree of a Statistic

Donald Shoup

Have you ever wondered how much urban land is devoted to streets and parking? I realize there are many problems inherent in calculating this sort of statistic. For example, it’s not clear whether a driveway alongside a house should be counted as a street or as parking, or maybe as neither, because some driveways serve primarily as open space between adjacent houses and are rarely used by cars. Nevertheless, it would be good to have even a rough estimate of the share of urban land in streets and parking.

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2017-05-31T22:38:10+00:00Categories: ACCESS 11, Fall 1997|Tags: Tools of the Trade: Practice‚ Measuring‚ and Models|

Transit Villages: Tools for Revitalizing the Inner City

Michael Bernick

The Bay Area Rapid Transit system (BART) helped pioneer the development of metropolitan rail transit around the country. But did it accomplish all original goals? The initial 1956 plan primarily aimed to save old city centers and reorganize sprawling suburbs by inducing subcenters there. Spaced about 2.5 miles apart, station stops were to become points of high accessibility that would attract high-density residences, retail shops, and office employers. By reshaping the land market through transit-induced access, BART's planners sought to reshape the metropolis and to eliminate traffic congestion.

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2017-05-31T22:40:27+00:00Categories: ACCESS 09, Fall 1996|Tags: Design‚ Development‚ and Housing, Tools of the Trade: Practice‚ Measuring‚ and Models|

The Total Cost of Motor-Vehicle Use

Mark Delucchi

What costs are involved in motor vehicle transportation? Many people consider only the dollars they spend on cars, maintenance, repair, fuel, lubricants, tires, parts, insurance, parking, tolls, registration, and fees. But motor vehicles cost society much more than what drivers spend on explicitly priced goods and services.

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2017-05-31T23:06:30+00:00Categories: ACCESS 08, Spring 1996|Tags: Equity in Transportation, Tools of the Trade: Practice‚ Measuring‚ and Models|