The truth about traffic studies

In a recent issue of Washington City Paper, Lydia DePillis raises the question of whether traffic consultants fudge their results. 

In the District of Columbia, any development proposal that requires wholesale zoning changes has to be accompanied by a study describing how the project might affect pedestrians and motor vehicles, and what could be done to lessen its impact. And since Washington is doing well these days, traffic studies have become a common—yet not well understood—part of civic debates.

Some Washingtonians have grown skeptical of the studies, which typically are conducted by traffic consultants working for developers. And the skepticism is understandable, according to DePillis, who says:

...consultants rarely tell communities that new development will cause any problems. The proof: Out of the 17 applications for campus plans and other projects that require big zoning changes filed over the past two years, every single analysis projected that the proposal would have only “slight,” “minimal,” “negligible,” or “no impact” on existing traffic conditions, sometimes provided that minor improvements were made.

As DePillis explains it, traffic consultants use formulas developed by the Institute of Transportation Engineers to estimate how many new trips a project is likely to generate. Because much of the data is based on developments in suburbs—where relatively few people get around by transit, walking, and bicycling—there's an opportunity for consultants in cities to adjust the numbers. They can point to buses, rail transit, bike lanes, bike-sharing, and even future streetcar service as reasons why a big new urban development won't generate much car traffic.

The city government, she says, generally wants the development, and doesn't have a strong incentive to dispute a traffic consultant's cheery projections. Indeed, DePillis quote Karina Ricks, a consultant who headed the District's Department of Transportation from 2005 to 2011, as saying, "At the end of the day, we are in favor of development. ... If the city stops growing, it starts dying again."

So are the projections wrong, then? From what DePillis reports, flaws are sometimes found by community groups that take a close look, but the logic behind the studies seems to be generally sound. 

Why is that? 

• If a project contains a mix of housing, retail, and offices, people will be able to go about some of their daily movements on foot. Mixed uses can reduce congestion.

• Big projects justify a substantial transportation investment, such as streetcars, also offsetting congestion.

• When there are more people and vehicles trying to get around in a limited space, some of the motorists will have an incentive to do something different: telecommute, move closer to work, use a bike. 

A view from the West

I wondered how closely the scenario outlined by DePillis fits other parts of the country, so I asked Patrick Siegman at Nelson\Nygaard Consulting Associates in San Francisco for his view.

"It never pays to produce slanted analyses," Siegman replied. In many of the California cities where his firm works (typically as a consultant to the municipality rather than to a private developer), proposed developments routinely run into strong resistance from citizens and city staff. Leaving ethical considerations aside, it would be "a really bad idea for a traffic consultant to start playing games with the traffic analysis," Siegman says, because the consultant's reputation would suffer.

He says:

City staff often wield considerable influence, over both the development process and over elected officials' opinions. If staff think that a developer and his consultants are fudging the traffic analysis, they may decide to write an unfavorable staff report, which may well break the project at its City Council vote.

In many, if not most, California cities, city staff are quite strict in specifying exactly how a developer's traffic consultant is to go about conducting a traffic study. It is not uncommon here for traffic studies to declare that a project will result in significant impacts on congestion, and for local elected officials to therefore vote down the project.

It's not uncommon for a traffic study to spark a controversy, Siegman notes. When a university housing project is proposed, for example, neighbors sometimes fear that it will increase the volume of automobile trips. Some of that fear may be justified. But if the university houses more of its student, faculty, and staff on campus, it may convert quite a few commuters into on-campus residents, who usually walk or bike to class.

"We've seen numerous cases," Siegman says, where on-campus housing resulted in no increase, or even a decrease, in automobile traffic. But the situation at each university is different—car ownership rates, parking policies, and the types of on-campus housing vary drastically from one campus to another—so Siegman says it's often necessary to conduct surveys and collect data at the campus in question.  It's unwise to simply apply formulas based on experience elsewhere. 

When a community is apprehensive about traffic problems that a development may generate, Siegman suggests these as possible responses:

If the fear is that too much traffic will result, put a trip cap on the new development, and require ongoing monitoring to ensure that traffic stays below the limit. Establish substantial fines for exceeding the traffic cap. Or, revoke the development’s use permit, and shut it down, until the project is back in compliance.

If the fear is spillover parking problems on nearby neighborhood streets, then establish a residential parking permit district, so that the city can ticket any commuters who try to park in residential areas. Or, set up a residential parking benefit district, where commuters can pay to park, and the resulting parking revenues are used to fund public improvements in the neighborhood.

But to get back to the Washington experience, it's worth remembering that some congestion is a good thing. It means a place is pulsing with life. If uses are mingled together, if the sidewalks and public spaces are made attractive, and if decent transit service is made available, the congestion may be welcomed, much of the time. 

Nobody goes to a downtown to look for free-flowing car traffic. They go there in quest of many other things. And if the place exudes vitality, the vitality that comes with crowds, many of them will come back again and again.

To download a pdf of the of the Pasadena Traffic Reduction Strategies Study, which looks at 10 economically thriving cities that have succeeded in significantly reducing vehicle traffic or drive-alone rates, click here.

For more in-depth coverage on this topic: 

• Subscribe to Better! Cities & Towns to read all of the articles (print+online) on implementation of greener, stronger, cities and towns.

• See the October-November 2011 issue of New Urban News (as our print newsletter was known for 15 years). Topics: HUD’s Choice Neighborhoods, Parking reform, transit-oriented parking policy, Obama vs. Congress, West Virginia town revitalizes, suburb remakes its center, ecological dividend, cul-de-sac makeover, thoroughfare manual, and much more.

• Get New Urbanism: Best Practices Guide, packed with more than 800 informative photos, plans, tables, and other illustrations, this book is the best single guide to implementing better cities and towns.

• See the September 2011 issue of New Urban News. Topics: Walk Score, sprawl retrofit, livability grants, Katrina Cottages, how to get a transit village built, parking garages, the shrinking Wal-Mart, Complete Streets legislation, an urban capital fund, and much more.

• See the July-August 2011 issue of New Urban News. Downtown makeover, agrarian urbanism, bike sharing, bike-ped issues, TIGER III livability grants, unlocking remnant land value, selling the neighborhood, Landscape Urbanism vs. New Urbanism, new urban resort, granny flats, The Great Reset.