The Trouble With Traffic Studies
(Source: Unsplash/CHUTTERSNAP.)
At their most earnest and professional, traffic studies are a helpful tool in the planner’s playbook. By carefully analyzing existing traffic conditions, anticipating future needs, and evaluating how potential changes to roadways will affect usage, they can provide important information to support more informed transportation decisions.
But that’s not how traffic studies often play out.
For the private sector, traffic studies may be required to show the impact of a proposed project on the transportation ecosystem. Predicted traffic volumes are used to assess whether additional infrastructure or traffic mitigation measures will be needed if that new business or housing is added. These studies are usually funded by the applicant to enhance their case with elected officials and regulators who must approve them.
In many cases, developers will try to “isolate the scale of the impact,” says Norm Marshall, a planner and author who has worked on projects across the U.S. Examples of this include focusing on a narrower geographical area than will actually be affected by a project, or neglecting to account for modes of transportation other than cars. Marshall cites a case of a warehouse distribution facility that assumes average vehicle counts for its traffic study, but later draws a higher-volume business like Amazon.
Another scenario in which private studies may become problematic is when impact fees are involved. In such cases, the developer may be seeking a dwindling slice of “remaining roadway capacity, and then there isn't any more for anybody else,” says Marshall. This creates an incentive to selectively minimize any traffic impacts on a project and hope that any fees accrue to subsequent developers.
Traffic studies conducted specifically for roadway projects come with a different, and higher dollar, set of difficulties. The U.S. Department of Transportation issues guidelines with its Manual on Uniform Traffic Studies that must be followed for all federal projects (they are “recommended and encouraged” for state and local departments). It includes detailed methodology for data collection on topics such as “vehicle turning movement counts” and “urban/suburban arterial segments.”
Strong Towns Founder Chuck Marohn, who documented his challenges with the road-building establishment in the book, Confessions of a Recovering Engineer, says those guidelines mask what is a highly subjective process. “The traffic study is at best a total guess with a veneer of technical credibility,” says Marohn.
Part of the problem is the assessment of risk versus reward. For an engineer tasked with designing a project, “the most conservative outcome is not the one that would spend the least amount of money or have the least amount of impact, but it's the one that maximizes the amount of traffic,” says Marohn. So a given transportation department may fear a minimal increase in congestion more than other adverse effects of their road building or highway expansions.
The tangled web of federal and state transportation funding leaves also plays a big part in the jockeying over traffic studies. While many departments struggle to fund routine maintenance needs, new road projects can bring new funding streams. So when it comes to executing the traffic studies, “The Department of Transportation, the County Highway Department, a city roads department, they're making a projection in a sense to justify a level of investment,” says Marohn.
Thanks to a requirement from the National Environmental Policy Act (NEPA), all federally funded transportation projects require an analysis of not doing the project at all. This so-called no-build option often uses selective data to show dire circumstances for taking no action, such as increased congestion and danger, and is routinely ignored by decision makers.
For elected officials facing transportation policy for the first time, Marohn advises deemphasizing traffic studies and doing a deeper dive on the underlying issues your municipality is trying to address. Ask transportation planners for the history of previous projects and compare their predictions with the current reality. If possible, hire a staff member proficient in the transportation planning process who shares your values and can do deeper research. Most important of all, says Marohn, you’ve got to be involved in the process before the next traffic study happens.
Both Marohn and Marshall can identify scenarios in which a well-targeted traffic study can provide vital data to enable better planning decisions. It’s the human element that makes traffic studies less than the slam-dunk they’re often presented as. “Just like lawyers spin things, engineers spin things,” warns Marshall.
Ben Abramson is a Staff Writer at Strong Towns. In his career as a travel journalist with The Washington Post and USA TODAY, Ben has visited many destinations that show how Americans were once world-class at building appealing, prosperous places at a human scale. He has also seen the worst of the suburban development pattern, and joined Strong Towns because of its unique way of framing the problems we can all see and intuit, and focusing on local, achievable solutions. A native of Washington, DC, Ben lives in Venice, Florida; summers in Atlantic Canada; and loves hiking, biking, kayaking, and beachcombing.