Regional accessibility metric offers powerful approach to transportation system planning

By Chris McCahill

Researchers at the University of Minnesota developed a measure of multimodal accessibility for the Minneapolis-St. Paul region, which they hope can be implemented in metropolitan areas around the nation as an alternative to commonly-used congestion metrics for prioritizing transportation projects and planning system improvements.

For decades, transportation system performance has been measured in terms of traffic congestion and delay, both at the project scale and the regional scale. Project designers and facility operators typically use level of service, a measure of traffic flow, to determine facility performance. Transportation planners and policymakers often turn to the Texas Transportation Institute’s Urban Mobility Report and other estimates of regional congestion to gauge system performance, set policy goals, and prioritize projects. But this approach has garnered fair criticism for its narrow focus on peak period vehicle movement and the emphasis it places on road capacity improvements.

As reported in The Atlantic Cities, the developers of the new accessibility measure flip the equation by asking what the value of accessibility is, rather than what the costs of congestion are. For example, the researchers estimated the number of jobs accessible within 30 minutes of every census block in the twin cities region for every minute of the day. The resulting maps show not only where the most accessible neighborhoods are, but also the net effects of adding, improving, or even removing different pieces of the transportation network. Unlike conventional measures of congestion, the tool accounts for transit availability, walking access, and land use patterns. Car travel would be an additional component.

This work, led by David Levinson and Andrew Owen at UMN’s Accessibility Observatory, requires a great deal of data and hefty computing power. The researchers say this would be the main obstacle to implementing it at a larger scale, but that it could be done if the funds were available. Nonetheless, the work is an important step in helping practitioners and policymakers understand different kinds of performance measures than those they’re used to. Earlier this year, SSTI partnered with Eno Center for Transportation and the Bipartisan Policy Center to release a report recommending metrics that could be used under MAP-21 in place of congestion measures, including average trip time and travel time reliability. The UMN work illustrates exactly how such measures could be used to coordinate transportation and land use decisions and to allocate funds in ways that get the greatest return on investment.

Chris McCahill is a Senior Associate at SSTI.