Economic and Crash Impacts of Traffic Roundabouts: A Real-World Analysis

The Roundabout at Geddes and Superior Roads, Washtenaw County, Michigan

The Federal Highway Administration (FHWA) says the following about Roundabouts.

“Roundabouts are designed to improve safety for all users, including pedestrians and bicycles.  …By reducing the number and severity of conflict points, and because of the lower speeds of vehicles moving through the intersection, roundabouts are a significantly safer type of intersection.”

Modern roundabout intersections have been constructed in Washtenaw County, Michigan in response to traffic crash mitigation needs at existing intersections. In some instances they have been constructed proactively where area growth predictions indicated future unsatisfactory intersection performance. Initial reactions to proposed roundabout intersections have been met with a variety of public comment ranging from unbridled enthusiasm to total disdain. Following construction, discussions typically evolve into identifying difficulties in traversing modern roundabout intersections and the resulting traffic crash experience once the new intersection is opened for public travel.

Very little information has been available relating to actual crash experiences at modern roundabout intersections, or the economic cost of these crashes.  This report evaluates the before-after crash experiences at twelve intersections in Washtenaw County where modern roundabouts replaced existing intersections. In this study, MS2 uses our Transportation Data Management System to identify traffic crash characteristics at each intersection prior to roundabout construction, then compares those characteristics with post construction statistics.  By comparing the crash characteristics with the economic crash cost before and after roundabout construction, MS2 identifies the net benefit/detriment achieved through implementing roundabouts.

For some roundabouts, our findings support the FHWA claims above. Other roundabouts, however, are a totally different story.

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