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Public opinion, traffic performance, the environment, and safety after the construction of double-lane roundabouts

Hu, Wen; McCartt, Anne T.; Jermakian, Jessica S.; Mandavilli, Srinivas
Transportation Research Record 2402 Truck and Bus Safety; Roundabouts
2014

This study evaluated the impact of double-lane roundabout conversions on public attitudes, traffic performance, the environment, and safety at two intersections near Bellingham, Washington, and evaluated whether older drivers avoided the roundabouts by taking an alternative route. Driver support for the roundabouts increased from 34% before construction to 70% one year after. One year after construction, more than 40% of drivers did not believe the signs and pavement markings adequately conveyed information about appropriate speeds, right-of-way rules, or navigating the roundabouts in the presence of large trucks. After accounting for other roadway changes, substantial declines were attributed to the roundabout conversions in the delays and queue lengths on minor roads, the proportion of queued vehicles, and fuel consumption and vehicle emissions. Analyses of crash rates per entering vehicles found that the roundabout conversions were associated with reduced rates of injury and fatal crashes combined and increased rates of property damage-only crashes. Only the increase in the property damage-only crash rate at one roundabout was significant. The odds that drivers 70 and older traveled the study corridor versus an alternative route after the roundabout conversions was 0.32 times the odds before. These findings generally are consistent with prior research finding substantial traffic, environmental, and injury-reduction benefits of single-lane roundabouts. However, it seemed the greater complexity of double-lane roundabouts may present challenges as some confusion persisted one year after construction, there was evidence that some older drivers may have taken an alternative route to avoid them, and property damage-only crash rates increased.