Abstract
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% at 1 year after construction. At 1 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, and navigation of the roundabouts in the presence of large trucks. After other roadway changes were accounted for, substantial declines in the delays and queue lengths on minor roads, the proportion of queued vehicles, fuel consumption, and vehicle emissions were attributed to the roundabout conversions. Analyses of crash rates per million 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 age 70 years and older traveled the study corridor instead of an alternative route after the roundabout conversions were 0.32 times the odds before the conversions. These findings are generally consistent with prior research finding substantial traffic, environmental, and injury reduction benefits of single-lane roundabouts. However, the greater complexity of double-lane roundabouts may present challenges, as some confusion persisted 1 year after construction, evidence that some older drivers may have taken an alternative route to avoid them was found, and the rates of property-damage-only crashes increased.
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