Typical circulating speeds in Clearwater's four one-lane roundabouts such as this one are 18 to 21 kph (11 to 13 mph), and typical approach speeds (measured at the crosswalks) are 23 to 26 kph (14 to 16 mph). Photo: Ken Sides, City of Clearwater, FL.Of the many changes that come with age, the following are particularly relevant for drivers as they negotiate intersections: narrowing of the visual field and the area of visual attention; decreased visual sensitivity to motion; a decline in the abilities to filter out less important information and continuously refocus on what is the most critical information; a decline in the abilities to perform multiple tasks simultaneously and process information from multiple sources; a disproportional increase in perception- reaction time with increase in complexity of the driving situation; and loss of the head, neck, and trunk flexibility needed to rapidly scan an intersection.
In short, older drivers need more time to perceive and evaluate situations, more time to make decisions and take action, and simpler, narrower scenes to take in—all needs that are well served by the lower traffic speeds and less complex vehicle paths of roundabouts. Events play out more slowly at roundabouts, with ample time for all intersection users to anticipate and adjust to the movements of other vehicles and pedestrians. Vehicle/vehicle conflicts and vehicle/pedestrian conflicts are reduced by about three-quarters and two-thirds, respectively, in single-lane roundabouts, and to a somewhat lesser extent in multiple -lane roundabouts.
Roundabouts are less complicated than conventional intersections controlled by stop signs or traffic signals for several reasons: Traffic threats come from only one direction. Color-coded signal bulbs and ever-cycling phases normally are not used in roundabouts. And the approaching driver need only scan straight ahead for pedestrians and about 30 degrees to the left for slow-moving approaching circulating traffic. Above all, roundabouts eliminate the need to judge gaps in fast head-on opposing traffic. Because older persons are more fragile, crash severity is especially significant. Roundabouts, intrinsically by design, limit vehicle speeds on entry and in the circulating lane. Roundabouts also separate opposing vehicle paths, thereby virtually eliminating the most serious types of crashes that occur at conventional intersections: head-on, left-turn, T-bone, and red-light running. Crashes that do occur at roundabouts tend to be either rear-end crashes or else low-angle, low-energy merging crashes with low closing speeds of 8 to 16 kilometers per hour, kph (5 to 10 miles per hour, mph). Because kinetic energy increases exponentially with velocity, roundabout crashes dissipate far less energy than those severe crash types at conventional intersections: right angles with closing speeds of 56 to 89 kph (35 to 55 mph) or head-on crashes with closing speeds of 113 to 177 kph (70 to 110 mph).
According to ongoing studies from FHWA and the National Cooperative Highway Research Program, roundabout injury crashes are reduced about 75 percent and fatalities by 90 percent or more compared with those at conventional intersections.
—Ken Sides, City of Clearwater, FL
Clearwater, FL, has the highest proportion of population aged 65 or older of any U.S. city with populations of 100,000 or more. Clearwater has built five roundabouts and has seven currently in design and five more in the pipeline, for a total of seventeen. All but the first one were proposed by—and strongly supported by —residents.
