Design for older drivers

In the United States, there is a trend toward an aging population, as well as individuals, continuing to drive until an older age. This trend has implications for all roadway design, including roundabout design, ranging from operations through geometric and sign design. In this regard, designers should consult available documents such as the Federal Highway Administration (FHWA) Older Driver Highway Design Handbook (7):

• The single greatest concern in accommodating older road users, both drivers and pedestrians, is the ability of these persons to safely maneuver through intersections.
• Driving situations involving complex speed-distance judgments under time constraints are more problematic for older drivers and pedestrians than for their younger counterparts.
• Older drivers are much more likely to be involved in crashes where the drivers were driving too fast for the curve or, more significantly, were surprised by the curved alignment.
• Many studies have shown that loss-of-control crashes result from an inability to maintain lateral position through the curve because of excessive speed, with inadequate deceleration in the approach zone. These problems in turn stem from a combination of factors, including poor anticipation of vehicle control requirements, induced by the driver’s prior speed, and inadequate perception of the demands of the curve.
• Older drivers have difficulties in allocating attention to the most relevant aspects of novel driving situations.
• Older drivers generally need more time than average drivers to react to events. 

While the Handbook is not specific to roundabouts, and since no age-related research has been conducted with U.S. roundabouts to date, these findings may apply to older persons encountering roundabouts, as well. The excerpts above all imply that lower, more conservative design speeds are appropriate. Roundabouts designed for low, consistent speeds cater to the preferences of older drivers: slower speeds; time to make decisions, act, and react; uncomplicated situations to interpret; simple decision-making; a reduced need to look over one’s shoulder; a reduced need to judge closing speeds of fast traffic accurately; and a reduced need to judge gaps in fast traffic accurately. For example, two-way stop-controlled intersections may be appropriate for replacement with a roundabout when a crash analysis indicates that age-related collisions are prevalent.