Study supports roadway intersection design changes

GAINESVILLE, Fla.—Changes in roadway intersection design can keep older drivers safer and on the road longer, according to a report by University of Florida (UF) researchers in Traffic Injury Prevention. Wider road shoulders, right-turn lanes that allow drivers to merge into traffic without stopping, and angle intersections no sharper than 90 degrees all led to better driving performance by older and younger drivers involved in a UF study of roadway intersection design.

"I think the research shows early support that environmental enhancements are conducive to older driver safety and improved performance," said principal investigator Sherrilene Classen, an assistant professor in the UF College of Public Health and Health Professions’ department of occupational therapy. "But what we found is that it didn’t just benefit older drivers, it benefited the younger drivers involved in the study, some of whom were between the ages of 35 and 54, which is also the safest group of drivers."

The UF study is the first to test the Federal Highway Administration’s proposed guidelines for highway design to increase safe driving ability of older drivers. Released in 2001, the guidelines include recommendations for four categories of roadway design. The UF researchers, members of the college’s National Older Driver Research and Training Center, focused on the recommendations for intersections in urban areas because of the high prevalence of crashes associated with them.

The study included 71 participants—39 drivers between the ages of 25 and 45, and 32 drivers aged 65 and older. Each completed a one-hour road course that included five intersections with traffic signals that met federal guidelines and five "unimproved" intersections that weren’t consistent with the guidelines. Testing was done in Gainesville in optimal driving conditions: daylight, good weather and non-peak traffic hours.

During the road course, instruments collected data on the car’s stability and speed and cameras recorded the drivers’ head movements. In addition, evaluators who sat in the passenger seat recorded data on the participants’ driving behaviors such as yielding, signaling, visual scanning, adjustment to stimuli/traffic signals, and gauging the distance between oncoming traffic.

The study results showed that the younger and older drivers had enhanced driving performance for three of the improved intersections:

• a widened receiving lane for left turns, which provides an extra 4 feet to the shoulder;
• right-turn lanes that channel drivers into the flow of oncoming traffic without requiring a complete stop; and
• intersections that are at a 90-degree angle, rather than a sharper angle, such as 75 degrees.

"The Classen … study is the first to measure changes in safe driving performance with improved intersections using objective driving measures taken directly from the vehicle," said David Eby, a research associate professor and head of the Social and Behavioral Analysis Division of the University of Michigan Transportation Research Institute. "Given the great expense involved in improving intersections, the study shows that these improvements lead to safer driving for older adults. This information is important for city planners who are in the process of improving intersections."