Vision Changes and Improving Roadway Visibility

What actually happens to a person's eyes as they age? Two of the key changes occur in the lens, which focuses light on the retina. The lens becomes less flexible and yellows with age. The reductions in flexibility make it harder to shift focus from a near object to a far object. In fact, presbyopia, or nearsightedness, is a common age-related visual change. The yellowing of the lens and other changes cause older adults to need more light to see. Although they benefit from additional lighting, they also are more susceptible to glare and require significantly more time to recover from it. One of the major consequences of these and other vision changes is that it is harder for older people to see at night.

Other changes occur as well, such as declines in peripheral vision. Because of these changes, older adults often are slower to react to objects outside of their central focus. Natural declines in peripheral vision often are made worse by glasses, which usually improve focal vision rather than vision in the entire visual field.

This older driver presumably checked her rearview mirror before backing out of her driveway. As people age, their peripheral vision and ability to shift focus from a near to a far object decline.

A number of infrastructure measures can reduce the impact of vision declines. One of the most obvious steps is to enlarge roadway signs and lettering. If drivers can read the information from farther away, they will have more time to make navigation decisions and can focus on safe maneuvers. The Manual on Uniform Traffic Control Devices (MUTCD) recommends sign and font sizes for various types of signs. According to Hari Kalla, FHWA's MUTCD program manager, "The 2003 edition of the MUTCD includes increased letter sizes for street signs based on research recommendations for older drivers."

Curves present another visual challenge. Older drivers may not detect sharp curves, especially at night and wherever the retroreflective pavement markers have faded. Declines in contrast sensitivity (the ability to discern brightness differences between adjacent areas) make it harder for older drivers to notice faded pavement markings, but those markings provide extremely important information to drivers under dark or rainy driving conditions.

One technique to improve curve detection for sharp curves is to use retroreflective pavement markings leading up to the curve and spaced throughout it. These pavement markings are highly visible at night, and researchers at FHWA's Turner-Fairbank Highway Research Center (TFHRC) are looking at configurations that will make it even easier for older drivers to detect sharp curves. Thomas M. Granda, Ph.D., team leader for the Human Centered Systems Team in FHWA's Office of Safety Research and Development, oversees the highway driving simulator at TFHRC. He says, "Our research team is using both the driving simulator and field research techniques to determine the best configurations for retroreflective pavement markings to make curve detection easier for drivers of all ages. And we involve older adults in all of our pedestrian and driving research."