Cognitive Changes and Making Roadway Navigation Easier

According to NHTSA's Medical Conditions and Driving: A Review of the Literature (1960-2000), the source of the most commonly occurring traffic violations leading to increased crashes involving older drivers, such as failure to obey stop signs or unsafe left turns, is not an "obedience" problem but rather "attentional errors." Such errors may signal cognitive decline, which can develop from a number of conditions, such as the early stages of Alzheimer's disease. Cognitive abilities also may be affected by the interactions of various medications taken for a number of chronic conditions.

Working memory is the ability to maintain information active in memory. A classic example is learning a new phone number and trying to remember it until you can dial it. With age and illness, the working memory capacity—the amount of information that can be held in memory at one time—often declines. There are many different types of attention. Selective attention is used continuously to filter out extraneous sensory information in order to focus on critical information, though most people may be largely unaware that they are doing it. On the other hand, divided attention is used to monitor and respond to multiple events at the same time. An example is the combined tasks of entering a freeway while tracking the curvature of the ramp to steer appropriately and keeping a safe distance from the cars ahead. In general, older adults often find it harder to screen out unnecessary information, especially when they are in unfamiliar situations. They may encounter difficulties when performing multiple tasks at the same time.

Reaction time is the time from when a stimulus appears to when a physical response is initiated. The reduced muscular flexibility of older adults contributes to slower responses. One aspect of age-related slowing in reaction time is slower information processing in the brain. As a result, older drivers may be slower to react when a traffic signal turns from red to green or when applying the brakes during an emergency situation.

Redundant street name signs can be used to improve the chances of drivers remembering critical navigation information when they need it. At one time or another, most people have read a road sign, been distracted shortly afterwards, and then realized that they could not remember the instructions. The distraction essentially wiped the information out of working memory. Given that working memory capacity can decline with age, these types of lapses become more likely for older drivers. Providing the information several times can help limit this problem. The repeated messages create opportunities for drivers to notice the information they need in advance of a decision point so they can prepare to change lanes or turn if need be.

Older drivers often prefer driving in familiar and predictable circumstances. Unfortunately, roadways, even familiar ones, change. For example, work zones may jolt a driver's expectations because of sudden lane closures or detours. When a driver encounters new circumstances, an increased burden is placed on working memory and attention. The driver has to devote more attention and resources to determining how to navigate the new conditions.

Changeable message signs are one way that transportation agencies alert drivers to new circumstances, and designing the messages so that drivers can easily understand them is important. The last thing any transportation professional wants to do is present a message that confuses the driver. FHWA's Highway Design Handbook for Older Drivers and Pedestrians provides preferred strategies for presenting information on changeable message signs. Signs should be designed for a maximum of two phases (for example, phase 1: Road Work Ahead; phase 2: Left Lane Closed). For words that are too long to display, care should be taken in selecting abbreviations. What does ACC mean, for example? Does it mean "access" or "accident"? What about DLY? Is it "delay" or "daily"? The more time that drivers of any age have to spend figuring out a message means the less time they have to focus on safely operating their vehicles.