Research on age-related driving concerns has shown that at around the age of 65 drivers face an increased risk of being involved in a vehicle crash. After the age of 75, the risk of driver fatality increases sharply, because older drivers are more vulnerable to both crash-related injury and death. Older drivers are also more likely to be involved in multiple-vehicle crashes. Much of the research "has shown the increase in crashes to be associated with an age-related decline in a range of mental and physical abilities."

Despite abundant research in these areas, little is known about the relationships among these various abilities. Most research has focused on a single ability or on only a portion of the full spectrum of abilities associated with driving. In addition, drawing conclusions about the relationships between these declining abilities and the causes of crashes involving older drivers is difficult. Efforts to discover relationships are confounded by variations in: (1) the populations studied, (2) the amount of driving, (3) highway and traffic conditions, and (4) the extent to which the older driver was at fault in the crash.

Attempting to provide more information about the relationships among these various abilities and about the relationship between declining ability and driver performance, the Association for the Advancement of Automotive Medicine (AAAM) conducted a study in Pontiac, Michigan and in Phoenix and Tucson, Arizona. A. James McKnight and James E. Lange described the results of the study in their article "Automated Screening Techniques for Drivers with Age-Related Ability Deficits." Their report appeared in the AAAM's book publishing the proceedings of its 41st annual conference in Orlando, Florida from November 10-11, 1997.

One finding was of particular note. Of all the psychomotor abilities tested, simple reaction time was shown to be the least related to driving performance. This is in contrast to a misconception generally held by the driving public--that a decline in reaction time with age closely relates to unsafe driving. This finding supported other research that has shown reaction time is "one of the less influential of deficits."

BACKGROUND

The mental and physical abilities associated with driving include: (1) "sensory abilities" such as visual acuity, (2) "attentional abilities" such as attention range, (3) "perceptual abilities" such as motion detection, (4) "cognitive abilities" such as long-term and short-term memory, and (5) "psychomotor abilities" such as reaction time. Of particular concern is the decline in mental ability, since it is difficult to determine when it begins and just what its effect on driving may be.

While much of the earlier research has used crashes as a measure of driving performance, this approach is limited in its ability to measure safe driving among individual drivers. Being involved in a crash does not necessarily demonstrate poor driving. The chances of being involved in a car crash can also be affected by the amount and type of driving. With older drivers, it is probably safe to assume that more able drivers do more driving overall, and under more types of conditions.

STUDY METHODS

The study involved 261 drivers ages 62 and over who held a driver's license at the time of the study and were actively driving. More than half the drivers (155) were "incident-involved," meaning they had been referred to licensing agencies for retesting, based on reports of driving problems made by the police, family members, physicians, or staff at the licensing agencies. Participants with clear physical problems, such as the effects of stroke or severe arthritis, were excluded from the study.

The remainder of the participants (106) were drivers who volunteered for the study after receiving information about it from senior citizens groups. They were "incident-free," meaning they had not faced referral because of suspect driving performance. These volunteers received $50 for their participation. Based on these two distinctions, however, it should not be assumed that all incidents for the first group were the result of a decline in ability. Nor should one assume that all the incident-free drivers were also free of any decline in driving ability.

The study examined a number of abilities in each of the five ability areas noted earlier: sensory, attentional, perceptual, cognitive, and psychomotor. Although the study's objective was to analyze the relationships between these various abilities and driver performance, the participants did not actually drive a car. Instead researchers measured their performance on a personal computer, which offered quick, accurate, and reliable results. For example, using the computer allowed the full spectrum of abilities to be tested within 30-60 minutes. Besides the time advantages of automation over manual testing, the computer allowed greater flexibility with the sequencing of the tests. All abilities were measured using the Automated Psychophysical Test (APT) and were scored in terms of time and error. Knowledge of computers did not factor into participants' performance, and certain design features were incorporated to make the testing more user-friendly for older drivers.

STUDY RESULTS

Results showed that correlations between visual acuity (sensory) and driving performance were "relatively low." This should not be interpreted to mean that vision does not play a significant role in driving performance. Rather, it reflects the fact that eyeglasses can improve visual acuity. The correlations of the attentional, perceptual, and psychomotor abilities with driving performance were "small to moderate." Of the five areas tested, the cognitive measures showed the most correlation with driving performance. The measurement of certain information-processing abilities, as well as the measurement of delayed short-term memory, "showed fairly strong correlations between errors and the presence of an unsafe driving incident."

Regarding the study's objective of examining the interrelationships among the various abilities, results showed "moderate to strong correlations" among the abilities. In fact, results showed that these various abilities correlate with one another more than they correlate with deficiencies in driver performance. This finding substantiated earlier research.

CONCLUSIONS

While the study suggested that "age-related deficit appears to pervade all aspects of ability to some extent," the authors advised "great caution" about drawing too many definite conclusions from this study. Certain factors about the sample population itself limited the study. The two sample groups studied did not reflect the entire population of older drivers. In addition, the fact that one group volunteered based on an incident-free driving record (as opposed to being selected at random from the population of older drivers) could introduce factors that the study did not cover. More research is needed before reaching definite conclusions on the relationships between age-related decline in abilities and driving performance.