Aging and time-sharing in highway driving.

Purpose: Proper time-sharing--visual attention allocation--between the road view ahead and other targets is an essential requirement for safe driving, along with other visual and attentional performance. Earlier on-road research has shown that neurologic problems (Alzheimer disease, brain injury) impair time-sharing during in-car tasks. This study analyzed age effects on time-sharing performance.

Methods: Thirty participants in three age groups (mean age 22, 34, and 67 years) drove an instrumented car a trip of 350 km and performed an in-car visual search task with either a motor (keying) or vocal response. The frequency and duration of glances at the in-car targets, total time eyes off the road during task, speed, and lateral displacement of the car were recorded. The participants were also tested on a battery of cognitive tasks during the midway break.

Results: The elderly used a longer total time looking at the in-car display and they traveled a longer distance with eyes away from the road. The number of long (>2 sec) glances and the car's lateral displacement on the road were larger among the elderly than the young drivers. The difference between the older and younger participants was larger when a motor (keying) response was required. The age effects were mediated by cognitive performance (best by the Trail Making A test) rather than by vision parameters.

Conclusion: Older drivers have difficulties in time-sharing in highway driving already at the age of 65 to 70 years.