Gap Acceptance by Older Drivers – A Field Investigation on Two-Lane Highways

This research investigates older drivers' gap acceptance behavior while waiting to enter an urban highway from an unsignalized minor street. It presents the results of a field study at eight intersections in Minnesota and Tennessee, on how old drivers select a gap from the mainline traffic stream for roadway entry, and the consequent impact on traffic operation and the risk of accidents. Distinctive gap selection and utilization patterns from older drivers have been found, which indicates that, if no improvements are made on traffic control, older drivers at unprotected roadway entrances are more likely to cause operation and safety problems perhaps due to declined perceptual capability and slow physical reactions. Comparisons with other drivers were made and the differences were found statistically significant. Poor gap selection is the leading causal factor to more than forty percent of traffic accidents at unsignalized intersections (1). Rural highways constitute over eighty percent of the total roadway mileage where nearly seventy percent of fatal crashes occur due to lack of signalization, poor roadway design, and other human and environmental factors. Older drivers (age 65 or older) make up an increasingly significant proportion of roadway users today. Studies show that age-related decline in sensory/perceptual skills not only affects the ability of older drivers to effectively operate the motor vehicle, but also creates a higher risk of accidents. For example, older people compose of less than one twelfth of the rural population but are involved in one sixth of the fatal accidents (2). While much of the study on collision prevention has been focused on signalized urban intersections, very limited effort was made for unsignalized intersections in rural areas, where even less attention has been given oder drivers. This study examines gap acceptance of older drivers while waiting to enter a main road from an unsignalized minor street. Specifically, it presents the result of eight rural intersection studies in Minnesota and Tennessee, on how elderly drivers judge the speed and gap time of an approaching vehicle in regard to their own driving experience before deciding whether to initiate a roadway entry. This type of problem was isolated for investigation because unsignalized intersections are where the continuity of travel is interrupted, and where turning movements are unprotected resulting in high accident rates. With generally declined perceptual and physical ability to operate the motor vehicle, older drivers are likely to encounter a greater level of difficulties as they make such roadway entrances.