Controlled Driving (Closed Course)
Wood (2002) employed a closed-circuit road test to study the effects of age and visual impairment on driving performance. Visual function was assessed with a battery of tests. The 139 participants were divided into the following five age and visual performance groups: young subjects with normal vision (mean age = 27); middle-aged subjects with normal vision (mean age = 52); older subjects with normal vision (mean age = 69); older subjects with mild ocular disease (mean age = 71); and older subjects with moderate/severe ocular disease (mean age = 71).
The test circuit was 5.1 km (3.2 mi), and participants were given a practice run in the opposite direction of the circuit to reduce familiarity effects. Two experimenters rode with each subject. The driving assessment tasks in this study were selected to provide a relatively high degree of complexity, and included road sign recognition, road hazard recognition and avoidance, lateral gap perception, a divided-attention task, a maneuvering task, and a reversing/parking task.
The road sign recognition task included 42 standard road signs located throughout the course, with a total of 65 items of information. Participants were required to report the information they saw on the signs. The total number of correctly identified items was recorded. The road hazard recognition and avoidance task employed nine 1 x 2.2 m (3 ft x 7 ft) sheets of 80-cm (30-in) thick gray foam placed on the roadway throughout the circuit. For hazard recognition, study participants were instructed to report when they saw a hazard and to avoid it by steering around it. The number of road hazards reported and the number hit were recorded.
For the gap perception task, nine pairs of traffic cones, with variable (lateral) spacing, were placed throughout the course. Six of the nine cone gaps were wide enough to drive through and three were too narrow. Participants were instructed to report when they saw a pair of cones and whether or not there was space to drive through them, and if so, to attempt the maneuver. If the gap was judged to be too narrow, participants were instructed to state so, and to drive around the cones. The number of correct gap widths was recorded, as was the subject’s ability to maneuver through or around the cones without hitting them.
For the divided attention task, five LEDs were mounted on the windshield, spaced at even intervals at the driver’s eye level. Each LED was illuminated three times throughout the run, and subjects were instructed to lightly tap the brake pedal in response to each LED illumination. The number of LEDs seen was recorded. The maneuvering task involved maneuvering through a series of nine cones separated by approximately 1.5 car lengths, placed on a straight section of the circuit. The cones were light gray to increase the visual requirements of the task, with the exception of the cones on each end, which were high contrast. The time to complete the task and number of cones hit were recorded. Two reverse/parking tasks were required, where participants backed the car into a standard-sized parking space marked with four high-contrast poles 1.2 m (4 ft) high, positioned at each of four corners of the parking space. Participants were instructed to reverse the vehicle so that it finished as straight and as centered within the space as possible; forward and reverse movements were allowed to accomplish this goal. The mean time to complete the task and the angle of the car within the space were measured.
Analysis of the driving measures indicated that they were not highly correlated, with the exception of hazards seen and hit. A composite driving score was derived that included road sign recognition, cone gap perception, maneuvering through cone gaps, number of divided attention lights seen, course completion time, and a combined score for hazard detection and avoidance. Older drivers with either normal vision or visual impairment had poorer driving performance compared with younger and middle-aged drivers with normal vision. Overall driving score also decreased for the older participants with ocular disease, as compared to those with normal vision. The driving tasks that involved recognition or divided attention, or that were timed (e.g., the road sign test, the LED task, and the course completion time) were most impaired in the older drivers. In contrast, the ability to recognize and avoid the road hazards was affected by visual status, but not age.
Wood (2002) notes that although the road circuit was free of other vehicles, it contained a relatively high information load in terms of the required driving tasks. A similar methodology could be applied to measure driver performance as a function of medication use, as it tests visual, perceptual, and cognitive skills as well as vehicle handling skills.