The effect of age and visual impairment on traffic sign detection

Older drivers have a high traffic crash rate. One factor that has consistently been reported as contributing to this problem is that of drivers failing to see and obey traffic signs in time. Researchers have attempted to determine the characteristics of traffic sign design that might improve their visibility and legibility, particularly for older drivers. However, much of this research has been laboratory-based or has employed simplistic on-road measurement techniques, which may not take into account the complexity of the normal driving environment. In response, the current study aimed to develop and apply a technique for the measurement of traffic sign recognition and legibility distances in an open road environment for participants of different ages and ocular status. Three studies were conducted as part of this project.\ud \ud Study 1 was undertaken in order to develop a simple and inexpensive technique for the measurement of on-road traffic sign legibility distances.\ud \ud The system was shown to have better than 90 percent accuracy for legibility distances up to 175m, and measurements between experimenters were consistent. The system was also easy to use and economical. This measurement system was utilised in all subsequent studies.\ud \ud Study 2 was designed to investigate differences in the traffic sign legibility distances of participants acting as drivers and passengers on a closed road circuit. This study was undertaken as participants were required to act as passengers and not drivers in open road experiments due to safety issues. Eighteen participants were divided into a young, middle-aged and older group. Sign legibility distances were determined for driver and passenger runs. The results indicated that there were no significant differences in the traffic sign legibility distances of participants acting as drivers or passengers. The results supported the use of participants as passengers in Study 3.\ud \ud Study 3 was undertaken on the open road to investigate the effect of age and ocular status on traffic sign detection under day and night-time conditions. Thirty-nine participants were divided into five groups: young, middle-aged and older groups with normal vision and two older groups with ocular disease (cataracts and age-related macular degeneration (ARMD)). Each participant undertook a series of vision assessments. On-road traffic sign recognition and legibility distances were also determined under high and low illumination conditions. Results showed that recognition and legibility distances were greater under high compared to low illumination. Although age was not significantly related to the traffic sign measures, there was a trend showing poorer performance with increasing age. The presence of ocular disease, however, did result in significantly reduced recognition and legibility distance performance, particularly for individuals with ARMD. Guide signs had the highest recognition and longest legibility distances of all sign categories while street signs showed the poorest recognition. The obtained traffic sign legibility distances were less than the predicted sign design distances used by road authorities for all of the participant groups except the young visually normal group. The greatest differences between the obtained and design distances were found among participants with ocular disease, especially those with ARMD. Of the vision measures investigated, high and low contrast static acuity, static visual fields and contrast sensitivity were the most highly correlated with sign detection. These four vision tests increased the prediction of sign recognition and legibility distances when compared to high contrast static visual acuity alone.\ud \ud This research has shown that the on-road measurement of traffic sign recognition and legibility distances can be successfully achieved through a simple measurement technique. Low illumination and the presence of ocular disease appear to be influential in traffic sign recognition and legibility distances. The project has highlighted that the traffic sign designs currently used on the road system do not take into account the range of visual abilities possessed by all drivers. Such information provides a basis for further research into the improvement of traffic sign design in order to provide a safer road environment for all segments of the driving population