redesigning the road environment to improve safety for older drivers (and pedestrians) as evidenced by the new guidelines for older drivers (Federal Highway Administration, 2000). Because automobile crashes are quite infrequent for the average driver, with a probability of 0.1 per year (Evans, 1991), it is sometimes difficult to show the effects of an intervention, such as changing signage, on crash rates. There is considerable evidence that older drivers (age 55 and older) adapt their driving patterns to compensate for weaknesses, such as reducing night driving and rush hour traffic exposure (Ball et al., 1998). Such strategies may not be considered acceptable by those working under time pressure, such as professional drivers.
Aging processes diminish the sensitivity of the visual system. One simple intervention is to increase the amount of light in the environment, particularly for work-related tasks. Care must be taken to avoid increasing glare in the process by controlling the light sources and the work surfaces. Field studies show that light levels in many U.S. office environments generally meet recommended levels for reading tasks of about 100 cd/m2 (Charness and Dijkstra, 1999). However, there is a dearth of information about optimal light levels for older workers. Some evidence suggests that legibility of print can be boosted differentially for older office workers by increasing light levels beyond existing guidelines (Charness and Dijkstra, 1999). Information about the effects of print size, contrast level, and luminance levels on print legibility for older adults is beginning to accumulate (Steenbekkers and van Beijsterveldt, 1998). It would be useful to extend this work to applied settings using typical clerical tasks and to assess the impact of contrast for monitor-based reading tasks.
Hearing capabilities decline normatively with age (Fozard and Gordon-Salant, 2001). Pure tone thresholds decline with age, particularly for higher frequency tones and more so in men than women. Speech comprehension shows noticeable changes (for monosyllabic words) after age 50. Older adults show more masking of signals by noise. Speech compression (e.g., in automated voice mail systems) and rapid speech rate affect older adults more than younger ones (e.g., Stine, Wingfield, and Poon, 1986). Most of these changes can be attributed to loss of hair cells in the cochlea and loss of cells in auditory areas in the brain as well as to general age-related slowing in comprehension processes.