Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity o fan isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues ofontogenetic changes in accident involvement and sensitivity to motion.Although nonvisual factors play a role in effective driving performance, driving is predominantly a visual task. Hills (1980) estimated that more than 90% of the information impinging on the driver is visual in nature. Among the many visual tasks required by the driver, estimating the velocity of other vehicles appears to be one of the more salient. Velocity estimation plays a role in various traffic maneuvers, including intersection crossing, merging, and overtaking. Underestimations of vehicle velocity may place drivers attempting these maneuvers at greater risk of accident involvement. This may be particularly true for older persons, in whom a disproportionate number of both pedestrian and driver accidents may involve errors of velocity estimation (Faulkner, 1975; Hills & Johnson, cited in Hills, 1980;Sheppard & Pattinson, 1986). The data reported in this article were gathered to determine whether the ability to estimate vehicle velocity changes systematically over the adult life span. Speed Estimation and ScalingThe manner in which human observers process velocity information remains unclear, but evidence suggests that such information is used to make decisions about some driving maneuvers. For example, increasing traffic velocity leads to reductions in the minimum time gaps allowed when crossing against traffic flow (Bottom & Ashworth, 1978). Velocity estimation is often inaccurate, however. Many drivers err in estimating the last moment to safely overtake a vehicle in the presence of oncoming traffic (Jones & Heimstra, 1964;Kaukinen, 1972), and at This research was supported by a grant from the National Institute on Aging (AG-00110-02).We thank the Pennsylvania Transportation Institute for the use of their test track; the Oneonta, New York, Police Department for the use of their radar unit; and especially Joyce A. Blake-Guzy for her invaluable assistance in data collection.Lawrence T. Guzy is now at the State University of New York at Oneonta.Correspondence concerning this article should be addressed to Charles T. Scialfa, who is now at the Department o fPsychology, University of Calgary, Calgary, Alberta, Canada T2N 1N4. 60 least some authors (Leibowitz, 1985;Mackie, 1972) have argued that overtaking accidents are due in part to misjudgments of the oncoming vehicle's velocity. Such an argument raises...

The research objective was to improve highway guide sign legibility by replacing the 40-year-old guide sign font with a new font called Clearview. It was believed that the current guide sign font’s thick stroke design, made with high-brightness materials and displayed to older vehicle operators, exhibited a phenomenon known as irradiation or halation. Irradiation becomes a problem if a stroke is so bright that it visually bleeds into the character’s open spaces, creating a blobbing effect that reduces legibility. The Clearview font’s wider open spaces allow irradiation without decreasing the distance at which the alphabet is legible. Results are presented of two daytime and two nighttime controlled field experiments that exposed 48 older drivers to high-brightness guide signs displaying either the current or the Clearview font. The Clearview font allowed nighttime recognition distances 16 percent greater than those allowed by the Standard Highway Series E(M) font, without increasing overall sign dimensions.

Contrast thresholds for sinusoidal gratings of 1.5-18 cpd were measured in young (M = 24 years) and older adults (M = 69 years). Thresholds were determined for stationary gratings, and for gratings that traveled along a circular path at 5, 10, and 15 deg/sec. For static gratings, age differences in thresholds were greater for intermediate and higher spatial frequencies. Grating motion increased thresholds for all observers, but older adults exhibited threshold increases at lower target velocities than the young. Age differences in velocity effects were generally greater at intermediate and higher spatial frequencies. Results are discussed in relation to age changes in temporal resolution and smooth pursuit gain.

Research on individual differences in and agerelated changes to glare sensitivity and to glare recovery time have been treated elsewhere in this