Academic journal article Human Factors

The Immediate Effects of Glare and Electrochromic Glare-Reducing Mirrors in Simulated Truck Driving

Academic journal article Human Factors

The Immediate Effects of Glare and Electrochromic Glare-Reducing Mirrors in Simulated Truck Driving

Article excerpt

In this experiment 12 experienced truck drivers drove a fixed-base driving simulator for three 8-h sessions under simulated nighttime driving conditions. Sessions included (a) no glare, (b) intermittent glare presented in the exterior rearview mirrors to simulate following vehicles, and (c) intermittent glare with electrochromic glare reduction. The driving task combined vehicle control on straight and curved road segments with detection of pedestrians appearing alongside the road and targets appearing in the rearview mirrors. The presence of glare slowed detection of pedestrians and, to a lesser extent, slowed the detection of targets appearing in mirrors. Glare was also associated with increased lane position variability, reduced speed on curves, and, most consistently, increased steering variability. We found only meager evidence that electrochromic glare reduction improved target detection performance and no evidence that glare reduction improved vehicle control, despite the fact that participants consist ently voiced positive preferences for glare reduction. The results will aid decision making that requires incorporation of the benefits of electrochromic glare-reducing mirrors.


Heavy-truck operations often involve nighttime driving. One well-recognized problem with nighttime driving is the annoyance and visual impairment caused by glare. Glare can be direct, as from headlights of oncoming vehicles, or indirect, as from headlights of following vehicles reflected from rearview mirrors. Glare from following vehicles can be more problematic for heavy-truck drivers because their needs for rearward information are often greater than those of passenger-car drivers (Flannagan & Sivak, 1994). In addition, prolonged exposure to glare resulting from extended shifts can contribute to driver fatigue (Pulling, Wolf, Sturgis, Vaillancourt, & Dolliver, 1980), which is a common problem associated with nighttime truck operations (McDonald, 1984).

Until recently, approaches to reduce the adverse effects of glare in driving tasks were not applicable to heavy trucks. Prismatic mirrors, which rotate so that the view out the back window is reflected off the dark interior of passenger cars, are not used in heavy trucks. Recent technological advances have provided new solutions for glare reduction that are applicable to heavy-truck operations. Electrochromic mirrors, which use an electric field to block or transmit light, offer the potential for variable reflectivity and for automatic adaptation to ambient light conditions when used with light sensors.

Flannagan, Sivak, Aoki, and Traube (1995) identified the visual factors that determine the optimal level of mirror reflectivity under various lighting conditions. Using subjective ratings obtained in an on-road study, they concluded that optimal rearview mirror reflectivity is a trade-off among (a) subjective discomfort caused by glare from the mirrors, (b) forward seeing ability, and (c) rearward seeing ability. The first two factors are improved by reducing mirror reflectivity, and the third factor is diminished by reducing mirror reflectivity (Flannagan et al., 1995). In a separate study, when visual performance and subjective discomfort were measured under different levels of glare reduction, it was found that more glare reduction was necessary to reduce subjective discomfort than was necessary to preserve forward seeing ability (Flannagan, Sivak, & Gellatly, 1990).

The effects of glare have been measured as decrements in visual performance in the presence of glare or as the time required to recover to a preestablished level of visual function following exposure to glare (Finlay & Wilkinson, 1984; Johansson & Ottander, 1964; Kinney & Connors, 1965; Sturgis & Osgood, 1982). Most experimental techniques used to study glare effects require participants to direct their attention to a single location to ensure precise control of glare dose and exposure. …

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