Windshield Glare from Bus Interiors: Potential Impact on City Transit Drivers at Night

Windshield glare at night is a safety concern for all drivers. Public transit bus drivers also face another concern about glare caused by interior lighting sources originally designed for passenger safety. The extent to which interior light reflections contribute to glare is unknown. Unique methods for measuring discomfort and disability glare during bus driving were developed. An initial simulation study measured windshield luminance inside of a New Flyer D40LF diesel bus parked in a controlled, artificial, totally darkened test environment. Findings indicated significant disability glare (from elevated luminance) in the drivers’ primary field of view due to interior reflections. Any reduction in contrast would result in less prominent glare if actual driving conditions differ. To assess this, levels of windshield glare were also measured with the bus parked on the roadside under the “background glow” of the urban environment. Findings reveal that under road conditions the extent of disability glare from interior reflections is much less, but not negligible, when contrast is reduced. The information gathered in these studies may be useful to manufacturers and transit authorities to improve conditions for drivers and the travelling public. Measurement methods developed in this study may prove useful for assessing elements of interior design. The difference between disability and discomfort glare is discussed. The results provide directions for implementation of glare control strategies.