CONTRAST REQUIREMENTS OF URBAN DRIVING

This paper addresses the problem of the specification of lighting for the automobile driving operation. The empirical relationship between a measure of driver visual performance and several methods of quantifying visibility is explored in an effort to develop roadway lighting specifications based on visibility needs. Physical contrast, equivalent contrast, relative contrast sensitivity, and glare exposure are discussed. Field measurements of the visual performance of 941 unalerted motorists are analyzed, and a precise method of quantifying visibility is identified. The form of the suggested visibility term uses physical contrast, contrast sensitivity, and a disability glare factor. A method of prescribing visibility in terms of safe stopping requirements is discussed. Follow-up research that will enhance the reliability of the measures, extend the general applicability of the concept, and further develop the prescription approach is outlined.