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Characteristics and Needs for Overhead Guide Sign Illumination from Vehicular Headlamps
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1999-09-01
[PDF-4.61 MB]
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Edition:Final Report 4/5/94 to 9/30/98
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Abstract:The Federal Highway Administration (FHWA) is concerned about changes in headlamp performance of the present fleet of vehicles in the US relative to its ability to properly illuminate traffic signs, especially overhead guide signs. If this is true, overhead guide sign luminance, a function of the type of sign sheeting and headlamp illumination, may be marginal or insufficient for a motorist to read and comprehend the sign in sufficient time to take proper action. A team of Kansas State University researchers was given a contract to determine the minimum luminance requirements for overhead guide signs and to determine if the illuminance from vehicle headlamps on highways was sufficient to provide drivers with this required minimum luminance. This report covers a literature review to determine the minimum luminance value needed, an overview of the equipment developed for field studies of vehicle headlamp illuminance, results of a small laboratory study to determine minimum luminance of highway guide signs, and the results of field studies to determine illuminance values from a sample of the fleet of vehicles on highways, and the results of a study of illuminance values obtained from the headlamps of 50 known vehicles of varying ages and types. Headlamp illuminance readings from samples of vehicles on the highway were taken at points where overhead and shoulder signs would be located. The report discusses minimum luminance values, the illuminance recording equipment, the conduct of the field studies and results, and the laboratory study and results. It concludes with calculations of sign luminance values based on the headlamp illuminance measurements and two assumed types of retroreflective material.
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