The Federal Highway Administration (FHWA) is concerned that too little illuminance from the present fleet of vehicles on US highways is getting to overhead guide sign locations. If this is true, overhead guide sign luminance, a function of the sign sheeting andthe external illuminance, may not be high enough for the sign to be read. A team of Kansas State University researchers was given a contract to determine in the laboratory, minimum luminance requirements for overhead guide signs and to determine if the illuminance from vehicle headlights on highways was sufficient to provide drivers with this required minimum luminance. This paper covers the components and operation of a computerized headlight measurement system (HMS) that was developed to record illuminance values at an overpass location. The system was designed to automatically measure and record "uplight" from vehicle headlights as a function of various vertical angles and distances from an overhead guide sign location. Headlight illuminance readings from a sample of over 1,000 vehicles, identified as to make/type/year and headlight type through their license plates, were taken at seven points over the highway. The paper discusses the design and operation of the system, the results of the illuminance readings broken down by vehicle/headlight type, and the safety implications of these results. (A)
Abstract