A model for estimating traffic sign illuminance and luminance as a function of pavement reflectance

Recent research activity has focused development of minimum retroreflectivity values for traffic signs which depends on reliable estimates of headlamp illuminance reaching traffic signs and the resultant luminance redirected back toward the driver. Research and experience published in the literature consistently indicate substantial differences between measured and modeled illuminance and luminance values. The principle issue identified was the lack of consideration of pavement reflectance. Therefore, the objective of this dissertation was to determine the impact of indirect illuminance as function of pavement reflectance on the sign luminance returned to the driver.; Measurements of headlamp illuminance falling on a sign and the returned sign luminance were recorded on concrete and asphalt pavement. Two sets of measurements were recorded, one with the indirect portion of the headlamp illumination baffled and another without baffling any headlamp illumination. The differences between these baffled and unbaffled measurements were the indirect illuminance values as a function of pavement reflectance.; The baffled and unbaffled measurements were compared to determine the impact of pavement reflectance. They were also compared to modeled estimates. For the modeled estimates, the retroreflective samples and headlamps used in the field were photometrically measured in an attempt to control for as many variables as possible.; It was determined that the traditional photometric modeling techniques provide reasonable estimates of illuminance and luminance. There is no immediate need to modify the traditional photometric modeling process in order to account for pavement reflectance. The impact of pavement reflectance does not explain the concerns about the lack of agreement between traditional photometric modeling estimates and field measurements.