Automated Mobile Highway Sign Retroreflectivity Measurement

摘要

Highway signs, which are used to promote highway safety and efficiency, need to command attention and give adequate time for driver response. At nighttime, the visibility of the signs depends on the retroreflectivity of the sheeting material on the signs. The retroreflectivity is a measure of the amount of light emanating from vehicle headlamps that is reflected directly back, by the sign, to the driver of the vehicle. The current practice for ensuring that the signs are performing at night as required consists of either visual inspection, measurement of retroreflectivity with a hand-held retroreflectometer, or systematic periodic replacement of signs regardless of whether they are deficient or not. None of these approaches are ideal. Visual inspection is too subjective, hand-held retroreflectometer measurements are tedious, time-consuming, and sometimes dangerous, and systematic replacement is not cost effective. This report describes a prototype of a digital video image analysis system that measures the brightness of highway signs using nighttime video images taken by a camera mounted in a moving vehicle.