Retroreflective Requirements for Traffic Signs: A STOP Sign Case Study

摘要

Poor sign reflectivity is a contributor to the high proportion of nighttime accidents. The study determined the performance of STOP signs based on their retroreflective properties. Thirty-five 30-inch STOP signs, including engineering grade and high intensity, were measured in the laboratory to determine their retroreflective properties. A subset of ten signs was taken to the field to determine how far they could be recognized by paid subjects. Mathematical relationships between the various retroreflective properties and recognition distance were developed. The overall specific intensity per unit area (SIA) was found to be a good measure for estimating the recognition distance of STOP signs. By computing the minimum sign viewing distance for various approach speeds, the required integrated SIA of STOP signs was found.