Peripheral Detection of Reflectorized License Plates

Abstract

This paper contains data on the peripheral detection distances of a reflectorized license plate (24 CIL) at night. Detection distances were obtained for two car heading angles (-3 degrees to the left and 10 degrees to the right), and seven detection angles (-30, −20, −10, 0, 10, 20, and 30 degrees) using two groups of 7 young and healthy drivers each. The order of presentation for the 7 detection angles was random and balanced. Each driver sat in a stationary car on a 2000 feet long runway and detected an approaching target under low beam conditions against a background containing a number of luminaires and other light sources. There were three parallel approach paths on the runway. A total of nine consecutive approaches were made for each detection angle. The approaches were divided into 3 blocks and within each block each approach path was randomly chosen once. Each subject detected a total of 63 approaching targets. The results of this study indicate that the average peripheral detection distance for a 30 degree peripheral detection angle can be as short as 25 percent of the average foveal detection distance, while a 20 degree peripheral detection angle resulted in an average peripheral detection distance 3 6 percent of the average foveal detection distance and a 10 degree peripheral detection angle resulted in an average peripheral detection distance of 54 percent of the average foveal detection distance. Based upon the peripheral detection distances obtained in this study we conclude that in roadway situations such as in horizontal curves where reflective targets could become visible for the first time in the periphery of a driver's visual field, appropriate increases in the reflecitvity of a target must be made in order to assure timely detection.