Target Size, Visibility, and Roadway Performance

Analysis of roadway tasks in terms of the CIE 19/2 visibility parameters has beensrestricted to calculation of VL at a fixed distance because there has been no way to adjust forsthe change of apparent size with distance. We use a rough ft of the absolute threshold contrastsdata as a function of luminance and size to allow the computation of VL as a function ofsdistance. Sample VL versus distance and VL versus time calculations are presented. Aspreliminary estimate of detection probability as a function of time is compared to Gallagherssmeasured results to see how current detection models compare to real results.