Described in this paper is a revised version of the ford motor company detect seeing distance model. The revised model, known as pcdetect, is written in quickbasic for ibm-compatible personal computers. Pcdetect calculates the distances at which a driver can see various objects on the road at night as illuminated by the headlamp system specified by the user. The revised algorithms are based on blackwell's recent contrast sensitivity research. They include new formulations for calculating contrast thresholds and take into account driver age, target size, background luminance, and individual differences. The revised model also incorporates a driver age factor for calculating veiling glare. The seeing distances calculated using the old and revised versions are generally in close correspondence. However, at low illumination levels, the new algorithm predicts seeing distances that are as much as 12 percent greater than the original version. This can be traced to differences between the old and revised contrast threshold functions. The age and variability factors in the new algorithm have a substantial impact on seeing distances. Against alow beam glare source at 300 ft, the seeing distance to a pavement edgeline was 413 ft for an average 20 yr old and 130 ft for a 15th percentile 70 yr old. This paper appears in transportation research record no. 1213, Human performance and highway visibility: design, safety, and methods.
Abstract