Influence of Vertical Alignment on Horizontal Curve Perception: Phase II: Modeling Perceived Radius

Abstract

Phase I of a study established that perception of horizontal curvature depends on the overlapping vertical alignment. A horizontal curve radius will be perceived incorrectly if the curve overlaps with a crest or sag vertical curve. Phase II quantified the extent of such erroneous perception. An experiment involving a three-dimensional static presentation was carried out to determine the mean value of perceived horizontal curve radius for different sets of alignment parameters. The results of the experiment were analyzed statistically to examine the effects of the alignment parameters on the perceived radius. The parameters that were found to significantly affect the perceived radius were the type of overlapping vertical curve, actual radius, and turning direction (on crest and sag curves) and sight distance (on sag curves). In addition, simple statistical models were developed using regression analysis to estimate the perceived radius of any horizontal curve in a combined alignment.