Influence of vertical alignment on perception of horizontal curvature
Since most of the driver's required information is obtained visually, the importance of the driver receiving precise visual cues from the road environment cannot be overstated. If the visual cues are confusing or in any way cause the driver to incorrectly assess the approaching road environment, the crash risk of the driver may increase. Of particular concern are the perceptual problems induced by superimposing horizontal and vertical curves. To investigate the effect of overlapping vertical
... lapping vertical alignment on the perceived horizontal curvature, dynamic and static computer generated three-dimensional presentations of the driver's view of a road were created. Phase I of the experiment collected qualitative data to test the hypothesis that overlapping crest curves made horizontal curvature appear sharper and overlapping sag curves made horizontal curvature appear less sharp. Phase II of the experiment quantified the perceived radius Rp. The statistical analysis of the Phase II data showed that horizontal curvature appeared consistently sharper when it was overlapped with a crest curve and consistently flatter when it was overlapped with a sag curve at a level of significance α = 5%. Overall this "optical illusion" effect was more prevalent when sag curves were overlapping horizontal curves. Several regression equations that predict driver perception of horizontal curvature were also developed. For sag vertical curves, the actual radius Ract, the turning direction, and the vertical curve parameter A affected the perceived radius Rp. However, for crest curves, the only geometric parameter found to be a significant predictor of Rp was the actual horizontal curve radius Ract.