| Summary: | 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 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. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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