Influence of vertical alignment on horizontal curve perception: effect of spirals and position of vertical curve

Abstract

Several studies have shown that the perception of horizontal curves can be influenced by an overlapping vertical alignment. A previous two-phase study investigated the hypothesis that a horizontal curve appears flatter when overlapping with a vertical sag curve and sharper when overlapping with a vertical crest curve. The study concluded that the hypothesis was valid. The study also developed several statistical models to estimate the perceived radius of horizontal curves in a combined alignment. This study extends the earlier work by investigating the effect of additional geometric parameters on the perception. The parameters examined include the presence of spiral curves, the length of the spirals, and the position of the vertical curve midpoint relative to the horizontal curve. It was found that (1) driver misperception of the horizontal curvature increases as the radius of the horizontal curve increases, (2) the presence of a spiral curve affects driver perception of the horizontal curvature in the case of crest combination only, (3) the length of the spiral curve has no effect on the perception whether on crest or sag combinations, and (4) while the effect of the position of the vertical curve midpoint relative to the horizontal curve is not statistically significant, it seems that the perception problem appears to diminish as the positive offsets increases.Key words: highway geometric design, visual perception, combined alignment.

Influence of highway three‐dimensional coordination on drivers’ perception of horizontal curvature and available sight distance

“…This time interval corresponds well with the preview times between 1 and 2 s used by Land and Lee [19]. Height and lateral position of driver's point of view were set consistently with previous research: 1.05 m above the road surface and 1.45 m to the right of the road centreline, respectively [8–10].…”

“…According to previous research, only 3D still images of the road were used [8–10]. Drivers were asked to fill a questionnaire and to rank 10 curves.…”

“…Driver's perception of the horizontal curvature on the combination of horizontal and vertical curves has also been studied by other authors [7–12]. The initial hypothesis set by Smith and Lamm [7] is that crest vertical curves combined with horizontal curves look sharper than the same horizontal curve placed on a flat road segment; whereas the sag combination looks flatter.…”

“…The initial hypothesis set by Smith and Lamm [7] is that crest vertical curves combined with horizontal curves look sharper than the same horizontal curve placed on a flat road segment; whereas the sag combination looks flatter. This effect has been studied using static and dynamic computer‐generated three‐dimensional (3D) renderings [8–11]. It was concluded that the probability of erroneous curve perception depended on: type of vertical curve (crest or sag); horizontal radius; crest curve parameter; and travelling direction.…”

Random-Parameter Multivariate Negative Binomial Regression for Modeling Impacts of Contributing Factors on the Crash Frequency by Crash Types

“…Many types of research have evaluated the safety of road geometry by visualization and computer simulation. Hassan et al simulated the influence of the 3D environment on driver vision and analyzed the influence of a combination of the horizontal and vertical curve on road safety [10][11][12][13][14]. en, the Federal Highway Administration developed the Interactive Highway Safety Design Model (IHSDM).…”