| The main focus of this research study was on evaluating visual demands on two-dimensional highway alignments with an emphasis on determining the effect of complex curves on visual demand. Complex curves are defined as combinations of simple, compound, and reverse curves in a series. Eighteen hypothetical alignments for two-lane rural highways have been developed following the standard guidelines of the Transportation Association of Canada (TAC) and American Association of State Highway Transportation Officials (AASHTO). These alignments were simulated in a low-cost driving simulator. A series of experiments was carried out using the visual occlusion method.; It has been observed that visual demand varies widely with the inverse of radius of curvature of the preceding and current elements, and the characteristics of the combination of the current and the preceding element. Visual demand also varies on identical tangents, depending on the deflection angle, inverse of radius, and turning direction of the preceding curve. The standard deviation of lateral positioning of the subject vehicle was evaluated with respect to the centre-line of the driving lane. This was supposed to have a considerable impact on visual demand evaluation, but it has been observed that this does not bear any significant relationship to visual demand. In addition to curves, tangents, as preceding elements have an immense impact on visual demand evaluation on following curves. Besides, visual demand on tangents has also been observed as highly dependent on the preceding curve and their turning directions. (Abstract shortened by UMI.)... |
