The highway geometric design guidelines do not deal with the horizontal and vertical alignment's joint design. The guidelines adopt a simplified approach based on the independent design of both the horizontal and vertical alignment followed by the check of the coordination of horizontal alignment and profile so as to avoid geometric combinations which can cause undesirable optical effects and reduced safety. Suggestions regarding the horizontal and vertical alignment's coordination come from studies based on the drawing of the road's perspective and by methods of presentation of the combined alignment through computer animation. These methods are limited with regards to the simulation of the perspective view of the highway from the driver's viewpoint, during the dynamic task of the driving. An experimental survey was carried out with an interactive driving simulator, considering the high potentials of the driving simulation systems for the analysis of the effects of the combined alignment on the driver's behavior. The objective was to verify whether Italian guidelines on the coordination of horizontal curves combined with sag vertical curves and with crest vertical curves are sufficient to avoid a wrong perception of the horizontal curvatures and to not affect the drivers' choice of operating speed on horizontal curves. The statistical analysis outcomes show that on the section at constant radius of the combined curves the V85 is less than or equal to that on the horizontal non-combined curves with the same radius. Results indicate that the suggestions by guidelines on the coordination of horizontal curves overlapping with crest and sag appear to be acceptable.
Abstract