Speeds and Lateral Placements on Two-Lane Rural Roads: Analysis at the Driving Simulator

The results of a virtual reality experimental survey, aimed at evaluating how cross-section width affects driver’s behaviour, are reported. Two two-lane rural roads were implemented in an interactive driving simulator. Each one is characterised by a different cross section width but same alignment. The configurations of the surveyed cross sections were those recommended by the Italian technical regulation for rural roads (type C1) and for local roads (type F2). The alignment was designed with tangents, clothoids and curves. 64 drivings were performed. Four parameters were determined on each geometrical element of the alignment with different cross section width: average speed, range of speed, average trajectory and range of lateral position on cross section. The narrowing of the cross section width causes the decrease of speed but does not alter the way the driver adjusts his speed driving from a design elements to another along the alignment. The adjustment of the speed is therefore affected exclusively by the geometry of the axis of the alignment. The values of speed obtained indicate that the assumption of the same maximum design speed (Vdmax) for the design of alignments with different cross section width determines a degree of safety, with respect to the stopping manoeuvre, that is inferior in alignments with a wider section. With respect to the values collected on cross section C1, on the cross section F2 a greater dispersion of speed and a greater number of cases of occupation of the shoulder and of the opposite lane (an event which was never recorded in section C1), were recorded. The importance of the shoulder in the driver’s choice of lateral position and his propensity to drive near the axis of the space he perceives as utilizable, consisting of the lane and shoulder, was confirmed