Influence of Sight Distance on Driver Speed Behavior for Low-Volume Roads

Recent studies have documented a noticeable disparity between design and operating speeds. An important reason for driving errors on two-lane rural roads is the misjudgment of road users concerning the real course of the road. Most of the problems we can detect at the road infrastructure on two-lane rural roads are related to unfavorable conditions of visibility. Inadequate sight distance is an important aspect and their availability influences driver’s behavior with a increase of the hazard. Mathematical models were developed to estimate vehicular speed on curves; in particular the 85th percentile speed for curves was estimated by using the radius of the curve under consideration, the radius of the previous curve and sight distance. The experimental investigation has been conducted employing traffic counters, able to record, for every vehicular passage in both senses: length, instant speed and direction of the vehicle. The plan of survey has been elaborated to satisfy different objectives of search (speed in free flow conditions, in entry and in gone out of the intersections, in rural to urban transition, etc.) and it has been applied to some roads belonging to the network of the Province of Salerno. The measures have been performed holding every section under observation for 2 or 3 hours. Then the data have been used for starting the formalization of some analytical relationships to predict the operating speeds.