Adaptation to Standards or New Design Shape? Level of Service and Safety by Varying a Grade-Level Intersection into a Roundabout

The study focused on grade-level non circular intersections and single-lane roundabouts belonging to a two-lane rural roads’ network in the Southern Italy located on a flat terrain that have been built before Italian Standard became law. A total of 104 intersections were studied during a study period of 8 years: 97 non circular intersections and 7 roundabouts. The main goal of this start-up phase about this road issue is to check whether improvements in terms of the level of safety (reduction in the number of crashes and injuries) and service (reduction in the waiting time to make the maneuver) can be achieved when two geometric solutions of intersections at grade are contemplated: (a.) adaptation to the road geometric Standards in force in Italy of non-circular existing intersections without changing the shape; (b.) shape’s modification of the non-circular intersection into a roundabout according to Italian Geometric Standard in force. According to a methodology based on the crash rates’ calculation, the results showed that 65 intersections (58 non circular intersections and 7 roundabouts) have been associated with a “low crash level”, 34 have been associated with a “high crash level” and the remaining with a “medium crash level”. The roundabouts were always characterized by a low crash level. Furthermore, the non circular intersections where additional geometric modules exist (e.g. left-turn lanes, deceleration lanes, divisional islands) as suggested by standard have low crash level as opposed to those belonging to the band of high dangerousness where these elements are missing. The results showed that the waiting times increase when the social costs increase, and that both geometric solutions are consistent to get the purpose but the roundabout is the best solution.