Approaches to Improving Geometric Configurations and Level of Service of Intersections under Low-Volume Conditions

The research examines a case study carried out in the Southern Italy where at-grade three-leg and four-leg intersections with stop control on the minor roads were investigated from the point of view of level of service LOS and crash phenomena. The main scope is to explore how a set of methods can be applied sequentially to check whether improvements to LOS, in terms of control delays and 95th percentile of the queues length distribution, and safety, in terms of number of expected crashes during a study period, can be achieved by improving the existing geometric configurations. The intersections investigated belong to a two-lane rural road network under low-volume conditions and they are located on a flat-rolling terrain. They have been built before National Standard became law. A total of 89 typical intersections were investigated and 550 crashes were observed over a period of 5 years (2005-2010). As first step, a crash level was associated with each site according to methodology based on the crash rate evaluation. Further step was focused on main three intersections characterized by high crash rate level. Comparisons in terms of LOS and number of crashes were carried out between existing configurations and new geometric solutions (I option: adjustment of the existing intersections to Standards by adopting left-turn lanes, right-turn lanes, median-refuge islands, lighting; II option: changing the shape into a roundabout). The results confirmed that both geometric solutions are reliable to improve LOS and reduce the crash cost but the roundabout is the best solution.