Operational Performance of Alternative Types of Intersections - A Systematic Comparison for Indiana Conditions

The growing traffic volumes and limited capacity of road intersections prompt highway engineers to look for solutions that are more efficient than conventional signalized intersections and less expensive than road interchanges. A number of alternative intersections have been proposed but none of them is universally superior. Guidelines are needed for making good initial selections to limit the number of design alternatives and to reduce the design cost. This paper presents research conducted at Purdue University aimed to developing guidelines to help designers in Indiana and other states in the initial selection process of alternative intersection types. This study focuses on isolated signalized intersections of busy major and minor roads where capacity problems are likely and conventional intersections might not be the best solution. The study scope includes conventional intersections, roundabouts, median U-turns, far-sided jughandles, near-sided jughandles, and continuous-flow intersections. All the considered types of intersections except roundabouts are signalized. This paper presents a practical approach based on a classification tree analysis to help designers select promising alternative intersections for given traffic conditions based on capacity, delays, and number of stops. The selected alternatives still have to be considered using other criteria such as cost, right-of-way, and safety. This approach can be applied to develop guidelines for Indiana conditions and for other states that have similar conditions. The paper also may be beneficial to researchers who develop guidelines for other states. The research results indicate that continuous-flow intersections prevail in most cases over the other studied intersection types. In spite of a short three-second critical gap, the roundabouts turned out to have the lowest capacity among all the studied types of intersections. Traffic operations deteriorate more rapidly at roundabouts with increasing traffic volumes than at other intersections, including conventional ones. Jughandles, near-sided and far-sided, perform better than conventional intersections. These conclusions are general and may not apply to all conditions. A catalog of scenarios was developed as part of the presented study to help select promising intersection types for specific traffic conditions.