Safety performance of alternative intersection designs: techniques, current findings, and research gaps

The use of Alternative Intersection Designs (AIDs), traditionally known as Unconventional Arterial Intersection Designs (UAIDs), has been proposed in the past two decades to improve the operational and safety performance of at-grade signalized intersections. Alternative intersection designs typically require only minor geometric modifications and therefore are considered cost-effective. A considerable amount of valuable research has been undertaken in recent years to evaluate and compare the operational performance of AIDs. In only a few studies, the safety aspects of some AIDs were analyzed. Previous research showed operational benefits of AIDs in terms of higher capacity, lower delays, among other measures. On the other hand, the results on safety performance of AIDs were neither solid nor conclusive. This may stem from the fact that quantifying the operational benefits is far easier than estimating safety. There is currently no collective effort to review the methods used to analyze the safety impacts of AIDs and summarize the previous research findings. This paper serves as an in-depth review of the safety performance of AIDs. Also, the paper identifies areas that need further research and improvements based on the reviewed methods and results. The lack of reliable crash data and robust crash analysis procedures are the main two issues associated with the safety evaluations of AIDs.