Interchange Complexity Model and Related Safety Implications

Abstract

Freeway interchanges accommodate large traffic volumes within a constrained area. When their design is complex and includes unexpected features, it may increase drivers’ workloads and lead to driving errors, thus increasing the likelihood of a crash. The study’s goal is to provide a tool for assessing the safety impacts of interchange complexity, promoting a simpler and safer design. This paper presents an interchange complexity model (ICM) that is based on estimations of aggregated drivers’ workload in interchanges. A database of 25 interchanges from the New Jersey interstate road system was used to examine the ICM and construct a resulting crash prediction model by comparing their interchange complexity index (ICI) with three years of crash data. Further on, nine additional interchanges were analyzed similarly in order to validate both the use of the ICM and the resulting crash prediction models. Actual observations of the validation data were relatively close to average model predictions. It is proposed that highway planners could use the ICM for estimating the complexity of interchange design alternatives and the implications for road safety to minimize driver errors and thus reduce crash occurrences.