Surrogate safety assessment of super DDI design: A case study in Denver, Colorado

Abstract

Abstract This paper aims to advance the current research on the new super diverging diamond interchange (Super DDI) design by evaluating the safety performance of its two versions (super DDI-1 and super DDI-2) using real-field data. Three interchanges were selected in Denver metro, Colorado as the potential candidates to model for future retrofit. This study considered four interchange designs (i.e., existing diamond, DDI, super DDI-1, and super DDI-2) to assess the safety performance using the combination of VISSIM, Synchro, and SSAM analyzing tools. Several microsimulation models (120 scenarios with 600 runs in total) were created with three peak hours (AM, Noon, and PM) for existing (the year 2020) and projected (the year 2030) traffic volumes. Based on the results, both super DDI versions showed high potential in improving safety. As an important finding from this research, super DDI designs outperformed DDI when considering adjacent signals, while DDI performed apparently similar or sometimes even insignificantly better compared to super DDI if no adjacent intersections were located in the vicinity and if the demand was lower than DDI’s capacity.