Evaluating Pedestrian Service of the New Super Diverging Diamond Interchange on Three Case Study Sites in Denver, Colorado

Ensuring safe and comfortable conditions for pedestrians necessitates specific strategies at intersections and service interchanges where traffic and pedestrians interact in complex ways with other modes of transportation. This study aims to investigate pedestrian performance at the new Super Diverging Diamond Interchange (Super DDI) using real-world locations (i.e., I-225 and Mississippi Ave, I-25 and 120th Ave, and I-25 and Hampden Ave in Denver, Colorado). Three alternative designs, typical DDI, and two versions of Super DDI were considered to make a reasonable comparison with the existing Conventional Diamond Interchange (CDI). A comprehensive series of simulation models (192 scenarios with 960 runs) were tested using VISSIM and Synchro to analyze pedestrian operation (travel time, number of stops, and waiting time) in various traffic and pedestrian distributions. As one of the primary contributions in this paper, pedestrian safety was evaluated based on a surrogate performance measure called design flag, introduced by the new National Cooperative Highway Research Program (NCHRP-948) guideline. The results indicated that the proposed new Super DDI designs are relatively safe when compared with CDI and DDI. For example, a pedestrian analysis of one of the most popular alternative interchanges, DDI, showed potential for unsafe pedestrian conditions in all aspects.