ITRE Researchers Team with NCDOT to Optimize DDIs in the State’s Most Congested Region

Diverging diamond interchange in Cornelius, NC.

For the last several years, ITRE has supported the North Carolina Department of Transportation’s (NCDOT) efforts to improve safety and traffic operations through the installation of Diverging Diamond Interchanges (DDI). This summer, ITRE completed the latest in a series of several national and state DDI studies which provided objective guidance on the impact of DDIs on surrounding signalized intersections.

A DDI is an innovative type of interchange that is designed to manage traffic by crisscrossing flows of vehicles in a manner that limits stopping and reduces conflict with through traffic. As part of the study, ITRE researchers identified a number of potential options to help integrate the DDI into the existing infrastructure and then used simulation to quantify the benefits provided by those options. Simulation results were then used to inform field tests which helped researchers better understand methods to keep traffic progressing through the traffic signals at the interchanges. With the assistance of NCDOT and the City of Concord, the research team implemented the signal timing strategies found to be most impactful at three DDI corridors in the Charlotte area.

At one of the most congested DDIs in the state, located in Catawba at I-77 and Catawba Avenue, the treatments reduced delays for vehicle exiting North I-77 in the afternoon by more than 30 seconds per vehicle. Shannon Warchol, ITRE Research Associate, said, “It was great to see the strategies we tested in the office implemented in the field and find that it improved the travel experience in some of the most congested areas.”