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Abstract

The diverging diamond interchange (DDI) and the continuous flow intersection (CFI) represent significant innovations in roadway design, offering superior operational performance and enhanced safety compared with conventional signalized ramp terminals and intersections. This study conducts a comprehensive evaluation of these two designs, focusing on both traffic flow and safety outcomes. The research begins by establishing a safety-integrated calibration and validation framework for microscopic traffic simulation models using PTV VISSIM, a leading microscopic traffic flow simulation software developed by the PTV Group Unlike traditional approaches, this framework incorporates surrogate safety analysis by embedding bivariate peak over threshold (POT) modeling from extreme value theory (EVT) to jointly capture conflict severity using time to collision (TTC) and maximum deceleration (MaxD). This dual-purpose modeling approach allows for the estimation of crash frequency directly from simulated conflicts while maintaining operational fidelity. The calibration achieved high accuracy, with GEH values below 5 for all movements and minimal speed errors, and simulation-based crash estimates for CFIs differing from observed frequencies by only 0.07 crashes per year. Validation using 2019 data further confirmed the predictive capability and generalizability of the models.

Complementing the simulation framework, the study utilizes an empirical Bayes (EB) methodology with crash and traffic data from 2006 to 2021 to evaluate six DDI and eight CFI sites in Utah against matched conventional signalized locations. The research developed state-specific crash modification factors (CMFs) and locally calibrated safety performance functions (SPFs), revealing substantial safety benefits for both designs. DDIs demonstrated a 47.8% reduction in fatal and injury (FI) crashes (CMF = 0.522) and a 28.07% reduction in property damage only (PDO) crashes (CMF = 0.719). Similarly, CFI sites showed a 30.7% decrease in FI crashes (CMF = 0.69), a 21.8% decrease in PDO crashes (CMF = 0.78), and a 24.5% decrease in total crashes (CMF = 0.76), preventing an estimated 378 FI and 629 PDO crashes over the analysis period. Collectively, these findings validate that when properly designed and operated, both DDIs and CFIs deliver meaningful improvements in safety performance and offer a robust, transferable framework for evaluating both the operational efficiency and safety of innovative intersection designs at regional and national levels.

How to Cite

Dhimal, Ramesh, Kiran Neupane, Yu "Fred" Song, and Milan Zlatkovic. Assessment of Safety and Operation Performances of CFIs and DDIs in Utah, CTIPS-26-004. North Dakota State University - Upper Great Plains Transportation Institute, Fargo: Center for Transformative Infrastructure Preservation and Sustainability, 2026.