Home Skip to main content

Research Reports
Report Details

Title:A Comprehensive Safety Assessment Methodology for Innovative Geometric Designs
Authors:Ziqi Song and Holly Lloyd
University:Utah State University
Publication Date:Jul 2018
Report #:MPC-18-357
Project #:MPC-480
TRID #:01680907
Keywords:Bayes' theorem, before and after studies, calibration, crash rates, diamond interchanges, evaluation and assessment, geometric design, highway safety, methodology, pedestrian safety, urban areas
Type:Research Report – MPC Publications



As the population grows and travel demands increase, alternative interchange designs have become increasingly popular. The diverging diamond interchange is an alternative design that has been implemented in the United States. This design can accommodate higher and unbalanced flow and improve safety at the interchange. As the diverging diamond interchange is increasingly considered as a possible solution to problematic interchange locations, it is imperative to investigate the safety effects of this configuration. This report describes the selection of a comparison group of urban diamond interchanges, crash data collection, calibration of functions used to estimate the predicted crash rate in the before and after periods, and the Empirical Bayes before and after analysis technique used to determine the safety effectiveness of the diverging diamond interchanges in Utah. A discussion of pedestrian and cyclist safety is also included. The analysis results demonstrated statistically significant decreases in crashes at most of the locations studied. This analysis can be used by UDOT and other transportation agencies as they consider future implementation of the diverging diamond interchanges.

How to Cite

Song, Ziqi, and Holly Lloyd. A Comprehensive Safety Assessment Methodology for Innovative Geometric Designs, MPC-18-357. North Dakota State University - Upper Great Plains Transportation Institute, Fargo: Mountain-Plains Consortium, 2018.

NDSU Dept 2880P.O. Box 6050Fargo, ND 58108-6050