Study Details

Study Title: Systematic Safety Evaluation of Diverging Diamond Interchanges Based on Nationwide Implementation Data

Authors: Abdelrahman et al.

Publication Date:JAN, 2021

Abstract: Diverging Diamond Interchanges (DDIs) are designed as an alternative to the conventional diamond interchange to enhance the operational and safety performance as they have a lower number of traffic conflict points. Since drivers may not be familiar with DDIs and wrong-way maneuvers might result, there is a need to evaluate the safety performance of DDIs and estimate reliable and representative Crash Modification Factors (CMFs). This study aims to evaluate the safety of DDIs using three methods, which are before-after study with comparison group, Empirical Bayes before-after method, and cross-sectional analysis. This study was conducted 8 based on a nationwide sample of 80 DDIs in 24 states. The analysis results indicated that converting conventional diamond interchange to diverging diamond interchanges could 10 significantly decrease the total, fatal-and-injury, rear-end, and angle/left turn crashes by 14%, 44%, 11%, and 55%, respectively. Moreover, the developed safety performance functions (SPFs) implied that two types of geometric characteristics (i.e., the distance between crossovers/ramp terminals and the speed limit of freeway exit ramps) have significant relationships with the frequency of specific crash types. This study contributes to the existing literature using a relatively large representative sample size, which provides more statistically significant safety measures. In addition, this study also explored the effects of different traffic and geometric characteristics on the safety performance of DDIs.

Study Citation: Abdelrahman, A., M. Abdel-Aty, J. Yuan, and M. Al-Omari. "Systematic Safety Evaluation of Diverging Diamond Interchanges Based on Nationwide Implementation Data". Presented at the 100th Annual Meeting of the Transportation Research Board, Paper No. 21-00026, Washington, D.C., (2021).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Interchange design

Countermeasure: Convert diamond interchange to Diverging Diamond Interchange (DDI) or Double Crossover Diamond (DCD)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.85814.24 StarsAllAllNot specifiedUrban and suburban
0.55844.24 StarsAllK,A,B,CNot specifiedUrban and suburban
0.9284 StarsAllONot specifiedUrban and suburban
0.88711.34 StarsRear endAllNot specifiedUrban and suburban
0.44855.24 StarsAngle,Left turnAllNot specifiedUrban and suburban
1.241-24.13 StarsSideswipeAllNot specifiedUrban and suburban
0.64335.73 StarsHead onAllNot specifiedUrban and suburban
1.762-76.23 StarsOtherAllNot specifiedUrban and suburban
0.84515.54 StarsSingle vehicleAllNot specifiedUrban and suburban