Safety Evaluation of Diverging Diamond Interchanges in Missouri

Boris R. Claros; Praveen Edara; Carlos Sun; Henry Brown

doi:10.3141/2486-01

Safety Evaluation of Seven of the Earliest Diverging Diamond Interchanges Installed in the United States

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2583-04 ◽

2016 ◽

Vol 2583 (1) ◽

pp. 25-33 ◽

Cited By ~ 6

Author(s):

Joseph E. Hummer ◽

Christopher M. Cunningham ◽

Raghavan Srinivasan ◽

Shannon Warchol ◽

Boris Claros ◽

...

Keyword(s):

United States ◽

Safety Evaluation ◽

The United States ◽

Diamond Interchanges

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Safety Evaluation for Turnarounds at Diamond Interchanges: Assessing the Texas U-Turn

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198118797186 ◽

2018 ◽

Vol 2672 (17) ◽

pp. 61-71 ◽

Cited By ~ 2

Author(s):

Karen K. Dixon ◽

Raul E. Avelar ◽

Maryam Shirinzadeh Dastgiri ◽

Bahar Dadashova

Keyword(s):

Performance Assessment ◽

Safety Evaluation ◽

Safety Performance ◽

Sampled Data ◽

Data Set ◽

Left Turn ◽

Reliable Assessment ◽

Street Traffic ◽

Diamond Interchanges ◽

Longitudinal Distance

Texas frontage road turnarounds at diamond interchange locations are a common treatment in the State of Texas. This configuration, also often referred to as the Texas U-turn, allows vehicles traveling on a one-way frontage road to access the opposing direction one-way frontage road via a U-turn before the terminal intersections at the diamond interchange. This technique removes two potential left-turn maneuvers from the adjacent at-grade intersections. The frontage road turnaround has operational benefits that result from shifting vehicles that would typically be occupying the intersection. The safety of these turnaround configurations, however, is not well known. This paper focuses on the observed safety performance of these turnaround configurations at diamond freeway interchanges in Texas. The authors first developed a large randomly sampled data set to facilitate a statistically reliable assessment of U-turn safety performance for Texas interchanges. Next they conducted a safety performance assessment at locations with and without turnarounds and determined that site features that significantly influence the number of crashes include the volume of cross street traffic, the cross street right-turn configuration at frontage roads, the minimum radius in the turnaround, the longitudinal distance from the U-turn exit to the closest downstream driveway, and the number of lanes on each frontage road. The safety performance findings at locations with and without turnarounds suggests that an agency could construct a turnaround to enhance facility operations with the knowledge that construction will not adversely impact safety. Although the research introduced in this paper focuses on Texas locations, the findings should be applicable to similar facilities in other states if the turnaround conditions are similar.

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

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/03611981211004961 ◽

2021 ◽

pp. 036119812110049

Author(s):

Ahmed Abdelrahman ◽

Mohamed Abdel-Aty ◽

Jinghui Yuan ◽

Ma’en M. A. Al-Omari

Keyword(s):

Empirical Bayes ◽

Safety Evaluation ◽

Safety Performance ◽

Cross Sectional ◽

Crash Frequency ◽

Left Turn ◽

Crash Modification Factors ◽

Diamond Interchanges ◽

Implementation Data ◽

Sectional Analysis

Diverging diamond interchanges (DDIs) are designed as an alternative to the conventional diamond interchanges to enhance operational and safety performance. As the popularity of the DDI is increasing and more DDIs are being constructed and proposed, the need has arisen to measure the actual safety benefits of DDIs as compared with the traditional diamond interchanges. This study evaluates the safety of DDIs using three methods: before–after study with comparison group, Empirical Bayes before–after method, and cross-sectional analysis. This study collected a nationwide sample of 80 DDIs in 24 states. The estimated crash modification factors indicated that converting conventional diamond interchange to DDIs could 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 implied that a longer distance between crossovers/ramp terminals and a lower speed limit on freeway exit ramps are significantly associated with lower crash frequency at diamond interchanges. This study contributes to the existing literature using a relatively large representative sample size, which provides more reliable evaluation results. In addition, this study also explored the effects of different traffic and geometric characteristics on the safety performance of DDIs.

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National-Level Safety Evaluation of Diverging Diamond Interchanges

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198119849589 ◽

2019 ◽

Vol 2673 (7) ◽

pp. 696-708

Author(s):

Timothy S. Nye ◽

Christopher M. Cunningham ◽

Elizabeth Byrom

Keyword(s):

Empirical Bayes ◽

Comparison Group ◽

National Level ◽

Group Analysis ◽

Safety Evaluation ◽

The United States ◽

Group Method ◽

Regression To The Mean ◽

Naive Method ◽

Diamond Interchanges

A national-level safety evaluation of Diverging Diamond Interchanges (DDIs) in the United States was completed. This study aimed to update previous evaluations and to expand the treatment group size of previous studies to provide a more robust and reliable safety assessment of DDI deployments. For this particular treatment, it was determined that, of the observational before-and-after evaluation methodologies, the comparison group approach yields the best evaluation results. The naïve method can be influenced by outside factors that cannot be accounted for (weather, crash reporting tendencies, etc.). The empirical Bayes method is unnecessary as DDIs are installed for operational benefits, meaning that risk of selection bias and regression-to-the-mean is minimal. This study recommends a total crashes crash modification factor (CMF) of 0.633 based on the comparison group analysis of 26 DDIs in 11 states. The comparison group method was also applied to a variety of crash variables for this study. Angle, rear-end, and sideswipe crashes were found to have CMFs of 0.441, 0.549, and 1.139, respectively. Fatal-and-injury crashes provided a CMF of 0.461. Daytime and nighttime crashes provided CMFs of 0.648 and 0.638, respectively.

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