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Mid-America Transportation Center

Safety Evaluation of Diverging Diamond Interchanges in Missouri

Final Report
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Researchers

  • Principal Investigator: Praveen Edara (edarap@missouri.edu 573-882-1900)
  • Project Status
    Complete
    About this Project
    Brief Project Description & Background
    The Missouri Department of Transportation (MoDOT) has constructed seven DDIs to date. Missouri was not only the first state to build a DDI, in 2009, but it also has the largest number of DDI designs built compared to any other state, with several more being planned. In addition to economic and operational benefits, the DDI design also offers significant safety benefits by reducing the total number of conflicts. Safety evaluation of the effectiveness of the diverging diamond interchange (DDI) design will be conducted in this project.
    Research Objective
    In this project, a system-wide approach will be taken to evaluate the safety of the DDI design by including all DDI sites that have been in operation for at least one year. The safety evaluation will include a thorough before-after analysis of crash frequency and crash severity using statistical methods such as count regression models and the Empirical Bayes (EB) method using treatment and control sites. The evaluation will also include a detailed investigation of law enforcement crash reports and diagrams to obtain additional insights into the severity and causes of crashes occurring at a DDI.
    Potential Benefits
    Safety benefits of DDIs will be estimated in this project. A DDI is a cost effective alternative interchange design that is being implemented in several states across the country. In addition to economic and operational benefits, the DDI design also offers significant safety benefits by reducing the total number of conflicts. The benefits in terms of reduction in crash frequency and crash severity will be quantified.
    Abstract
    Safety evaluation of the effectiveness of the diverging diamond interchange (DDI) design will be conducted in this project. The Missouri Department of Transportation (MoDOT) has constructed seven DDIs to date. Missouri was not only the first state to build a DDI, in 2009, but it also has the largest number of DDI designs built compared to any other state, with several more being planned. In addition to economic and operational benefits, the DDI design also offers significant safety benefits by reducing the total number of conflicts. In 2009, MoDOT sponsored a research study evaluating the first DDI interchange in Springfield, Missouri. The study had limited crash data to perform safety analysis, because the DDI had not long been deployed. Based on limited data, the study concluded that the DDI was operating safely. In this project, a system-wide approach will be taken to evaluate the safety of the DDI design by including all DDI sites that have been in operation for at least one year. The safety evaluation will include a thorough before-after analysis of crash frequency and crash severity using statistical methods such as count regression models and the Empirical Bayes (EB) method using treatment and control sites. The evaluation will also include a detailed investigation of law enforcement crash reports and diagrams to obtain additional insights into the severity and causes of crashes occurring at a DDI.
    Project Amount
    $ $92,146