Semester of Graduation
Fall 2024
Degree
Master of Civil Engineering (MCE)
Department
Civil and Environmental Engineering
Document Type
Thesis
Abstract
Even though diamond and cloverleaf interchanges are commonly used in road networks, comparative studies on their operational safety and efficiency remain limited. Also, previous studies have explored the impact of Connected and Autonomous Vehicles (CAVs) at diamond interchanges, but the effects on cloverleaf interchanges are not yet thoroughly investigated. This study addresses these gaps by evaluating the traffic operation and safety performance of cloverleaf interchanges compared to diamond interchanges. It also assesses the influence of various Market Penetration Rates (MPRs) of CAVs on travel time, queue lengths, and conflict points at cloverleaf interchanges, considering different weaving lengths.
Data on peak-hour traffic volumes and roadway geometry were collected from eight interchanges in Louisiana—four cloverleaf and four diamond—for analysis. A comprehensive microsimulation analysis using VISSIM and the Surrogate Safety Assessment Model (SSAM) was developed. The VISSIM model was calibrated and validated using field observations and the Regional Integrated Transportation Information System (RITIS). Measures of effectiveness included travel time, queue lengths, delay, level of service, and total conflicts.
The study found that cloverleaf interchanges outperform diamond interchanges in traffic operation but pose higher safety risks, particularly in weaving segments. Cloverleaf interchanges with Collector-Distributor (C-D) roads manage high traffic volumes (>7000vph) more effectively, while diamond interchanges with roundabouts offer superior safety performance. At lower volumes (vph), cloverleaf interchanges excel in traffic operation, though diamond interchanges with roundabouts maintain better safety. Increasing weaving lengths at cloverleaf interchanges without C-D roads improved safety and operations, while changes in signal timings and roundabout diameters had modest effects on diamond interchanges.
Moreover, integrating CAVs at cloverleaf interchanges showed significant benefits, with travel times decreased by 40% and vehicle conflicts declined by 26% at 100% MPRs compared to the base scenario. Future studies are recommended to use driving behavioral data for more accurate VISSIM calibration and consider larger samples to enhance the robustness of results.
Date
8-22-2024
Recommended Citation
Khadka, Nischal, "Analysis of Traffic Operation and Safety at Cloverleaf and Diamond Interchanges with and without Connected and Autonomous Vehicles" (2024). LSU Master's Theses. 6030.
https://repository.lsu.edu/gradschool_theses/6030
Committee Chair
Hany Hassan