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An Evaluation of Operational Efficiency between Single Point Urban Interchange with frontage road and Tight Diamond Interchange
AdvisorTian, Zong Z.
Civil and Environmental Engineering
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Signalized urban interchanges are frequently used as junctions between freeways and local arterials to date. In recent years, many new interchange or intersection designs like Diverging Diamond Interchange (DDI) and Continuous-flow Intersection (CFI) have emerged across the world. However, most of the interchanges are still using conventional urban interchange designs. Among new designs, Single Point Urban Interchange (SPUI) and Tight Diamond Interchange (TDI) are the most popular. Comparison and evaluation of the safety and operation of interchanges are important in transportation engineering to choose the most appropriate option for a location. Recently, many research have been devoted to the standard TDI and SPUI. Most of them consistently prove that the SPUI outperforms TDI in operation efficiency, but few research have compared the SPUI with frontage road (SPUI-F) with TDI. This research aims to fill this gap. With this motivation, there was a real case which could be used as testing the operational efficiency between the TDI and SPUI-F. The Nevada Department of Transportation (NDOT) switched the TDI, which was located at I-580/Plumb Ln, to SPUI-F in 2003. Since this interchange has experienced TDI and SPUI-F, the Measures of Effectiveness (MOEs) for each of them can be compared. To perform this comparison, layouts of both interchanges were modeled in VISSIM. The models were calibrated using the existing volume. Several volume scenario groups were designed for testing the operational efficiency of both options. Three MOEs, including average delay, average speed and average queue length, were selected to show the operational efficiency. The results revealed that the TDI is more efficient in comparison to the SPUI-F. However, TDI might not satisfy the driver’s expectation because of the stopping between the two signals, for which SPUI-F does not have such a problem.