United States Department of Transportation
i
Proposing the Super DDI Design To Improve the Performance of Failing Service Interchanges in Denver Metro, Colorado
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2022-06-01
[PDF-3.16 MB]
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Edition:Final Report
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Abstract:This study evaluates two versions of the new super diverging diamond interchange (Super DDI) design as a possible alternative to improve the performance of failing service interchanges in the Denver, Colorado, metro. Three interchanges, Interstate 225 and Mississippi Ave, Interstate 25 and 120th Ave, and Interstate 25 and Hampden Ave, were identified in Denver as the potential candidates to model for future retrofit. Several microsimulation models were created to test four interchange designs. i.e., existing conventional diamond interchange (CDI), diverging diamond interchange (DDI), Super DDI-1, and Super DDI-2. The traffic operation, safety, and pedestrian performance were evaluated using the combination of VISSIM, Synchro, and Surrogate Safety Assessment Model (SSAM) analyzing tools. As an important finding from this research, Super DDI designs outperformed DDI in terms of vehicular operation and safety when considering adjacent signals and when higher traffic demand exists, while DDI performed similarly or sometimes insignificantly better compared with Super DDI if no adjacent intersections were located in the vicinity and if the demand was lower than DDI’s capacity. On the other hand, the analysis of pedestrian performance showed that a relatively safe condition is expected for pedestrians in the proposed new Super DDI designs compared with CDI and DDI.
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