Early Findings on the Operational Impacts of Double Crossover Diamond Interchanges

摘要

Operational and safety issues at many freeway-to-surface street interchanges have increased in recent years, as they are unable to handle larger traffic volumes, especially the oftentimes heavy left-turning demands at many interchanges. Limitations in right-of-way availability, high right of way costs, and expensive bridge structures have pushed engineers to find innovative solutions to solve some of these issues. Examples of these innovative designs include the roundabout interchange, the single point urban interchange, and the double crossover diamond (DCD) interchange (also known as the diverging diamond interchange, DDI), among others. This paper provides results from the first 1.5 years of a research study commissioned by the Federal Highway Administration to evaluate the first few DCD installations in the US (FHWA Project Number DTFH61-10-C-00029). This paper includes summary findings on operational performance at DCD interchanges built in recent years at 1-44 and MO-13 in Springfield, MO; US-60 and National Avenue in Springfield; 1-270 and Dorsett Road in Maryland Heights, MO; and US-129 and Bessemer Street in Alcoa, TN. The paper focuses mostly on the operational conditions of these interchanges, although safety assessment, simulation analysis, and design guidance are all part of the overall project. Performance measures presented in this paper include peak-hour queue lengths, spillback and blockage, origin-destination travel times, signal compliance, erratic maneuvers, field-observed conflicts, and vehicle speed profiles. The paper also includes assessments of walkability and bikeability, as well as user perceptions. The paper will provide tentative conclusions on the operational performance of DCD interchanges to this point and will describe the program of future work planned to fully investigate the operational and safety impacts of DCDs under aforementioned project.