United States Department of Transportation
i
Right-Turn Traffic Volume Adjustments in Traffic Signal Warrant Analysis
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2015-01-01
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[PDF-2.14 MB]
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TRIS Online Accession Number:01651575
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Edition:Final Report
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Abstract:To accomplish this research, a comprehensive literature review of existing guidelines and findings based on national and local studies was conducted. Ultimately, guidelines for consistent application for adjusting right-turn traffic volumes were developed for the state of Nevada. The comprehensive literature review focused on the state-of-the-practice on handling minor-street right-turn volumes while conducting signal warrant studies. Further, a comprehensive agency survey was conducted through the Institute of Transportation Engineers (ITE) community discussion to acquire valuable information from practicing engineers. It was found that the limited guidance in the Manual on Uniform Traffic Control Devises (MUTCD) is not sufficient to provide clear directions on determining whether or how much right turns impact the signal warrant analysis. In reality, most traffic engineers have done the reduction based on engineering judgment incorporating key factors such as geometry and main street volumes. The Pagones Theorem and the method proposed by the National Cooperative Highway Research Program (NCHRP) have been adopted by some states and local agencies. However, there is no literature found to document the detailed methodologies of the Pagones Theorem and the NCHRP method. Additionally, these methods do not consider the main-street volume distribution which affects the intersection operations. It is common that some agencies adopt internal procedures but they do not necessarily publish them. The authors' approach for developing the new right-turn volume adjustment guidelines is based on traffic operations measures, i.e. delay or level-of-service (LOS). This LOS-based approach has been successfully applied to determining intersection control types. The proposed guideline is based on the delay equivalent relationship between right-turn and through traffic. The right-turn volume equals to an equivalent number of through vehicles, which would produce the same control delay on the minor street. The equivalent factor is applied to determine level of right-turn reduction. Because equivalent factors are calculated based on delay, they incorporate major influencing factors of the right-turn and through traffic inherently, such as conflicting flow rates, capacity, critical headways, and follow-up headways. Especially, the volume ratio in the two directions of the main street is considered. From the analysis, the uneven volume distribution has a greater impact on the right-turn movement of the minor street. Therefore, only considering the main street volume can cause over or under estimation of the influence of the main street traffic to the minor street. Further, regression equations were developed based for all the configurations. The advantage of these equations is to yield a precise equivalent factor given a specific volume scenario. At last, the proposed guidelines were tested at three intersections. The case studies revealed that the guidelines are easy to use and can yield more reasonable results than previous guidelines.
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