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This dissertation was based on the research project, Right-Turn Traffic Volume Adjustment in Traffic Signal Warrants, sponsored by the Nevada Department of Transportation (NDOT). Right-turn traffic does not affect intersection performance in the same magnitude as through or left-turn traffic. Therefore, it is necessary to apply an adjustment to the right-turn volume when conducting signal warrant analysis. Without any reduction, an intersection with heavy right-turn volume might mislead the signal warrant analysis result, and could make a difference in whether a signal is deemed warranted or not. Firstly, a comprehensive literature review was conducted focused on the state-of-the-practice on handling minor-street right-turn volumes while conducting signal warrant studies. Further, an agency survey at the Institute of Transportation Engineers (ITE) community discussion was performed to acquire valuable information from practicing engineers. It was found that the limited guidance in the Manual of Uniform Traffic Control Devises (MUTCD) is not sufficient to provide a clear direction 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 judgments by incorporating key factors such as geometry and main street volume. Sometimes agencies develop and adopt internal procedures but do not necessarily publish them. Based on the lack of an adequate guideline, a new one is needed to estimate the reduction factor for right-turn traffic on the minor street when conducting a traffic signal warrant study. The proposed guideline is based on the delay equivalent relationship between right-turn and through traffic. The right-turn volume equals an equivalent number of through vehicles, which would produce the same control delay on the minor street. The equivalent factor is defined as the measurement of the reduction of right turns. Because equivalent factors are calculated based on delay, it incorporates major impact factors of the right-turn and through traffic inherently, such as flow rates, conflicting flow rates, capacity, critical headways, and follow-up headways. Especially, the volume ratio in the two directions of the main street is considered. The research found that uneven volume distribution has a greater impact on the right-turn movement on the minor street. Therefore, just considering the main street volume can cause over- or under-estimation of the impact of the main street traffic on the minor street. Further, regression models were developed for all the configurations with calibrated regression coefficients. The advantage of these models is that they could give an equivalent factor for a specific volume scenario. The proposed guidelines were tested at three intersections and the results indicated that it is convenient to use and easily help to determine right-turn volume equivalents. At last, pedestrian impact on right-turn traffic adjustment was discussed. Usually, pedestrians crossing the main street would block right-turn vehicles on the minor street, and on the other hand, the through vehicles on the minor street can use this gap to cross an intersection. A Monte Carlo model was built to simulate the real operation of two-way stop-control (TWSC) intersections, and further validated with field data that was collected at one intersection near the University of Nevada, Reno (UNR) campus. With this model, minor-street through capacity considering pedestrian crossings was estimated. Using this enlarged capacity allows accurate calculation of equivalent factors by considering the counter impact of pedestrians on right turns. In summary, this research focused on the right-turn adjustment in the signal warrant. The decision of reducing the right turns on the minor street is somewhat subjective. Therefore, this study developed a practical guidance for determining the percentage of right turns to be considered in the signal warrant analysis. Based on the data analysis and case study results, statewide uniform guidelines were developed for implementation in the State of Nevada.
Right-turn lanes provide space for the deceleration and storage of right-turn vehicles, and separate turning vehicles from through movements. Dual right-turn lanes are increasingly used at urban intersections primarily for two reasons: (1) to accommodate high right-turn demands and avoid turn-pocket overflows, and/or (2) to prevent right-turn vehicles that exit from a nearby upstream freeway off-ramp (on the left of the roadway) from abruptly changing too many lanes toward the right-turn lane at the intersection. In addition, a number of other factors may affect the decisions on the installation of dual right-turn lanes. However, warrants for dual right lane installation are almost non-existent, leaving traffic engineers to rely on engineering judgment. This research aims to develop warrants for installation of dual right-turn lanes at signalized intersections. Both the operational and safety benefits/costs were analyzed by surveying traffic engineers and by conducting traffic simulation-based analysis. Microscopic traffic simulation model, VISSIM, was used to quantify the operation benefits and Surrogate Safety Assessment Model (SSAM) developed by Siemens was used to analyze the safety gains due to installation of dual right-turn lanes.
This report serves as a comprehensive guide to traffic signal timing and documents the tasks completed in association with its development. The focus of this document is on traffic signal control principles, practices, and procedures. It describes the relationship between traffic signal timing and transportation policy and addresses maintenance and operations of traffic signals. It represents a synthesis of traffic signal timing concepts and their application and focuses on the use of detection, related timing parameters, and resulting effects to users at the intersection. It discusses advanced topics briefly to raise awareness related to their use and application. The purpose of the Signal Timing Manual is to provide direction and guidance to managers, supervisors, and practitioners based on sound practice to proactively and comprehensively improve signal timing. The outcome of properly training staff and proactively operating and maintaining traffic signals is signal timing that reduces congestion and fuel consumption ultimately improving our quality of life and the air we breathe. This manual provides an easy-to-use concise, practical and modular guide on signal timing. The elements of signal timing from policy and funding considerations to timing plan development, assessment, and maintenance are covered in the manual. The manual is the culmination of research into practices across North America and serves as a reference for a range of practitioners, from those involved in the day to day management, operation and maintenance of traffic signals to those that plan, design, operate and maintain these systems.