Evaluation of Off-ramp Right Turn Control at Single Point Urban Interchanges Without Frontage Roads

Book excerpt: This study focused on the control of the off-ramp right turn movement at single point urban interchanges (SPUIs) without frontage roads. The objective of this research project was to evaluate the safety and efficiency of traffic control for off-ramp right turns. For the purposes of this project, two common forms of off-ramp right turn traffic control were investigated: signal control and yield control. The process followed during this research focused on two main aspects of the off-ramp right turn movement: safety and operations. The project was composed of the following stages: literature review, safety analysis and operation analysis. Literature Review: A literature review was conducted to provide the research team a broader perspective on other studies concerned with this aspect of SPUIs. The review was looking for the various traffic controls and interchange configurations that could particularly affect the safety and operation efficiency of off-ramp right turn movement. Safety Analysis: Long-term trends in crash occurrences and short-term observations of conflicts at six study sites (12 off-ramp locations) were analyzed. Crash rates and conflict rates were determined in order to compare and contrast the two means of assessing safety as well as how they relate to the type of the traffic control used at the off-ramps. Operations Analysis: Detailed traffic data collected at the study sites were used to calculate actual delays for off-ramp right turn movements at the study sites. These field data were also used to conduct simulations of interchange sites, which supplemented the calculations based on the limited sample of study sites. The simulation models provided a means of testing different combinations of off-ramp right turn control types and overall interchange conditions in order to determine the effects of signal and yield control.