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CHAPTER 1 Research Overview 1.1â Background and Introduction The determination of signalized intersection level of service (LOS) is the central task in many analyses of current and future traffic conditions for traffic planning, intersection design, and determination of appropriate traffic signal timing. The current method of estimating the average delay by movement in the 2016 version of TRBâs Highway Capacity Manual (HCM) recommends the adjustment of right-turn volumes to take into account right-turn-on-red (RTOR) operation (TRB 2016). However, the HCM includes limited guidance for determining RTOR volume. The existing HCM delay model computes capacity using only the portion of time for which a turn signal is green, ignoring any additional capacity for right-turn movements that may result from RTOR operations. The HCM recommends that the analyst directly measure RTOR volume or, in the case of an exclusive right-turn lane, suggests that RTOR volume can be estimated by using the volume of a shadowed left-turn phase. Given that these methods are unlikely to pro- duce an accurate estimate of RTOR volume in some cases, an opportunity exists to improve the analysis of RTOR operation in capacity analysis. 1.1.1â RTOR Volume and Capacity Modeling Research conducted under NCHRP Project 03-136 sought to develop improved techniques for estimating the performance of RTOR movements through two methods: estimating the RTOR volume and estimating RTOR capacity. Both methods primarily use data types that would typi- cally be available to practitioners, such as turning movement counts, basic signal timing data, and basic intersection attributes. The resulting RTOR volume estimates can be used with existing implementations of the HCM methodology by adjusting the input volume for right-turn move- ments, while the alternative capacity expression requires adjustment of the capacity calculation method internal to signal analysis models. Model 1B uses a statistical model form that accounts for the distribution of RTOR volumes and uses variables that are more likely to be available from field count data. Therefore, it is the most promising of the model forms for implementation. Additional models are presented that use simpler mathematical forms or fewer variables. Concurrent with this research, the team developed a spreadsheet tool to permit users to enter values corresponding to various scenarios and obtain results from the developed methods. This document is aimed at transportation practitioners and provides guidance on use of the spread- sheet tool as well as information about the developed methods. 1.1.2â When to Prohibit RTORs Another research need taken on by NCHRP Project 03-136 was the development of guidance for whether to allow RTORs at a given intersection. Such guidance exists among several different 1Â Â
2ââ Right-Turn-on-Red Site Considerations and Capacity Analysis: Practitionerâs Guide documents, but a comprehensive survey of the guidance had not been previously undertaken. This document includes the results of a survey of guidance on whether to allow RTORs at locations and a synthesis of the results of this literature search. 1.2â Overview of the Spreadsheet Tool The main purpose of the spreadsheet tool that the research team developed is to allow a user to view estimated RTOR-adjusted volumes and capacities based on mathematical models devel- oped as part of this project. The development of a complete capacity model duplicating the HCM Computational Engine or commercial tools like Highway Capacity Software, with full capabilities, was beyond the scope of this study. Limitations of the spreadsheet tool are discussed in ChapterÂ 3. However, in addition to the spreadsheet tool, the RTOR volume models were also incorporated into the HCM Computational Engine. This is also described in ChapterÂ 3. 1.3â Organization of this Guide â¢ ChapterÂ 1 introduces the document and the spreadsheet tool. â¢ ChapterÂ 2 presents the review and synthesis of RTOR guidance for site selection. This infor- mation could be integrated into guidance documents, such as future editions of the NCHRP Report 812: Signal Timing Manual, Second Edition (Urbanik etÂ al. 2015). â¢ ChapterÂ 3 presents the spreadsheet tool and includes details that are useful for using the spreadsheet tool. Three examples are presented for three different applications: an intersection with a right-turn movement of interest featuring a single right-turn lane, a dual right-turn lane group, and a shared right-turn lane. â¢ ChapterÂ 4 provides a summary of the models for RTOR volume and capacity used in the spreadsheet tool, as well as an additional discussion of the results for estimating delay.