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Suggested Citation:"7. Conclusion." National Academies of Sciences, Engineering, and Medicine. 2023. Right-Turn-on-Red Operation at Signalized Intersections with Single and Dual Right-Turn Lanes: Evaluating Performance. Washington, DC: The National Academies Press. doi: 10.17226/27264.
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Page 111
Suggested Citation:"7. Conclusion." National Academies of Sciences, Engineering, and Medicine. 2023. Right-Turn-on-Red Operation at Signalized Intersections with Single and Dual Right-Turn Lanes: Evaluating Performance. Washington, DC: The National Academies Press. doi: 10.17226/27264.
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Page 111
Page 112
Suggested Citation:"7. Conclusion." National Academies of Sciences, Engineering, and Medicine. 2023. Right-Turn-on-Red Operation at Signalized Intersections with Single and Dual Right-Turn Lanes: Evaluating Performance. Washington, DC: The National Academies Press. doi: 10.17226/27264.
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Page 113
Suggested Citation:"7. Conclusion." National Academies of Sciences, Engineering, and Medicine. 2023. Right-Turn-on-Red Operation at Signalized Intersections with Single and Dual Right-Turn Lanes: Evaluating Performance. Washington, DC: The National Academies Press. doi: 10.17226/27264.
×
Page 113
Page 114
Suggested Citation:"7. Conclusion." National Academies of Sciences, Engineering, and Medicine. 2023. Right-Turn-on-Red Operation at Signalized Intersections with Single and Dual Right-Turn Lanes: Evaluating Performance. Washington, DC: The National Academies Press. doi: 10.17226/27264.
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7. CONCLUSION 7.1 Overview of the Research This research developed models of RTOR volume and capacity using data collected from 260 intersections distributed across 25 U.S. states and the District of Columbia, as described in Chapter 5. Models were developed for three lane configurations on the subject approach: single exclusive right-turn lane, dual right-turn lanes, and shared through and right-turn lane. The models use measures of conflicting volume and signal timing. Several models of RTOR volume were developed, including some that incorporate a wider range of variables and others that use fewer variables for easier implementation. These models were developed using a variety of statistical models, as described in detail in Chapter 6. The models were validated by comparison with example data from selected intersections that had been set aside from the model-development dataset. An advantage of RTOR volume models is that their output can be directly integrated into existing HCM analysis tools, since there is a field in most of these tools for entering an RTOR volume. Two models of RTOR capacity were also developed, including one model that used expressions found in the literature and a second model that developed new expressions using data from a microsimulation experiment to develop the appropriate equation form. These models were also validated by comparison with example data. The capacity models presented herein may facilitate improvement of the current models for delay estimation. Additional work is needed to integrate these into existing HCM analysis tools as well as to understand how they would influence calculation of delay. To facilitate development of the models, an effort was undertaken to synthesize prior research and understand current practice in RTOR modeling through a practitioner survey. Chapter 2 presents the literature search, while Chapter 4 presents a more detailed comparative examination of the models reported in that research. Chapter 3 presents the results of the practitioner survey. The survey results indicated that few practitioners have well-established, documented practices for handling RTOR in LOS analyses, and few are able to obtain actual RTOR counts. The literature review uncovered several prior studies that proposed methods of estimating RTOR volume and capacity. However, previous studies did not propose a method that can examine both single exclusive, dual, and shared lanes. 7.2 Development of Practitioner Guide Another product of this research was the development of a practitioner guide, which is provided as a separate document. This guide is intended for use by individuals who are tasked with performing an analysis for which the products of this research may be of use, such as an analysis of RTOR volume. The guide is accompanied by a spreadsheet containing sample calculations from the models presented herein. In addition, the RTOR models were incorporated into the 110

HCM Computational Engine. The guide also contains a chapter that presents an overview of criteria for RTOR site selection. 7.3 Implementation of Research Products This research produced models of RTOR volume and capacity. Of these, the models of RTOR volume can be directly used by analysts to estimate RTOR volumes, which are an input parameter for the HCM analysis and several software tools that perform the same or similar analyses. Analysts may use the equations taken directly from this report, the spreadsheet accompanying the practitioner guide, or the HCM Computational Engine. For example, the HCM Computational Engine (Figure 45) contains a line for entering RTOR volumes. The updated HCM Computational Engine prepared by this research is able to automatically generate the RTOR volume number based on the other input data. This could be implemented in software packages such as the Highway Capacity Software, Sidra Intersection, Synchro, or Vistro. Figure 45. Place for entry of RTOR volume in the HCM Computational Engine The capacity models could be used to provide estimates of RTOR capacity, but additional work is likely needed to understand how to make use of this information in use cases such as delay estimation, as discussed in Chapter 6. 111

Given that the main research products are relatively straightforward to use and can yield estimates that can be directly used in existing tools, the largest barrier to implementation would seem to be lack of knowledge of the research products. This can be mitigated by spreading information about the research products. This research has yielded a set of tools that can help with this task, including a draft presentation on the research and the practitioner guide. Beyond the efforts of the research team in producing this work and preparing articles to disseminate the results, organizations that may be able to assist with dissemination of the research products include the following: • The Transportation Research Board (TRB), as the organization sponsoring this NCHRP research, frequently hosts webinars. The present research could be a topic for such a webinar, possibly combined with other research related to new developments of the HCM. • The TRB committee most closely related to the HCM is the Highway Capacity and Quality of Service committee, which includes a subcommittee on interrupted-flow facilities. This group includes many practitioners who may be able to encourage the use of the methodologies developed in this research among colleagues. • The Institute of Transportation Engineers (ITE) brings together many transportation professionals whose work involves highway capacity analyses. There are likely to be opportunities to discuss RTOR analysis in workshops and other events hosted by ITE, in which presentation of the research products could be mentioned. • The National Operations Center of Excellence hosts a Knowledge Center on its website that presents information on a variety of topics. This information tends to focus on traffic management and planning, including publications related to highway capacity analysis. In addition to methods of estimating RTOR volume and capacity, this research also produced guidance on site selection for RTOR based on a synthesis of existing publications on this topic, including documents such as highway design manuals compiled by state DOTs. This information is included in the practitioner guide. Such information may be of interest to individuals whose work focuses on traffic control devices and who maintain such manuals. The same organizations listed above would likely be able to help disseminate the practitioner guide. 7.4 Prioritized Recommendations for Future Research This section presents additional research needs that are suggested by the study findings. These are prioritized according to their importance, in the opinion of the research team, and are presented in order of priority from greatest to least. 7.4.1 Application of Capacity Models in the HCM Delay Equation This research developed estimates of the capacity provided by RTOR during applicable intervals at a traffic signal. The primary use of capacity estimates is to provide an input to the delay equation (through the volume-to-capacity ratio). As discussed in Chapter 6, it is not immediately clear whether the existing delay equation will provide the best estimates of delay by adjusting either volume or capacity as a direct input or whether the equation form itself (or at least the 112

uniform delay component) should be reconsidered given the time-dependent nature of RTOR movements compared to other movements. 7.4.2 Balancing Efficiency and Safety in Right-Turn-on-Red Guidance The implementation or prohibition of RTOR is a policy decision that directly involves a tradeoff between intersection efficiency and safety. There are relatively few fatal and injury crashes attributed to RTOR, mainly because the maneuver is usually done at relatively low speeds. Nonetheless, RTOR may present a hazard, especially to nonmotorized users (i.e., pedestrians and bicyclists), and if nothing else tends to make intersections less comfortable for nonmotorized traffic. The models developed in this study showed that presence of pedestrians tended to reduce RTOR flow rates. At locations with large numbers of nonmotorized users, RTOR is frequently but not always prohibited. Alternatives to prohibition of RTOR include, for example, the use of dynamic blank-out NO TURN ON RED signs that can be activated when a pedestrian phase is in service. Many agencies have adopted the Vision Zero perspective, which seeks to completely eliminate fatalities and serious injuries or the Safe System approach which seeks to reduce casualties, in part by reducing conflicts between motorized and nonmotorized traffic. In addition, many jurisdictions seek to reduce traffic congestion by encouraging alternatives to driving. Given such policy movements, it does not seem unlikely that prohibition of RTOR may be encouraged to promote safer operation for nonmotorized users. At the same time, however, a need to reduce fuel consumption was the original impetus to permit RTOR nationally in the United States in the 1970s, and while the maneuver is less commonly permitted in other countries, some countries have begun to allow turns on red under certain circumstances. There is a need to better quantify the benefit and cost of the maneuver, not only from a vehicle perspective but also considering nonmotorized users. For nonmotorized users, safety as quantified in terms of fatal and injury crashes is not the only relevant criterion for making this evaluation; rather, the ease and comfort with which such users can make their way through or across an intersection is also important. In this context it will be important to consider the potential for underreporting of pedestrian crashes in police data sets, possibly by augmenting them with information derived from emergency department and hospital admissions records. 7.4.3 Examination of Impacts of Pedestrians and Bicycles This research examined 260 intersections and included over 8,000 5-minute observations. Of these, there were 1,133 observations with at least one pedestrian but only 114 observations with six or more pedestrians. Most of the observations with large numbers of pedestrians were from one intersection. There were also very few observations with substantial bicycle traffic. The models developed in this study did show that conflicting pedestrians tend to decrease the RTOR flow rate. However, the impact of bicycles and the influence of bicycle lane and right-turn lane design was not directly taken into consideration. Additional research would be needed to determine the potential effects on RTOR volume and capacity. 113

7.4.4 Examination of Impact on Signal Timing Outcomes It is known that using zero as the RTOR volume or otherwise ignoring the existence of the RTOR maneuver causes the delay of right-turn movements to be overestimated. In the development of traffic signal timing, overestimation of delay on a movement would tend to cause its green time to be inflated since more split time would tend to be given to a movement in an attempt to reduce its estimated delay. The introduction of improved RTOR volume and capacity estimation methods would likely have an impact on the outcomes of signal timing optimization. Additional work is needed to assess the use of these methods in the development of signal timing plans. 114

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The determination of the level-of-service (LOS) at signalized intersections is an important activity for decision-making in the allocation of resources for managing public roads, estimating the impact of new developments, and designing signal timing plans. There is a need to develop models of right-turn-on-red (RTOR) volume to permit users of the Highway Capacity Manual methodology to estimate the RTOR rather than rely on collection of field data, which often does not include RTOR as a separate quantity.

NCHRP Web-Only Document 368: Right-Turn-on-Red Operation at Signalized Intersections with Single and Dual Right-Turn Lanes: Evaluating Performance, from TRB's National Cooperative Highway Research Program, addresses these needs through the development of models for RTOR volume prediction and the development of improved guidance for whether to allow RTOR.

The document is supplemental to NCHRP Research Report 1068: Right-Turn-on-Red Site Considerations and Capacity Analysis: Practitioner's Guide.

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