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Suggested Citation:"3. Findings from Practitioner Survey." 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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Suggested Citation:"3. Findings from Practitioner Survey." 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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Suggested Citation:"3. Findings from Practitioner Survey." 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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Suggested Citation:"3. Findings from Practitioner Survey." 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 40
Suggested Citation:"3. Findings from Practitioner Survey." 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 41
Suggested Citation:"3. Findings from Practitioner Survey." 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 41
Page 42
Suggested Citation:"3. Findings from Practitioner Survey." 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 42

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3. FINDINGS FROM PRACTITIONER SURVEY As part of this study, the research team conducted an online survey of practitioners. Appendix A contains a copy of the survey instrument. There were 46 survey respondents altogether. This chapter describes the results of the survey. The survey first asked respondents to identify the type of organization that they worked for. Figure 6 shows a breakdown of the self-reported organization types. Most of the respondents were employees of state and provincial DOTs and municipal agencies, with several consultants also represented. Some county highway department employees and researchers also responded, as well as some who felt that none of the provided descriptions were applicable to them. Academic / Research, 4 Other, 6 Tollway / Toll Bridge, 0 Consultant, 9 State/Province DOT, 12 Tribal Transportation Agency, 0 Municipal Agency, 11 MPO, 0 County Highway Department, 4 Figure 6. Respondents by organization type. Another question asked survey respondents what sort of growth patterns they experienced in their location. Figure 7 presents the responses to this question. Not all of the respondents answered this question, but nearly all of those who did reported high or moderate levels of growth, with only a single respondent indicating a mixed level of growth and none of the respondents reporting stable growth or a condition of economic distress. 36

High growth Moderate growth Stable Economically distressed Mixed 0 1 2 3 4 5 6 7 Number of Responses Figure 7. Types of growth experienced in the areas managed by the respondents. The survey also asked respondents to identify which of a series of descriptions was the best match for their own job description. Figure 8 shows the results. Respondents could make multiple selections in this response. Most respondents selected traffic engineering or traffic operations/TSMO among their duties, and these were the most common job duties selected. However, there was representation among other potential categories, including planning, design, construction, management, and maintenance. Traffic Operations / TSMO 34 Traffic Engineering 25 Program Management 8 Long-Range Planning 7 Work Zone Design 3 Construction Management 3 Roadway Design 2 Roadway Maintenance 1 Other 3 0 10 20 30 40 Number of Responses Figure 8. Best description of job duties selected by respondents. The survey asked respondents to identify the number of traffic signals for which their organization managed the signal timing. Figure 9 shows the responses to this question. There were some respondents who indicated that they did not manage any signals. Among the others, there was a broad representation of both smaller and larger agencies. 37

None 1 to 9 10 to 49 50 to 99 100 to 499 500 to 999 1000 to 4999 5000 or more 0 2 4 6 8 10 12 14 Number of Responses Figure 9. Numbers of signals managed by respondents. The frequency of signal timing was also of interest for this study and as a piece of general information about managing signal systems. The survey asked respondents to identify the percentage of signals in their system that are retimed each year. Respondents could enter a number from 0 to 100%. Figure 10 shows a cumulative frequency diagram of these responses. This chart indicates that the median value is 20%, so, on average, agencies retime approximately one fifth of their agency’s signals every year. A few agencies stated that they retime 100% of their signals annually. None of the respondents indicated that they retime none of their signals, but about 30% of the respondents stated that they retime 10% or fewer of their signals each year. 100% Cumulative Frequency 80% 60% 40% 20% 0% 0% 20% 40% 60% 80% 100% Percentage of Signals Retimed Annually Figure 10. Frequency of retiming: cumulative frequency of the percentages of signals being retimed annually, as reported by respondents. The next survey question was intended to develop a sense of how often agencies undertake LOS analyses for different use cases. Respondents could rank the frequency of this activity from never to always, with some options in between. Figure 11 shows the results. 38

• For new development, almost all of the respondents indicated that they carry out LOS analyses either always or most of the time, with a few respondents selecting sometimes. None of the respondents answered never. • While most respondents indicated that they do LOS analyses when adding new signals to existing intersections, it was less frequent than for new development. There were two respondents selecting never and more answering sometimes. • Similarly, for retiming existing signals, a majority of respondents still indicated that they usually carry out LOS analyses, although there were more indicating never or sometimes. Never 0 Existing Intersection New Development Sometimes 2 About half the time 0 Most of the time 9 Always 23 Never 2 Retiming Existing Adding Signals to Sometimes 5 About half the time 2 Most of the time 8 Always 17 Never 2 Sometimes 9 Signals About half the time 3 Most of the time 9 Always 14 0 5 10 15 20 25 Number of Responses Figure 11. How often LOS analyses are done under different use cases. The next two questions sought to determine existing agency policies and practices with regard to RTOR estimation. First, the survey asked respondents to choose a statement that best fit their policies for estimating RTOR. Figure 12 shows the responses. Only a few agencies indicated that they have formal procedures from which deviation is discouraged. A few more indicated that they do have written optional guidance. Most of the others indicated somewhat more informal or ad hoc procedures. Taken together, the responses indicate that the determination of RTOR volumes is based on engineering judgment in most jurisdictions. 39

We have formal procedures, and deviations need to be justified We have written guidance (or guidance from another agency), but analysts can deviate from it based on their judgment Nothing is written down, but we have some generally-accepted practices that have developed over time We talk it over and make decisions on a case-by-case basis I'm the only person who works on this, so it's up to me to make a decision Other 0 1 2 3 4 5 6 7 8 9 10 Number of Responses Figure 12. Respondent policies regarding RTOR estimation procedures. Next, the survey asked respondents to indicate how they performed RTOR estimation. Agencies were able to choose as many statements as they felt were applicable to their situation. Figure 13 shows the results. 40

RTOR is estimated based on engineering judgment and past 17 experience RTOR is based on the default values 12 from the signal timing software RTOR is obtained from recent traffic 8 counts at the intersection itself RTOR is assumed to be zero 4 RTOR is estimated using observed RTOR from older traffic counts at the 1 intersection itself RTOR is estimated based on the volumes for conflicting motor vehicle 1 or pedestrian movements RTOR is estimated based on 0 observations from similar intersections Other 6 0 5 10 15 20 Number of Responses Figure 13. Respondent practices for RTOR estimation. The responses show that only a few respondents stated that they assume zero for the RTOR proportion. At the same time, only a minority of agencies actually directly measure RTOR counts in the field. Most of the others either rely on default software values or engineering judgment and past experience. One respondent indicated that they try to estimate RTOR by considering volumes of conflicting vehicle or pedestrian movements. Since reviewing comparable locations is a standard forecasting and estimation technique, the fact that none of the respondents indicated the use of this method suggests an overall shortage of RTOR data. The detailed responses to some of the survey questions revealed other information. One respondent from a vendor indicated that they provide an RTOR report that can help identify RTOR volumes using detector data. Two respondents indicated that they use methods contained in NCHRP Report 457: Engineering Study Guide for Evaluating Intersection Improvements (Bonneson and Fontaine 2001). That report presents a guide to engineering studies for evaluating intersection improvements. The guide focuses mostly on geometric improvements and some 41

changes to signal timing. However, that report does not appear to include explicit guidance for adjusting RTOR volumes. The practitioner survey indicated that LOS estimation is an important element of signalized intersection management, especially for new traffic signals, and remains important for retiming existing signals. A majority of respondents stated that LOS analyses were part of those activities. Specific to estimation of RTOR volumes for LOS analysis, only a few agencies relied on field measurement of RTOR. Most agencies relied on judgment or software defaults. Therefore, a reasonable conclusion of this survey is that, in most cases, estimation of RTOR is an underexplored facet of developing signal timing among most practitioners. 42

Next: 4. Exploration of Right-Turn-On-Red Models »
Right-Turn-on-Red Operation at Signalized Intersections with Single and Dual Right-Turn Lanes: Evaluating Performance Get This Book
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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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