National Academies Press: OpenBook

Traffic Signal Control Strategies for Pedestrians and Bicyclists (2022)

Chapter: Chapter 4 - Signal Timing Basics

« Previous: Chapter 3 - Performance Measures Related to Serving Pedestrians and Bicyclists
Page 20
Suggested Citation:"Chapter 4 - Signal Timing Basics." National Academies of Sciences, Engineering, and Medicine. 2022. Traffic Signal Control Strategies for Pedestrians and Bicyclists. Washington, DC: The National Academies Press. doi: 10.17226/26491.
×
Page 20
Page 21
Suggested Citation:"Chapter 4 - Signal Timing Basics." National Academies of Sciences, Engineering, and Medicine. 2022. Traffic Signal Control Strategies for Pedestrians and Bicyclists. Washington, DC: The National Academies Press. doi: 10.17226/26491.
×
Page 21
Page 22
Suggested Citation:"Chapter 4 - Signal Timing Basics." National Academies of Sciences, Engineering, and Medicine. 2022. Traffic Signal Control Strategies for Pedestrians and Bicyclists. Washington, DC: The National Academies Press. doi: 10.17226/26491.
×
Page 22
Page 23
Suggested Citation:"Chapter 4 - Signal Timing Basics." National Academies of Sciences, Engineering, and Medicine. 2022. Traffic Signal Control Strategies for Pedestrians and Bicyclists. Washington, DC: The National Academies Press. doi: 10.17226/26491.
×
Page 23
Page 24
Suggested Citation:"Chapter 4 - Signal Timing Basics." National Academies of Sciences, Engineering, and Medicine. 2022. Traffic Signal Control Strategies for Pedestrians and Bicyclists. Washington, DC: The National Academies Press. doi: 10.17226/26491.
×
Page 24
Page 25
Suggested Citation:"Chapter 4 - Signal Timing Basics." National Academies of Sciences, Engineering, and Medicine. 2022. Traffic Signal Control Strategies for Pedestrians and Bicyclists. Washington, DC: The National Academies Press. doi: 10.17226/26491.
×
Page 25
Page 26
Suggested Citation:"Chapter 4 - Signal Timing Basics." National Academies of Sciences, Engineering, and Medicine. 2022. Traffic Signal Control Strategies for Pedestrians and Bicyclists. Washington, DC: The National Academies Press. doi: 10.17226/26491.
×
Page 26

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

20 This chapter first covers signal timing principles for pedestrians and bicycles to provide a better understanding of signal timing fundamentals. Then, it provides a toolbox of signal timing and design treatments to improve pedestrian and bicycle mobility and safety at signalized inter- sections. Each treatment includes a detailed description as well as applications, expected opera- tional and safety outcomes, and specific operational details for implementation. 4.1 Understanding Signal Systems Implementing treatments for pedestrians and bicycles requires an understanding of vehicular signal system principles. Prior to exploring new treatments for non-motorized users, agencies must understand the equipment and controller(s) currently being used and how they influence operations. Existing indications, for example, may create conditions that affect how the inter- section operates for all users. Agencies may be limited in what they can achieve using the existing setup to implement new treatments. The introduction to the toolbox in Chapter 5 notes which treatments are likely to require new equipment. Equipment needs are also summarized for each treatment—when applicable—in the toolbox (Chapters 6–10). For additional information on vehicular signal systems, refer to the Manual on Uniform Traffic Control Devices (MUTCD) and NCHRP Report 812: Signal Timing Manual, 2nd Edition (STM2). 4.2 Pedestrian Intervals The pedestrian phase consists of three intervals: Walk, Flashing Don’t Walk (FDW), and pedestrian phase end buffer, during which steady Don’t Walk is displayed but conflicting traffic will not be released. During the rest of the cycle, the pedestrian phase is inactive, and a steady Don’t Walk continues to be displayed, as shown in Exhibit 4-1. The Walk interval typically begins at the start of the concurrent vehicular green interval and is the time during which pedes- trians are supposed to begin crossing. The FDW interval informs pedestrians that the crossing phase will soon end and that they should no longer begin to cross. If there is a countdown signal, it counts down during the FDW phase, reaching “0” and going blank when the FDW interval ends. During the pedestrian phase end buffer, which typically lasts only a few seconds, the dis- play goes to solid Don’t Walk to warn pedestrians that the pedestrian phase is imminently about to end. Pedestrians are expected to use this interval, along with the FDW interval, to complete their crossing. 4.2.1 Walk Interval The Walk interval is the time window within which pedestrians are supposed to begin crossing. It should be long enough for pedestrians to perceive the phase change and enter the C H A P T E R 4 Signal Timing Basics

Signal Timing Basics 21   street. e MUTCD (2009) recommends that the Walk interval be at least 7 s long but allows it to be as short as 4 s. In areas with pedestrian volumes great enough that pedestrians queue several rows deep, the minimum Walk interval should be longer than 7 s. When the pedestrian phase runs concurrently with a parallel vehicular phase, the Walk interval can oen run for far longer than its minimum, giving pedestrians additional crossing opportunities without constraining trac ow (see Section 7.3). 4.2.2 Pedestrian Clearance Interval Pedestrian clearance time needed is the time required for a pedestrian to cross the street, beginning from when they rst step o the curb. It is the crosswalk length divided by a pedestrian design speed of 3.5  per second (/s), a speed attainable by more than 90% of the population. If slower pedestrians routinely use a crossing, a lower pedestrian design speed may be used. e MUTCD (2009) also describes an option—albeit rarely implemented—to use a pedestrian design speed of up to 4 /s in conjunction with a pushbutton that slower pedestrians may use to request a longer clearance time (see Exhibit 4-2). e MUTCD (2009) also species a clearance need for pedestrians who begin crossing at the start of the Walk interval. e combined duration of the Walk interval, FDW interval, and pedestrian phase end buer should be enough for a person to cross the street at a speed of 3 /s beginning at the pedestrian pushbutton, if there is one, or 6  from the edge of the curb. is requirement is typically constraining only for long crossings. Normal practice is to design the crossing with a preliminary pedestrian timing that ignores this second clearance need and then check whether it is satised; if this need is not satised, increase the length of the Walk interval until it is. Section 7.4 oers more detail about pedestrian clearance needs and related pedestrian timing. Note: The figure assumes that some pedestrians will finish clearing the crosswalk during the vehicular yellow and red clearance intervals. Exhibit 4-1. Pedestrian intervals (STM2).

22 Trafc Signal Control Strategies for Pedestrians and Bicyclists 4.2.3 FDW Interval and Pedestrian Phase End Buffer Together, the FDW interval and the pedestrian phase end buer supply the pedestrian clear- ance need. Relative to a concurrent vehicle phase, the FDW interval may end (and the phase end buer may begin) during the green, at the onset of the yellow, during the yellow, or at the end of the yellow for the concurrent vehicle phase. e only constraint is that the remaining time until the end of the vehicle phase’s red clearance, which is the pedestrian phase end buer, must be at least 3 s. Many agencies choose to end the FDW interval at the onset of the yellow for the concurrent vehicle phase, in which case the phase end buer will be the same length as the vehicular yellow plus red clearance time. Once the length of the pedestrian phase end buer has been determined, the minimum length of the FDW interval is the pedestrian clearance time needed (Equation 7-4) minus the length of the phase end buer. Some agencies choose not to count the pedestrian phase end buer against the needed pedestrian clearance time. is practice gives pedestrians more clearance time, which has some advantages but also some disadvantages, as discussed in greater detail in Section 7.4. 4.3 Pedestrian Call Modes: Actuated or Recall Pedestrian phases can be actuated or on recall. If actuated, the controller places a call for the pedestrian phase when a pedestrian is detected. “On recall” means that a call for pedestrian service is placed automatically every cycle. While a number of passive pedestrian detection technologies are available today (e.g., microwave, infrared, video camera), most agencies still rely on pushbuttons for pedestrian detection due to concerns in detection accuracy. For details on pedestrian call modes and their eect on pedestrian delay and vehicle opera- tions, see Section 7.5. Exhibit 4-2. Example of extended pushbutton press signage.

Signal Timing Basics 23   4.4 Accessible Pedestrian Signals Accessible pedestrian signals (APS) help persons with low vision or hearing impairments know when the Walk signal is being displayed. ese signals use sound, tactile arrows, and vibrotactile feedback to communicate to pedestrians (see Exhibit 4-3). Typically, they serve a dual function as both standard pedestrian pushbuttons and APS. At signals without stan- dard pushbuttons (e.g., pretimed intersections, phases with pedestrian recall), the need for APS can still be met by providing similar pushbutton units without requiring that the pedestrian call mode become actuated when the button is pushed. For more detail on this concept, see Section 8.4. e MUTCD requires that APS provide both audible and vibrotactile Walk indications. Pushbuttons for APS should be located in accordance with the provisions of the MUTCD, Sec- tion 4E.08—namely, they should be located as close as possible to the crosswalk line furthest from the center of the intersection and as close as possible to the curb ramp. Additional detail on implementation can be found in the MUTCD, Sections 4E.09–4E.11. e proposed Accessibility Guidelines for Pedestrian Facilities in the Public Right-of-Way (U.S. Access Board, 2011) includes a requirement for APS wherever pedestrian signals are installed and refers to the MUTCD standards for APS features and functioning. e guidelines have not been nalized and adopted by the U.S. Department of Justice and U.S. DOT, but they may be considered best practice. Several municipalities and states, including Minnesota and Maryland, install APS at all reconstructed or newly signalized intersections. Many jurisdictions— such as New York City; Portland, OR; and Seattle, WA—also have policies to install APS when requested by a member of the public and when the location meets other requirements. One of these requirements is typically that the location is already signalized. Source: Harkey et al. (2011). www.apsguide.org Exhibit 4-3. Pushbutton- integrated APS.

24 Traffic Signal Control Strategies for Pedestrians and Bicyclists 4.5 Signal Timing Principles for Bicycles Traditionally, bicycles have been expected to follow general vehicular traffic signals or, on shared-use paths, pedestrian signals. Another solution that is becoming increasingly popular in the United States and already used widely in Europe is bicycle-specific signals, which allow bicycles to have a signal phase that may differ from that of vehicles and pedestrians. Where bicycles follow a vehicular signal, signal timing for the vehicle phase should include the needs of bicycles. Cyclists typically need more time than drivers to clear an intersection, especially with large intersection crossings, due to their lower speed and acceleration. For bicy- cles beginning from a standing start, on a fresh green, their needed clearance time can be met by providing a sufficiently long minimum green period. For those arriving on a stale green, their clearance time need can be met by lengthening the red clearance time—a practice followed in many European countries—or by extending the green. Clearance time needs for bicycles can be met more efficiently if bikes can be detected. For more detail, see Section 9.1. Cyclists can also follow bicycle signals, which have bike-specific signal heads that control bicycle phases. Bicycle phases may run concurrently with compatible vehicle phases or as an exclusive separate phase (e.g., for a diagonal bicycle crossing where all vehicular movements are stopped). In the U.S., using bicycle signals at this time requires approval from FHWA’s MUTCD office. An interim approval for their use has been in force since 2012, and applications (“requests to experiment”) that meet its terms will be approved. One of the terms that limits application of bicycle signals is that there must not be any permitted conflicts with turning vehicles, including right turns. As of March 2019, there are 480 intersections that are currently using bicycle signal faces across the United States (Monsere et al., 2019). 4.6 Traffic Signal Controller Elements Overview Exhibit 4-4 outlines elements in most modern controllers that can be leveraged to implement various treatments for non-motorized users. Specific implementation may vary by controller type. Feature Definition Use Applicable Treatments Timing Options Min. Green 2 Represents the least amount of time that a green signal indication will be displayed for a movement. Most modern controllers provide two or more minimum green parameters that can be invoked by a time- of-day plan or external input. Bicycle detectors can activate Min. Green 2 (Bike Green), extending the minimum green time for bicyclists. Min. Green 2 for bicycle use can vary based on the size of intersection and intersection type. This is currently used in Portland, OR. • Bicycle Detection (Section 9.4). • Signal Progression for Bicycles (Section 9.2). Advance Walk A pedestrian overlap configuration, programmed as a number of seconds, where the pedestrian phase starts before the corresponding vehicle phase. Advance Walk provides a leading pedestrian interval (LPI), allowing pedestrians to enter the crosswalk before conflicting vehicles. • Leading Pedestrian Intervals (Section 6.5). • Pedestrian Overlaps with Leading Pedestrian Intervals and Vehicular Holds (Section 6.7). Exhibit 4-4. Signal controller features facilitating treatments for non-motorized users.

Signal Timing Basics 25   detection may be desirable to allow for late-night free operation). • Causes the FDW interval to extend past the yield point, delaying minor-street movements until the FDW interval has ended. The delay to minor streets is only noticeable under low-volume conditions. Pedestrian Recycle Allows pedestrian service in the programmed ring to recycle if there is a pedestrian call registered on the phase in service or if pedestrian recall is programmed for the phase and there are no serviceable opposing calls. • Reduces pedestrian delay by allowing for late pedestrian service and for the pedestrian phase to reservice if remaining service time allows. • Can be used under actuated and non- actuated operation. • Reservice (Section 7.2). Force Coord Pedestrian Yield Option Forces a pedestrian phase in Rest in Walk to fully terminate in time for the coordinated phase to yield on time when there are no conflicting calls. If used in conjunction with Pedestrian Recycle, the pedestrian phase will serve again if the coordinated phases do not yield (i.e., if there are no conflicting calls). • Reservice (Section 7.2). Delay Walk A pedestrian overlap configuration, programmed as a number of seconds, where the pedestrian phase starts after the corresponding vehicle phase. Allows turning vehicles queued at the intersection to clear the crosswalk before pedestrians enter. • Pedestrian Overlaps with Leading Pedestrian Intervals and Vehicular Holds (Section 6.7). Steady Don’t Walk The period of time after the Walk and FDW have completed their timing. The duration of the steady Don’t Walk interval is not a programmable parameter in the controller but is simply the length of the concurrent vehicle phase minus the Walk and FDW intervals. Part of the overall pedestrian clearance interval. Must be displayed for at least 3 s before the release of conflicting vehicles, per the MUTCD. N/A Alternate Walk/Pedestrian Clear The amount of time the Walk indication is displayed when an alternate Walk call (for a special-needs pedestrian) is being serviced. Alternate Walk can provide a longer Walk interval for slower pedestrians with an extended push of a pedestrian button. A supplement sign is often used to inform pedestrians of the feature. Cameras can also be used to detect user type and initiate Alternate Walk. • Accessible Signals without Pushbutton Actuation (Section 8.4). • Maximizing Walk Interval Length (Section 7.3). Phase Options Pedestrian Recall The controller places a continuous call for pedestrian service on a phase, causing the pedestrian Walk and clearance intervals to occur every cycle. Typically used for locations and times with high pedestrian-volumes. • Pedestrian Recall versus Actuation (Section 7.5). Rest in Walk (Actuated Rest in Walk) The controller dwells in the pedestrian Walk interval while the coordinated phase is green, regardless of pedestrian calls. • Often used when there are high pedestrian-volumes, such as in downtown environments or locations near schools. • Does not require any pedestrian detection (although pedestrian • Maximizing Walk Interval Length (Section 7.3). • Pedestrian Recall versus Actuation (Section 7.5). Feature Definition Use Applicable Treatments Exhibit 4-4. (Continued). (continued on next page)

26 Traffic Signal Control Strategies for Pedestrians and Bicyclists Exhibit 4-4. (Continued). Bicycle Phase Separates bicycle movements from other conflicting traffic. • Not needed when bicycle movements can occur concurrently with other compatible vehicle phases (e.g., bicycles crossing with the concurrent vehicular movement while right-turning vehicles are stopped). • Useful for diagonal bicycle crossings in which all vehicular movements are stopped. • Exclusive Pedestrian and Bicycle Phases (Section 6.3). • Minimum Green and Change Interval Settings for Bicycle Clearance (Section 9.1). • Signal Progression for Bicycles (Section 9.2). Vehicle-Based Features Flashing Yellow Arrow (FYA) A protected-permitted left-turn display that features a flashing yellow arrow in addition to the standard red, yellow, and green arrows. When illuminated, the FYA allows waiting motorists to make a left- hand turn after yielding to oncoming traffic. FYA can be programmed with a Negative Pedestrian or Not Pedestrian condition. If FYA is on and a pedestrian call comes, the pedestrian waits. If there is time remaining in the through phase, either the FYA would terminate early or the pedestrian phase would be served in the next cycle without FYA. • Protected-Only Left Turns to Address Non- motorized User Conflicts (Section 6.1). Right-Turn Overlaps Right-turn movements operating in exclusive lanes are assigned to more than one phase that is not conflicting (e.g., non- conflicting left-turn phase from the cross street). Right-turn overlaps can be applied with the adjacent through green. If a pedestrian call is placed, the right turn can get an FYA or red arrow instead of the green arrow. • Pedestrian Overlaps with Leading Pedestrian Intervals and Vehicular Holds (Section 6.7). Time of Day Most signals have several timing plans that operate at different times of day. Uses a “dummy phase” to allow different types of operations throughout the day, such as exclusive pedestrian phases during off-peak times. • Exclusive Pedestrian and Bicycle Phases (Section 6.3). Alternate Phases Phase is served every other cycle (even/odd). Typically used for split phase. N/A Feature Definition Use Applicable Treatments Bibliography Harkey, D. L., Carter, D. L., Barlow, J. M., & Bentzen, B. L. (2011). NCHRP Web-Only Document 150: Accessible Pedestrian Signals: A Guide to Best Practices (Workshop Edition 2010) [Website adaptation]. Transportation Research Board of the National Academies, Washington, DC. http://www.apsguide.org/ Manual on Uniform Traffic Control Devices for Streets and Highways. (2009). FHWA, U.S. DOT. http://mutcd. fhwa.dot.gov/ Monsere, C., Kothuri, S., Hurwitz, D., Cobb, D., Fink, C., Schultheiss, B., Hillman, T., Shaw, G., & Boudart, J. (2019). NCHRP Web-Only Document 273: Road User Understanding of Bicycle Signal Faces on Traffic Signals. Transportation Research Board, Washington, DC. Urbanik, T., Tanaka, A., Lozner, B., Lindstrom, E., Lee, K., Quayle, S., Beaird, S., Tsoi, S., Ryus, P., Gettman, D., Sunkari, S., Balke, K., & Bullock, D. (2015). NCHRP Report 812: Signal Timing Manual, 2nd Edition. Trans- portation Research Board, Washington, DC. U.S. Access Board. (2011). (Proposed) Public Rights-of-Way Accessibility Guidelines. Washington, DC. 

Next: Chapter 5 - Introduction to Treatments »
Traffic Signal Control Strategies for Pedestrians and Bicyclists Get This Book
×
 Traffic Signal Control Strategies for Pedestrians and Bicyclists
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

In the United States, traffic signal timing is traditionally developed to minimize motor vehicle delay at signalized intersections, with minimal attention paid to the needs of pedestrians and bicyclists. The unintended consequence is often diminished safety and mobility for pedestrians and bicyclists.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 969: Traffic Signal Control Strategies for Pedestrians and Bicyclists is a guidebook that provides tools, performance measures, and policy information to help agencies design and operate signalized intersections in a way that improves safety and service for pedestrians and bicyclists while still meeting the needs of motorized road users.

Supplemental to the report are presentations of preliminary findings, strategies, and summary overview.

READ FREE ONLINE

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!