Decision-Making Guide for Traffic Signal Phasing (2020)

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.

5 2 Traffic Signal Phasing Concepts and Definitions The following terms are used in this guide as defined below. Many of the definitions included are from the MUTCD (FHWA 2009b) and the Signal Timing Manual, 2nd Edition (NCHRP 2015). 2.1 Traffic Signal Basics 1. Approach – all lanes of traffic moving toward an intersection or a midblock location from one direction, including any adjacent parking lane(s) (FHWA 2009b). 2. Detector – a device used for determining the presence or passage of vehicles or pedestrians (FHWA 2009b). 3. Geometric Offset – the perpendicular distance between the centerline of opposing left-turn lanes. Geometric Offset is shown in Figure 2. Figure 2 - Geometric Offset (Adapted from (FHWA 2009c) 4. Interval – the part of a signal cycle during which signal indications do not change (FHWA 2009b). Interval is depicted in Figure 3. 5. Movement – A term used to describe the user (e.g., vehicle or pedestrian) action taken at an intersection (e.g., vehicle turning movement or pedestrian crossing) (NCHRP 2015).

6 Figure 3 - Typical Traffic Signal Cycle 6. Pedestrian Change Interval – an interval during which the flashing UPRAISED HAND (symbolizing DONT WALK) signal indication is displayed (FHWA 2009b). The pedestrian intervals are depicted in Figure 4. 7. Pedestrian Clearance Time – the time provided for a pedestrian crossing in a crosswalk, after leaving the curb or shoulder, to travel to the far side of the traveled way or to a median (FHWA 2009b). The pedestrian intervals are depicted in Figure 4. Figure 4 - Depiction of Pedestrian Intervals (Source: FHWA 2009b) 8. Red Clearance Interval – an interval that follows a yellow change interval and precedes the next conflicting green interval (FHWA 2009b). Refer to Figure 3. 9. Signal Coordination – the establishment of timed relationships between adjacent traffic control signals (FHWA 2009b). 10. Signal Cycle Length – the time required for one complete sequence of signal indications (FHWA 2009b). Refer to Figure 3. 11. Signal Face – an assembly of one or more signal sections that is provided for controlling one or more traffic movements on a single approach (FHWA 2009b). Refer to Figure 5. 12. Signal Head – an assembly of one or more signal faces that is provided for controlling traffic movements on one or more approaches (FHWA 2009b). Refer to Figure 5.

7 13. Signal Indication – the illumination of a signal lens or equivalent device (FHWA 2009b). Refer to Figure 5. 14. Signal Lens – that part of the signal section that redirects the light coming directly from the light source and its reflector, if any (FHWA 2009b). Refer to Figure 5. Figure 5 - Components of a Traffic Signal 15. Signal Phase – the right-of-way, yellow change, and red clearance intervals in a cycle that are assigned to an independent traffic movement or combination of movements (FHWA 2009b). 16. Signal Section – the assembly of a signal housing, signal lens, if any, and light source with necessary components to be used for displaying one signal indication (FHWA 2009b). Refer to Figure 5. 17. Split – the portion of the signal cycle length allocated to each phase. Split time consists of green time plus change and clearance intervals (NCHRP 2015). Refer to Figure 3. 18. Walk Interval – an interval during which the WALKING PERSON (symbolizing WALK) signal indication is displayed (FHWA 2009b). 19. Yellow Change Interval – the first interval following the green or flashing arrow interval during which the steady yellow signal indication is displayed (FHWA 2009b). Refer to Figure 3. 2.2 Signal Indications 1. Steady Circular Green – Vehicular traffic is permitted to proceed after yielding right-of-way to pedestrians lawfully within an associated crosswalk and other vehicles lawfully within the

8 intersection. Vehicular traffic turning left or making a U-turn movement shall yield the right-of- way to other vehicles approaching from the opposite direction. Pedestrians facing a circular green signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk (FHWA 2009b). 2. Steady Green Arrow – Vehicular traffic is permitted to cautiously enter the intersection only to make the movement indicated by such arrow. Pedestrians facing a green arrow signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, shall not cross the roadway (FHWA 2009b). 3. Steady Circular Yellow – Vehicular traffic is warned that the related green movement or flashing arrow movement is being terminated or that a steady red indication will be displayed immediately thereafter when vehicular traffic shall not enter the intersection. Pedestrians facing a steady circular yellow signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, shall not start to cross the roadway (FHWA 2009b). 4. Flashing Circular Yellow – Vehicular traffic is permitted to cautiously proceed after yielding right- of-way to pedestrians lawfully within an associated crosswalk and other vehicles lawfully within the intersection. Vehicular traffic turning left or making a U-turn movement shall yield the right- of-way to other vehicles approaching from the opposite direction. Pedestrians facing a flashing circular yellow signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk. Pedestrians shall yield the right-of-way to vehicles lawfully within the intersection at the time that the flashing yellow signal indication is first displayed (FHWA 2009b). 5. Steady Yellow Arrow – Vehicular traffic is warned that the related green movement or flashing arrow movement is being terminated or that a steady red indication will be displayed immediately thereafter when vehicular traffic shall not enter the intersection. Pedestrians facing a steady yellow arrow signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, shall not start to cross the roadway (FHWA 2009b). 6. Flashing Yellow Arrow – Vehicular traffic is permitted to cautiously enter the intersection only to make the movement indicated by such arrow after yielding right-of-way to pedestrians lawfully within an associated crosswalk and other vehicles lawfully within the intersection. Vehicular traffic turning left or making a U-turn movement shall yield the right-of-way to other vehicles approaching from the opposite direction. Pedestrians facing a flashing yellow arrow signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk. Pedestrians shall yield the right-of-way to vehicles lawfully within the intersection at the time that the flashing yellow signal indication is first displayed (FHWA 2009b). 7. Steady Circular Red – Vehicular traffic, unless entering the intersection to make another movement permitted by another signal indication, shall stop at a clearly marked stop line and shall remain stopped until a signal indication to proceed is displayed. Except when a traffic control device is in place prohibiting a turn on red or a steady red arrow signal indication is displayed, vehicular traffic facing a steady circular red signal indication is permitted to enter the intersection to turn right, or to turn left from a one-way street into a one-way street, after stopping. The right to proceed with the turn shall be subject to the rules applicable after making a stop at a STOP

9 sign. Pedestrians facing a steady circular red signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, shall not enter the roadway (FHWA 2009b). 8. Flashing Circular Red – Vehicular traffic shall stop at a clearly marked stop line and shall remain stopped until a signal indication to proceed is displayed. The right to proceed with the turn shall be subject to the rules applicable after making a stop at a STOP sign. Pedestrians facing a flashing circular red signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk. Pedestrians shall yield the right-of-way to vehicles lawfully within the intersection at the time that the flashing red signal indication is first displayed (FHWA 2009b). 9. Steady Red Arrow – Vehicular traffic shall not enter the intersection to make the movement indicated by the arrow, and, unless entering the intersection to make another movement permitted by another signal indication, shall stop at a clearly marked stop line and shall remain stopped until a signal indication or other traffic control device permitting the movement is displayed. Pedestrians facing a steady red arrow signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, shall not enter the roadway (FHWA 2009b). 10. Flashing Red Arrow –Vehicular traffic, if intending to turn in the direction indicated by the arrow, shall stop at a clearly marked stop line. The right to proceed with the turn shall be limited to the direction indicated by the arrow and shall be subject to the rules applicable after making a stop at a STOP sign. Pedestrians facing a flashing red arrow signal indication, unless otherwise directed by a pedestrian signal indication or other traffic control device, are permitted to proceed across the roadway within any marked or unmarked associated crosswalk. Pedestrians shall yield the right-of-way to vehicles lawfully within the intersection at the time that the flashing red signal indication is first displayed (FHWA 2009b). 2.3 Phase Mode 1. Vehicle Phase Mode – the manner in which motorists are directed to make a certain movement. Every turning movement, both left and right turns, has an associated phase mode. 2. Permissive-Only Mode – a mode of traffic signal operation in which left or right turns are permitted to be made on a circular green signal indication, a flashing yellow arrow signal indication, or a flashing red arrow signal indication after yielding to conflicting pedestrians, if any, and/or opposing traffic, if any. When a circular green signal indicated is displayed, both left and right turns are permitted unless otherwise prohibited by another traffic control device. (FHWA 2009b). 3. Protected-Only Mode – a mode of traffic signal operation in which left or right turns are made only when a green arrow signal indication is displayed. During this phase, movements are given the right-of-way and do not conflict with any other traffic or pedestrian movements (FHWA 2009b). 4. Protected-Permissive Mode – a mode of traffic signal operation in which both permissive-only and protected-only modes can occur on an approach during the same cycle. 5. Dynamic or Variable Left-Turn Mode – the mode of traffic signal operation changes among protected-only, protected-permissive, or permissive-only during different periods of the day or as traffic conditions change.

10 2.4 Phase Sequence 1. Phase Sequence – the order in which signal phases are served during a signal cycle (NCHRP 2015). 2. Leading Left-Turn Sequence – a signal sequence which starts opposing left-turn phases prior to the through phases (NCHRP 2015). 3. Lagging Left-Turn Sequence – a signal sequence which serves opposing left-turn phases after the through phases (NCHRP 2015). 4. Lead-Lag Left-Turn Sequence – a signal sequence where one left-turn movement begins with the adjacent through movement and the opposing left-turn movement begins at the end of the conflicting through movement (NCHRP 2015). 5. Split Phasing – a signal sequence where all movements of a single approach are simultaneously given the right-of-way, followed by all movements on the opposing approach (NCHRP 2015). 6. Reservicing – a signal sequence where one phase is served more than once in the same signal cycle. 2.5 Yellow Trap 1. Yellow Trap – a condition that leads the left-turning user into the intersection believing the opposing user is seeing yellow (NCHRP 2015). The “yellow trap” occurs when a driver assumes that opposing traffic also has a yellow indication that will allow the driver to turn left despite the approach of oncoming traffic. 2.6 Actuation 1. Actuation – initiation of a change in or extension of a traffic signal phase through the operation of any type of detector (FHWA 2009b). 2. Pretimed Operation – a type of traffic control signal operation in which none of the signal phases function on the basis of actuation (FHWA 2009b). 3. Fully Actuated Operation – a type of traffic control signal operation in which all signal phases function on the basis of actuation (FHWA 2009b). 4. Semi-Actuated Operation – a type of traffic control signal operation in which at least one, but not all, signal phases function on the basis of actuation (FHWA 2009b). 2.7 Right-Turn Movements 1. Right-Turn Overlap – Right-turn movements are given a protected green arrow signal indication at the same time as the cross-street’s protected left turn. 2.8 Pedestrian Phasing 1. Concurrent Mode – Pedestrians are directed to cross a street at the same time as the parallel vehicle movements. There may be conflicts with permissive left- and/or right turns on green. 2. Protected Mode – Pedestrians are directed to cross a street at the same time as the parallel through vehicle movements, but conflicting left- and right-turn movements are prohibited during the crossing.

11 3. Exclusive Mode – A portion of the traffic signal cycle is configured such that no vehicular movements are served concurrently with pedestrian traffic. This is also known as a pedestrian scramble or “Barnes Dance”. 4. Leading Pedestrian Interval (LPI) – A pedestrian interval option that starts a few seconds before the adjacent through vehicular phase, allowing pedestrians to establish a presence in the crosswalk, and thereby reducing conflicts with turning vehicles (NCHRP 2015). 5. Crossing Phase Extension – provides additional crossing time for slower pedestrians when needed through pushbutton actuation or other means of pedestrian detection. 2.9 Meaning of Acronyms and Abbreviations 1. AADT – Annual Average Daily Traffic 2. AASHTO - American Association of State Highway and Transportation Officials 3. ADT – Average Daily Traffic 4. APS – Accessible Pedestrian Signal 5. CMF – Crash Modification Factor 6. FHWA – Federal Highway Administration 7. FYA – Flashing Yellow Arrow 8. GIS – Geographic Information System 9. HCM – Highway Capacity Manual 10. HSM – Highway Safety Manual 11. IA – Interim Approval 12. ITE – Institute of Transportation Engineers 13. LPI – Leading Pedestrian Interval 14. MUTCD – Manual on Uniform Traffic Control Devices for Streets and Highways 15. MPH – miles per hour 16. NCHRP – National Cooperative Highway Research Program 17. PROWAG – Public Right-of-Way Accessibility Guidelines 18. RTOR – Right Turn on Red 19. SPF – Safety Performance Function 20. TRB- Transportation Research Board 21. USDOT – United States Department of Transportation 22. VPH – Vehicles per hour