Signal Timing Manual - Second Edition (2015)

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Chapter 4. Signal Design CHAPTER 4 SIGNAL DESIGN CONTENTS 4.1 DETECTION.............................................................................................................................. 4-2 4.1.1 High-Speed-Approach Vehicle Detection ........................................................................ 4-5 4.1.2 Low-Speed-Approach Vehicle Detection ......................................................................... 4-7 4.1.3 Left-Turn-Lane Vehicle Detection ...................................................................................... 4-7 4.1.4 Right-Turn-Lane Vehicle Detection ................................................................................... 4-8 4.1.5 Pedestrian Detection ............................................................................................................... 4-8 4.1.6 Bicycle Detection ....................................................................................................................... 4-8 4.1.7 Emergency Vehicle Detection .............................................................................................. 4-9 4.1.8 Bus Detection .............................................................................................................................. 4-9 4.1.9 Rail Detection ............................................................................................................................. 4-9 4.1.10 Other Detection ....................................................................................................................... 4-9 4.2 SIGNAL CABINET EQUIPMENT .......................................................................................... 4-9 4.2.1 Cabinet ......................................................................................................................................... 4-12 4.2.2 Controller ................................................................................................................................... 4-12 4.2.3 Detector Cards .......................................................................................................................... 4-13 4.2.4 Flasher and Flash Transfer Relays ................................................................................... 4-13 4.2.5 DC Power .................................................................................................................................... 4-13 4.2.6 Load Switches ........................................................................................................................... 4-14 4.2.7 Signal Monitor .......................................................................................................................... 4-14 4.2.8 Uninterruptible Power Supply Backup .......................................................................... 4-14 4.3 DISPLAYS ................................................................................................................................4-14 4.3.1 Vehicle Displays ....................................................................................................................... 4-15 4.3.2 Pedestrian Displays ................................................................................................................ 4-22 4.3.3 Bicycle Displays ....................................................................................................................... 4-22 4.3.4 Transit Displays ....................................................................................................................... 4-23 4.4 SIGNALIZED SYSTEM DESIGN .......................................................................................... 4-23 4.5 COMPREHENSIVE DESIGN CONSIDERATIONS ........................................................... 4-25 4.6 REFERENCES ................................................................................................................ ........ 4-26 Signal Timing Manual, Second Edion

Chapter 4. Signal Design LIST OF EXHIBITS Exhibit 4-1 Flow of Inputs and Outputs among Detectors, Signal Cabinet Equipment, and Displays ........................................................................................... 4-1 Exhibit 4-2 Chapter Organization Based on Signal Equipment ......................................... 4-2 Exhibit 4-3 Types of Traf‚ic Signal Detection ............................................................................ 4-3 Exhibit 4-4 Basic Detection Layout ............................................................................................... 4-4 Exhibit 4-5 Detection Objectives .................................................................................................... 4-5 Exhibit 4-6 Decision Zone ................................................................................................................. 4-6 Exhibit 4-7 Limits of Decision Zone .............................................................................................. 4-7 Exhibit 4-8 Bicycle Detection Examples ...................................................................................... 4-9 Exhibit 4-9 Basic Equipment in a Type 332 Signal Cabinet .............................................. 4-10 Exhibit 4-10 Basic Equipment in a NEMA TS-2 Signal Cabinet ......................................... 4-11 Exhibit 4-11 Signal Equipment Equivalents .............................................................................. 4-12 Exhibit 4-12 Advance Signal Placement to Address Horizontal Curve .......................... 4-15 Exhibit 4-13 Advance Signal Placement to Address Vertical Curve ................................ 4-15 Exhibit 4-14 Programmable Vehicle Signal Heads and Signal Louvers ......................... 4-16 Exhibit 4-15 Left-Turn Signal Displays ....................................................................................... 4-17 Exhibit 4-16 Left-Turn Phasing Guidelines ............................................................................... 4-18 Exhibit 4-17 Critical Left-Turn-Related Crash Count ............................................................ 4-19 Exhibit 4-18 Minimum Sight Distance to Oncoming Vehicles ........................................... 4-19 Exhibit 4-19 Illustration of the Yellow Trap ............................................................................. 4-20 Exhibit 4-20 Illustration of the Flashing Yellow Arrow ....................................................... 4-21 Exhibit 4-21 Typical Pedestrian Signal Displays ..................................................................... 4-22 Exhibit 4-22 Example Bicycle Display (Caltrans) and Placement at Intersection .................................................................................................................. 4-23 Exhibit 4-23 Typical Light Rail Signal Displays for a Single LRT Route ......................... 4-23 Exhibit 4-24 Physical Components of an Interconnected Signal System ...................... 4-24 Signal Timing Manual, Second Edion

Chapter 4. Signal Design LIST OF EXHIBITS Exhibit 4-1 Flow of Inputs and Outputs among Detectors, Signal Cabinet Equipment, and Displays ........................................................................................... 4-1 Exhibit 4-2 Chapter Organization Based on Signal Equipment ......................................... 4-2 Exhibit 4-3 Types of Traf‚ic Signal Detection ............................................................................ 4-3 Exhibit 4-4 Basic Detection Layout ............................................................................................... 4-4 Exhibit 4-5 Detection Objectives .................................................................................................... 4-5 Exhibit 4-6 Decision Zone ................................................................................................................. 4-6 Exhibit 4-7 Limits of Decision Zone .............................................................................................. 4-7 Exhibit 4-8 Bicycle Detection Examples ...................................................................................... 4-9 Exhibit 4-9 Basic Equipment in a Type 332 Signal Cabinet .............................................. 4-10 Exhibit 4-10 Basic Equipment in a NEMA TS-2 Signal Cabinet ......................................... 4-11 Exhibit 4-11 Signal Equipment Equivalents .............................................................................. 4-12 Exhibit 4-12 Advance Signal Placement to Address Horizontal Curve .......................... 4-15 Exhibit 4-13 Advance Signal Placement to Address Vertical Curve ................................ 4-15 Exhibit 4-14 Programmable Vehicle Signal Heads and Signal Louvers ......................... 4-16 Exhibit 4-15 Left-Turn Signal Displays ....................................................................................... 4-17 Exhibit 4-16 Left-Turn Phasing Guidelines ............................................................................... 4-18 Exhibit 4-17 Critical Left-Turn-Related Crash Count ............................................................ 4-19 Exhibit 4-18 Minimum Sight Distance to Oncoming Vehicles ........................................... 4-19 Exhibit 4-19 Illustration of the Yellow Trap ............................................................................. 4-20 Exhibit 4-20 Illustration of the Flashing Yellow Arrow ....................................................... 4-21 Exhibit 4-21 Typical Pedestrian Signal Displays ..................................................................... 4-22 Exhibit 4-22 Example Bicycle Display (Caltrans) and Placement at Intersection .................................................................................................................. 4-23 Exhibit 4-23 Typical Light Rail Signal Displays for a Single LRT Route ......................... 4-23 Exhibit 4-24 Physical Components of an Interconnected Signal System ...................... 4-24 Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-1 CHAPTER 4. SIGNAL DESIGN Effective signal timing requires appropriate signal design. While signal timing parameters can be changed relatively easily, signal design elements are typically static and more dificult (and costly) to change. In order to produce a signal timing plan that meets the objectives chosen for a site, the signalized intersection design must be tailored to its speciic operating environment and work as a foundation for the signal timing. Appropriate infrastructure provides a signal timing practitioner with options, allowing him or her to adjust timing values to meet site-specific needs in the near-term as well as the future. Within agencies, signal design is typically separate from signal timing. It is therefore important for signal timing practitioners to understand the effects of signal design on intersection operations, so that they can offer guidance to signal designers and ensure all aspects of the signal timing can be accommodated. Exhibit 4-1 illustrates the low of inputs and outputs to and from the various pieces of signal equipment at an individual signalized intersection. As previously discussed in Chapter 3, there are three main categories of signal equipment at an intersection: (1) detection, (2) cabinet equipment, and (3) displays. Detectors sense users and provide the cabinet equipment with information about their presence at an intersection. The cabinet equipment (the controller in particular) interprets the inputs from the detectors and translates them to outputs based on the signal timing plan. The output information is then forwarded to the displays in order to allow users to move through the intersection. This chapter discusses the signal design elements that directly influence signal ming, but not every feature described in this chapter will be required in every operang environment. Exhibit 4-1 Flow of Inputs and Outputs among Detectors, Signal Cabinet Equipment, and Displays Signal Timing Manual, Second Edion

Chapter4-2 4. Signal Design Using the signal equipment categories, this chapter has been organized into four main sections (as depicted in Exhibit 4-2). The irst three sections summarize design information for the equipment at an individual signalized intersection, while the last section focuses on the equipment required for system operations (i.e., communications for monitoring and coordination). In addition to the information provided in this chapter, a signal designer should consult the current edition of the Manual on Uniform Trafic Control Devices (MUTCD) (1) and any design standards relevant to the local jurisdiction before completing a signalized intersection design. 4.1 DETECTION Detectors sense the presence of roadway users, and provide the controller with information it can use to determine whether a particular phase needs to be served. Detection should be designed with an understanding of actual controller operations because detectors can operate in one of two modes—pulse or presence. This manual assumes detection operates in presence mode because it is the safest mode for trafic signal operations. The detection layout should change depending on how the detectors are being operated and will affect a variety of intersection operations. In combination with the controller, detectors are responsible for 1. Identifying user presence for a movement and its corresponding phase. 2. Extending a phase. 3. Identifying gaps in trafic where a phase should end due to no trafic or ineficient low. 4. Providing safe phase termination for high-speed vehicle movements by minimizing the chance of a driver being in the decision zone (also known as a Type II dilemma zone) at the onset of the yellow indication (explained further in Section 4.1.1). 5. Monitoring intersection performance using measures of effectiveness (MOEs) logs. 6. Possibly counting trafic volumes and identifying vehicle types (e.g., trucks, bicycles, emergency vehicles, and transit vehicles). Chapter 10 contains additional information on special applications. Exhibit 4-3 shows several categories of detectors that can be used at an intersection. While the same type of detection can be used to detect motorized vehicles and bicycles, push buttons located near the sidewalk ramps are most appropriate for pedestrians. Motorized vehicle and bicycle detectors can either be in-ground (units placed in the roadway pavement) or above-ground (units positioned above the roadway on signal mast arms or light poles). Exhibit 4-2 Chapter Organiza on Based on Signal Equipment Phases are a way for the controller to me mulple movements based on the desired outcome. (Detailed informaon is available in Chapter 5, but phases will be referenced at a high level throughout the rest of this chapter.) Signal Timing Manual, Second Edion

Chapter4-2 4. Signal Design Using the signal equipment categories, this chapter has been organized into four main sections (as depicted in Exhibit 4-2). The irst three sections summarize design information for the equipment at an individual signalized intersection, while the last section focuses on the equipment required for system operations (i.e., communications for monitoring and coordination). In addition to the information provided in this chapter, a signal designer should consult the current edition of the Manual on Uniform Trafic Control Devices (MUTCD) (1) and any design standards relevant to the local jurisdiction before completing a signalized intersection design. 4.1 DETECTION Detectors sense the presence of roadway users, and provide the controller with information it can use to determine whether a particular phase needs to be served. Detection should be designed with an understanding of actual controller operations because detectors can operate in one of two modes—pulse or presence. This manual assumes detection operates in presence mode because it is the safest mode for trafic signal operations. The detection layout should change depending on how the detectors are being operated and will affect a variety of intersection operations. In combination with the controller, detectors are responsible for 1. Identifying user presence for a movement and its corresponding phase. 2. Extending a phase. 3. Identifying gaps in trafic where a phase should end due to no trafic or ineficient low. 4. Providing safe phase termination for high-speed vehicle movements by minimizing the chance of a driver being in the decision zone (also known as a Type II dilemma zone) at the onset of the yellow indication (explained further in Section 4.1.1). 5. Monitoring intersection performance using measures of effectiveness (MOEs) logs. 6. Possibly counting trafic volumes and identifying vehicle types (e.g., trucks, bicycles, emergency vehicles, and transit vehicles). Chapter 10 contains additional information on special applications. Exhibit 4-3 shows several categories of detectors that can be used at an intersection. While the same type of detection can be used to detect motorized vehicles and bicycles, push buttons located near the sidewalk ramps are most appropriate for pedestrians. Motorized vehicle and bicycle detectors can either be in-ground (units placed in the roadway pavement) or above-ground (units positioned above the roadway on signal mast arms or light poles). Exhibit 4-2 Chapter Organiza on Based on Signal Equipment Phases are a way for the controller to me mulple movements based on the desired outcome. (Detailed informaon is available in Chapter 5, but phases will be referenced at a high level throughout the rest of this chapter.) Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-3 Designers should irst refer to adopted local or state practices, guidelines, or policies, if available, when selecting a detection technology. Practitioners can also refer to the Federal Highway Administration’s Trafic Detector Handbook (2) for additional information about these different types of detection. Each has advantages and disadvantages related to performance, reliability, and installation. While most designs will utilize the same type of detection along a single corridor, these detector types can be used in combination. When developing detection plans, designers need to consider the potential signal phasing options, expected travel speeds, and user mix at the intersection (e.g., number of trucks and slow-moving pedestrians). An agency should always consider maintenance efforts associated with the installation of new equipment, but this chapter explains concepts assuming detection on all approaches. Trafic signal detection on all approaches provides the most lexibility, allowing for effective responsiveness and Exhibit 4-3 Types of Traffic Signal Detecon Signal Timing Manual, Second Edion

Chapter4-4 4. Signal Design facilitating the measurement of demand and travel characteristics over time. Detection on all approaches also allows adaptable late-night operations. Generally accepted vehicle detection locations, in order of priority, are as follows: 1. Minor street approaches and left-turn lanes at the stop bar. 2. Major street approaches set back from the stop bar. 3. Major street approaches at the stop bar. Depending on the objectives for the signalized intersection, detection may only be required at some locations. Each detection location has its own bene its. Stop bar presence detectors are able to drop calls when permitted turns are made (i.e., left-turn or right-turn-on-red) and no other vehicles are present, reducing inef icient transitions. Setback detectors, on the other hand, can provide decision zone (Type II dilemma zone) protection and have the ability to provide more ef icient gap outs than is possible with stop bar detection zones. (Gapping out is explained in detail in Chapter 6.) Combinations of setback detection and stop bar detection can be used in either through lanes or left- turn lanes to increase ef iciency. Detection zones can vary based on location-speci ic issues, the type of detection technology used, and the approach speed. Exhibit 4-4 illustrates a basic approach for detection zone placement at the intersection of a major street, high-speed approach (shown left/right) and a minor street, low-speed approach (shown top/bottom). Note that the stop bar detection is shown as long zones. Depending on the type of detection technology, these zones can be made up of a single longer zone or multiple smaller zones. For example, if inductive loops are being used, a stop bar detection zone might be made up of three inductive loops. Detection zones can also be tied together, meaning that several detection zones can essentially send the same message to the controller. For example, if there are two detectors in separate lanes tied together, a vehicle can drive over either one of them to Exhibit 4-4 Basic Detecon Layout Signal Timing Manual, Second Edion

Chapter4-4 4. Signal Design facilitating the measurement of demand and travel characteristics over time. Detection on all approaches also allows adaptable late-night operations. Generally accepted vehicle detection locations, in order of priority, are as follows: 1. Minor street approaches and left-turn lanes at the stop bar. 2. Major street approaches set back from the stop bar. 3. Major street approaches at the stop bar. Depending on the objectives for the signalized intersection, detection may only be required at some locations. Each detection location has its own bene its. Stop bar presence detectors are able to drop calls when permitted turns are made (i.e., left-turn or right-turn-on-red) and no other vehicles are present, reducing inef icient transitions. Setback detectors, on the other hand, can provide decision zone (Type II dilemma zone) protection and have the ability to provide more ef icient gap outs than is possible with stop bar detection zones. (Gapping out is explained in detail in Chapter 6.) Combinations of setback detection and stop bar detection can be used in either through lanes or left- turn lanes to increase ef iciency. Detection zones can vary based on location-speci ic issues, the type of detection technology used, and the approach speed. Exhibit 4-4 illustrates a basic approach for detection zone placement at the intersection of a major street, high-speed approach (shown left/right) and a minor street, low-speed approach (shown top/bottom). Note that the stop bar detection is shown as long zones. Depending on the type of detection technology, these zones can be made up of a single longer zone or multiple smaller zones. For example, if inductive loops are being used, a stop bar detection zone might be made up of three inductive loops. Detection zones can also be tied together, meaning that several detection zones can essentially send the same message to the controller. For example, if there are two detectors in separate lanes tied together, a vehicle can drive over either one of them to Exhibit 4-4 Basic Detecon Layout Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-5 register a call for that movement. This is inef icient from a timing standpoint. For detection zones being used to extend (or call and extend) a phase, detection channels should be designed by lane for more ef icient lane-by-lane detection and the ability to count users on a lane-by-lane basis. In addition to detector locations, detection plans often include a description of the size, number, and functionality of each detector, as well as a wiring diagram that shows how detectors are associated with phases. In general, detectors can either call and/or extend a phase. If a phase is not being served and vehicles approach the intersection, the detectors can tell the controller that there are vehicles waiting and “call” the phase. If a phase is in the process of being served and additional vehicles approach the intersection after the initial queue departs, the detectors can ask the controller to “extend” the current phase to accommodate the vehicles. Exhibit 4-5 summarizes the primary objectives for different types of detection, with detailed information provided throughout the remainder of Section 4.1. Type of Detecon Primary Objecve(s) High-Speed-Approach Vehicle Detecon □ Serving the standing queue at the beginning of green □ Safely terminang the phase once there is a conflicng call Low-Speed-Approach Vehicle Detecon □ Calling phases on low-speed approaches □ Serving the standing queue at the beginning of green □ Minimizing delay by reducing calls on permi€ed movements Le‚-Turn-Lane Vehicle Detecon □ Calling le‚-turn phases □ Serving the standing queue at the beginning of green □ Minimizing delay by reducing inefficient transions □ Prevenng vehicles from being stranded in the intersecon Right-Turn-Lane Vehicle Detecon □ Minimizing delay by reducing calls due to right-turn-on-red □ Calling right-turn phases (if used) Pedestrian Detecon □ Calling pedestrian phases Bicycle Detecon □ Calling either associated motorized vehicle phases or independent bicycle phases □ Prevenng accidental motorized vehicle actuaons if using independent bicycle phases □ Eliminang need for bicycles to use pedestrian phases Emergency Vehicle Detecon □ Enabling preferenal treatment opons for emergency vehicles Bus Detecon □ Enabling preferenal treatment opons for transit Rail Detecon □ Ensuring safe and efficient signal ming sequencing before, during, and a‚er train arrivals 4.1.1 High-Speed-Approach Vehicle Detecon High-speed detection requires detectors located upstream of the stop bar in order to determine when it is safe to terminate a phase as well as for measuring queue and performance. While setback (or advance/upstream) detection can also be used to clear queues at the stop bar (using minimum green or variable initial, which are discussed in Chapter 6), stop bar detectors can be used on high-speed approaches in combination with setback detection. Stop bar detectors can more ef iciently clear queues at the stop bar and can accommodate calls if there is traf ic that enters the roadway downstream of the setback detectors. Therefore, a combination of stop bar and setback detection provides the most ef icient operations. If used with setback detection, stop bar detectors should be disconnected (using controller programming) once the initial queue clears. Exhibit 4-5 Detecon Objecves Signal Timing Manual, Second Edion

Chapter4-6 4. Signal Design This will prevent the phase from being extended unnecessarily and allow for more eficient operations. The design of setback detection on high-speed approaches requires special attention. The detectors must be placed in a manner that allows the controller to terminate phases while vehicles still have enough time to stop. This relationship is often described using the term “dilemma zone,” which has historically been applied to two scenarios that are often confused. The term dilemma zone was initially used with regard to yellow change intervals (i.e., Type I dilemma). Later, the term dilemma zone was used with regard to detection design (and also known as an indecision zone, Type II dilemma zone, or decision zone). This manual uses the term dilemma zone with regard to yellow change interval timing and decision zone with regard to setback detection design. Dilemma zones are a result of the yellow clearance interval timing—when a yellow is too short for a vehicle to safely enter the intersection, but the vehicle is too close to the stop bar to safely stop. A dilemma zone can be addressed with an appropriate yellow clearance interval, which is explained in detail in Chapter 6. A decision zone is not related to clearance interval timing, but rather to the human factors of driver perception, reaction, and judgment. It is the length of roadway where each individual driver may make a different decision upon seeing the yellow signal indication; some vehicles may stop and others may go. The location of the decision zone is illustrated in Exhibit 4-6. For more information on Type I and Type II dilemma zones, practitioners should refer to NCHRP Report 731 (3). The decision zone has historically been deined using a variety of measures, including distance to the stop bar (4, 5), travel time to the stop bar (6), and stopping sight distance (7). Based on trends from these previous studies, the limits of the decision zone tend to be between 5.5 and 2.5 seconds of travel time from the stop bar. Exhibit 4-7 provides quick reference distances representing the beginning and end of the decision zone (if 5.5 seconds from the stop bar is considered the beginning and 2.5 seconds from the stop bar is considered the end). In order to design with the decision zone in mind, one detector (or more in some complex designs) should be placed Exhibit 4-6 Decision Zone Signal Timing Manual, Second Edion

Chapter4-6 4. Signal Design This will prevent the phase from being extended unnecessarily and allow for more eficient operations. The design of setback detection on high-speed approaches requires special attention. The detectors must be placed in a manner that allows the controller to terminate phases while vehicles still have enough time to stop. This relationship is often described using the term “dilemma zone,” which has historically been applied to two scenarios that are often confused. The term dilemma zone was initially used with regard to yellow change intervals (i.e., Type I dilemma). Later, the term dilemma zone was used with regard to detection design (and also known as an indecision zone, Type II dilemma zone, or decision zone). This manual uses the term dilemma zone with regard to yellow change interval timing and decision zone with regard to setback detection design. Dilemma zones are a result of the yellow clearance interval timing—when a yellow is too short for a vehicle to safely enter the intersection, but the vehicle is too close to the stop bar to safely stop. A dilemma zone can be addressed with an appropriate yellow clearance interval, which is explained in detail in Chapter 6. A decision zone is not related to clearance interval timing, but rather to the human factors of driver perception, reaction, and judgment. It is the length of roadway where each individual driver may make a different decision upon seeing the yellow signal indication; some vehicles may stop and others may go. The location of the decision zone is illustrated in Exhibit 4-6. For more information on Type I and Type II dilemma zones, practitioners should refer to NCHRP Report 731 (3). The decision zone has historically been deined using a variety of measures, including distance to the stop bar (4, 5), travel time to the stop bar (6), and stopping sight distance (7). Based on trends from these previous studies, the limits of the decision zone tend to be between 5.5 and 2.5 seconds of travel time from the stop bar. Exhibit 4-7 provides quick reference distances representing the beginning and end of the decision zone (if 5.5 seconds from the stop bar is considered the beginning and 2.5 seconds from the stop bar is considered the end). In order to design with the decision zone in mind, one detector (or more in some complex designs) should be placed Exhibit 4-6 Decision Zone Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-7 upstream of the stop bar, starting at the beginning of the decision zone. Detection at the beginning of the decision zone can then be programmed to prevent a phase from terminating before a vehicle clears the decision zone (using the passage timer, which is discussed further in Chapter 6). Approach Vehicular Speed (Miles Per Hour) Beginning of Decision Zone (5.5 Seconds from Stop Bar) End of Decision Zone (2.5 Seconds from Stop Bar) 35 285 feet 125 feet 40 325 feet 145 feet 45 365 feet 165 feet 50 405 feet 180 feet 55 445 feet 200 feet When a phase maxes out (as explained in Chapter 6) or is forced off by coordination (which is discussed in Chapter 7), there is no decision zone protection. The more max out (or force-off) occurrences, the less effective the decision zone protection. Conversely, the fewer max out (or force-off) occurrences, the more effective the decision zone protection. Strategies to reduce max out occurrences include lane-by-lane detection; establishing detector settings to get vehicles to the end of the decision zone; and complex, multiple-detector designs. Designers should refer to the ITE Manual of Trafic Detector Design (8) for more information. 4.1.2 Low-Speed-Approach Vehicle Detec­on The objectives for low-speed approach detection are primarily calling the low-speed approach phases, clearing the standing queue, and minimizing delay. Because of the lower speeds, there is less need for decision zone protection. As shown in Exhibit 4-4, the use of stop bar detection only for low-speed approaches is typical practice. This large area detection design at the stop bar facilitates the primary objective of clearing queues without prematurely ending the phase. The use of large (80-foot) detection zones (either through a single larger detection zone or multiple smaller detectors) allows the passage time to be reduced to zero (creating more ef‡iciency), prevents premature termination of the phase due to sluggish traf‡ic, and allows for immediate termination when the last vehicle passes the stop bar (9). This detection design also allows the controller to drop a call if a vehicle turns left on a permitted movement or right-on-red (through the use of non-locking memory, which is described in Chapter 6). 4.1.3 Le‚-Turn-Lane Vehicle Detec­on As shown in Exhibit 4-4, the recommended detection design for left-turn movements should match the design for low-speed approaches. This type of design is particularly helpful when the signal is operating in protected-permitted mode (described in detail in Section 4.3.1), as the call will be dropped if the left-turning vehicle turns during the permitted interval. If the left-turn movement operates in permitted or protected-permitted mode, it may be desirable to extend the stop bar detection zone beyond the stop bar into the intersection or crosswalk. This minimizes the potential for stranding a turning vehicle in the intersection. Note that if the left-turn movement occurs at a higher speed, then additional setback detection may be required; some designs use setback detection in left-turn lanes to increase ef‡iciency. Exhibit 4-7 Limits of Decision Zone Signal Timing Manual, Second Edi­on

Chapter4-8 4. Signal Design 4.1.4 Right-Turn-Lane Vehicle Detec on If a right-turn movement is in an exclusive right-turn lane (or lanes), detection can be provided for those vehicles. However, it may be desirable to place a delay on those detection zones. Delay will prevent a call from immediately going to the controller (explained in detail in Chapter 6). Instead, a call will be placed only if a vehicle has to wait for a certain amount of time. This prevents the phase from being prematurely called when a vehicle is able to quickly turn right-on-red. 4.1.5 Pedestrian Detec on Pedestrians are vulnerable users of the transportation system and are frequently at risk for con­licts with other users. Pedestrian detection should be placed in a clear and expected fashion to support ease of use and compliance with the Americans with Disabilities Act (ADA) requirements and the guidelines contained in the MUTCD (1). FHWA’s Pedestrian Facilities User Guide—Providing Safety and Mobility (10) provides additional information. Pedestrian crossings are generally provided between pedestrian generators/ destinations and on all quadrants of a signalized intersection, unless a speci­ic issue or objective would dictate otherwise. For example, a signal designer might reconsider a crossing at a location with very low pedestrian activity and very high left-turn (or right- turn) vehicular volume under protected-permitted operations. There may also be cases in which vehicular modes are explicitly prioritized above pedestrians based on local policy or practice. If possible, wiring and the cabinet equipment should support independent operation of each crosswalk. Independent operation of each pedestrian crossing allows the total crossing time to be different between phase pairs. For example, the pedestrian crossings on the north and south sides of an intersection can be given different walk and pedestrian clearance times if they are operated independently. Per MUTCD guidance, (1) the length of the crosswalk and (2) the distance from the pedestrian detector to the far side of the traveled way both impact the minimum required pedestrian service interval (walk and clearance times) (1). The longer the crosswalk or the further the distance of the pedestrian detector to the edge of the pavement, the greater the amount of time required to serve pedestrians. While the length of the crosswalk is not generally decided by the signal designer (or signal timer), he or she should attempt to locate pedestrian detection in an intuitive location, near the curb/ramp at the beginning of the painted crosswalk, in order to minimize the time required for pedestrian movements. 4.1.6 Bicycle Detec on If bicycle detection is provided (as shown in Exhibit 4-8), defining its desired functionality (e.g., call, extend, or count) will in­luence the size and location of the required detection. Regardless of the speci­ic location, the signal designer may want to consider setback bicycle detection to minimize accidental vehicle actuations, which can be common when bicycle detectors are located at stop bars. This is particularly important when there are independent bicycle phases being used at an intersection. Signal Timing Manual, Second Edi on

Chapter4-8 4. Signal Design 4.1.4 Right-Turn-Lane Vehicle Detec on If a right-turn movement is in an exclusive right-turn lane (or lanes), detection can be provided for those vehicles. However, it may be desirable to place a delay on those detection zones. Delay will prevent a call from immediately going to the controller (explained in detail in Chapter 6). Instead, a call will be placed only if a vehicle has to wait for a certain amount of time. This prevents the phase from being prematurely called when a vehicle is able to quickly turn right-on-red. 4.1.5 Pedestrian Detec on Pedestrians are vulnerable users of the transportation system and are frequently at risk for con­licts with other users. Pedestrian detection should be placed in a clear and expected fashion to support ease of use and compliance with the Americans with Disabilities Act (ADA) requirements and the guidelines contained in the MUTCD (1). FHWA’s Pedestrian Facilities User Guide—Providing Safety and Mobility (10) provides additional information. Pedestrian crossings are generally provided between pedestrian generators/ destinations and on all quadrants of a signalized intersection, unless a speci­ic issue or objective would dictate otherwise. For example, a signal designer might reconsider a crossing at a location with very low pedestrian activity and very high left-turn (or right- turn) vehicular volume under protected-permitted operations. There may also be cases in which vehicular modes are explicitly prioritized above pedestrians based on local policy or practice. If possible, wiring and the cabinet equipment should support independent operation of each crosswalk. Independent operation of each pedestrian crossing allows the total crossing time to be different between phase pairs. For example, the pedestrian crossings on the north and south sides of an intersection can be given different walk and pedestrian clearance times if they are operated independently. Per MUTCD guidance, (1) the length of the crosswalk and (2) the distance from the pedestrian detector to the far side of the traveled way both impact the minimum required pedestrian service interval (walk and clearance times) (1). The longer the crosswalk or the further the distance of the pedestrian detector to the edge of the pavement, the greater the amount of time required to serve pedestrians. While the length of the crosswalk is not generally decided by the signal designer (or signal timer), he or she should attempt to locate pedestrian detection in an intuitive location, near the curb/ramp at the beginning of the painted crosswalk, in order to minimize the time required for pedestrian movements. 4.1.6 Bicycle Detec on If bicycle detection is provided (as shown in Exhibit 4-8), defining its desired functionality (e.g., call, extend, or count) will in­luence the size and location of the required detection. Regardless of the speci­ic location, the signal designer may want to consider setback bicycle detection to minimize accidental vehicle actuations, which can be common when bicycle detectors are located at stop bars. This is particularly important when there are independent bicycle phases being used at an intersection. Signal Timing Manual, Second Edi on Chapter 4. Signal Design 4-9 4.1.7 Emergency Vehicle Detecon Emergency vehicles, depending on desired outcomes, may receive preferential treatment (priority or preemption) at signalized intersections (explained in detail in Chapter 10). Design components to consider are priority/preemption receivers at the intersection, a controller interface in the signal cabinet to call the appropriate phase(s), and a controller (hardware and irmware) to support priority or preemption service. 4.1.8 Bus Detecon Specialized bus signal phasing or timing requires bus detection to call bus priority phase(s). Bus priority adjusts signal timing while maintaining coordination (if present) as the bus approaches a signalized intersection. More information about preferential treatment, bus priority, and design considerations is available in Chapter 10. 4.1.9 Rail Detecon The MUTCD provides trafic control guidance with respect to railroads and light rail transit (LRT) (1). Rail that is on-street or has crossings near trafic signals has its own unique impacts on signalized trafic systems, based on its proximity to the signalized intersections and the modal priority hierarchy. Railroad and commuter rail (and some LRT) often operate in a semi-exclusive right-of-way, and will have the highest priority at a nearby signalized intersection, typically preempting signal timing. Appropriate detection for railroad vehicles (advance and simultaneous) and appropriate connections to nearby trafic signals can be important for ensuring safe and eficient signal timing sequencing before, during, and after train arrivals. Details about rail preemption are discussed in Chapter 10. 4.1.10 Other Detecon Special detection may be employed at unique locations such as movable bridges, one-lane bridges and tunnels, and metered freeway entrance ramps in order to provide preemption or priority control of the trafic signals (see Chapter 10). 4.2 SIGNAL CABINET EQUIPMENT The signal cabinet houses the control equipment at an individual intersection. Exhibit 4-9 illustrates and labels the typical components found inside a Type 332 signal cabinet, and Exhibit 4-10 does the same for a NEMA TS-2 signal cabinet. (Other common cabinet styles include Type 336, NEMA TS-1, and ITS.) Different cabinet styles have Exhibit 4-8 Bicycle Detec on Examples Signal cabinet components should be designed for exis ng and future needs. Signal Timing Manual, Second Edion

Chapter4-10 4. Signal Design different layouts, internal operations, and terminology, but the general functionality and many components are largely interchangeable among modern signal hardware. Cabinet styles can be differentiated using several metrics (e.g., size or mounting type), but one of the most important distinguishing characteristics is how the controller is connected to other cabinet equipment. There are two types of connections—parallel and serial. A signal cabinet with parallel connections directly wires the controller to every individual input and output, while a cabinet with serial connections connects the Exhibit 4-9 Basic Equipment in a Type 332 Signal Cabinet Signal Timing Manual, Second Edion

Chapter4-10 4. Signal Design different layouts, internal operations, and terminology, but the general functionality and many components are largely interchangeable among modern signal hardware. Cabinet styles can be differentiated using several metrics (e.g., size or mounting type), but one of the most important distinguishing characteristics is how the controller is connected to other cabinet equipment. There are two types of connections—parallel and serial. A signal cabinet with parallel connections directly wires the controller to every individual input and output, while a cabinet with serial connections connects the Exhibit 4-9 Basic Equipment in a Type 332 Signal Cabinet Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-11 controller to cabinet equipment through serial interface units (e.g., Bus interface units in NEMA TS-2 cabinets). Type 332, Type 336, and NEMA TS-1 signal cabinets use parallel connections, while NEMA TS-2 and ITS signal cabinets use serial connections. The following sections highlight a few typical cabinet components and their relationships to signal timing, but not every piece of equipment that could be in a signal cabinet is discussed in this section. Signal designers should consult relevant standard drawings and speci‚ications. Exhibit 4-10 Basic Equipment in a NEMA TS-2 Signal Cabinet Signal Timing Manual, Second Edion

Chapter4-12 4. Signal Design 4.2.1 Cabinet The cabinet should be located along the minor street in a position where it is easy for a practitioner to simultaneously see the inside of the cabinet and displays for several phases, making troubleshooting and ield observations more effective. Signal cabinets should also be located in a space that is easy to access (e.g., parking for maintenance vehicles), but shielded (or away) from the roadway to minimize the likelihood of crashes or “knockdowns.” 4.2.2 Controller The controller is the piece of equipment in the signal cabinet that translates input information from the detectors into output information for the displays. Signal timing parameters (programmed into the controller software) determine how the controller interprets the detector and display information. Much like a computer, there are various components of a controller that practitioners often reference. Exhibit 4-11 relates the basic controller elements to well-known computer equivalents. In general, there is a cabinet that houses the controller, the controller that acts much like a computer, and an operating system that runs a chosen irmware. Historically, there are two families of standards that have driven trafic signal control: (1) the National Electric Manufacturers Association (NEMA) family and (2) the Type 170 family, which is based on the California Department of Transportation (Caltrans) standard. While controllers operating under either standard are essentially timed in the same manner, the terminology will have some differences. Like all technology, controllers continue to evolve, and there are now many hybrid versions of the NEMA and Type 170 standards: • NEMA TS-1 Controller is an older style that is connected to TS-1 cabinet devices through three MS-type connectors (designated A, B, and C) with a designated pin A controller can be thought of as the “computer” behind traffic signal control. Exhibit 4-11 Signal Equipment Equivalents Signal Timing Manual, Second Edion

Chapter4-12 4. Signal Design 4.2.1 Cabinet The cabinet should be located along the minor street in a position where it is easy for a practitioner to simultaneously see the inside of the cabinet and displays for several phases, making troubleshooting and ield observations more effective. Signal cabinets should also be located in a space that is easy to access (e.g., parking for maintenance vehicles), but shielded (or away) from the roadway to minimize the likelihood of crashes or “knockdowns.” 4.2.2 Controller The controller is the piece of equipment in the signal cabinet that translates input information from the detectors into output information for the displays. Signal timing parameters (programmed into the controller software) determine how the controller interprets the detector and display information. Much like a computer, there are various components of a controller that practitioners often reference. Exhibit 4-11 relates the basic controller elements to well-known computer equivalents. In general, there is a cabinet that houses the controller, the controller that acts much like a computer, and an operating system that runs a chosen irmware. Historically, there are two families of standards that have driven trafic signal control: (1) the National Electric Manufacturers Association (NEMA) family and (2) the Type 170 family, which is based on the California Department of Transportation (Caltrans) standard. While controllers operating under either standard are essentially timed in the same manner, the terminology will have some differences. Like all technology, controllers continue to evolve, and there are now many hybrid versions of the NEMA and Type 170 standards: • NEMA TS-1 Controller is an older style that is connected to TS-1 cabinet devices through three MS-type connectors (designated A, B, and C) with a designated pin A controller can be thought of as the “computer” behind traffic signal control. Exhibit 4-11 Signal Equipment Equivalents Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-13 coniguration. A D-connector is typically present to provide more features, but it is not NEMA speciied. (Each supplier has developed a different D-connector.) Most modern controllers are TS-2, but some are operated (in a hybrid mode) in TS-1 cabinets and do not take advantage of all TS-2 features. • NEMA TS-2 Type 1 Controller is the current NEMA controller type, leveraging all of the capabilities and features of the TS-2 standard. This controller only works in a TS-2 cabinet with synchronous data link control communication. • NEMA TS-2 Type 2 Controller is compatible with both TS-2 and TS-1 style cabinets. • Type 170 Controller is an older/original style with standardized hardware. It uses Caltrans series cabinets (i.e., 332, 334, and 336) through a C1 connector. • Type 2070 Controller is evolved from the 170 standard, but will work in Caltrans cabinets or any NEMA style cabinet. (Note that adaptors and/or interface cards are required, as well as a controller irmware appropriate to the coniguration.) • Advanced Transportation Controller (ATC) represents the next generation of controller. The standard provides an open-architecture software platform that acts as a universal interface between application programs and the ATC controller units. The signal designer should ensure that all inputs and outputs can be accommodated by the controller (and style of cabinet). Modiied cabinets that allow for additional hardware and/or other intelligent transportation system (ITS) devices might need to be procured. 4.2.3 Detector Cards Detector cards (which are also referred to as “detector ampliiers” when used with inductive loops) identify user actuations from the ield detectors and pass the information along to the signal controller. Most detector cards can handle between one and four detector channels and various modes of operation. Connections and capabilities of detector cards will vary with the method of detection technology being used, but typically work with standard detector racks/input iles, provided suficient slots are available in the signal cabinet. 4.2.4 Flasher and Flash Transfer Relays The lasher makes it possible for the displays to lash 50 to 60 times per minute (i.e., 50 percent time power-on, plus or minus 5 percent). This lashing power is used for lashing don’t walk, lashing yellow arrows, night-time lash, and other lashing indications as needed. The lash transfer relays are used by the signal monitor to disconnect the controller and transfer the signal to emergency lashing operations. Emergency lash operations (typically all indications lashing red) must be conigured through appropriate cabinet wiring. 4.2.5 DC Power Most cabinet equipment (e.g., detector card racks, communications equipment, and other auxiliary equipment) operates in a 12/24-volt DC environment. DC power Adequate detector rack space should be provided to allow for near-term and possible long-term needs. Signal Timing Manual, Second Edion

Chapter4-14 4. Signal Design equipment is handled in a variety of manners depending on the type of cabinet and traf ic signal controller. 4.2.6 Load Switches Load switches are essentially electrical gating (or relay) devices that allow the controller, which operates in a 12/24-volt DC environment, to direct a 120-volt AC current to various signal displays. (Note that load switches are called “switch packs” in a Caltrans series installation.) Each load switch (and associated wiring) plugs into load switch bays in the back panel of the cabinet. The number of load switch bays will dictate the number of output channels that the signal designer has available at the intersection. A load switch is typically required for each vehicle signal phase, each pedestrian phase, and each overlap. 4.2.7 Signal Monitor Modern traf ic signal monitors have many advanced features to improve safety and enhance maintenance of traf ic signals. The NEMA malfunction management unit (MMU) and the older con lict monitoring unit (CMU) are important safety devices. While these devices are often called con lict monitors, they have evolved from simple con lict and voltage monitoring to enhanced fault monitoring. Enhanced monitors have features beyond monitoring con licting phases or con licting indications in a signal head. The enhanced monitors detect and respond to improper voltages caused by malfunctions of the controller unit (CU), load switches, or incorrect wiring of the cabinet. They will identify the type of fault (e.g., con lict, red fail, clearance fail, dual indication, or communications faults in the cabinet) and which signal heads were active at the time of the fault, and they can retrieve historical data about the fault. The monitors will remain in fault mode until reset. 4.2.8 Uninterrupble Power Supply Backup There are some locations where an uninterruptible power supply (UPS)/battery backup system (BBS) may be necessary or desirable when utility power is not available. A UPS can provide emergency power to connected equipment by supplying power from a separate source (e.g., batteries, solar, or wind). The system can also function as a power conditioner and/or voltage regulation device. Installing UPS systems at locations where there have been power issues helps reduce downtime and electrical damage to equipment. For example, a signalized intersection that is equipped with a UPS can continue to operate through short-term power losses. MUTCD guidance states “except for traf ic control signals interconnected with light rail transit systems, traf ic control signals with railroad preemption or coordinated with lashing-light signal systems should be provided with a backup power supply” (1). UPS systems consist of an enclosure or cabinet, the batteries, the power inverter/conditioner, a battery charger (usually integral to the inverter), and automatic and manual bypass switches. It is also desirable to have an external lashing light to indicate whether the signal is operating on commercial power or UPS (without opening the cabinet). 4.3 DISPLAYS Once detection has been processed by the signal cabinet equipment, the signal Ensuring that there are enough load switch bays for exis ng and future phasing is recommended. The selec on of a UPS should be based on agency objec ves and system needs. UPS systems can operate in a variety of modes (i.e., fully opera onal, dimmed, flashing, or variable), that can affect the length of me a baery charge will last. displays can be used to direct intersection users. The MUTCD contains guidance on Signal Timing Manual, Second Edion

Chapter4-14 4. Signal Design equipment is handled in a variety of manners depending on the type of cabinet and traf ic signal controller. 4.2.6 Load Switches Load switches are essentially electrical gating (or relay) devices that allow the controller, which operates in a 12/24-volt DC environment, to direct a 120-volt AC current to various signal displays. (Note that load switches are called “switch packs” in a Caltrans series installation.) Each load switch (and associated wiring) plugs into load switch bays in the back panel of the cabinet. The number of load switch bays will dictate the number of output channels that the signal designer has available at the intersection. A load switch is typically required for each vehicle signal phase, each pedestrian phase, and each overlap. 4.2.7 Signal Monitor Modern traf ic signal monitors have many advanced features to improve safety and enhance maintenance of traf ic signals. The NEMA malfunction management unit (MMU) and the older con lict monitoring unit (CMU) are important safety devices. While these devices are often called con lict monitors, they have evolved from simple con lict and voltage monitoring to enhanced fault monitoring. Enhanced monitors have features beyond monitoring con licting phases or con licting indications in a signal head. The enhanced monitors detect and respond to improper voltages caused by malfunctions of the controller unit (CU), load switches, or incorrect wiring of the cabinet. They will identify the type of fault (e.g., con lict, red fail, clearance fail, dual indication, or communications faults in the cabinet) and which signal heads were active at the time of the fault, and they can retrieve historical data about the fault. The monitors will remain in fault mode until reset. 4.2.8 Uninterrupble Power Supply Backup There are some locations where an uninterruptible power supply (UPS)/battery backup system (BBS) may be necessary or desirable when utility power is not available. A UPS can provide emergency power to connected equipment by supplying power from a separate source (e.g., batteries, solar, or wind). The system can also function as a power conditioner and/or voltage regulation device. Installing UPS systems at locations where there have been power issues helps reduce downtime and electrical damage to equipment. For example, a signalized intersection that is equipped with a UPS can continue to operate through short-term power losses. MUTCD guidance states “except for traf ic control signals interconnected with light rail transit systems, traf ic control signals with railroad preemption or coordinated with lashing-light signal systems should be provided with a backup power supply” (1). UPS systems consist of an enclosure or cabinet, the batteries, the power inverter/conditioner, a battery charger (usually integral to the inverter), and automatic and manual bypass switches. It is also desirable to have an external lashing light to indicate whether the signal is operating on commercial power or UPS (without opening the cabinet). 4.3 DISPLAYS Once detection has been processed by the signal cabinet equipment, the signal Ensuring that there are enough load switch bays for exis ng and future phasing is recommended. The selec on of a UPS should be based on agency objec ves and system needs. UPS systems can operate in a variety of modes (i.e., fully opera onal, dimmed, flashing, or variable), that can affect the length of me a baery charge will last. displays can be used to direct intersection users. The MUTCD contains guidance on Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-15 trafic signal display types and positions for the most common applications (1). For a safe and effective signal design, the displays must support initial and future phasing, as well as be positioned for maximum visibility for each group of users. The displays, support structure, and wiring should relect consideration of both near-term and long- term needs in order to provide maximum timing lexibility. 4.3.1 Vehicle Displays Vehicle displays are the most common type of indication at signalized intersections. While most practitioners are familiar with them, the following sections provide guidance on the more atypical displays and situations that may need to be addressed during design. 4.3.1.1 Display Visibility All displays at an intersection should be easy to see and interpret. This is particularly important when it comes to vehicle displays because there are usually more of them at an intersection than other types of displays. It is important that intersection users establish line-of-sight as they approach an intersection and correctly interpret what they see. Use of strategic signal head placement can ensure line-of-sight is available regardless of the horizontal and vertical geometry on an approach (as shown in Exhibit 4-12 and Exhibit 4-13). Exhibit 4-12 Advance Signal Placement to Address Horizontal Curve Exhibit 4-13 Advance Signal Placement to Address Vercal Curve Signal Timing Manual, Second Edion

Chapter4-16 4. Signal Design Intersections with limited visibility and/or high-speed approaches may require advance warning “signal ahead” signs. While some beacons lash continuously, they are more effective when they start a few seconds before the onset of yellow. Some controllers have built-in warning systems to determine when to activate the sign prior to terminating the phase, but most systems use a simple overlap to turn on the sign at a predetermined time before the yellow. These timed overlaps occur after a gap in trafic is detected, reducing the effectiveness of decision zone detection because vehicles may arrive during the timed overlap. Some controllers have smart features to overcome this limitation. Avoiding confusing or contradictory vehicular displays is also important when designing a signal. Programmable signal heads and signal louvers are treatments that can be used to focus the signal indication in the direction of the desired users and away from users for whom the indication is not intended (as depicted in Exhibit 4-14). 4.3.1.2 Le-Turn Displays Selecting left-turn signal phasing is the most common phasing decision to be made during design of a signalized intersection. States and local agencies often have criteria for selecting speciic signal phasing. Many of these guidelines indicate that a left-turn phase can be justiied based on factors that ultimately tie back to the operational or safety beneits derived, including the following: • Left-turn and opposing through volumes, • Number of opposing through and turn lanes, • Cycle length, • Speed of opposing trafic, • Sight distance, and • Crash history. Exhibit 4-14 Programmable Vehicle Signal Heads and Signal Louvers Signal Timing Manual, Second Edion

Chapter4-16 4. Signal Design Intersections with limited visibility and/or high-speed approaches may require advance warning “signal ahead” signs. While some beacons lash continuously, they are more effective when they start a few seconds before the onset of yellow. Some controllers have built-in warning systems to determine when to activate the sign prior to terminating the phase, but most systems use a simple overlap to turn on the sign at a predetermined time before the yellow. These timed overlaps occur after a gap in trafic is detected, reducing the effectiveness of decision zone detection because vehicles may arrive during the timed overlap. Some controllers have smart features to overcome this limitation. Avoiding confusing or contradictory vehicular displays is also important when designing a signal. Programmable signal heads and signal louvers are treatments that can be used to focus the signal indication in the direction of the desired users and away from users for whom the indication is not intended (as depicted in Exhibit 4-14). 4.3.1.2 Le-Turn Displays Selecting left-turn signal phasing is the most common phasing decision to be made during design of a signalized intersection. States and local agencies often have criteria for selecting speciic signal phasing. Many of these guidelines indicate that a left-turn phase can be justiied based on factors that ultimately tie back to the operational or safety beneits derived, including the following: • Left-turn and opposing through volumes, • Number of opposing through and turn lanes, • Cycle length, • Speed of opposing trafic, • Sight distance, and • Crash history. Exhibit 4-14 Programmable Vehicle Signal Heads and Signal Louvers Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-17 There are ive options for left-turn signal phasing at an intersection (described in detail in Chapter 5): permitted, protected, protected-permitted, split phasing, and prohibited. Exhibit 4-15 depicts various combinations of permitted, protected- permitted, and protected left-turn signal phasing displays. Split phasing uses the same type of displays as protected phasing, but requires additional programming in the controller. Prohibited movements will not require any displays. From a design perspective, wiring and signal cabinet equipment should be provided to support potential signal phasing changes. The lowchart shown in Exhibit 4-16 (in combination with material presented in Exhibit 4-17 and Exhibit 4-18) can help a practitioner determine whether a separate left-turn phase is needed and whether the operational mode should be permitted, protected-permitted, or protected. The lowchart provides a structured evaluation procedure that promotes consistent application of left-turn signal phasing. The guidelines in Exhibit 4-16 were derived from a variety of sources (10, 11, 12) and require separate evaluation of each left-turn movement on the subject road. The main objective of the lowchart is to identify the least-restrictive left-turn operational mode that can meet desired operational and safety objectives. Exhibit 4-15 Le -Turn Signal Displays Signal Timing Manual, Second Edion

Chapter4-18 4. Signal Design Exhibit 4-16 Le -Turn Phasing Guidelines Signal Timing Manual, Second Edion

Chapter4-18 4. Signal Design Exhibit 4-16 Le -Turn Phasing Guidelines Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-19 Number of Le-Turn Movements on Subject Road Period during which Crashes Are Considered (Years) Crical Le-Turn-Related Crash Count (Crashes Per Period) When Considering Protected-Only (Cpt) When Considering Protected-Permied (Cp+p) One 1 6 4 2 11 6 3 14 7 Two 1 11 6 2 18 9 3 26 13 Oncoming Traffic Speed Limit (Miles Per Hour) Minimum Sight Distance to Oncoming Vehicles (SDc) (Feet) 25 200 30 240 35 280 40 320 45 360 50 400 55 440 60 480 In order to account for the inherent variability of crash data, the critical left-turn crash counts identi ied in Exhibit 4-17 are based on an underlying average critical crash frequency. The underlying averages are 1.3 crashes per year and 3.0 crashes per year for protected-permitted and protected-only left-turn phasing, respectively. If the reported crash count for existing operations exceeds the critical value, then it is likely that the subject intersection has an average left-turn crash frequency that exceeds the aforementioned average (5 percent chance of error), and a more restrictive operational mode would likely improve the safety of the left-turn maneuver. Note that the lowchart has two alternative paths following the check of opposing traf ic speed. One path requires knowledge of left-turn delay; the other requires knowledge of the left-turn and opposing through volumes. The left-turn delay referred to in the lowchart is the delay incurred when no left-turn phase is provided (i.e., the left-turn movement operates in the permitted mode). 4.3.1.3 Flashing Yellow Arrow Displays One protected-permitted left-turn display that warrants additional discussion is the recently introduced lashing yellow arrow (FYA) display. (Refer to Chapter 5 for additional guidance on protected-permitted operations.) This indication features a lashing yellow output, which must be accommodated in the signal design with • Individual wires to/from the cabinet to each of the four indications in the FYA signal head; • A signal monitor with the functionality to accommodate the FYA indication; and • An additional load switch for the lashing yellow indication or an unused load switch channel on a pedestrian load switch (the unused yellow output), as load switches only contain three outputs. Exhibit 4-17 Crical Le-Turn-Related Crash Count Exhibit 4-18 Minimum Sight Distance to Oncoming Vehicles Signal Timing Manual, Second Edion

Chapter4-20 4. Signal Design Practice has shown that the FYA indication is more effective than other permitted indications (i.e., steady green ball) at reducing the critical false “go” interpretation by users and resulting yellow trap conditions (14, 15). The yellow trap is a condition where a left-turning user interprets the onset of a steady yellow ball indication and incorrectly assumes oncoming through trafic sees the same steady yellow ball indication. This can be problematic if the left-turning user attempts to “sneak” through the intersection on yellow when oncoming trafic still sees a green indication. Exhibit 4-19 illustrates the yellow trap that can occur with a doghouse signal, and Exhibit 4-20 illustrates how an FYA can mitigate that condition. Source: Adapted from Signalized Intersecons: An Informaonal Guide (16) Exhibit 4-19 Illustraon of the Yellow Trap Signal Timing Manual, Second Edion

Chapter4-20 4. Signal Design Practice has shown that the FYA indication is more effective than other permitted indications (i.e., steady green ball) at reducing the critical false “go” interpretation by users and resulting yellow trap conditions (14, 15). The yellow trap is a condition where a left-turning user interprets the onset of a steady yellow ball indication and incorrectly assumes oncoming through trafic sees the same steady yellow ball indication. This can be problematic if the left-turning user attempts to “sneak” through the intersection on yellow when oncoming trafic still sees a green indication. Exhibit 4-19 illustrates the yellow trap that can occur with a doghouse signal, and Exhibit 4-20 illustrates how an FYA can mitigate that condition. Source: Adapted from Signalized Intersecons: An Informaonal Guide (16) Exhibit 4-19 Illustraon of the Yellow Trap Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-21 There are signal timing mitigations other than the FYA that can be implemented to help with the yellow trap problem. For example, the yellow trap could be mitigated Exhibit 4-20 Illustra on of the Flashing Yellow Arrow Signal Timing Manual, Second Edion

Chapter4-22 4. Signal Design through the installation of signs, forcing a minor street call, or installing a lashing red arrow (FRA). The FRA indication is an alternative to the FYA (that needs controller irmware and a signal monitor that is compatible with the FRA), which requires vehicles to make a complete stop prior to making their movement. 4.3.1.4 Right-Turn Displays Permitted, protected-permitted, and protected displays are all options to support various right-turn signal phasing. The simplest display (permitted) should be used unless more complex designs are necessary to improve capacity or clarify complex phasing. If protected phasing is necessary (or may be necessary in the future), signal designers should provide a separate overlap load switch (or load bay position for a future load switch) for right-turn displays used for exclusive right-turn lanes, rather than tying the right-turn arrow indication to the compatible left-turn signal phase. The latter is often done to simplify wiring and reduce load switch channels, but sacriices lexibility in signal timing, which may result in less effective trafic operations. Pedestrian conlicts and right-turn-on-red laws should also be considered when selecting the type of signal indication to use for a right-turn movement. 4.3.2 Pedestrian Displays There are two typical styles of pedestrian displays (shown in Exhibit 4-21): (1) those with a countdown timer for the lashing don’t walk (FDW) interval and (2) those without any countdown timer. Signal timing requirements are equivalent for both pedestrian signal displays. The reader should refer to the MUTCD for determining the use of countdown pedestrian displays (1). Source: Adapted from the MUTCD (1) 4.3.3 Bicycle Displays The signal designer should minimize conlicts for bicycles while retaining effective operations. Bicycle movements can be served concurrently with motorized vehicle phases (and/or pedestrian phases) or served independently with a separate bicycle signal phase. Experimental use of bicycle displays (following FHWA guidance) is in place, but the displays are not part of the 2009 MUTCD. Bicycle displays tend to be used Exhibit 4-21 Typical Pedestrian Signal Displays Signal Timing Manual, Second Edion

Chapter4-22 4. Signal Design through the installation of signs, forcing a minor street call, or installing a lashing red arrow (FRA). The FRA indication is an alternative to the FYA (that needs controller irmware and a signal monitor that is compatible with the FRA), which requires vehicles to make a complete stop prior to making their movement. 4.3.1.4 Right-Turn Displays Permitted, protected-permitted, and protected displays are all options to support various right-turn signal phasing. The simplest display (permitted) should be used unless more complex designs are necessary to improve capacity or clarify complex phasing. If protected phasing is necessary (or may be necessary in the future), signal designers should provide a separate overlap load switch (or load bay position for a future load switch) for right-turn displays used for exclusive right-turn lanes, rather than tying the right-turn arrow indication to the compatible left-turn signal phase. The latter is often done to simplify wiring and reduce load switch channels, but sacriices lexibility in signal timing, which may result in less effective trafic operations. Pedestrian conlicts and right-turn-on-red laws should also be considered when selecting the type of signal indication to use for a right-turn movement. 4.3.2 Pedestrian Displays There are two typical styles of pedestrian displays (shown in Exhibit 4-21): (1) those with a countdown timer for the lashing don’t walk (FDW) interval and (2) those without any countdown timer. Signal timing requirements are equivalent for both pedestrian signal displays. The reader should refer to the MUTCD for determining the use of countdown pedestrian displays (1). Source: Adapted from the MUTCD (1) 4.3.3 Bicycle Displays The signal designer should minimize conlicts for bicycles while retaining effective operations. Bicycle movements can be served concurrently with motorized vehicle phases (and/or pedestrian phases) or served independently with a separate bicycle signal phase. Experimental use of bicycle displays (following FHWA guidance) is in place, but the displays are not part of the 2009 MUTCD. Bicycle displays tend to be used Exhibit 4-21 Typical Pedestrian Signal Displays Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-23 in locations where conveying special signal phasing for bicycle movements (and/or clariication of trafic control for bicycle movements) is advantageous to the desired outcomes of the signalized intersection operations. Exhibit 4-22 shows an example of a bicycle display, per the California MUTCD (17), and an example of the placement of a near-side bicycle display at an intersection. 4.3.4 Transit Displays If exclusive transit phasing is needed (or is likely to be needed in the future), signal cabinet and controller selection should explicitly consider this need, as well as conduit sizing. Exhibit 4-23 shows alternative LRT displays, which can also be used for exclusive transit movements. Note that different jurisdictions will have different standards for transit displays, so agency standards should be veriied before installation. Source: Adapted from the MUTCD (1) 4.4 SIGNALIZED SYSTEM DESIGN Once individual intersections have been designed with detection, cabinets, and displays, they often need a way to transmit information and work as a system. From a maintenance and operations perspective, every intersection should have some form of communication because it is necessary for updating the local clock, monitoring faults, Exhibit 4-22 Example Bicycle Display (Caltrans) and Placement at Intersec€on Exhibit 4-23 Typical Light Rail Signal Displays for a Single LRT Route Signal Timing Manual, Second Edi­on

Chapter4-24 4. Signal Design accessing performance data, and remotely making timing adjustments. Communication can be achieved by interconnecting the signal controllers to a ield master/master controller or connecting the signal controllers to a central system that directly monitors them. A system of trafic signals is typically composed of the following (illustrated in Exhibit 4-24): • A series of local controllers, • Communications hardware (e.g., conduit and wiring) and software, and • A “master” controller or “central” system. A communications system allows a practitioner to monitor signals from a remote location and upload/download signal timing information from each individual intersection controller; it also allows the system to sync for time-of-day based control. Streamed video images can significantly change the communications requirements of a system, but provide the ability for practitioners to visually monitor signal operations and timing remotely. There are many alternative system conigurations that may be appropriate based on the size of the system and the nature of the communications. If a group of signals is using closed-loop operations, the individual intersection controllers do not communicate with a central system; they communicate with a master controller (which Exhibit 4-24 Physical Components of an Interconnected Signal System Signal Timing Manual, Second Edion

Chapter4-24 4. Signal Design accessing performance data, and remotely making timing adjustments. Communication can be achieved by interconnecting the signal controllers to a ield master/master controller or connecting the signal controllers to a central system that directly monitors them. A system of trafic signals is typically composed of the following (illustrated in Exhibit 4-24): • A series of local controllers, • Communications hardware (e.g., conduit and wiring) and software, and • A “master” controller or “central” system. A communications system allows a practitioner to monitor signals from a remote location and upload/download signal timing information from each individual intersection controller; it also allows the system to sync for time-of-day based control. Streamed video images can significantly change the communications requirements of a system, but provide the ability for practitioners to visually monitor signal operations and timing remotely. There are many alternative system conigurations that may be appropriate based on the size of the system and the nature of the communications. If a group of signals is using closed-loop operations, the individual intersection controllers do not communicate with a central system; they communicate with a master controller (which Exhibit 4-24 Physical Components of an Interconnected Signal System Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-25 can be conigured to communicate with a central system). Conversely, a system can be set up so that all intersections communicate with a central system, which is generally located at a trafic management center (TMC) or signal shop. Signal timing plans will typically reside in the local controllers in the ield, but may also reside in a central system database. Timing plans for most systems that do not directly control intersections from a central system can have timing parameters adjusted by (1) hand-keying new parameters directly into the controller or (2) downloading new elements from PC-based software (e.g., through a direct serial connection, Ethernet connection, or dial-up modem). More information about uploading and downloading timing plans is available in Chapter 8. 4.5 COMPREHENSIVE DESIGN CONSIDERATIONS If possible, a practitioner should always design a signal with future conditions in mind. Although signal designs should be consistent with the agency objectives and system needs, a comprehensive signal design would • Provide detection for all movements and modes—including motorized vehicles, non-motorized vehicles, pedestrians, and transit users—which allows for (1) fully-actuated or “free” signal operations and (2) measuring the performance for all movements and modes. • Provide advance detection for higher speed approaches to allow for decision zone protection or more eficient green extension. • Avoid lane use that requires speciic signal phasing, such as shared left-through lanes (typically requiring split phasing), where possible. • Incorporate mast arm lengths and signal poles to support future signal displays (e.g., typically extend mast arms to the center of the farthest left-turn lane even if a left-turn display is not required upon construction). • Include communications between the trafic management location (center and/or shop) to the controllers for monitoring of signal operations and adjustment of signal timing. • Provide for additional capacity in the terminal facilities, detector slots, underground conduits, and other cabinet space necessary to support future signal timing, communications, and automated data collection/performance measurement needs. Some lessons learned, speciic to future needs and possible equipment problems, include the following: • Providing enough conduit space (e.g., two 3-inch conduits with ducts across approaches from the cabinet and one 3-inch conduit across other approaches). • Locating pull boxes and pole foundations outside of possible future widening. • Installing spare conductors for unused load bay positions for future load switches, plus at least 10 percent spares for conductors that fail. If one of the critical paths fails, having excess capacity available will allow a practitioner to get a signal back in service more quickly. The traffic signal design and layout should support as much signal ming flexibility as possible for exisng and future condions. Signal Timing Manual, Second Edion

Chapter4-26 4. Signal Design 4.6 REFERENCES 1. Manual on Uniform Trafic Control Devices for Streets and Highways, 2009 Edition. United States Department of Transportation, Federal Highway Administration, Washington, D.C., 2009. 2. Klein, L. A., M. K. Mills, and D. R. P. Gibson. Trafic Detector Handbook, 3rd Edition. Report FHWA-HRT-06-108, Federal Highway Administration, United States Department of Transportation, 2006. 3. McGee, Sr., H., K. Moriarty, K. Eccles, M. Liu, T. Gates, and R. Retting. NCHRP Report 731: Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections. Transportation Research Board of the National Academies, Washington, D.C., 2012. 4. Parsonson, P. S., R. W. Roseveare, and J. R. Thomas, Jr. Small-Area Detection at Intersection Approaches. Trafic Engineering, Vol. 44, No. 5, 1974, pp. 8–17. 5. Zegeer, C. V., and R. C. Deen. Green Extension Systems at High-Speed Intersections. ITE Journal, Vol. 48, No. 11, 1978, pp. 19–24. 6. Chang, M. S., C. J. Messer, and A. J. Santiago. Timing Traf˜ic Signal Change Intervals Based on Driver Behavior. In Transportation Research Record 1027, TRB, National Research Council, Washington, D.C., 1985, pp. 20–30. 7. A Policy on Geometric Design of Highways and Streets, 6th Edition. American Association of State Highway and Transportation Of˜icials, Washington, D.C., 2011. 8. Bonneson, J. A., and P. T. McCoy. Manual of Trafic Detector Design, 1st Edition. Institute of Transportation Engineers, Washington, D.C., 1994. 9. Lin, F. B. Optimal Timing Settings and Detector Lengths of Presence Mode Full- Actuated Control. In Transportation Research Record 1010, TRB, National Research Council, Washington, D.C., 1985, pp. 37–45. 10. Zegeer, C. V., C. Seiderman, P. Lagerwey, M. Cynecki, M. Ronkin, and R. Schneider. Pedestrian Facilities User Guide—Providing Safety and Mobility. Report FHWA-RD- 01-102, Federal Highway Administration, United States Department of Transportation, 2002. 11. Kell, J. H., and I. J. Fullerton. Manual of Trafic Signal Design. Institute of Transportation Engineers, Washington, D.C., 1982. 12. Orcutt, Jr., F. L. The Trafic Signal Book. Prentice Hall, Englewood Cliffs, New Jersey, 1993. 13. Chapter 3: Signals. In Trafic Engineering Manual. Florida Department of Transportation, Tallahassee, Florida, 1999, pp. 121–159. 14. Brehmer, C. L., K. C. Kacir, D. A. Noyce, and M. P. Manser. NCHRP Report 493: Evaluation of Trafic Signal Displays for Protected/Permissive Left-Turn Control. Transportation Research Board of the National Academies, Washington, D.C., 2003. 15. Noyce, D. A., C. R. Bergh, and J. R. Chapman. NCHRP Web-Only Document 123: Evaluation of the Flashing Yellow Arrow Permissive-Only Left-Turn Indication Field Implementation. Transportation Research Board of the National Academies, Washington, D.C., 2007. Signal Timing Manual, Second Edion

Chapter4-26 4. Signal Design 4.6 REFERENCES 1. Manual on Uniform Trafic Control Devices for Streets and Highways, 2009 Edition. United States Department of Transportation, Federal Highway Administration, Washington, D.C., 2009. 2. Klein, L. A., M. K. Mills, and D. R. P. Gibson. Trafic Detector Handbook, 3rd Edition. Report FHWA-HRT-06-108, Federal Highway Administration, United States Department of Transportation, 2006. 3. McGee, Sr., H., K. Moriarty, K. Eccles, M. Liu, T. Gates, and R. Retting. NCHRP Report 731: Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections. Transportation Research Board of the National Academies, Washington, D.C., 2012. 4. Parsonson, P. S., R. W. Roseveare, and J. R. Thomas, Jr. Small-Area Detection at Intersection Approaches. Trafic Engineering, Vol. 44, No. 5, 1974, pp. 8–17. 5. Zegeer, C. V., and R. C. Deen. Green Extension Systems at High-Speed Intersections. ITE Journal, Vol. 48, No. 11, 1978, pp. 19–24. 6. Chang, M. S., C. J. Messer, and A. J. Santiago. Timing Traf˜ic Signal Change Intervals Based on Driver Behavior. In Transportation Research Record 1027, TRB, National Research Council, Washington, D.C., 1985, pp. 20–30. 7. A Policy on Geometric Design of Highways and Streets, 6th Edition. American Association of State Highway and Transportation Of˜icials, Washington, D.C., 2011. 8. Bonneson, J. A., and P. T. McCoy. Manual of Trafic Detector Design, 1st Edition. Institute of Transportation Engineers, Washington, D.C., 1994. 9. Lin, F. B. Optimal Timing Settings and Detector Lengths of Presence Mode Full- Actuated Control. In Transportation Research Record 1010, TRB, National Research Council, Washington, D.C., 1985, pp. 37–45. 10. Zegeer, C. V., C. Seiderman, P. Lagerwey, M. Cynecki, M. Ronkin, and R. Schneider. Pedestrian Facilities User Guide—Providing Safety and Mobility. Report FHWA-RD- 01-102, Federal Highway Administration, United States Department of Transportation, 2002. 11. Kell, J. H., and I. J. Fullerton. Manual of Trafic Signal Design. Institute of Transportation Engineers, Washington, D.C., 1982. 12. Orcutt, Jr., F. L. The Trafic Signal Book. Prentice Hall, Englewood Cliffs, New Jersey, 1993. 13. Chapter 3: Signals. In Trafic Engineering Manual. Florida Department of Transportation, Tallahassee, Florida, 1999, pp. 121–159. 14. Brehmer, C. L., K. C. Kacir, D. A. Noyce, and M. P. Manser. NCHRP Report 493: Evaluation of Trafic Signal Displays for Protected/Permissive Left-Turn Control. Transportation Research Board of the National Academies, Washington, D.C., 2003. 15. Noyce, D. A., C. R. Bergh, and J. R. Chapman. NCHRP Web-Only Document 123: Evaluation of the Flashing Yellow Arrow Permissive-Only Left-Turn Indication Field Implementation. Transportation Research Board of the National Academies, Washington, D.C., 2007. Signal Timing Manual, Second Edion Chapter 4. Signal Design 4-27 16. Chandler, B. E., M. C. Myers, J. E. Atkinson, T. E. Bryer, R. Retting, J. Smithline, J. T. P. Wojtkiewicz, G. B. Thomas, S. P. Venglar, S. Sunkari, B. J. Malone, and P. Izadpanah. Signalized Intersections: An Informational Guide, Second Edition. Report FHWA-SA- 13-027, Federal Highway Administration, United States Department of Transportation, 2013. 17. California Manual on Uniform Trafic Control Devices, 2012 Edition. California Department of Transportation, 2012. Signal Timing Manual, Second Edion