Traffic Signal Design Guide & Timing Manual June 2015 5 in. Alabama Department of Transportation TRAFFIC SIGNAL DESIGN GUIDE & TIMING MANUAL June 2015 Prepared by: The University Transportation Center for of Alabama Andrew Sullivan, P.E. Steven L. Jones, Ph.D. Elsa Tedla Ehsan Doustmohammadi Steering Committee Stacey Glass, P.E., ALDOT Maintenance Bureau Robert Blankenship, ALDOT Maintenance Bureau Tim Barnett, P.E., ALDOT Office of Safety Operations Stuart Manson, P.E., ALDOT Office of Safety Operations Gary Moore, ALDOT Traffic Design Section Kim Norton, ALDOT Traffic Design Section Preston Franklin, ALDOT Traffic Design Section Russell Dicks, ALDOT Traffic Design Section Menasse Kumlachew, ALDOT Maintenance Bureau DISCLAIMER This manual provides guidelines and recommended practices for designing and timing traffic signals in the State of Alabama. This manual can not address or anticipate all possible field conditions that will affect a traffic signal design. It remains the ultimate responsibility of the design engineer to ensure that a signal design is appropriate for prevailing traffic and field conditions. TABLE OF CONTENTS 1. Introduction 1.1. Overview ..................................................................................................... 1-1 1.2. Purpose ....................................................................................................... 1-1 1.3. Scope and Organization ............................................................................... 1-2 1.4. Organization ................................................................................................. 1-2 1.5. Terms and Definitions .................................................................................. 1-3 1.6. Legend ......................................................................................................... 1-3 1.7. Limitations .................................................................................................... 1-3 2. Traffic Signal Warrants and Justification 2.1. Overview ...................................................................................................... 2-1 2.2. MUTCD Warrant Guidelines ......................................................................... 2-1 2.3. When a Traffic Study is Required ................................................................. 2-2 2.4. Submitting a Traffic Study to ALDOT............................................................ 2-2 2.5. Preparing a Traffic Study for a Permit Signal ................................................ 2-6 2.6. Right Turn Volume Adjustments ................................................................. 2-16 2.7. ALDOT Policy Regarding Warrants ........................................................... 2-18 2.8. Alternative Treatments ............................................................................... 2-19 2.9. Access Management Considerations ........................................................ 2-21 2.10. Warrants for Removal of Traffic Signals .................................................... 2-21 3. Signal Operation and Phasing 3.1. Signal Phasing Definitions ........................................................................... 3-1 3.2. ALDOT Typical Phase Numbering Scheme.................................................. 3-4 3.3. Left Turn Phasing ......................................................................................... 3-4 3.4. Warrants for Left Turn Phasing .................................................................... 3-5 3.5. Types of Left Turn Phases ........................................................................... 3-8 3.6. Protected-Permissive Phasing and Left Turn Traps ..................................... 3-9 3.7. Lead-Lag and Lag-Lag Left Turn Phasing .................................................. 3-11 3.8. Combining Permissive, Protected, and Protected-Permissive .................... 3-11 3.9. Protected-Permissive Phasing for Dual Lefts ............................................ 3-12 3.10. Split Phasing ............................................................................................. 3-12 3.11. Phase Overlaps ......................................................................................... 3-14 4. Signal Layout and Pole Placement 4.1. Box Span .................................................................................................... 4-1 4.2. Z-Span ........................................................................................................ 4-2 4.3. Suspended Box Span ................................................................................. 4-3 4.4. Mast-Arm Installations ................................................................................. 4-4 4.5. Pole Placement for Span Wire Designs ....................................................... 4-5 4.6. Computing Pole Heights for Span Wire Designs ......................................... 4-8 4.7. Signal Pole Types for Span Wire Designs ................................................. 4-11 4.8. Twin Mast-Arm Installations ...................................................................... 4-14 Alabama Department of Transportation Traffic Signal Design Guide and Timing Manual 5. Traffic Signal Heads 5.1. Permissible Arrangements .......................................................................... 5-1 5.2. Standard Head Sizes .................................................................................. 5-4 5.3. LED Heads................................................................................................... 5-4 5.4. Optically Programmed Heads ...................................................................... 5-6 5.5. Louvers ........................................................................................................ 5-7 5.6. Backplates ................................................................................................... 5-8 5.7. Signal Head Location ................................................................................... 5-9 5.8. Offset Intersections .................................................................................... 5-13 6. Vehicle Detection 6.1. Inductive Loop Detectors .............................................................................. 6-1 6.2. Video Detection ........................................................................................... 6-9 6.3. Microwave Detection ................................................................................. 6-14 6.4. Magnetometers ......................................................................................... 6-15 6.5. Special Detection Circumstances .............................................................. 6-15 6.6. Summary .................................................................................................. 6-16 7. Pedestrian Features 7.1. When to Provide Crosswalks ....................................................................... 7-1 7.2. When to Provide Pedestrians Signal Heads ................................................. 7-2 7.3. Pedestrian Phase Intervals .......................................................................... 7-3 7.4. Actuated vs. Non-Actuated Ped Phasing ...................................................... 7-4 7.5. Pedestrian Signals and Channelizing Islands ............................................... 7-5 7.6. Detection and Signs ..................................................................................... 7-6 7.7. Mounting Heights for Pedestrian Signals ...................................................... 7-6 7.8. Pedestrian Phasing ...................................................................................... 7-7 7.9. Countdown Pedestrian Displays ................................................................... 7-8 7.10. Handicap Accessible Pedestrian Signals ..................................................... 7-8 7.11. Pedestrian Hybrid Beacons .......................................................................... 7-8 8. Power Service, Signal, Wiring, and Conduit 8.1. Power Service .............................................................................................. 8-1 8.2. Signal Wiring ................................................................................................ 8-6 8.3. Conduit and Junction Boxes ....................................................................... 8-13 8.4. Junction Boxes ........................................................................................... 8-18 Alabama Department of Transportation Traffic Signal Design Guide and Timing Manual 9. Signal Pre-Emption 9.1. Types of Signal Pre-Emption ........................................................................ 9-1 9.2. Railroad Pre-Emption ................................................................................... 9-1 9.3. Emergency Pre-Emption .............................................................................. 9-9 9.4. Transit Pre-Emption ................................................................................... 9-16 9.5. Pedestrian Pre-Emption ............................................................................. 9-16 9.6. Pre-Emption Hierarchy ............................................................................... 9-16 9.7. Operational Impacts of Signal Pre-Emption ................................................ 9-16 10. Signal Interconnect and Coordination Methods 10.1. Time-Based Coordination