CHAPTER 21 - FUNDAMENTALS OF SIGNAL TIMING - PRETIMED SIGNALS

CHAPTER 21 - FUNDAMENTALS OF SIGNAL TIMING - PRETIMED SIGNALS

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Unformatted text preview: Chapter 21 Fundamentals of Signal Timing and Design Pretimed Signals Fundamentals of Signal Design and Timing 1. Development of a phase plan and sequence . 2. Determination of all yellow and all red transition intervals. 1. Determination of lost times in the cycle. 1. Determination of the sum of critical lane volumes. 5. Determination of cycle length . 6. Allocation of available effective green time to the various phases; splitting the green. 7. Checking pedestrian crossing requirements. Signal Phasing and the Development of Phase Plans 1. Phasing is generally an issue of whether or not to provide left-turn protection for a given LT movement. 2. Addition of LT protection phases can increase saturation flow rates by removing conflicts between left turns and opposing through movements. 3. Additional phases may cause additional delay. 4. Phase sequences must be designed and displayed in accordance with MUTCD standards and criteria. 5. Phasing must be consistent with lane geometry and lane use in the intersection. Through Movement Without Turning Movements Through Movement With Protected Right and Left Turns from Shared Lanes Through Movement With Permitted Right and Left Turns from Shared Lanes Through Movement With Permitted Left Turn from Exclusive Lane and Permitted Right Turn from Shared Lane Through Movement With Protected Left Turn from Exclusive Lane and Permitted Right Turn from Shared Lane Illustration of Signal Phase Symbols A Two - Phase Signal A Two - Phase Signal The Issue of Left-Turn Protection 1. Protected (or compound) left turns are generally needed when: v LT 200 veh/h, or v LT x (v o /N o ) 50,000 ITE criteria are violated. 1. Permitted turns are generally adequate where: v LT 2 veh/cycle (sneakers) ITE Criteria Fully Protected or Compound? Fully protect if 2 or more of the following conditions exist: 1. Left-turn flow rate is greater than 320 veh/h. 2. Opposing flow rate is greater than 1,100 veh/h. 3. Opposing speed limit is greater than or equal to 45 mi/h. 4. There are two or more left-turn lanes. Fully Protected or Compound? Fully protect if any one of the following conditions exist: 1. There are 3 opposing lanes the opposing speed is 45 mi/h or greater. 1. Left-turn flow rate exceeds 320 veh/h and truck presence is 2.5% or more. 1. The opposing flow rate exceeds 1,100 veh/h and there are 2.5% or more left turns. 1. Seven or more LT accidents have occurred over three years under compound phasing. 1. Delay to LT vehicles is acceptable under fully protected phasing and the engineer judges that additional LT accidents would occur under compound phasing. Left-Turn Protection: Left-Turn Protection: An Exclusive Left-Turn Phase An Exclusive Left-Turn Phase Leading and Lagging Green: Leading and Lagging Green: Splitting the LT Protection Phase Splitting the LT Protection Phase Options Using Leading and/or Lagging Green Phasing 1. A leading green can be used without a lagging green, or vice-versa (e.g. green, or vice-versa (e....
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This note was uploaded on 01/18/2011 for the course PROJECT MA PM 587 taught by Professor Lee during the Spring '10 term at Keller Graduate School of Management.

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CHAPTER 21 - FUNDAMENTALS OF SIGNAL TIMING - PRETIMED SIGNALS

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