CHAPTER 22 - FUNDAMENTALS OF SIGNAL TIMING - ACTUATED CONTROL

CHAPTER 22 - FUNDAMENTALS OF SIGNAL TIMING - ACTUATED CONTROL

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CHAPTER 22 Fundamentals of Signal Timing: Actuated Signals
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Define Actuated Signal: A traffic signal for which the timing of A traffic signal for which the timing of phases and/or cycle length and/or the phases and/or cycle length and/or the sequence of phases is dependent upon sequence of phases is dependent upon vehicle arrivals as indicated by traffic vehicle arrivals as indicated by traffic detectors placed on one or more detectors placed on one or more approaches to the intersection. approaches to the intersection.
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1. Semi-Actuated Control Detectors are placed on the minor street only. The “green” is given to the major street except when”needed” to service minor street vehicles. 2. Full-Actuated Control Detectors are placed on all intersection approaches. Phase timing and/or sequence vary according to controller settings and vehicle actuations. 3. Adaptive Control Full actuated control with additional features such as various priority schemes. Basic Types of Actuated Control
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1. The flexibility to react to short-term peaks in demand. 2. Cycle-by-cycle flexibility helps to avoid individual cycle failures. 3. Flexibility in phasing: LT phases can be implemented only when LT demand exists. 4. By providing flexibility, timings can be arranged to accommodate both peak and off-peak periods. 5. By providing flexible cycles, capacity to any given lane group may be altered every cycle in response to demand. Principal Benefits of Actuated Control
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Time (Green Phases) Vehicles 0 2 4 6 8 10 12 14 1 2 3 4 5 Demand Capacity With pretimed signals, the capacity of each phase is With pretimed signals, the capacity of each phase is constant. constant. With actuated signals, the capacity of each phase With actuated signals, the capacity of each phase can be varied to reflect changing demand. can be varied to reflect changing demand.
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1. Variable cycle length makes coordination with other signals difficult; , modern technology has substantially overcome this, although at considerable cost. 2. Variable cycle length and phase sequences/timings makes analysis and prediction of actual operations more difficult. Limitations of Actuated Control
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1. Detector provides information to the controller. 2. Must specify the location of detectors, and which phases are activated by which detectors. 3. Types of detectors: Passage or Point Detector : Provides indication of vehicles crossing the detector. It does not sense how long a vehicle resides over the detector. Presence or Area Detector: Generates a pulse that remains continuous until the vehicle no longer occupies it. The Detector in Actuated Control
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Types of Passage (or Point) Detectors: 1. Inductive Loop 2. Microloop 1. Magnetic Loop 2. Ultrasonic Types of Presence (or Area) Detectors: 1. “Long” Magnetic Loops 2. Multiple Loops
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Types of Controllers: National Electronics Manufacturing Association (NEMA) Type 170/270 For each actuated phase, the following settings must be determined: 1 . Minimum Green 2. Passage Time (Vehicle Interval, Unit Extension) 3. Maximum Green 4. Change Interval (yellow) 5. Clearance Interval (all red)
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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 22 - FUNDAMENTALS OF SIGNAL TIMING - ACTUATED CONTROL

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