13 - Chapter7-Signal Control Characteristics2

13 - Chapter7-Signal Control Characteristics2 - Traffic...

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Traffic Control at Signalized Intersections TTE 4004 10/21/11
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Chapter 7 Introduction Intersection and Traffic Control Signalized Intersection Traffic Signal Timing
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Controller Cabinet
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Cabinet Elements Controller
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Cabinet Elements Detectors
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Cabinet Elements Loops
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Cabinet Elements Conflict Monitor Load Switches
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Cabinet Elements Power Distribution Surge Protection
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Cabinet Elements Police Panel
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Signal Systems
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Signal Displays Signal heads—various configurations
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Traffic Signal Advantages Orderly movement of traffic Increase capacity If operated correctly Decrease crashes (number & severity) Certain types (like right angle) Coordinated to progress traffic flow If a system is in place Interrupt heavy traffic for access Minor street vehicles & pedestrians
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Traffic Signal Disadvantages Even warranted signals can be ineffective Ill designed Ineffectively placed Improperly operated Poorly maintained Improperly designed signals Excessive delay Disobedience Use of less efficient routes Increased crashes (especially rear-end)
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Basic Concepts
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Signal Timing Terminology Green time: the “go” indication for a particular movement or set of movements Yellow time: the change interval, warns drivers that the signal is changing from green to red Red time: the “stop” indication for a particular movement or set of movements All-red time / Clearance interval: the all red indication
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Signal Timing Terminology Initial: Gives the traffic enough time to start moving and assures minimum green Extension: Extends the phase time until the queue has been serviced Maximum: Prevents unreasonably long cycles by limiting the length of time that a phase may be extended
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The phase begins with the initial interval to guarantee a minimum green time INITIAL (Typically 10 sec)
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After the initial interval, the phase enters its extension interval INITIAL EXTENSION (Assume 3 sec)
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Extension interval: No car in the first second INITIAL EXTENSION 1 SEC
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INITIAL EXTENSION 2 SEC Extension interval: No car in second #2
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A car arrives before the third second and resets the extension interval timer. INITIAL This starts the extension process over again
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INITIAL EXTENSION 1 SEC Extension interval begins again: No car in the first second
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Again, there is no car in second #2 INITIAL EXTENSION 2 SEC
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Another car arrives (behind the first car) before the third second and resets the extension interval timer again.
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13 - Chapter7-Signal Control Characteristics2 - Traffic...

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