Lecture 15 - The Pennsylvania State University Department...

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The Pennsylvania State University Department of Civil and Environmental Engineering Lecture 15: Traffic Stream Parameters CE 321: Highway Engineering Fall 2007
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Purpose of Traffic Analysis Primary purpose / function of a highway is safety and mobility. Traffic analysis is means of measuring vehicle performance. Vehicles per unit time. Vehicle types. Vehicle speeds. Variation in traffic flow over time. Influences number of lanes, pavement types, geometric design, traffic control devices.
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Congestion in America will Continue to Get Worse and Worse WHY ?
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Visit Any Urban/Suburban Area and Try To Drive From One Side of Town To The Other ! Photo Courtesy of Acclaim Images
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Automobile is America Primary Mode of Transportation Allowed Life Activity Sprawl Totally Dependent on Auto / Trucks
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Congestion Traffic Continues to Grow Uncontrolled Development Development on Local Roadways
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How Many Vehicles Can Travel On An Expressway Lane/ Hour ?
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Capacity Seconds / Hour = 3600 Headway (Vehicle spacing) Human factor
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Capacity Is: 2,400 Vehicles/Hr/Lane
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Traffic Stream Parameters Uninterrupted flow Free from influence of traffic control devices Examples: freeways, multi-lane highways, and two-lane highways Interrupted flow Influenced by signals, stop signs
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Traffic Parameters Macrscopic parameters Flow (vehicles / hour): q Speed (miles / hour): u Density (vehicles / mile): k Microscopic parameters Spacing—distance between successive vehicles, front bumper to front bumper (ft/veh) Headway—the time between successive vehicles, front bumper to front bumper (sec/veh)
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Flow the number of vehicles that pass a point during a specified period of time (also known as rate of flow or sometimes volume although volume and flow are really different; volume is a one hour flow rate).
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