chapter5_notes_ - Chapter 5 Fundamentals of Traffic Flow...

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Chapter 5 Fundamentals of Traffic Flow and Queuing Theory 5.1 INTRODUCTION Highways seek high mobility (speed) while considering safety. Understanding traffic flow and queuing is the key to evaluating highway performance (mobility provided) 5.2 TRAFFIC STREAM PARAMETERS Consider uninterupted flow: No stop signs No traffic signals 5.2.1 Traffic Flow, Speed, and Density Traffic flow: q = n t (5.1) Where: q = traffic flow in vehicles per unit time, n = number of vehicles passing some designated roadway point during time t , t = duration of time interval. In addition to the total number of vehicles passing a point in some time interval, consider the time between the passing of successive vehicles Headway - time between the passage of the front bumpers of successive vehicles, at some designated highway point Time headways are related to t , as defined in Eq. 5.1, by t = h i i = n 1 (5.2) Where: t = duration of time interval, h i = time headway of the i th vehicle (the time that has transpired between the arrival of vehicle i and i -1), n = number of measured vehicle time headways at some designated roadway point. Substituting Eq. 5.2 into Eq. 5.1 gives n i = i h n q = 1 (5.3) or
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