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Published byHalle Silvers Modified over 2 years ago

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Learning Objectives To define and apply basic measures of traffic flow, including; Speed Volume Density Spacing and Headway Lane occupancy Clearance and gap

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**Traffic Flow Complex: between vehicles and drivers, among vehicles**

Stochastic: variability in outcome, cannot predict with certainty Theories and models Macroscopic: aggregate, steady state Microscopic: disaggregate, dynamics Human factor: driver behavior

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**Speed (v) Rate of motion Individual speed Average speed**

Time mean speed Arithmetic mean Space mean speed Harmonic mean

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Individual Speed (1) Spot Speed

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Time Mean Speed Mile post Observation Period

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Space Mean Speed Observation Distance Observation Period

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Volume (q) Number of vehicles passing a point during a given time interval Typically quantified by Rate of Flow (vehicles per hour)

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Volume (q)

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**Density (k) Number of vehicles occupying a given length of roadway**

Typically measured as vehicles per mile (vpm), or vehicles per mile per lane (vpmpl)

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Density (k)

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Density (k)

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Spacing (s) Front bumper to front bumper distance between successive vehicles S2-3 S1-2

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**Headway (h) Time between successive vehicles passing a fixed point**

T=0 sec T=3sec h1-2=3sec

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Spacing and Headway spacing headway

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Spacing and Headway What are the individual headways and the average headway measured at location A during the 25 sec period? A

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**Spacing and Headway A h1-2 h2-3**

What are the individual headways and the average headway measured at location A during the 25 sec period? A h1-2 h2-3

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Lane Occupancy Ratio of roadway occupied by vehicles L3 L2 L1 D

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**Clearance (c) and Gap (g)**

Front bumper to back bumper distance and time Clearance (ft) or Gap (sec) Spacing (ft) or headway (sec)

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