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

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

Speed (v) Rate of motion Individual speed Average speed Time mean speed Arithmetic mean Space mean speed Harmonic mean

Individual Speed (1) Spot Speed

Time Mean Speed Mile post Observation Period

Space Mean Speed Observation Distance Observation Period

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

Volume (q)

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)

Density (k)

Density (k)

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

Headway (h) Time between successive vehicles passing a fixed point T=0 sec T=3sec h1-2=3sec

Spacing and Headway spacing headway

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

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

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

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