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

2. 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

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

4. Individual Speed
(1)
Spot Speed

5. Time Mean Speed
Mile post
Observation Period

6. Space Mean Speed
Observation Distance
Observation Period

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

8. Volume (q)

9. 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)

10. Density (k)

11. Density (k)

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

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

14. Spacing and Headway
spacing
headway

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

16. 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

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

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