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Understanding Traffic Flow: Key Measures and Concepts

This guide explores fundamental measures of traffic flow essential for efficient transportation management. Key topics include speed, volume, density, spacing, headway, lane occupancy, and clearance. Learn to differentiate between macroscopic and microscopic traffic models, and understand the stochastic nature of traffic behavior. Additionally, we delve into various speed definitions—individual, average, time mean, and space mean speeds. By grasping these concepts, you can better analyze and manage traffic conditions, ultimately enhancing roadway safety and efficiency.

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Understanding Traffic Flow: Key Measures and Concepts

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Presentation Transcript

  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=3sec T=0 sec 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 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)

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