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CE 578 Highway Traffic Operations

CE 578 Highway Traffic Operations. Lecture 16: Freeways Basic Sections. Objectives. HCM 2000 procedure process Significant variables Adjustment factors. HCM Procedure Process. Input data two parallel computations Two tracks to take for FFS Given the FFS and the adjusted volume.

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CE 578 Highway Traffic Operations

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  1. CE 578 Highway Traffic Operations Lecture 16: Freeways Basic Sections Michael Dixon

  2. Objectives • HCM 2000 procedure process • Significant variables • Adjustment factors Michael Dixon

  3. HCM Procedure Process • Input data • two parallel computations • Two tracks to take for FFS • Given the FFS and the adjusted volume Michael Dixon

  4. HCM Procedure Input Data • Geometric data • Number of lanes • Grade • Lane width • Lateral clearance (right shoulder width) • Interchange density • FFS • Base free-flow speed (BFFS) or measured FFS • Volume • Drive population • Volume (vph) • Vehicle mix • PHF Michael Dixon

  5. HCM Free-Flow Speed Two tracks with field measured FFS or estimating FFS Michael Dixon

  6. HCM Field Measured Free-Flow Speed Track • Measured at volumes up to 1300 pc/hr/ln • Conducted at a location that is representative of the segment • Speeds of all passenger cars or a systematic sample • The average of the passenger car speeds is the field measured FFS Michael Dixon

  7. HCM Estimated Free-Flow Speed Track Michael Dixon

  8. HCM Estimated Free-Flow Speed Track (cont.) Michael Dixon

  9. HCM Estimated Free-Flow Speed Track (cont.) Michael Dixon

  10. HCM Estimated Free-Flow Speed Track (cont.) Michael Dixon

  11. HCM Estimated Free-Flow Speed Track (cont.) Michael Dixon

  12. HCM Volume Adjustment Michael Dixon

  13. HCM Volume Adjustment (cont.) Michael Dixon

  14. HCM Volume Adjustment (cont.) • Hourly volume is adjusted up to a peak 15-minute volume by V/PHF • PHF variations are larger for rural areas and off-peak periods Michael Dixon

  15. HCM Volume Adjustment (cont.) • If the percentage of RVs is small relative to that of trucks • Buses operate similarly to trucks • Equivalents for extended freeway segments and specific grades Michael Dixon

  16. HCM Volume Adjustment for Grades • Extended segment • No grade of 3% or more is longer than 0.25 miles or, • No grade of < 3% is longer than 0.50 miles • Everything else should be analyzed as a specific grade Michael Dixon

  17. HCM Volume Adjustment for Grades (cont.): Extended Segments • Level: • Rolling: • Mountainous Michael Dixon

  18. HCM Volume Adjustment for Grades (cont.): Extended Segments Michael Dixon

  19. HCM Volume Adjustment for Grades (cont.): Specific Grades • Exhibit 23-9 • Trends of ET are as follows: • Decreases with %heavy vehicles • Increases with length of grade • Increases with % grade • Trends for ER are similar (see Exhibit 23-10) • Trends for ET are similar for downgrades • No adjustment needed for RVs on downgrades Michael Dixon

  20. HCM Defining Speed-Flow Curve • Approaches that you can take: • Interpolate in the figure given in Exhibit 23-3 • Use equations below Exhibit 23-3 Michael Dixon

  21. HCM Defining Speed-Flow Curve: Interpolation Michael Dixon

  22. HCM Defining Speed-Flow Curve: Equations Michael Dixon

  23. HCM Defining Speed-Flow Curve: Equations • Note that the equation you use depends on which of the free-flow and adjusted volume conditions are satisfied. • If your FFS is 68 and your adjusted volume is 1200 pc/hr/ln which equation do you use? • If your FFS is 62 and your adjusted volume is 1700 pc/hr/ln which equation do you use? Michael Dixon

  24. HCM Calculate the Prevailing Speed • Interpolating from Exhibit 23-3 • Equations Michael Dixon

  25. HCM Calculate the Density • q = u * k • q = your adjusted volume (vp) • u = your calculated speed • Solve for k in units of pc/mi/ln Michael Dixon

  26. HCM Determine the LOS Michael Dixon

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