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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

CE 578 Highway Traffic Operations

Lecture 16: Freeways Basic Sections

Michael Dixon


Objectives
Objectives

  • HCM 2000 procedure process

  • Significant variables

  • Adjustment factors

Michael Dixon


Hcm procedure process
HCM Procedure Process

  • Input data

  • two parallel computations

  • Two tracks to take for FFS

  • Given the FFS and the adjusted volume

Michael Dixon


Hcm procedure input data
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


Hcm free flow speed
HCM Free-Flow Speed

Two tracks with field measured FFS or estimating FFS

Michael Dixon


Hcm field measured free flow speed track
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







Hcm volume adjustment
HCM Volume Adjustment

Michael Dixon



Hcm volume adjustment cont1
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


Hcm volume adjustment cont2
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


Hcm volume adjustment for grades
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


Hcm volume adjustment for grades cont extended segments
HCM Volume Adjustment for Grades (cont.): Extended Segments

  • Level:

  • Rolling:

  • Mountainous

Michael Dixon



Hcm volume adjustment for grades cont specific grades
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


Hcm defining speed flow curve
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




Hcm defining speed flow curve equations1
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


Hcm calculate the prevailing speed
HCM Calculate the Prevailing Speed

  • Interpolating from Exhibit 23-3

  • Equations

Michael Dixon


Hcm calculate the density
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


Hcm determine the los
HCM Determine the LOS

Michael Dixon


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