CE 578 Highway Traffic Operations

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CE 578 Highway Traffic Operations - PowerPoint PPT Presentation

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

Lecture 16: Freeways Basic Sections

Michael Dixon

Objectives
• HCM 2000 procedure process
• Significant variables

Michael Dixon

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
• Geometric data
• Number of lanes
• 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

Two tracks with field measured FFS or estimating FFS

Michael Dixon

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

• 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

• 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

• 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

• Exhibit 23-9
• Trends of ET are as follows:
• Decreases with %heavy vehicles
• Increases with length of grade
• Trends for ER are similar (see Exhibit 23-10)
• Trends for ET are similar for downgrades

Michael Dixon

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: 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
• Interpolating from Exhibit 23-3
• Equations

Michael Dixon

HCM Calculate the Density
• q = u * k