CE 578 Highway Traffic Operations

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CE 578 Highway Traffic Operations

• Lecture 22 Diverge Area Special Cases, Influence
  Area Speeds, and Freeway Weaving Sections

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Objectives

• Diverge area special cases
• Influence area speeds
• Basic process of weaving section analysis
• Important variables
• Limitations of methodology

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Diverge Area Special Cases

• Two-lane off-ramps
• Lane drops
• Major diverge areas
• Off-ramps on ten-lane freeways
• Left-hand off-ramps

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Two-Lane Off-Ramps
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Two-Lane Off-Ramps (cont.)

• four-lanes PFD 1.00
• six-lanes PFD 0.45
• eight-lanes PFD 0.26
• for calculating DR, LDeff 2LD1 LD2

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Lane Drops

• Single lane off-ramp with lane drop
  ramp-roadway capacity governs
• Two lane off-ramp with lane drop see major
  diverge segment procedure

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Major Diverge Area
Analyze each leg as a basic section to determine
their respective capacities and compare to demand
volumes.
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Off-Ramp on Ten-Lane Freeways
Similar to the on-ramp procedure, but with
different values for the volumes in lane 5 (v5).
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Left-Hand Off-Ramps

• Same as for On-Ramps except
• Conversion from v12 to v23 or v34
• Six-lane freeway 1.05
• Eight-lane freeway 1.10

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Influence Area Speeds

• Read pages 25-18 and 25-19

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Weaving Section Issues

• Diverse traffic streams
• Differences in lane utilization
• Ease of lane change
• Predicting speeds
• Predicting density

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Basic Process

• Adjust the volume
• Predict the space mean
• Check for constraints on lane changing
• Reassess the space mean speed
• Compute the average space mean speed
• Compute the density
• Determine the LOS
• Determine the weaving capacity

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Basic Process (cont.)
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Important Weaving Section Variables

• Demand volumes
• Weaving section length
• Number of lanes
• Weaving section configuration
• Terrain type
• Free-flow speed

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Demand Volumes, Terrain Type, and Free-Flow Speed

• Adjusted volume See basic segment methodology
• Free-flow speed See basic segment methodology

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Weaving Section Length

• Less than 2500 ft
• Measure from entrance gore to exit gore

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Number of Lanes and Weaving Section Configuration

• N?Total lanes in weaving section
• Nw?lanes needed for weaving equilibrium
• Nw(max)?maximum lanes available for weaving
  vehicles

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Number of Lanes and Weaving Section Configuration
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Number of Lanes and Weaving Section Configuration
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Limitations

• Ramp metering
• Oversaturated conditions
• Effects of speed limits
• Collector distributor roadways
• Urban streets
• Known weaving volumes