1. 3/17/06Michael Dixon1 CE 578 Highway Traffic Operations Lecture 22: Diverge Area Special Cases, Influence Area Speeds, and Freeway Weaving Sections

2. 3/17/06Michael Dixon2 Objectives Diverge area special cases Influence area speeds Basic process of weaving section analysis Important variables Limitations of methodology

3. 3/17/06Michael Dixon3 Diverge Area Special Cases Two-lane off-ramps Lane drops Major diverge areas Off-ramps on ten-lane freeways Left-hand off-ramps

4. 3/17/06Michael Dixon4 Two-Lane Off-Ramps

5. 3/17/06Michael Dixon5 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

6. 3/17/06Michael Dixon6 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

7. 3/17/06Michael Dixon7 Major Diverge Area Analyze each leg as a basic section to determine their respective capacities and compare to demand volumes.

8. 3/17/06Michael Dixon8 Off-Ramp on Ten-Lane Freeways Similar to the on-ramp procedure, but with different values for the volumes in lane 5 (v5).

9. 3/17/06Michael Dixon9 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

10. 3/17/06Michael Dixon10 Influence Area Speeds Read pages 25-18 and 25-19

11. 3/17/06Michael Dixon11 Weaving Section Issues Diverse traffic streams Differences in lane utilization Ease of lane change Predicting speeds Predicting density

12. 3/17/06Michael Dixon12 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

13. 3/17/06Michael Dixon13 Basic Process (cont.)

14. 3/17/06Michael Dixon14 Important Weaving Section Variables Demand volumes Weaving section length Number of lanes Weaving section configuration Terrain type Free-flow speed

15. 3/17/06Michael Dixon15 Demand Volumes, Terrain Type, and Free-Flow Speed Adjusted volume: See basic segment methodology Free-flow speed: See basic segment methodology

16. 3/17/06Michael Dixon16 Weaving Section Length Less than 2500 ft Measure from entrance gore to exit gore L

17. 3/17/06Michael Dixon17 Number of Lanes and Weaving Section Configuration N  Total lanes in weaving section N w  lanes needed for weaving equilibrium N w (max)  maximum lanes available for weaving vehicles

18. 3/17/06Michael Dixon18 Number of Lanes and Weaving Section Configuration

19. 3/17/06Michael Dixon19 Number of Lanes and Weaving Section Configuration

20. 3/17/06Michael Dixon20 Limitations Ramp metering Oversaturated conditions Effects of speed limits Collector distributor roadways Urban streets Known weaving volumes