3/22/06Michael Dixon1 CE 578 Highway Traffic Operations Lecture 24: Freeway Weaving Section II

3/22/06Michael Dixon2 Objectives Weaving speeds Unconstrained/constrained operations Capacity VR and R ratio recommendations

3/22/06Michael Dixon3 Calculating Weaving Speeds

3/22/06Michael Dixon4 Trends Reflected in the Weaving Speeds Weave section length (L) increase  speeds; lane change intensity Proportion of weaving vehicles in total flow (VR) increase  speeds Average total flow per lane (v/N) increase  speeds Constrained operations [NW > NW(max)]  speeds Type B are most efficient for large weaving flows  higher weaving speeds Type A speeds are most sensitive to weave section length Type B and C configurations have higher non-weaving speed sensitivity to the VR ratio

3/22/06Michael Dixon5 Interpreting N W and N W (max) N W N W (max) Counting N W (max) Where N W < NW(max) Where N W > N W (max) See Exhibit 24-7

3/22/06Michael Dixon6 Determining Type of Operation If N W > N W (max) then constrained, otherwise unconstrained If operations are constrained, then recalculate the space mean speeds with the constrained constants for a, b, c, and d.

3/22/06Michael Dixon7 Compute the Overall Average Space Mean Speed and Density

3/22/06Michael Dixon8 Determine Capacity Function of –N –VR –L –Configuration type –FFS of the mainline freeway section Exhibit 24-8 You can interpolate between values in Exhibit 24-8

3/22/06Michael Dixon9 Determine Capacity (Example) VR= 0.35 Type = A L = 1000 ft FFS = 65 mph N = 3 lanes

3/22/06Michael Dixon10 Determine Capacity (Example)

3/22/06Michael Dixon11 Purpose of VR (and R Ratio) Adequacy of configuration Identify appropriate configuration Estimate weaving segment capacity

3/22/06Michael Dixon12 VR Restrictions Type A: 1.0 (N = 2); 0.45 (N = 3); 0.35 (N = 4); 0.25 (N = 5) Type B: 0.80 Type C: 0.50

3/22/06Michael Dixon13 R Restrictions Type C: 0.40 with v w1 from A to D

3/22/06Michael Dixon14 Interpreting VR and R Limits The limits on VR and R –field observed limitations –If calculated values exceed recommended thresholds… –Erratic traffic behavior with poor predictability

3/22/06Michael Dixon15 Application See MathCad worksheet