CE 578 Highway Traffic Operations

1
CE 578 Highway Traffic Operations

• Lecture 24 Freeway Weaving Section II

2
Objectives

• Weaving speeds
• Unconstrained/constrained operations
• Capacity
• VR and R ratio recommendations

3
Calculating Weaving Speeds
4
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 gt 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

5
Interpreting NW and NW (max)

• NW
• NW(max)
• Counting NW(max)
• Where NW lt NW(max)
• Where NW gt NW (max)
• See Exhibit 24-7

6
Determining Type of Operation
If NW gt NW(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.
7
Compute the Overall Average Space Mean Speed and
Density
8
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

9
Determine Capacity (Example)

• VR 0.35
• Type A
• L 1000 ft
• FFS 65 mph
• N 3 lanes

10
Determine Capacity (Example)
11
Purpose of VR (and R Ratio)

• Adequacy of configuration
• Identify appropriate configuration
• Estimate weaving segment capacity

12
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

13
R Restrictions

• Type C 0.40 with vw1 from A to D

14
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

15
Application

• See MathCad worksheet