Calibrating Relationships for Freeway Analysis Chapter 12

1

• Calibrating Relationships for Freeway Analysis
  (Chapter 12)
• Why conduct calibrations of the F/S/D
  relationships?
• How can we use the relationships?
• Planning Facilities
• TSM Strategies
• Work Zone Assessment
• Incident Evaluation

2

• S/F/D Relationships
• SMSS(n)(d)/?t
• F(S)(D)
• How do we measure density?
• Air Photo
• Loop Detector (Occupancy)
• D(5280)(t)/(Lv)(LD)
• tfraction of time loop is occ.
• LvAvg. Veh. Length
• LDLoop Detector Length

3
D(52.8)( OCC)/(Lv)(LD)OCC (?
tOCC)(100)/T tOCCoccupancy time of individual
vehicles tonT Selected time period
4
(No Transcript)
5

• Need to collect headway data
• F(3600)/Haverage
• Headway Types P-P, P-T, T-P, and T-T
• Consider only P-P pairs
• FP(3600)/Happ
• Fitting the data using regression
• y a bx Simple Linear regression
• Non-Linear y a ebx

6

• Five Basic Assumptions
• SF exists
• DJ exists
• maximum flow exists
• Orthogonality at SF
• Discontinuity at capacity

7
Greenshield Model (Linear)
8
(No Transcript)
9
(No Transcript)
10
(No Transcript)
11
Greenberg Model (Logarithmic)
12
(No Transcript)
13
Underwood Model Exponential
14
(No Transcript)
15
(No Transcript)
16

• Other Forms
• Two Linear Segments Fig 12-4
• Three Linear Segments Fig 12-5
• Edie Hypothesis (Exp. Logarith.) Fig 12-8
• Bell Curve Fig 12-9

17

• Problem 12-1
• S57.5(1-0.008D)
• Sf57.5, 1/DJ0.008, DJ125 vpm
• F125S-2.174S2
• F57.5D-0.46D2
• Dc57.5/0.9262.5 vpmpl
• Fc57.5(62.5)-.46(62.5)2 1,797 vphpl

18

• Problem 12-2
• S61.2e-0.015D
• Sf61.2, Dc66.7
• Flow/speed F66.7S ln(61.2/S)
• Flow Density F61.2De-D/66.7
• Capacity(66.7)(61.2)/2.718 1,502 vphpl