CE 578 Highway Traffic Operations
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Transcript of CE 578 Highway Traffic Operations
CE 578 Highway Traffic Operations
Lecture 4: HCM Directional Analysis
Objectives
• Understand two-lane highway performance measures
• Relate two-lane highway conditions to input variables
• Calculate adjusted volume• Calculate performance measures
– ATS– PTSF
Two-Lane Highway Performance Measures
• Percent-time-spent-following (PTSF)• Average travel speed (ATS)• Average travel time• Passing supply vs passing demand
HCM Procedure (Chapter 12)• Precept—Mobility
– Consistent high speed– Infrequent passing delays
• Precept—Access – Infrequent passing delays– Freedom to maneuver– Safety– Speed not a primary concern
HCM Procedure Two-Lane Highway Classes
• Different highways and different expectations
• Primary arterials: serve long distance trips, major inter-city travel, daily commuter routes, high travel speed expected
• Secondary roadways: high speed not expected, scenic route, rugged terrain, recreational route, short trips, trip ends
Level of Service Measurement by Highway Classification
• Class I: PTSF and ATS– Passing delay is expected to be at a minimum– High speed is expected
• Class II: PTSF– Higher levels are acceptable but drivers are still
sensitive to this measure– ATS is generally not an issue
• Drivers will not be on the highway long• Or do not expect high speeds
Estimating Two-Lane Highway Level of Service Measures
• Microscopic simulation– TRAR– TWOPAS– Yu and Washburn
• Deterministic procedures– US HCM two-way methodology (not
necessary)– US HCM directional methodology– Polus
US HCM Procedures—General Approach
Input Highway Conditions
Adjustments andCalculations
ComputePerformanceMeasure(s)
US HCM Performance Measures—Base Conditions
• 12 ft lanes• 6 ft shoulders• No no-passing zones• 100% passenger cars• No impediments to through traffic• Level terrain• 50/50 traffic split by direction
Base Condition PTSF Estimation: Graph (50/50 directional split)
US HCM Level-of-Service—Class I Facilities
US HCM Level-of-Service—Class II Facilities
Original HCM Directional Analysis Procedure
• Relative to two-way analysis procedure– Split traffic by direction– Analyze each direction of traffic separately– Volume adjustments are the same for general terrain– ATS
• Equation 20-15• adjustments (use 20-19)
– PTSF • Coefficients for BPTSF (use 20-21)• Equations 20-16 and 20-17• adjustments (use 20-20)
(take care to use analysis direction flow and opposing flow, not two-way flow)
Modified HCM Directional Analysis Procedure
• No change in volume adjustments• No change in ATS calculation• PTSF calculation
– Same BPTSF equation– New PTSF equation– New BPTSF coefficients
• See Table 9 (handout)– New adjustments replacing fnp
• See Table 10 (handout)
od
dadjdd vv
vfBPTSFPTSF
Exercise—Estimating Performance Measures
• Given (Ideal Conditions): – Terrain = level– % Trucks = 0.0%– % RVs = 0.0%– class I highway with base conditions,– PHF = 0.85– vd = 750 pcph, – vo = 450 pcph, – no no-passing zones, – FFS of 60 mph– 60/40 directional split
• Find – ATSd– PTSFd and– LOS
Application• Given
– Class I– V = 600 vph– Terrain = Rolling– 60/40 split– 60% no-passing zones– PHF = 0.90– 10% Trucks 5% RVs– FFS = 65 mph
Combining Directional Performance Measures
• ATS– See HCM 2000 Chapter 20 pp 20-12
and 20-29
TT1VMT1ATS d
TT2VMT2ATS o
VMT1 0.25V
PHF Lt VMT2 0.25
VoPHF
Lt
ATS cVMT1 VMT2
TT1 TT2
Combining Directional Performance Measures (cont.)
• PTSF– See HCM 2000 Chapter 20 pp 20-12 and 20-
29
PTSFcTT1 PTSF1 TT2 PTSF2
TT1 TT2
Things to Note from Assignment 5
• How to combine directional performance estimates into a two-way estimate
• How to perform an iteration to maintain consistency between the factors and the adjusted volumes.
• Limitations of HCM methodologies (stay tuned)
Review Assignment 3
• See website for the problems and solutions
Limitations
• Sensitivity to highway section length• Intersection operations• Capacity conditions