CE 578 Highway Traffic Operations

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# CE 578 Highway Traffic Operations - PowerPoint PPT Presentation

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.

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### 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 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
• Deterministic procedures
• US HCM two-way methodology (not necessary)
• US HCM directional methodology
US HCM Procedures—General Approach

Input Highway

Conditions

Calculations

Compute

Performance

Measure(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
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
• PTSF
• Coefficients for BPTSF (use 20-21)
• Equations 20-16 and 20-17

(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)
Exercise—Estimating Performance Measures
• Given:
• class I highway with base conditions,
• vd = 750 pcph,
• vo = 450 pcph,
• no no-passing zones,
• FFS of 60 mph
• 50/50 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
Combining Directional Performance Measures (cont.)
• PTSF
• See HCM 2000 Chapter 20 pp 20-12 and 20-29
Discrepancies before and after modifications
• HCM 2000 two-way vs HCM 2000 directional (combined)
• ATS
• ATSc = 56 mph; ATStwo-way = 56.5 mph
• PTSF
• PTSFc = 81.8; PTSFtwo-way = 62.7
• Is this significant?
Things to Note from Assignment 5
• How to combine directional performance estimates into a two-way estimate
• How to implement modified HCM procedure to maintain consistency with two-way analysis
• 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