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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 adjusted volume Calculate performance measures ATS PTSF.

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ce 578 highway traffic operations

CE 578 Highway Traffic Operations

Lecture 4: HCM Directional Analysis

objectives
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
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
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
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
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
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
US HCM Procedures—General Approach

Input Highway

Conditions

Adjustments and

Calculations

Compute

Performance

Measure(s)

us hcm performance measures base conditions
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
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
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
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
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
Combining Directional Performance Measures
  • ATS
    • See HCM 2000 Chapter 20 pp 20-12 and 20-29
combining directional performance measures cont
Combining Directional Performance Measures (cont.)
  • PTSF
    • See HCM 2000 Chapter 20 pp 20-12 and 20-29
discrepancies before and after modifications
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
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
Review Assignment 3
  • See website for the problems and solutions
limitations
Limitations
  • Sensitivity to highway section length
  • Intersection operations
  • Capacity conditions
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