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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.

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CE 578 Highway Traffic Operations

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  1. CE 578 Highway Traffic Operations Lecture 4: HCM Directional Analysis

  2. Objectives • Understand two-lane highway performance measures • Relate two-lane highway conditions to input variables • Calculate adjusted volume • Calculate performance measures • ATS • PTSF

  3. Two-Lane Highway Performance Measures • Percent-time-spent-following (PTSF) • Average travel speed (ATS) • Average travel time • Passing supply vs passing demand

  4. 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

  5. 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

  6. 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

  7. 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

  8. US HCM Procedures—General Approach Input Highway Conditions Adjustments and Calculations Compute Performance Measure(s)

  9. 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

  10. Base Condition PTSF Estimation: Graph (50/50 directional split)

  11. US HCM Level-of-Service—Class I Facilities

  12. US HCM Level-of-Service—Class II Facilities

  13. 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)

  14. 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)

  15. 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

  16. 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

  17. Combining Directional Performance Measures • ATS • See HCM 2000 Chapter 20 pp 20-12 and 20-29

  18. Combining Directional Performance Measures (cont.) • PTSF • See HCM 2000 Chapter 20 pp 20-12 and 20-29

  19. 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?

  20. 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)

  21. Review Assignment 3 • See website for the problems and solutions

  22. Limitations • Sensitivity to highway section length • Intersection operations • Capacity conditions

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