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Level Of Service
Level Of Service
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Level Of Service

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  • 1. Highway Level of Service1 Wali Memon Twitter: walimemon
  • 2. Outline 1. Definitions 2. Level of Service (LOS) 3. Freeway Segment LOS Determination a. Free-flow speed b. Flow Rate 4. Multilane Highway LOS 5. Design Traffic Volume2 Wali Memon Twitter: walimemon
  • 3. I-5 Average Daily Traffic3 Wali Memon Twitter: walimemon from the WSDOT 2001 Annual Traffic Report
  • 4. Freeway Defined A divided highway with full control of access and two or more lanes for the exclusive use of traffic in each direction. Assumptions No interaction with adjacent facilities (streets, other freeways) Free-flow conditions exist on either side of the facility being analyzed Outside the influence or ramps and weaving areas4 Wali Memon Twitter: walimemon
  • 5. Basic Freeway Segment5 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 6. Definitions Freeway Capacity The maximum sustained 15-min flow rate, expressed in passenger cars per hour per lane, that can be accommodated by a uniform freeway segment under prevailing traffic and roadway conditions in one direction of flow.6 Wali Memon Twitter: walimemon
  • 7. Definitions – Flow Characteristics Undersaturated Traffic flow that is unaffected by upstream or downstream conditions. Queue discharge Traffic flow that has just passed through a bottleneck and is accelerating back to the FFS of the freeway. Oversaturated Traffic flow that is influenced by the effects of a downstream bottleneck.7 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 8. Speed vs. Flow Sf Free Flow Speed Uncongested Flow Speed (mph) Sm Optimal flow, Congested Flow Flow (veh/hr) capacity, vm8 Wali Memon Twitter: walimemon
  • 9. Uncongested Flow9 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 10. Definitions – Free-Flow Speed Free-Flow Speed (FFS) The mean speed of passenger cars that can be accommodated under low to moderate flow rates on a uniform freeway segment under prevailing roadway and traffic conditions. Factors affecting free-flow speed Lane width Lateral clearance Number of lanes Interchange density Geometric design10 Wali Memon Twitter: walimemon
  • 11. Definitions Passenger car equivalents Trucks and RVs behave differently Baseline is a freeway with all passenger cars Traffic is expressed in passenger cars per lane per hour (pc/ln/hr or pcplph) Driver population Non-commuters suck more at driving They may affect capacity Capacity Corresponds to LOS E and v/c = 1.011 Wali Memon Twitter: walimemon
  • 12. Definitions – Level of Service (LOS) Chief measure of “quality of service” Describes operational conditions within a traffic stream. Does not include safety Different measures for different facilities Six measures (A through F) Freeway LOS Based on traffic density12 Wali Memon Twitter: walimemon
  • 13. Levels of Service LOS A Free-flow operation From Highway Capacity Manual, 2000 LOS B Reasonably free flow Ability to maneuver is only slightly restricted Effects of minor incidents still13 easily absorbed Wali Memon Twitter: walimemon
  • 14. Levels of Service LOS C Speeds at or near FFS Freedom to maneuver is noticeably restricted Queues may form behind any significant blockage. From Highway Capacity Manual, 2000 LOS D Speeds decline slightly with increasing flows Density increases more quickly Freedom to maneuver is more noticeably limited Minor incidents create queuing14 Wali Memon Twitter: walimemon
  • 15. Levels of Service LOS E Operation near or at capacity No usable gaps in the traffic stream Operations extremely volatile Any disruption causes queuing From Highway Capacity Manual, 2000 LOS F Breakdown in flow Queues form behind breakdown points15 Demand > capacity Wali Memon Twitter: walimemon
  • 16. Freeway LOS16 Wali Memon Twitter: walimemon
  • 17. Freeway LOS LOS Calculation Does not consider Special lanes reserved for a particular type of vehicle (HOV, truck, climbing, etc.) Extended bridge and tunnel segments Segments near a toll plaza Facilities with FFS < 55 mi/h or > 75 mi/h Demand conditions in excess of capacity Influence of downstream blockages or queuing Posted speed limit Extent of police enforcement Intelligent transportation system features Capacity-enhancing effects of ramp metering17 Wali Memon Twitter: walimemon
  • 18. Freeway LOS Input Geometric Data Measured FFS or BFFS Volume BFFS Input BFFS Adjustment Volume Adjustment Lane width PHF Number of lanes Number of lanes Interchange density Measured Driver population Lateral clearance FFS Input Heavy vehicles Compute FFS Compute flow rate Define speed-flow curve Compute density using flow rate and speed Determine speed using speed-flow curve18 Wali Memon Twitter: walimemon Determine LOS
  • 19. 19 Wali Memon LOS Criteria for Basic Freeway Segments Twitter: walimemon Freeway LOSFrom Highway Capacity Manual, 2000
  • 20. Freeway LOS Determining FFS Measure FFS in the field Low to moderate traffic conditions FFS = BFFS − f Use a baseline and adjust it (BFFS) LW − f LC − f N − f ID FFS = free-flow speed (mph) BFFS = base free-flow speed, 70 mph (urban), 75 mph (rural) fLW = adjustment for lane width (mph) fLC = adjustment for right-shoulder lateral clearance (mph)20 Wali Memon fN = adjustment for number of lanes (mph) Twitter: walimemon fID = adjustment for interchange density (mph)
  • 21. Freeway LOS Lane Width Adjustment (fLW) Base condition (fLW = 0) Average width of 12 ft. or wider across all lanes21 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 22. Freeway LOS Lateral Clearance Adjustment (fLC) Base condition (fLC = 0) 6 ft. or greater on right side 2 ft. or greater on the median or left side22 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 23. Freeway LOS Number of Lanes Adjustment (fN) Base condition (fN = 0) 5 or more lanes in one direction Do not include HOV lanes fN = 0 for all rural freeway segments23 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 24. Freeway LOS Interchange Density Adjustment (fIC) Base condition (fIC = 0) 0.5 interchanges per mile (2-mile spacing) Interchange defined as having at least one on-ramp Determined over 6-mile segment24 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 25. Freeway LOS Determining Flow Rate V vp = Adjust hourly volumes to get pc/ln/hr PHF × N × f HV × f p vp = 15-minute passenger-car equivalent flow rate (pcphpl) V = hourly volume (veh/hr) PHF = peak hour factor N = number of lanes in one direction fHV = heavy-vehicle adjustment factor25 Wali Memon Twitter: walimemon fP = driver population adjustment factor
  • 26. Freeway LOS Peak Hour Factor (PHF) Typical values 0.80 to 0.95 Lower PHF characteristic or rural or off-peak V Higher PHF typical of urban peak-hour PHF = V15 × 4 V = hourly volume (veh/hr) for hour of analysis V15 = maxiumum 15-min. flow rate within hour of analysis26 4 = Number of 15-min. periods per hour Wali Memon Twitter: walimemon
  • 27. Freeway LOS Heavy Vehicle Adjustment (fHV) Base condition (fHV = 1.0) No heavy vehicles Heavy vehicle = trucks, buses, RVs Two-step process Determine passenger-car equivalents (ET) Determine fHV27 Wali Memon Twitter: walimemon
  • 28. Freeway LOS Passenger-Car Equivalents (ET) Extended segments method Determine the type of terrain and select ET No one grade of 3% or more is longer than 0.25 miles OR No one grade of less than 3% is longer than 0.5 miles28 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 29. Freeway LOS Passenger-Car Equivalents (ET) Specific grades method Any grade of 3% or more that is longer than 0.25 miles OR Any grade of less than 3% that is longer than 0.5 miles29 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 30. Freeway LOS From Highway Capacity Manual, 200030 Wali Memon Twitter: walimemon
  • 31. Freeway LOS Passenger-Car Equivalents (ET)31 Wali Memon Twitter: walimemon
  • 32. Freeway LOS Passenger-Car Equivalents (ET) Composite grades method Determines the effect of a series of steep grades in succession Method OK if… All subsection grades are less than 4% OR Total length of composite grade is less than 4000 ft. Otherwise, use a detailed technique in the Highway Capacity Manual (HCM)32 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 33. Freeway LOS Determine fHV 1 f HV = 1 + PT (ET − 1) + PR (E R − 1) fHV = Heavy vehicle adjustment factor ET, ER = Passenger-car equivalents for trucks/buses and RVs PT, PR = Proportion of trucks/buses and RVs in traffic stream33 Wali Memon Twitter: walimemon
  • 34. Freeway LOS Driver Population Adjustment (fP) Base condition (fP = 1.0) Most drivers are familiar with the route Commuter drivers Typical values between 0.85 and 1.00 Two-step process Determine passenger-car equivalents (ET) Determine fHV34 Wali Memon Twitter: walimemon
  • 35. Freeway LOS Define Speed-Flow Curve Select a Speed-Flow curve based on FFS35 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 36. Freeway LOS Determine Average PC Speed (S) Use vp and FFS curve to find average passenger car speed (S)36 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 37. Freeway LOS Determine Average PC Speed (S)For 70 < FFS ≤ 75 mph AND (3400 – 30FFS) < vp ≤ 2400  160  v p + 30 FFS − 3400   2.6 S = FFS −  FFS −   30 FFS − 1000      3    For 55 < FFS ≤ 70 mph AND (3400 – 30FFS) < vp ≤ (1700 + 2.6 10FFS) 1  v p + 30 FFS − 3400   S = FFS −  (7 FFS − 340)  40 FFS − 1700    9     For 55 < S = FFS mph AND vp < (3400 – 30FFS) FFS ≤ 7537 Wali Memon Twitter: walimemon
  • 38. Freeway LOS Determine Density vp D= Calculate density using: S D = density (pc/mi/ln) vp = flow rate (pc/hr/ln) S = average passenger-car speed (mph)38 Wali Memon Twitter: walimemon
  • 39. 39 Wali MemonLOS Criteria for Basic Freeway Segments LOS Twitter: walimemon Determine Freeway LOSFrom Highway Capacity Manual, 2000
  • 40. Freeway LOS Example Determine the typical LOS for SR 520 eastbound near Microsoft (MP 10.25 – shown in the picture below) at 7 a.m. and 10 p.m.Geometry 11 ft. lane width Left lateral clearance = 5 ft. Right lateral clearance = 4 ft.Other 7 am PHF = 0.95 10 pm PHF = 0.99 2% trucks from WSDOT’s SRWeb 3% buses http://srview.wsdot.wa.gov/40 Wali Memon Twitter: walimemon
  • 41. Freeway LOS Determine FFS41 Wali Memon Twitter: walimemon
  • 42. Freeway LOS Determine FFS42 Wali Memon Twitter: walimemon
  • 43. Freeway LOS Determine FFS from Microsoft MapPointIn a 6-mile stretch fromI-405 to Redmond thereare 5 interchanges43 Wali Memon Twitter: walimemon
  • 44. Freeway LOS Determine FFS44 Wali Memon Twitter: walimemon
  • 45. Freeway LOS Determine Flow Rate (vp)45 At 7am the ½ hour volume is about 4000 veh/hr Wali Memon Twitter: walimemon At 10 pm the ½ hour volume is about 1700 veh/hr Graph from the Puget Sound Regional Council’s Puget Sound Trends, No. T6, July 1997
  • 46. Freeway LOS Determine Flow Rate (vp)46 Wali Memon Twitter: walimemon
  • 47. Freeway LOS Determine LOS47 Wali Memon Twitter: walimemon
  • 48. 48 Wali Memon LOS Criteria for Basic Freeway Segments Twitter: walimemon Freeway LOSFrom Highway Capacity Manual, 2000
  • 49. Multilane Highway LOS49 Wali Memon Twitter: walimemon
  • 50. Multilane Highway LOS Multilane Highway LOS Similar to Freeway LOS A few minor differences50 Wali Memon Twitter: walimemon
  • 51. Multilane Highway LOS Base Conditions for Multilane Highway Level terrain, with grades no greater than 2 percent Minimum lane width = 12 ft Objects no closer than 6 ft from the edge of the traveled pavement (at the roadside or median) No direct access points along the roadway Divided highway Traffic stream composed entirely of passenger cars Free flow speed of 60 mph or more Driver population composed principally of regular users51 Wali Memon Twitter: walimemon
  • 52. Multilane Highway LOS Free Flow Speed (FFS) Measure FFS in the field Low to moderate traffic conditions FFS = BFFS − f Use a baseline and adjust it (BFFS) LW − f LC − f M − f A FFS = free-flow speed (mph) BFFS = base free-flow speed, 60 mph is typically used fLW = adjustment for lane width (mph) fLC = adjustment for right-shoulder lateral clearance (mph)52 Wali Memon fM = adjustment for median type (mph) Twitter: walimemon fA = adjustment for access points (mph)
  • 53. Multilane Highway LOS Lane Width Adjustment (fLW) Base condition (fLW = 0) Average width of 12 ft. or wider across all lanes Same as Freeway LOS53 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 54. Multilane Highway LOS Lateral Clearance Adjustment (fLC) TLC = LC R + LC L Base condition (fLC = 0) 12 ft or greater TLC LCL = 6 ft for undivided highways From Highway Capacity Manual, 2000 (accounted for in median type adjustment) LCL = 6 ft for two-way left-turn lanes54 Wali Memon Twitter: walimemon
  • 55. Multilane Highway LOS Median Adjustment (fM) Base condition (fM = 0) Divided highway55 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 56. Multilane Highway LOS Access-Point Density Adjustment (fA) For each access point/mi FFS decreases by 0.25 mph Base condition (fA = 0) 0 access points per mile For NAPM ≤ 40: fA = 0.25 × NAPM For NAPM > 40: fA = 1056 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 57. Multilane Highway LOS Determining Flow Rate V vp = Adjust hourly volumes to get pc/ln/hr PHF × N × f HV × f p vp = 15-minute passenger-car equivalent flow rate (pcphpl) V = hourly volume (veh/hr) PHF = peak hour factor N = number of lanes in one direction fHV = heavy-vehicle adjustment factor57 Wali Memon Twitter: walimemon fP = driver population adjustment factor Same as Freeway LOS
  • 58. Multilane Highway LOS Heavy Vehicle Adjustment (fHV) Base condition (fHV = 1.0) No heavy vehicles Heavy vehicle = trucks, buses, RVs Two-step process Determine passenger-car equivalents (ET) Determine fHV58 Wali Memon Twitter: walimemon Same as Freeway LOS
  • 59. Multilane Highway LOS Passenger-Car Equivalents (ET) Extended segments method Determine the type of terrain and select ET No one grade of 3% or more is longer than 0.5 miles OR No one grade of less than 3% is longer than 1 mile59 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 60. Multilane Highway LOS Passenger-Car Equivalents (ET) Specific grades method Any grade of 3% or more that is longer than 0.5 miles OR Any grade of less than 3% that is longer than 1 mile60 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 61. Multilane Highway LOS Same as Freeway LOS From Highway Capacity Manual, 200061 Wali Memon Twitter: walimemon
  • 62. Multilane Highway LOS Passenger-Car Equivalents (ET)62 Wali Memon Twitter: walimemon Same as Freeway LOS
  • 63. Multilane Highway LOS Passenger-Car Equivalents (ET) Composite grades method Determines the effect of a series of steep grades in succession Method OK if… All subsection grades are less than 4% OR Total length of composite grade is less than 4000 ft. Otherwise, use a detailed technique in the Highway Capacity Manual (HCM)63 Wali Memon Same as Freeway LOS Twitter: walimemon From Highway Capacity Manual, 2000
  • 64. Multilane Highway LOS Determine fHV 1 f HV = 1 + PT (ET − 1) + PR (E R − 1) fHV = Heavy vehicle adjustment factor ET, ER = Passenger-car equivalents for trucks/buses and RVs PT, PR = Proportion of trucks/buses and RVs in traffic stream Same as Freeway LOS64 Wali Memon Twitter: walimemon
  • 65. Multilane Highway LOS Driver Population Adjustment (fP) Base condition (fP = 1.0) Most drivers are familiar with the route Commuter drivers Typical values between 0.85 and 1.00 Same as Freeway LOS65 Wali Memon Twitter: walimemon
  • 66. Multilane Highway LOS Determine Average PC Speed (S) Use vp and FFS curve to find average passenger car speed (S)66 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 67. Multilane Highway LOS Determine Average PC Speed (S)For 55 < FFS ≤ 60 mph AND vp > 1400  3  v p − 1400   1.31 S = FFS −  FFS − 13   28FFS − 880     10     For 50 < FFS ≤ 55 mph AND vp > 1400     1.31  34  219  v p − 1400   S = FFS −  FFS −    41   205 FFS − 1181   171       5  For 55 < FFS ≤ 75 mph AND vp < (3400 – 30FFS)  1 56  v p − 1400   1.31 S = FFS −  FFS −     5 9  36 FFS − 1120      67 Wali Memon Twitter: walimemonFor vp < 1400 S = FFS
  • 68. Multilane Highway LOS Determine LOS Use vp and passenger car speed (S)68 Wali Memon Twitter: walimemon From Highway Capacity Manual, 2000
  • 69. Multilane Highway LOS Determine Density vp D= Calculate density using: S D = density (pc/mi/ln) vp = flow rate (pc/hr/ln) S = average passenger-car speed (mph)69 Wali Memon Twitter: walimemon
  • 70. Multilane Highway LOS LOS Criteria for Multilane Highways From Highway Capacity Manual, 200070 Wali Memon Twitter: walimemon
  • 71. Design Traffic Volumes71 Wali Memon Twitter: walimemon
  • 72. Design Traffic Volumes Need to select the appropriate hourly traffic volume to get the design LOS72 Wali Memon Twitter: walimemon
  • 73. Definitions Annual average daily traffic (AADT) Annual traffic averaged on a daily basis Design hourly volume (DHV) Traffic volume used for design calculations Typically between the 10th and 50th highest volume hour of the year (30th highest is most common) K-factor Relationship between AADT and DHV DHV73 K= Wali Memon AADT Twitter: walimemon
  • 74. Definitions Directional distribution factor (D) Factor reflecting the proportion of peak-hour traffic traveling in the peak direction Often there is much more traffic in one direction than the other Directional design-hour volume (DDHV) DDHV = K × D × AADT74 Wali Memon Twitter: walimemon
  • 75. Typical Graph Highest 100 Hourly Volumes Over a One-Year 0.15 Period for a Typical Roadway Hourly volume as a proportion of AADT 0.14 0.13 0.12 0.11 0.10 0 20 40 60 80 10075 Wali Memon Twitter: walimemon Number of hours (annually) with specified or greater volumes
  • 76. WSDOT Graphs76 Wali Memon Twitter: walimemon
  • 77. Primary References Mannering, F.L.; Kilareski, W.P. and Washburn, S.S. (2005). Principles of Highway Engineering and Traffic Analysis, Third Edition. Chapter 6 Transportation Research Board. (2000). Highway Capacity Manual 2000. National Research Council, Washington, D.C.77 Wali Memon Twitter: walimemon

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