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  1 Transportation Engineeringand Planning C. S. Papacostas & P. D. Prevedouros 3rd Edition in SI Units Chapter 4 Capacity and Level of Service Analysis © 2005 Pearson Education South Asia Pte Ltd 2 4.5 Highways : Uninterrupted Flow ãConcept of Loss of Service (LOS)ãLOS A : Free-flow conditionãAve spacing about 167m (27 car length)ãHigh level of physical and psychological comfortãLOS B : Reasonable free-flowãFree flow speed maintainedã16 car length spacingãManeuver slightly restrictedãStill high level of comfort © 2005 Pearson Education South Asia Pte Ltd 3 4.5 Highways : Uninterrupted Flow ãLOS C : Near or at free-flow speedãManeuver noticeably restrictedã11 car length spacingãMinor incidents can be absorbedãLOS D : Speed beginning to decline with increasing flowãManeuver limitedãReduced comfort levelsãMinor incidents cause queueã8 car length spacing © 2005 Pearson Education South Asia Pte Ltd 4 4.5 Highways : Uninterrupted Flow ãLOS E : Operation at capacityãVolatile operation –no usable gap in the traffic streamã6 car length spacingãLittle room to maneuver ãAny disruption (lane changing, veh entering from a ramp) established shock wave propagating upstreamãIncidents cause serious breakdown with extensive queuingãPoor comfort © 2005 Pearson Education South Asia Pte Ltd 5 4.5 Highways : Uninterrupted Flow ãLOS F : Breakdowns in vehicular flowãQueues formingãCaused by traffic incidentsãPoints of recurring congestion © 2005 Pearson Education South Asia Pte Ltd 6 4.5 Highways : Uninterrupted Flow ãPeak hour factor (PHF)–a measure of demand uniformity or demand peakingãWhere N t is the max no. of vehicles counted during any interval t within the hour   2 © 2005 Pearson Education South Asia Pte Ltd 7 Example 4.3 –Uniform demand ãAssume that 50 vehicles were counted during each of all possible 5-min intervals during the peak hour. Compute the PHFSolutionãV = 600 veh/hãq = 50 (60/5) = 600 veh/hãPHF = 1.00 © 2005 Pearson Education South Asia Pte Ltd 8 Example 4.4 –Extremely Peaked Demand ãConsider the extreme case where 250 vehicles were counted during a 15-min interval and no vehicle were observed during the rest of the hour SolutionãV = 250 veh/hãq = 250 (60/15) = 1000 veh/hãPHF = 0.25 © 2005 Pearson Education South Asia Pte Ltd 9 4.5 Highways : Uninterrupted Flow ãFig : speed-flow relationship per freeway lane © 2005 Pearson Education South Asia Pte Ltd 10 4.5 Highways : Uninterrupted Flow ãTable summarizes speed, flow, saturation, and density levels corresponding to the 6 LOS © 2005 Pearson Education South Asia Pte Ltd 11 4.5 Highways : Uninterrupted Flow ãDensityis the measure of effectiveness that primarily determines LOSãOnce density is known, LOS is determined based on above table © 2005 Pearson Education South Asia Pte Ltd 12 4.5 Highways : Uninterrupted Flow  3 © 2005 Pearson Education South Asia Pte Ltd 13 4.5 Highways : Uninterrupted Flow © 2005 Pearson Education South Asia Pte Ltd 14 4.5 Highways : Uninterrupted Flow ãFree-flow speed(FFS)ãCollected under free-flow condition (i.e LOS A or B) or ã FFS = BFFS –f  LW  –f  LC  –f  N  –f  ID ã f  LW , f  LC , f  N , f  ID can be estimated using tables in HCM 2000 © 2005 Pearson Education South Asia Pte Ltd 15 4.5 Highways : Uninterrupted Flow Where ãW = lane width (3 or 3.4 m)ãLC = lateral clearance (from 0 to 1.8m)ãN = number of lanes per direction (2,3,4)ãACCESS –number of interchanges per km (from 0 to 1.2) © 2005 Pearson Education South Asia Pte Ltd 16 Example 4.5 : LOS Estimation ãAn extended freeway segment with largely level terrain has an observed free-flow speed of approximately 110km/h, 3 lanes/direction, a 1-m lateral clearance, and about 1 interchange/km. It has an observed volume of 3080 veh/h with corresponding PHF = 0.88 and 154 trucks and buses, no recreational vehicle. An all-commuter motorist composition may be assumed. Estimate the LOS for this set of conditions © 2005 Pearson Education South Asia Pte Ltd 17 Example 4.5 : Solution ãLOS C (Table 4.5.1)   © 2005 Pearson Education South Asia Pte Ltd 18 4.6 Highways : Interrupted Flow ãTypes of SignalãDemand-actuated or pretimedãFully actuatedãIsolated intersection controlãArterial system controlãNetwork system control  4 © 2005 Pearson Education South Asia Pte Ltd 19 4.6 Highways : Interrupted Flow ãSignal detector ãInductive loop detector ãPassage detection and presence detectionãController unitãBrain of a traffic control systemãReceives “calls” from detectors and interfaces with signal display equipment to to provide for sequencing and timing of traffic signal display   © 2005 Pearson Education South Asia Pte Ltd 20 4.6 Highways : Interrupted Flow ãSignal timingsãSequence -phasing, and duration –green timeãSignal phasingãminimize the potential hazards arising from the conflicts of vehicular and pedestrian movementsãWhile maintaining the efficiency of flow through the intersectionãIncrease no. of phases promotes safety, reduces efficiency © 2005 Pearson Education South Asia Pte Ltd 21 4.6 Highways : Interrupted Flow ã3 common phasing schemes   © 2005 Pearson Education South Asia Pte Ltd 22 4.6 Highways : Interrupted Flow ãCycle length–complete sequence of signal indicationãLong cycle lengths cause substantial delay © 2005 Pearson Education South Asia Pte Ltd 23 4.6 Highways : Interrupted Flow ãToo short –cause congestion or endanger the pedestriansãAppropriate cycle length (Webster’s) ãWhere C o = optimal cycle length (sec)L = total lost time during a cycle, which consists of the startup delay minus the portion of yellow utilised by driver CS = sum of the flow ratios of critical movements © 2005 Pearson Education South Asia Pte Ltd 24 4.6 Highways : Interrupted Flow ãBefore estimate cycle length, phasing must be setãNo technique or computer algorithm can produce an optimal phasing schemesãTedious analysis of many combinations of phasing schemes and lane channalization options on each approachãBest phasing scheme is the one couple with C o results in shortest delay
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