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Chapter3trafficstreamcharacteristicsTrafficstreamaremadeupofindividualdriversandvehiclesinteractingwitheachotherandwiththephysicalelementsoftheroadwayanditsgeneralenvironment.becausebothdriverbehaviorandvehiclecharacteristicsvary,individualvehicleswithinthetrafficstreamdonotbehaveinexactlythesameway,eveninsimilarcircumstances,becausedriverbehaviorvarieswithlocalcharacteristicsanddrivinghabits.5.1TypesoffacilitiesuninterruptedflowinterruptedflowUninterruptedflowfacilitieshavenoexternalin-terruptionstothetrafficstream.Pureuniterrupt-edflowexistsprimarilyonfreeway,wheretherearenointersectionsatgrade,trafficsignals,ST-OPorYIELDsigns,orotherinterruptionsexter-naltothetrafficstreamitself.Interruptedflowfacilitiesarethosethatincorporatefixedexternalinterruptionsintotheirdesignandoperation.Themostfrequentandoperationallysignificantexternalinterruptionisthetrafficsignal.Thetrafficsignalalternativelystartsandstopsagiventrafficstream,creatingaplatoonsofvehiclesprogressingdownthefacility.5.2Trafficstreamparameters(1)macroscopicparametersvolumeorrateofflowspeeddensity(2)MicroscopicparametersthespeedofindividualvehiclesheadwayspacingvolumeTrafficvolumeisdefinedasthenumberofvehiclespassingapointonahighway,oragivenlaneordirectionofahighway,duringaspecifiedtimeinterval.theunitofmeasurementforvolumeissimply“vehicles,”althoughitisoftenexpressedas“vehiclesperunittime.”交通量是指在特定的时间段内,通过道路某一地点、某一断面或某一条车道的交通实体数。测量交通量的单位通常被称为“辆”,虽然通常被表示为“辆/单位时间”。时间的单位通常用“每天”或“每小时”表示。hourlyvolumeDailyvolumesareusedtoestablishtrendsovertime,andforgeneralplanningpurposes.Detaileddesignorcontroldecisionsrequireknowledgeofhourlyvolumeforthepeakhouroftheday.RateofflowRatesofflowaregenerallystatedinunitsof“vehiclesperhour,”butrepresentflowsthatexistforperiodsoftimelessthanonehour.Avolumeof200vehiclesobservedovera15minuteperiodmaybeexpressedasarateof200*4=800vehicles/hour,eventhough800vehicleswouldnotbeobservedifthefullhourwerecounted.The800vehicles/hourbecomesarateofflowthatexistsfora15minuteinterval.DailyVolume•AADT(AverageAnnualDailyTraffic年平均日交通量)theaverage24hourvolumeatagivenlocationoverafull365dayyear;thenumberofvehiclespassingasiteinayeardividedby365days.•AAWT(AverageAnnualWeekdayTraffic年平均工作日交通量)theaverage24dayyear;thenumberofvehiclespassingasiteonweekdaysinayeardividedbythenumberofweekdays.•AWT(AverageWeekdayTraffic平均工作日交通量)Theaverage24hourweekdayvolumeatagivenlocationoveradefinedtimeperiodlessthanoneyear;acommonapplicationistomeasureanADTforeachmonthoftheyear.•ADT(AverageDailyTraffic平均日交通量)Theaverage24hourvolumeatagivenlocationoveradefinedtimeperiodlessthanoneyear;acommonapplicationistomeasureanADTforeachmonthoftheyear.一、交通量的表达方式在交通量观测和统计分析及实际应用中,常见的交通量有以下几种:1.平均交通量由于交通量是随时间变化的,对于不同的计量时间,有不同的表达方式,通常有如下的表达式:式中:Qi——计算期内各单位时间的交通量;n——计算期内的单位时间总数。niiQnADT11)(平均日交通量71301365171)(301)(3651)(iiiiiiQWADTQMADTQAADT周平均日交通量月平均日交通量年平均日交通量二、交通量在空间上的变化在同一时间或相似交通条件下,交通量在不同区段、不同方向和不同车道上其分布情况不一样。1.地域分布经济发达省份与经济欠发达省份之间交通量有明显差别。2.城乡分布一般是城市道路交通量高于郊区道路,近郊又高于远郊,乡村道路交通量最低。3.方向分布一条道路往返两个方向的交通量,在较长时间内大体上是相近的。但是在某段时间内,两个方向的交通量会有很大差别。(方向分布系数KD=主要行车方向交通量/双向交通量*100%)4.车道分布当同向车行道有两条以上车道时,处于不同位置的车道,其交通量分布也不一样。三、交通量的时间分布交通量随着时间变化而出现的变化,反映了社会与经济活动等对交通的需求。1.一年内月交通量的变化一年中每个月交通量是不相同的。年平均日交通量与月平均日交通量之比,称为交通量月变系数M(或称月不均系数,月换算系数),即式中:k——当月的天数,可以取30、31、28、29天;Qi——观测日的交通量。月变系数表示交通量的月变规律。kiiiiQkQMADTAADTK1365113651=月平均日交通量年平均日交通量月DistributionofADTvolume10,00011,00012,00013,00014,00015,00016,00017,00018,00019,00020,000123456789101112monthofyearvolume(veh/day)2、一周内日交通量的变化在一周七天中,交通量也是逐日变化的。显示这种变化的曲线图,叫交通量日变图。用各个周日的交通量日变系数K日表示交通量的日变规律。交通量日变系数K日,是以年平均日交通量(AADT);除以某周日的平均日交通量(ADT);某周日的平均日交通量等于全年所有某周日交通量的总和除以全年某周日的总天数。即式中:Qi——周i的平均交通量,在实际计算时iiidQQK7171=观测日交通量周平均日交通量全年所有周一的天数量总和全年所有周一的日交通iQVolume•Hourlyvolumesandpeakhourvolume(小时流量,高峰小时流量)Dailyvolumes,whileusefulforplanningpurposes,cannotbeusedalonefordesignoroperationalanalysispurposes.Volumevariesconsiderableoverthe24hoursoftheday,withperiodsmaximumflowoccurringduringthemorningandeveningcommuter“rushhours”.Thesinglehourofthedaythathasthehighesthourlyvolumeisreferredtoasthepeakhour.thepeak-hourvolumeisgenerallystatedasadirectionalvolume.Trafficgoingonewayduringthemorningpeakisgoingtheoppositewayduringtheeveningpeak,bothsidesofafacilitymustgenerallybedesignedtoaccommodatethepeakdirectionalflowduringthepeakhour.DDHV=AADT*K*DK:proportionofdailytrafficoccurringduringthepeakhourD:proportionofpeakhourtraffictravelinginthepeakdirectionofflowFordesign,theproportionofAADToccurringduringthe30thpeakhouroftheyear,Ifthe365peakhourvolumesoftheyearatagivenlocationarelistedindescendingorder,the30thpeakhouris30thonthelistandrepresentsavolumethatisexceededinonly29hoursoftheyear.课堂练习:某公路需要进行拓宽改建,经调查预测得该公路在规划年的年平均日交通量为50000辆小汽车/日。设计小时交通量系数K=0.15.取一条车道的设计通行能力为1500辆小汽车/h。试问该公路该修几条车道?SubhourlyvolumesandrateofflowVolumesobservedforperiodsoflessthanonehouraregenerallyexpressedasequivalenthourlyratesofflow.Forexample,1000vehiclescountedovera15-minuteintervalcouldbeexpressedas1000vehs/0.25h=4000veh/h.therateofflowof4000veh/hisvalidforthe15-minuteperiod
本文标题:Chapter3trafficstreamcharacteristics(交通流特性)
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