公路通行能力外文翻譯文獻PAGE1公路通行能力外文翻譯文獻(文檔含中英文對照即英文原文和中文翻譯)HighwayCapacityAndLevelsofServiceCapacityDefinedAgeneralizeddefinitionofcapacityis:Thecapacityofanyelementofthehighwaysystemisthemaximumnumberofvehicleswhichhasareasonableexpectationofpassingoverthatsection(ineitheroneorbothdirections)duringagiventimeperiodunderprevailingroadwayandtrafficconditions.Asamplingofcapacitiesformodernhighwayelementsisasfollows:FacilityCapacityinPassengerCarsFreewaysandexpresswaysawayfromrampsandweavingsections,perlaneperhour2000Two-Lanehighways,totalinbothdirections,perhour2000Three-lanehighways,totalineachdirection,perhour2000Twelve-footlaneatsignalizedintersection,perhourofgreensignaltime(nointerferenceandidealprogression)1800Intreatingcapacity，TRBCircular212dividesfreewaysintocomponents:basicfreewaysegmentsandthoseinthezoneofinfluenceofweavingareasandrampjunctions.Capacitiesofexpressways，multilanehighways，andtwo-andthree-lanefacilitiesalsohavethetwocomponents:basicandthoseinthezoneofinfluenceofintersections.Eachoftheseistreatedseparatelybelow.Speed-Volume-CapacityRelationshipsforBasicFreewayandMultilaneHighwaySegmentsAknowledgeoftherelationshipsamongspeed，volume，andcapacityisbasictounderstandingtheplaceofcapacityinhighwaydesignandoperation.Figurel3.1，whichgivessucharelationshipforasinglefreewayorexpresswaylane,isusedforillustrativepurposes.Ifalonevehicletravelsalongatrafficlane，thedriverisfreetoproceedatthedesignspeed.ThissituationisrepresentedatthebeginningoftheappropriatecurveattheupperleftofFig.13.1.Butasthenumberofvehiclesinthelaneincreases,thedriver'sfreedomtoselectspeedisrestricted.Thisrestrictionbringsaprogressivereductioninspeed.Forexample，manyobservationshaveshownthat，forahighwaydesignedfor70mph(113km/h)，whenvolumereaches1900passengercarsperhour，trafficisslowedtoabout43mph(69km/h).Ifvolumeincreasesfurther,therelativelystablenormal-flowconditionusuallyfoundatlowervolumesissubjecttobreakdown.ThiszoneofinstabilityisshownbytheshadedareaontherightsideofFig.13.1.Onepossibleconsequenceisthattrafficflowwillstabilizeatabout2000vehiclesperhouratavelocityof30to40mph(48to64km/h)asshownbythecurvedsolidlineonFig.13.1.Often，however,thequalityofflowdeterioratesandasubstantialdropinvelocityoccurs;inextremecasesvehiclesmaycometoafullstop.Inthiscasethevolumeofflowquicklydecreasesastrafficproceedsunderaconditionknownas‘forcedflow.’VolumesunderforcedflowareshownbythedashedcurveatthebottomofFig.13.1.Readingfromthatcurve，itcanbeseenthatifthespeedfallsto20mph(32km/h)，therateofflowwilldropto1700vehiclesperhour;at10mph（16km/h)theflowrateisonly1000;and,ofcourse，ifvehiclesstop，therateofflowis0.Theresultofthisreductioninflowrateisthatfollowingvehiclesallmustsloworstop，andtherateofflowfallstothelevelsshown.Eveninthosecaseswherethecongestionlastsbutafewseconds,additionalvehiclesareaffectedafterthecongestionattheoriginallocationhasdisappeared.A‘shockwave’developswhichmovesalongthetrafficlaneinthedirectionoppositetothatofvehicletravel.Suchwaveshavebeenobservedseveralmilesfromthesceneoftheoriginalpointofcongestion，withvehiclesslowingorstoppingandthenresumingspeedfornoapparentreasonwhatsoever.Effectsoftheimpositionofspeedlimitsof60,50,and40mpharesuggestedbythedottedlinesonFig.13.1.A55-mph(88km/h)curvecouldalsobedrawnmidwaybetweenthe60and50mphdottedcurvestoreflecttheeffectsofthefederallyimposed55-mphlimit,butthisisconjecturalsincethelevelofenforcementvariessowidely.Vehiclespacing，oritsreciprocal,trafficdensity,probablyhavethegreatesteffectoncapacitysinceitgeneratesthedriver'sfeelingoffreedomorconstraintmorethananyotherfactor.Studiesofdriversastheyfollowothervehiclesindicatethatthetimerequiredtoreachapotentialcollisionpoint，ratherthanvehicleseparation，seemstocontrolbehavior.However，thistimevarieswidelyamongdriversandsituations.Fieldobservationshaverecordedheadways(timebetweenvehicles)rangingfrom0.5to2sec,withanaverageofabout1.5s.Thus，thecalculatedcapacityofatrafficlanebasedonthis1.5saverage,regardlessofspeed，willbe2400vehiclesperhour.Butevenunderthebestofconditions,occasionalgapsinthetrafficstreamcanbeexpected，sothatsuchhighflowsarenotcommon.Rather,asnoted，theyarenearerto2000passengercarsperhour.The‘LevelofService’ConceptAsindicatedinthediscussionoftherelationshipsofspeed,volumeordensity,andvehiclespacing,operatingspeedgoesdownanddriverrestrictionsbecomegreaterastrafficvolumeincrease.‘Levelofservice’iscommonlyacceptedasameasureoftherestrictiveeffectsofincreasedvolume.Eachsegmentofroadwaycanberatedatanappropriatelevel，AtoFinclusive，toreflectitsconditionatthegivendemandorservicevolume.LevelArepresentsalmostidealconditions;LevelEisatcapacity;LevelFindicatesforcedflow.Thetwobestmeasuresforlevelofserviceforuninterruptedflowconditionsareoperatingortravelspeedandtheradioofvolumetocapacity達到最大限度的廣播，calledthev/cratio.Fortwo-andthree-laneroadssightdistanceisalsoimportant.Abbreviateddescriptionsofoperatingconditionsforthevariouslevelsofserviceareasfollows:LevelA—Freeflow;speedcontrolledbydriver'sdesire，speedlimits,orphysicalroadwayconditions.LevelB—Stableflow;operatingspeedsbeginningtoberestricted;littleornorestrictionsonmaneuverabilityfromothervehicles.LevelC—Stableflow;speedsandmaneuverabilitymorecloselyrestricted.LevelD—Approachesunstableflow;tolerablespeedscanbemaintainedbuttemporaryrestrictionstoflowcausesubstantialdropsinspeed.Littlefreedomtomaneuver，comfortandconveniencelow.LevelE—Volumesnearcapacity;speedtypicallyinneighborhoodof30mph(48km/h);flowunstable;stoppagesofmomentaryduration.Abilitytomaneuverseverelylimited.LevelF—Forcedflow，low-operatingspeeds，volumesbelowcapacity;queuesformed.AthirdmeasureoflevelofservicesuggestedinTRBCircular212istrafficdensity.Thisis，foratrafficlane，theaveragenumberofvehiclesoccupyingamile(1.6km)oflaneatagiveninstant.Toillustrate，iftheaveragespeedis50mph，avehicleisinagivenmilefor72s.Ifthelanecarrying800vehiclesperhour，averagedensityisthen16vehiclespermile;spacingis330ft(100m)，centertocenter.Theadvantageofthedensityapproachisthatthevariouslevelsofservicecanbemeasuredorportrayedinphotographs.From:ClarksonH.OglesbyandR.GaryHicks“Highwayengineering”,1982公路通行能力和服務水平通行能力的定義道路通行能力的廣義定義是：在繁忙的道路和交通條件下公路系統任何元素的通行能力是對在指定的時間通過一斷面（一個或兩個方向）的最大數量的車輛有一個合理的預期。一個現代公路通行能力的的抽樣情況如下：設施小客車通行能力遠離斜坡和交織路段的高速公路和每小時每個車道的車流量2000兩車道公路，每小時兩個方向的車流量2000三車道公路，每小時一個方向的車流量2000有信號的交叉路口的十二英寸車道，在綠燈條件下每小時的車流量（沒有干擾的理想通行條件下）1800關于通行能力處理量，運輸交通委員會發布的公路通行能力手冊將高速公路劃分為以下部分：基本高速公路路段，這些區域有影響的交織地區和砸道連接處，高速公路，多車道公路。兩車道和三車道的通行能力同樣有兩部分組成：基本路段和這些區域有影響作用的交叉路口。基本高速公路和多車道公路路段速度，車流量和通行能力的關系速度，車流量和通行能力之間關系是了解某一地方公路設計和運行能力的基礎。圖3.1說明了高速公路中速度、車流量和通行能力之間的關系。如果司機駕駛一輛汽車一直自由的以設計時速獨自行駛在一個行車道上，這種情形在左上角的圖13.1中以適當的曲線表示出來。但隨著車道上車輛數目的增加，司機自由選擇速度受到限制。例如，許多研究表明，一個高速公路的設計速度為70英里每小時（113km/h），當車輛容量達到1900輛每小時時，交通速度下降到43英里每小時（69km/h）。如果車輛數進一步增加，則建立在低車輛數目的相關穩定和正常的流動條件將會被打破。這種不穩定的區域如右側圖13.1陰影區域所示。一個可能的結果是交通流量將如圖13.1的實曲線所示以30到40英里每小時（48到64km/h）的速度下穩定在大約2000車輛每小時。然而在通常情況下，車流量的質量惡化，車速大幅度下降；在極端情況下車輛可能完全停止。在這種情況下，車流量迅速下降，這種情況下的交通受益被稱為“強制性流動”。強制性流動下的車流量如圖13.1下部的虛曲線所示。從曲線上可以看出，如果速度下降到20應力每小時（32km/h），車流量將下降到1700輛每小時，以10英里每小時（16km/h）的流量算只有1000輛車；當然如果車輛停止，車輛流速為0。流速減少的結果是以后的車輛都必須減速或者停止，車輛流速下降到顯示的水平。即使在這種情況下，交通擁擠的情況人在持續。短暫時間后，擁擠處原來的車輛離開后，其他的車輛又會受到影響。一個沿著相反車道行駛的車輛的沖擊波逐漸形成。這樣的沖擊波已經在視野里從原來的擁擠點達到幾英里。伴隨著車輛減速或者停止，而且不會明顯恢復原來的速度。速度限制在60、50和40英里每小時的影響在圖13.1中的虛線表示出來。55英里每小時（88km/h）的曲線也可以畫在60和50英里每小時的虛線中來反映聯邦政府限制的55英里每小時的速度的影響。但是因為執法水平的寬泛和多樣性，這只是推測而已。車輛間距，或者它的倒數，交通密度可能對通行能力有最大的影響，因為它對于司機形成自由或者約束的感覺比其他任何因素都要多。對于司機的研究顯示，他們跟隨