公路通行能力外文翻譯文獻(xiàn)

公路通行能力外文翻譯文獻(xiàn)PAGE1公路通行能力外文翻譯文獻(xiàn)(文檔含中英文對(duì)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(dá)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(wù)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(tǒng)任何元素的通行能力是對(duì)在指定的時(shí)間通過(guò)一斷面（一個(gè)或兩個(gè)方向）的最大數(shù)量的車(chē)輛有一個(gè)合理的預(yù)期。一個(gè)現(xiàn)代公路通行能力的的抽樣情況如下：設(shè)施小客車(chē)通行能力遠(yuǎn)離斜坡和交織路段的高速公路和每小時(shí)每個(gè)車(chē)道的車(chē)流量2000兩車(chē)道公路，每小時(shí)兩個(gè)方向的車(chē)流量2000三車(chē)道公路，每小時(shí)一個(gè)方向的車(chē)流量2000有信號(hào)的交叉路口的十二英寸車(chē)道，在綠燈條件下每小時(shí)的車(chē)流量（沒(méi)有干擾的理想通行條件下）1800關(guān)于通行能力處理量，運(yùn)輸交通委員會(huì)發(fā)布的公路通行能力手冊(cè)將高速公路劃分為以下部分：基本高速公路路段，這些區(qū)域有影響的交織地區(qū)和砸道連接處，高速公路，多車(chē)道公路。兩車(chē)道和三車(chē)道的通行能力同樣有兩部分組成：基本路段和這些區(qū)域有影響作用的交叉路口。基本高速公路和多車(chē)道公路路段速度，車(chē)流量和通行能力的關(guān)系速度，車(chē)流量和通行能力之間關(guān)系是了解某一地方公路設(shè)計(jì)和運(yùn)行能力的基礎(chǔ)。圖3.1說(shuō)明了高速公路中速度、車(chē)流量和通行能力之間的關(guān)系。如果司機(jī)駕駛一輛汽車(chē)一直自由的以設(shè)計(jì)時(shí)速獨(dú)自行駛在一個(gè)行車(chē)道上，這種情形在左上角的圖13.1中以適當(dāng)?shù)那€(xiàn)表示出來(lái)。但隨著車(chē)道上車(chē)輛數(shù)目的增加，司機(jī)自由選擇速度受到限制。例如，許多研究表明，一個(gè)高速公路的設(shè)計(jì)速度為70英里每小時(shí)（113km/h），當(dāng)車(chē)輛容量達(dá)到1900輛每小時(shí)時(shí)，交通速度下降到43英里每小時(shí)（69km/h）。如果車(chē)輛數(shù)進(jìn)一步增加，則建立在低車(chē)輛數(shù)目的相關(guān)穩(wěn)定和正常的流動(dòng)條件將會(huì)被打破。這種不穩(wěn)定的區(qū)域如右側(cè)圖13.1陰影區(qū)域所示。一個(gè)可能的結(jié)果是交通流量將如圖13.1的實(shí)曲線(xiàn)所示以30到40英里每小時(shí)（48到64km/h）的速度下穩(wěn)定在大約2000車(chē)輛每小時(shí)。然而在通常情況下，車(chē)流量的質(zhì)量惡化，車(chē)速大幅度下降；在極端情況下車(chē)輛可能完全停止。在這種情況下，車(chē)流量迅速下降，這種情況下的交通受益被稱(chēng)為“強(qiáng)制性流動(dòng)”。強(qiáng)制性流動(dòng)下的車(chē)流量如圖13.1下部的虛曲線(xiàn)所示。從曲線(xiàn)上可以看出，如果速度下降到20應(yīng)力每小時(shí)（32km/h），車(chē)流量將下降到1700輛每小時(shí)，以10英里每小時(shí)（16km/h）的流量算只有1000輛車(chē)；當(dāng)然如果車(chē)輛停止，車(chē)輛流速為0。流速減少的結(jié)果是以后的車(chē)輛都必須減速或者停止，車(chē)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(xù)。短暫時(shí)間后，擁擠處原來(lái)的車(chē)輛離開(kāi)后，其他的車(chē)輛又會(huì)受到影響。一個(gè)沿著相反車(chē)道行駛的車(chē)輛的沖擊波逐漸形成。這樣的沖擊波已經(jīng)在視野里從原來(lái)的擁擠點(diǎn)達(dá)到幾英里。伴隨著車(chē)輛減速或者停止，而且不會(huì)明顯恢復(fù)原來(lái)的速度。速度限制在60、50和40英里每小時(shí)的影響在圖13.1中的虛線(xiàn)表示出來(lái)。55英里每小時(shí)（88km/h）的曲線(xiàn)也可以畫(huà)在60和50英里每小時(shí)的虛線(xiàn)中來(lái)反映聯(lián)邦政府限制的55英里每小時(shí)的速度的影響。但是因?yàn)閳?zhí)法水平的寬泛和多樣性，這只是推測(cè)而已。車(chē)輛間距，或者它的倒數(shù)，交通密度可能對(duì)通行能力有最大的影響，因?yàn)樗鼘?duì)于司機(jī)形成自由或者約束的感覺(jué)比其他任何因素都要多。對(duì)于司機(jī)的研究顯示，他們跟隨