公路通行能力和服务水平 毕业论文外文翻译

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1、HighwayCapacityAndLevelsofServiceCapacityDefinedAgeneralizeddefinitionofcapacityis:Thecapacityofanyelementofthehighwaysystemisthemaximumnumberofvehicleswhichhasareasonableexpectationofpassingoverthatsection(ineitheroneorbothdirections)duringagiventimeperiodunderprevailingroadwayandtrafficconditions.

2、Asamplingofcapacitiesformodernhighwayelementsisasfollows:FacilityCapacityinPassengerCarsFreewaysandexpresswaysawayfromrampsandweavingsections,perlaneperhour2000Two-Lanehighways,totalinbothdirections,perhour2000Three-lanehighways,totalineachdirection,perhour2000Twelve-footlaneatsignalizedintersection

3、,perhourofgreensignaltime(nointerferenceandidealprogression)1800Intreatingcapacity，TRBCircular212dividesfreewaysintocomponents:basicfreewaysegmentsandthoseinthezoneofinfluenceofweavingareasandrampjunctions.Capacitiesofexpressways，multilanehighways，andtwo-andthree-lanefacilitiesalsohavethetwocomponen

4、ts:basicandthoseinthezoneofinfluenceofintersections.Eachoftheseistreatedseparatelybelow.Speed-Volume-CapacityRelationshipsforBasicFreewayandMultilaneHighwaySegmentsAknowledgeoftherelationshipsamongspeed，volume，andcapacityisbasictounderstandingtheplaceofcapacityinhighwaydesignandoperation.Figurel3.1，

5、whichgivessucharelationshipforasinglefreewayorexpresswaylane,isusedforillustrativepurposes.Ifalonevehicletravelsalongatrafficlane，thedriverisfreetoproceedatthedesignspeed.ThissituationisrepresentedatthebeginningoftheappropriatecurveattheupperleftofFig.13.1.Butasthenumberofvehiclesinthelaneincreases,

6、thedriver'sfreedomtoselectspeed7isrestricted.Thisrestrictionbringsaprogressivereductioninspeed.Forexample，manyobservationshaveshownthat，forahighwaydesignedfor70mph(113km/h)，whenvolumereaches1900passengercarsperhour，trafficisslowedtoabout43mph(69km/h).Ifvolumeincreasesfurther,therelativelystablenorma

7、l-flowconditionusuallyfoundatlowervolumesissubjecttobreakdown.ThiszoneofinstabilityisshownbytheshadedareaontherightsideofFig.13.1.Onepossibleconsequenceisthattrafficflowwillstabilizeatabout2000vehicle