铁工专业毕业设计文献翻译.docx

铁工专业毕业设计文献翻译.docx

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铁工专业毕业设计文献翻译

HighwayTypes

Allstatehighwaysystemsandmostofthelocalhighwayandstreetsystemsencompassseveraltypeorclassesofhighway.Atoneextremearehigh-speed,high-volumefacilitiescarryingthoughtraffic,withnoattemptmadetoserveabuttingpropertyorpurelylocaltraffic.Attheotherarelocalruralroadsorstreetsthatcarrylowvolumes,sometimesatlowspeeds,andwithaprimaryfunctionoflandservice.

Definitionsforthevarioustypesofhighways（andformanyotherhighwayterm）werepreparedin1968byan（then）AASHOSpecialcommitteeonNomenclature.ThesearepublishedasAASHOHighwayDefinitions.someoftheseareasfollows:

Expressway-Dividedarterialhighwayforthoughtrafficwithfullorpartialcontrolofaccessandgenerallywithgradeseparationsatmajorintersection.

Freeway-Expresswaywithfullcontrolofaccess.

Parkway-Arterialhighwayfornoncommercialtraffic,withfullorpartialcontrolofaccess.andusuallylocatedwithinaparkoraribbonofparklikedevelopment.

Controlofaccess–Conditionwheretherightofowneroroccupantsofabuttinglandorotherpersonstoaccess.light,air,orviewinconnectionwithahighwayisfullorpartiallycontrolledbypublicauthority.

Fullcontrolofaccessmeansthattheauthoritytocontrolaccessisexercisedtogivepreferencetothoughtrafficbyprovidingaccessconnectionswithselectedpublicroadsonlyandbyprohibitingcrossingsatgradeordirectprivatedrivewayconnections.

Partialcontrolofaccessmeansthattheauthoritytocontrolaccessistogivepreferencetothoughtraffictodegreethat.inadditiontoaccessconnectionswithselectedpublicroads,theremanybesomecrossingsatgradeandsomeprivatedrivewayconnections.

Theotherhighwaytypeslackthefeatureofaccesscontrol.theyinclude:

Majorstreetormajorhighway–Arterialhighwaywithinintersectionsatgradeanddirectaccesstoabuttingproperty,andonwhichgeometricdesignandtraffic–controlmeasuresareusedtoexpeditethesafemovementofthoughtraffic.

Thoughstreetorthoughhighway–Everyhighwayorportionthereofonwhichvehiculartrafficisgivenpreferentialrightofway,andattheentrancestowhichvehiculartrafficfromintersectinghighwaysisrequiredbylawtoyieldrightofwaytovehiclesonsuchthroughhighwayinobediencetoeitherastopsignoryieldsign,whensuchsignsareerected.

Localroad–Streetorroadprimarilyforaccesstoresidence,business,orotherabuttingproperty.

Precisedefinitionforotherhighwaytypessuchasarterial,beltbypass,radial,frontagealsoaregiven,Ingeneralthelabelexplainthefunction.

Itshouldbepointedouthere,however,thatthefreeway,astypifiedbytheInterstateSystemrepresentthehighesttypehighwayfacility,forallotherclassescertainimportantadvantagesmustbesacrificed.Incapsuleform.theseincludethefollowing.

Capacity–Onfreewaytheabsenceofintersectionsorcrossingsatgradetheeliminationofmajorfrictionthroughaccesscontrolpermitunrestricted,full–timeusemovingvehicles,ratherthanrestricted,part–timeflow.

Reducedtraveltime–Onfreeway,timelossesfromstoppingandwaitingatintersectionsareeliminated.Inaddition,mostoftheconflictsthatcontributetoaccidentsareeliminatedexceptunderunusualcircumstances,Driversnormallycanandtravelathigherandsustainedspeeds.

Safeoperation–Onfreeway,eliminationofconflictsatintersectionsandalongbothmarginsoftheroadwayandthebarringofpedestriansfromtherightofwayusuallybringsubstantialreductionsinaccidents.

Permanence–accesscontrolalongfreewaypreventsthegrowthofbusinessesorotheractivitiesalongtheroadwaymargin,Withoutaccesscontrol,theseactivitiesgenerateunorderedtrafficandparking,Inashorttime,capacityisreducedandaccidentpotentialissubstantiallyincreased.

Reducedoperatingcoat,fuelconsumption,airpollution,andnoise-smootheroperationsandfewerstopsreducefuelconsumptionandotheroperatingcostsReducefuelconsumptioninturnreducesairpollution.Smootheroperationwithfewerstopsalsogreatlyreducenoise,particularlythatfromtrucks.

HighwayCrossSection

Theprincipalelementsofahighwaycrosssectionconsistofthetravellanes,shoulders,andmedians（forsomemultilanehighways）.marginalelementsincludemedianandroadsidebarriers,curbs,gutters,guardrails,sidewalks,andsideslopes.

Travellanewidthsusuallyvaryfrom10ftto12ft.mostarterialshave12-fttravellanessincetheextracostforconstructing12-ftlanesover10-ftlanesisusuallyoffsetbythelowermaintenancecostforshouldersandpavementsurface,resultinginthereductionofwheelconcentrationsatthepavementedges.Ontwo-lane,two-wayruralroad.Lanewidthsof10ftor11ftmaybeused,buttwofactorsmustbeconsideredwhenselectingalanewidthlessthan12ftwide,thefirstisthatithasbeenshownthatwhenpavementsurfacearelessthan22ft,theaccidentratesforlargetruckstendtoincrease,Second,thecapacityofahighwaysignificantlydecreasesasthelanewidthiseducedfrom12ft.Lanewidthsof10ftarethereforeusedonlyonlow-speedfacilities.Lanesthatare9ftwideareusedoccasionallyinurbanareasiftrafficvolumeislowandthereareextremeright-of-wayconstraints.

Theshouldersiscontiguouswiththetraveledlaneandprovidesanareaalongthehighwayforvehiclestostop,particularlyduringanemergency.Shouldersarealsousedtolaterallysupportthepavementstructure.theshoulderwidthisknownaseithergradedorusable,dependingonthesectionoftheshoulderbeingconsidered.pavementtotheintersectionoftheshoulderslopeandtheplaneofthesideslope,Theusableshoulderwidthisthatpartofthegradedshoulderthatcanbeusedtoaccommodateparkedvehicle.Theusablewidthisthesameasthegradedwidthwhenthesideslopisequaltoorflatterthan4:

1,astheshoulderbreakisusuallyroundedtoawidthbetween4ftand6ft,therebyincreasingtheusablewidth.

Whenavehiclestopontheshoulder,itisdesirableforittobeatleast1ftandpreferably2ftfromtheedgeofthepavement.Basedonthis,AASHTOrecommendthatusableshoulderwidthofleast10ftandpreferably12ftbeusedonhighwayshavingalargenumberoftrucksandonhighwayswithhightrafficvolumesandhighspeeds.However,itmaynotalwaysbefeasibletoprovidethisminimumwidth,particularlywhentheterrainisdifficultorwhentrafficvolumeislow.Aminimumshoulderwidthof2ftmaythereforebeusedonthelowesttypeofhighways.but6-to8-ftwidthsshouldpreferablybeused.Thewidthforusableshoulderwithinthemedianfordividedarterialshavingtwolaneineachdirection.Howevermaybereducedto3ft,sincediversrarelyusethemedianshoulderforstoppingontheseroads,Theusablemedianshoulderwidthfordividedarterialswiththreeormorelaneineachdirectionshouldbeatleast8ft,sincedriversindifficultyonthelanenexttothemedianoftenfinditdifficulttomaneuvertotheoutsideshoulder.

Itisessentialthatallshouldersbeflushedwiththeedgeofthetraveledlameandbeslopedtofacilitatethedrainageofsurfacewateronthetraveledlanes.Recommendedslopesare2percentto6percentforbituminousandconcrete-surfacedshoulders.and4percentto6percentforgravelorcrushed-rockshoulders.

Amedianisthesectionofadividedhighway,thatseparatesthelanesinopposingdirections,Thewidthofamedianisthedistancebetweentheedgesofedgesoftheinsidelanes,includingthemedianshouldersthefunctionsofamedianinclude:

（1）providingarecoveryareaforout-controlvehicles,

（2）separatingopposingtraffic,（3）providingstoppingareasduringemergencies,（4）providingstorageforleft-turnandU-turningvehicles,（5）providingrefugeforpedestrians,（6）reducingtheeffectofheadlightglare,（7）providingtemporarylanesandcrosss-oversduringmaintenanceoperations.medianscaneitherberaised,flush,ordepressed.Raisedmediansarefrequentlyusedinurbanarterialstreetsbecausetheyfacilitatethecontrolofleft-turntrafficatintersectionsbyusingpartofthemedianwidthforleft-turn-onlylanes.Somedisadvantagesassociatedwithraisedmedianincludepossiblelossofcontrolofthevehiclebythedriverifthemedianisaccidentallystuckandthecastingofashadowfromoncomingheadlights,whichresultsindrivershavingdifficultyseeingthecurb.

Flushmediansarecommonlyusedonurbanarterials.Theycanalsobeusedonfreeways.Butwithamedianbarrier.Tofacilitatedrainageofsurfacewater,theflushmedianshouldbecrowned.Thepracticeinurbanareasofconvertingflushmediansintotwo-wayleft-turnlanesisratherpopular,sincethishelpstoincreasethecapacityoftheurbanhighwaywhileprovidingsomeofthefeaturesofamedian.

Depressedmediansaregenerallyusedonfreewayandaremoreeffectiveindrainingsurfacewater.Asideslopeof6:

1issuggestedfordepressedmedian,althoughaslopeof4;1maybeadequate.

Medianwidthvaryfromaminimumof2ftto80ftormore,medianwidthsshouldbeaswideaspossiblebutshouldbebalancedwiththeotherelementofcrosssectionandthecostinvolved.Ingeneral,thewiderthemedian,themoreeffectiveitisinprovidingsafeoperatingconditions,AASHTOrecommendaminimumwidthof10ftforfour-laneurbanfreeways,whichisadequatefortwo4ftshoulders,andaftmedianbarrier.Aminimumof22ft,preferably26ft,isrecommendedforsixormorelanesoffreeway.

Medianwidthforurbancollectorstreets,however,varyfrom2ftto40ft,dependingonthemediantr