Unit7SuperelevationandWideningofCurves翻译

Unit7SuperelevationandWideningofCurves第七单元道路的超高与加宽SuperelevationisthebankingofaroadwayaroundacurveasillustratedinFigure7-1.Thepurposeofemployingsuperelevationoftheroadwaycrosssectionistocounterbalancethecentrifugalforce,oroutwardpull,ofavehicletraversingahorizontalcurve.Sidefrictiondevelopedbetweenthetiresandtheroadsurfacealsoconterbalancestheoutwardpullofthevehicle.Acombinationofthesetwoconceptsallowsavehicletonegotiatecurvessafelyathigherspeedsthanwouldotherwisebepossible.如图7-1所示，超高是道路曲线段的路堤。道路横断面的超高设计是为了让车辆经过水平断面曲线时能抵抗离心力，或者是向外的拉力。轮胎与道路表面产生的侧向摩擦力也能抵抗车辆的拉力。这两种概念的结合使得车辆在较高的车速下有可能能够安全通过曲线段。Incorporatingsuperelevationintoaroadway’sdesignmayhelpavoidroadsideobstaclesthatmightotherwisetobeimpactedbythealignment.Incontrast,superelevationmaynotbedesirableforlow-speedroadwaystohelplimitexcessivespeedsorinurbansettingstolimitimpactstoabuttingusesordrainagesystemsandutilities.Moreover,superelevationmaynotbedesirablewhenconsideringpedestrianorbicycleaccommodationsalongtheroadwaysegment.Likeotherroadwaydesignelements,designersmustconsiderthetrade-offsofintroducingsuperelevationinaroadway’sdesign.将道路超高与道路设计相结合可能会解决道路线型影响而产生的问题。然而，设计时速较低打的道路最好不设置超高，以避免行驶速度过快，同时城市道路也不宜设置超高，以减少对周围环境，排水系统以及公共设施的影响。除此之外，考虑行人或者骑自行车的人的路段也不宜设置超高。与其它道路设计因素一样，设计者们必须考虑道路设计中是否需要设置超高。7.1MaximumSuperelevationRates最大超高值Themaximumratesofsuperelevationusedonhighwaysarecontrolledbyfourfactors:climateconditions(i.e.,frequencyandamountofsnowandice);terrainconditions(i.e.,flat,rolling,ormountainous);typeofarea(i.e.ruralorurban);andfrequencyofveryslow-movingvehicleswhoseoperationmightbeaffectedbyhighsuperelevationratesic.Considerationofthesefactorsjointlyleadstotheconclusionthatnosinglemaximumsuperelevationrateisuniversallyapplicableandthatarangeofvaluesshouldbeused.However,usingonlyonemaximumsuperelevationratewithinaregionofsimilarclimateandlanduseisdesirable,assuchapracticepromotesdesignconsistency.公路中的最大超高值由四个因素控制：气候条件（比如降雪，结冰的频率和多少）；地形条件（比如平原，丘陵或山区）；地区类型（比如乡村或者城市）；时速很慢且操作易受超高影响的车辆使用道路的频率。考虑到这些因素会共同导致一个结果，那就是没有一个公用的最大超高值能适用于所有的道路，只有一个超高值范围。然而，在一个气候与地质相似的区域，使用一个最大超高值是理想的，因为该做法能保证设计一致性。Thehighestsuperelevavtionrateforhighwaysincommonuseis10percent,although12percentisusedinsomecases.Superelevationratesabove8percentareonlyusedinareaswithoutsnowandice.Althoughhighersuperelevationratesofferanadvantagetothosedriverstravellingathighspeed,currentpracticeconsidersthatratesinexcessof12percentarebeyondpracticallimits.Thispracticerecognizesthecombinedeffectsofconstructionprocess,maintenancedifficulties,andoperationofvehiclesatlowspeeds.尽管有些案例中使用的最大超高值是12%，但是公路最大超高值通常来说是10%。仅在一些没有降雪，结冰的地方道路超高值才会在8%以上。尽管更大的超高值会给高速行驶的驾驶员带来好处，但超高值超过12%会使得时速超过目前的限制速度。超高值超过12%会影响施工过程，给道路维修带来困难，车辆难以低速行驶。Wheretrafficcongestionorextensivemarginaldevelopmentactstorestricttopspeeds,itiscommonpracticetoutilizealowmaximumrateofsuperelevationusually4to6percent.Similarly,eitheralowmaximumrateofsuperelevationornosuperelevatiomisemployedwithinimportantintersectionareasorwherethereisatendencytodriveslowlybecauseofturningandcrossingmovements,warningdevices,andsignals.Intheseareasitisdifficulttowarpcrossingpavementsfordrainagewithoutprovidingnegativesuperelevationforsometurningmovements.对于交通拥堵或者大面积的微弱发展会限制最大时速的路段，通常会使用小的最大超高值，即4%-6%。同样的，在重要的十字路口，或者由于转弯或者斑马线，报警装置或者信号而需要缓慢行驶的地方可以使用小的最大超高值或者不设置超高。在这些地方，因为排水问题，不在某些转弯处设置反超高难以使交叉路口路面弯曲。Insummary,itisrecommendedthat总而言之，有以下建议(1)severalrates,ratherthanasinglerate,ofmaximumsuperelevationshouldberecognizedinestablishingdesigncontrolsforhighwaycurves;在确定公路曲线段设计控制因素时，应知道有多个而非一个最大超高值；(2)arateof12percentshouldnotbeexceeded;最大超高值不应超过12%；(3)arateof4or6percentisapplicableforurbandesigninareaswithlittleornoconstraints;在限制较少或者没有限制的的地方最大超高值可在4%-6%之间；(4)superelevationmaybeomittedonlow-speedurbanstreetswheresevereconstraintsarepresent.在设计时速低，有严格限制的城市街道不应该设置超高。7.2MethodsofAttainingSuperelevation实现超高的方法Fourmethodsareusedtotransitionthepavementtoasuperelevatedcrosssection.Thesemethodsinclude:将路面转变为超高的横坡度的4种方法。包括：(1)revolvingatraveledwaywithnormalcrossslopesaboutthecenterlineprofile;(2)revolvingatraveledwaywithnormalcrossslopesabouttheinside-edgeprofile;(3)revolvingatraveledwaywithnormalcrossslopesabouttheoutside-edgeprofile;(4)revolvingastraightcross-slopetraveledwayabouttheoutside-sideedgeprofile.将正常横坡度的行车道绕道路中心线旋转将正常横坡度的行车道绕行车道内侧边缘旋转将正常横坡度的行车道绕行车道外侧边缘旋转将单一直线横坡的行车道绕行车道外侧边缘旋转Figure7-2illustratesthesefourmethods.Themethodsofchangingcrossslopearemostconvenientlyintermsofstraightlinerelationship,butitisemphasizedthattheangularbreaksbetweenthestraight-lineprofilesaretoberoundedinthefinisheddesign.图7-2说明了这四种方法。就直线而言，改变横坡度是最简便的方法，但是这种方法强调在最终确定的设计中直线型行车道之间的断裂角是圆形的。Theprofilereferencelinecontrolsfortheroadway’sverticalalignmentthroughthehorizontalcurve.AlthoughshownasahorizontallineinFigure7-2,theprofilereferencelinemaycorrespondtoatangent,averticalcurve,oracombinationofthetwo.Figure7-2a),theprofilereferencelinecorrespondstothecenterlineprofile.InFigure7-2b)andFigure7-2c),theprofilereferencelineisrepresentedasa“theoretical”centerlineprofileasitdoesnotcoincidewiththeaxisofrotation.InFi