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1、CHAPTER4CROSSSECTIONELEMENTSGENERALToassureconsistencyinthispolicy,theterms“roadway”and“traveledway”aredefinedbyAASHTOasfollows:Roadway:Theportionofahighway,includingshoulders,forvehicularuse.Adividedhighwayhastwoormoreroadways(seeExhibits4-1and4-2).Traveledway:Theportionoftheroadwayforthe
2、movementofvehicles,exclusiveofshoulders(seeExhibits4-1and4-2).PAVEMENTSurfaceTypeTheselectionofpavementtypeisdeterminedbasedonthetrafficvolumeandcomposition,soilcharacteristics,weather,performanceofpavementsinthearea,availabilityofmaterials,energyconservation,initialcost,andtheoverallannua
3、lmaintenanceandservice-lifecost.Thestructuraldesignofpavementsisnotincludedinthispolicy,butisaddressedintheAASHTOGuideforDesignofPavementStructures(1).Importantpavementcharacteristicsthatarerelatedtogeometricdesignaretheeffectondriverbehaviorandtheabilityofasurfacetoretainitsshapeanddimens
4、ions,todrain,andtoretainadequateskidresistance.High-typepavementsretaintheirshapeanddonotravelattheedgesifplacedonastablesubgrade.Theirsmoothnessandpropercross-slopedesignenabledriverstosteereasilyandkeeptheirvehiclesmovingintheproperpath.Attheotherextreme,low-typesurfaceshaveatendencytowa
5、rdraveling,whichreducestheireffectivewidthandrequiresgreatersteeringefforttomaintainacorrectpath.Accordingly,low-typesurfacesareusedwheretrafficvolumeislight.Whiletheselectionofdesignspeedisdependentonmanyfactorsotherthanpavementsurfacetype,high-typesurfacesprovideforhigheroperatingspeedst
6、handolow-typesurfaces.Therefore,thesurfacetypeprovidedshouldbeconsistentwiththeselecteddesignspeedforthehighway.CrossSlopeUndividedtraveledwaysontangents,oronflatcurves,haveacrownorhighpointinthemiddleandacrossslopedownwardtowardbothedges.Unidirectionalcrossslopesacrossthe309AASHTO—Geometr
7、icDesignofHighwaysandStreetsExhibit4-1.TypicalCrossSection,NormalCrown310CrossSectionElementsExhibit4-2.TypicalCrossSection,Superelevated311AASHTO—GeometricDesignofHighwaysandStreetsentirewidthofthetraveledwaymaybeutilized.Thedownwardcrossslopemaybeaplaneorrou
