L3 Geometric design of highways 公路线型设计

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1、L3 Geometric design of highways 公路线型设计 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望Lesson3GeometricdesignofhighwaysvTextAAlignmentDesignvalignmentlanm()ntn.队列，线形；v课文A线路设计vTextBGradesv课文B坡度vTextCSightDistancev课文C视距geometric,dmetrk adj.几何学的v1/9Thealignmento

2、faroadisshownontheplaneviewandisaseriesofstraightlinescalledtangentsconnectedbycircularcurves.Inmodernpracticeitiscommontointerposetransitionorspiralcurvesbetweentangentsandcircularcurves.vTangenttn(d)()ntn.数切线，数正切adj.切线的，相切的；vinterposentpzvi.干预；插入；vtransitiontrnz()n;trn-;-s-n.过渡；转变；vcircularskjladj

3、.循环的；圆形的；vspiralspar()ln.螺旋；旋涡；螺旋形之物adj.螺旋形的；盘旋的vt.使成螺旋形；使作螺旋形上升vi.盘旋；成螺旋形；螺旋形上升（过去式spiraled/spiralled，过去分词spiraled/spiralled，现在分词spiraling/spiralling，第三人称单数spirals，副词spirally）vspiralcurve螺旋曲线vcircularcurve圆形曲线v1/9Thealignmentofaroadisshownontheplaneviewandisaseriesofstraightlinescalledtangentsconne

4、ctedbycircularcurves.vInmodernpracticeitiscommontointerposetransitionorspiralcurvesbetweentangentsandcircularcurves.v翻译？v1/9Thealignmentofaroadisshownontheplaneviewandisaseriesofstraightlinescalledtangentsconnectedbycircularcurves.v翻译v公路的线路显示在平面图上，是一系列由圆曲线连接的切线而成。vInmodernpracticeitiscommontointerpo

5、setransitionorspiralcurvesbetweentangentsandcircularcurves.v翻译v在现代实践（做法）中，在切线和圆曲线之间插入过渡线（螺旋线）是常见做法。v2/9Alignmentmustbeconsistent.Suddenchangesfromflattosharpcurvesandlongtangentsfollowedbysharpcurvesmustbeavoided;otherwise,accidenthazardswillbecreated.Likewise,placingcircularcurvesofdifferentradiien

6、dtoend(compoundcurves)orhavingashorttangentbetweentwocurvesispoorpracticeunlesssuitabletransitionsbetweenthemareprovided.Long,flatcurvesarepreferableatalltimes,astheyarepleasinginappearanceanddecreasepossibilityoffutureobsolescence.However,alignmentwithouttangentisundesirableontwo-laneroadsbecauseso

7、medrivershesitatetopassoncurves.Long,flatcurvesshouldbeusedforsmallchangesindirection,asshortcurvesappearaskink.Alsohorizontalandverticalalignmentmustbeconsideredtogether,notseparately.Forexample,asharphorizontalcurvebeginningnearacrestcancreateaseriousaccidenthazard.v2-1/9vAlignmentmustbeconsistent

8、.Suddenchangesfromflattosharpcurvesandlongtangentsfollowedbysharpcurvesmustbeavoided;otherwise,accidenthazardswillbecreated.Likewise,placingcircularcurvesofdifferentradiiendtoend(compoundcurves)orhavingashorttangentbetweentwocurvesispoorpracticeunlesssuitabletransitionsbetweenthemareprovided.vConsis

9、tentknsst()ntadj.连续的连续的vradiiredan.半径（radius的复数）vcompoundcurve复合曲线vsharpcurve急弯曲线；锐曲线；急弯；小半径曲线vtransitiontrnznn.过渡；转变v2-2/9vLong,flatcurvesarepreferableatalltimes,astheyarepleasinginappearanceanddecreasepossibilityoffutureobsolescence.However,alignmentwithouttangentisundesirableontwo-laneroadsbecaus

10、esomedrivershesitatetopassoncurves.Long,flatcurvesshouldbeusedforsmallchangesindirection,asshortcurvesappearaskink.Alsohorizontalandverticalalignmentmustbeconsideredtogether,notseparately.Forexample,asharphorizontalcurvebeginningnearacrestcancreateaseriousaccidenthazard.flatcurve平缓曲线；平滑曲线；大曲率曲线prefe

11、rableprfrbladj.更好的，更可取的；更胜一筹的pleasingpli:ziadj.令人愉快的；obsolescence,bsulesnsn.废弃；Undesirablendzarb()ladj.不良的；不受欢迎的；kinkkkn.扭结；蜷缩vt.使扭结vi.扭结v2/9Alignmentmustbeconsistent.Suddenchangesfromflattosharpcurvesandlongtangentsfollowedbysharpcurvesmustbeavoided;otherwise,accidenthazardswillbecreated.Likewise,p

12、lacingcircularcurvesofdifferentradiiendtoend(compoundcurves)orhavingashorttangentbetweentwocurvesispoorpracticeunlesssuitabletransitionsbetweenthemareprovided.Long,flatcurvesarepreferableatalltimes,astheyarepleasinginappearanceanddecreasepossibilityoffutureobsolescence.However,alignmentwithouttangen

13、tisundesirableontwo-laneroadsbecausesomedrivershesitatetopassoncurves.Long,flatcurvesshouldbeusedforsmallchangesindirection,asshortcurvesappearaskink.Alsohorizontalandverticalalignmentmustbeconsideredtogether,notseparately.Forexample,asharphorizontalcurvebeginningnearacrestcancreateaseriousaccidenth

14、azard.v3/9Avehicletravelinginacurvedpathissubjecttocentrifugalforce.Thisisbalancedbyanequalandoppositeforcedevelopedthroughsuperelevationandsidefriction.Fromahighwaydesignstandpoint,bothsuperelevationandsidefrictioncannotexceedcertainmaximums,andthesecontrolsplacelimitsonthesharpnessofcurvesthatcanb

15、eusedwithadesignspeed.v3/9Avehicletravelinginacurvedpathissubjecttocentrifugalforce.Thisisbalancedbyanequalandoppositeforcedevelopedthroughsuperelevationandsidefriction.Fromahighwaydesignstandpoint,bothsuperelevationandsidefrictioncannotexceedcertainmaximums,andthesecontrolsplacelimitsonthesharpness

16、ofcurvesthatcanbeusedwithadesignspeed.centrifugal,sentrfjug()l;sentrfjg()ln.离心机；adj.离心的；centrifugalforce离心力sidefriction横向摩擦superelevation,sju:p,eliveinn.（铁路或公路的）超高;弯面倾斜度;道路弯面加倾度超高超高（SuperelevationSuperelevation）公路平曲线路段，为抵销离心力，提高外侧路面之高度standpointstn(d)pntn.立场；观点sharpness:pnisn.锐利；锐度designspeed设计速度v4/

17、9vUsuallythesharpnessofagivencircularcurveisindicatedbyitsradius.However,foralignmentdesign,sharpnessiscommonlyexpressedintermsofdegreeofcurve,whichisthecentralanglesubtendedbya100-ftlengthofcurve.Degreeofcurveisinverselyproportionaltotheradius.v4/9vUsuallythesharpnessofagivencircularcurveisindicate

18、dbyitsradius.However,foralignmentdesign,sharpnessiscommonlyexpressedintermsofdegreeofcurve,whichisthecentralanglesubtendedbysubtendedbya100-ftlengthofcurve.Degreeofcurveisinverselyproportionaltotheradius.vindicatednd,ketdv.v5/9vTangentsectionsofhighwayscarrynormalcrossslope;curvedsectionsaresuperele

19、vated.Provisionmustbemadeforgradualchangefromonetotheother.Thisusuallyinvolvesmaintainingthecenterlineofeachindividualroadwayatprofilegradewhileraisingtheouteredgeandloweringtheinneredgetoproducethedesiredsuperelevation.Wherethealignmentconsistsoftangentsconnectedbycircularcurves,introductionofsuper

20、elevationisbegunontangentbeforethecurveisreached,andfullsuperelevationisattainedsomedistancebeyondthepointofcurve.vtangentsectionv5/9vTangentsectionsofhighwayscarrynormalcrossslope;curvedsectionsaresuperelevated.Provisionmustbemadeforgradualchangefromonetotheother.vThisusuallyinvolvesmaintainingthec

21、enterlineofeachindividualroadwayatprofilegradewhileraisingtheouteredgeandloweringtheinneredgetoproducethedesiredsuperelevation.vWherethealignmentconsistsoftangentsconnectedbycircularcurves,introductionofsuperelevationisbegunontangentbeforethecurveisreached,andfullsuperelevationisattainedsomedistance

22、beyondthepointofcurve.v6-1/9Ifavehicletravelsathighspeedonacarefullyrestrictedpathmadeupoftangentsconnectedbysharpcircularcurve,ridingisextremelyuncomfortable.Asthecarapproachesacurve,superelevationbeginsandthevehicleistiltedinward,butthepassengermustremainverticalsincethereisnocentrifugalforcerequi

23、ringcompensation.Whenthevehiclereachesthecurve,fullcentrifugalforcedevelopsatonce,andpullstherideroutwardfromhisverticalposition.Toachieveapositionofequilibriumhemustforcehisbodyfarinward.Astheremainingsuperelevationtakeseffect,furtheradjustmentinpositionisrequired.Thisprocessisrepeatedinreverseorde

24、rasthevehicleleavesthecurve.Wheneasementcurvesareintroduced,thechangeinradiusfrominfinityonthetangenttothatofthecircularcurveiseffectedgraduallysothatcentrifugalv6-2/9forcealsodevelopsgradually.Bycarefulapplicationofsuperelevationalongthespiral,asmoothandgradualapplicationofcentrifugalforcecanbehada

25、ndtheroughness(canbe)avoided.approachprtn.方法；途径；接近;vt.接近；vi.靠近tilttltn.倾斜vt.使倾斜；使翘起vi.倾斜；翘起takeeffect生效；起作用easementizm()ntn.缓和；减轻easementcurve缓和曲线farfadj.远的；久远的adv.很；遥远地；到很远的距离；到很深的程度n.远方v6-1/9vIfavehicletravelsathighspeedonacarefullyrestrictedpathmadeupoftangentsconnectedbysharpcircularcurve,riding

26、isextremelyuncomfortable.vAsthecarapproachesacurve,superelevationbeginsandthevehicleistiltedinward,butthepassengermustremainverticalsincethereisnocentrifugalforcerequiringcompensation.vWhenthevehiclereachesthecurve,fullcentrifugalforcedevelopsatonce,andpullstherideroutwardfromhisverticalposition.Toa

27、chieveapositionofequilibriumhemustforcehisbodyfarinward.vAstheremainingsuperelevationtakeseffect,furtheradjustmentinpositionisrequired.v6-2/9vThisprocessisrepeatedinreverseorderasthevehicleleavesthecurve.vWheneasementcurvesareintroduced,thechangeinradiusfrominfinityonthetangenttothatofthecircularcur

28、veiseffectedgraduallysothatcentrifugalforcealsodevelopsgradually.vBycarefulapplicationofsuperelevationalongthespiral,asmoothandgradualapplicationofcentrifugalforcecanbehadandtheroughness(canbe)avoided.Approachprtn.方法；途径；接近vt.接近；着手处理vi.靠近tilttltn.倾斜vt.使倾斜；使翘起vi.倾斜；翘起takeeffect生效；起作用easementizm()ntn.缓

29、和；减轻easementcurve缓和曲线v7/9vEasementcurveshavebeenusedbytherailroadsformanyyears,buttheiradoptionbyhighwayagencieshasbecomeonlyrecently.Thisisunderstandable.Railroadtrainsmustfollowtheprecisealignmentofthetracks,andthediscomfortdescribedherecanbeavoidedonlybyadoptingeasementcurves.Ontheotherhand,themo

30、tor-vehicleoperatorisfreetoalterhislateralpositionontheroadandcanprovidehisowneasementcurvesbysteeringintocircularcurvesgradually.However,thisweavingwithinatrafficlane(butsometimesintootherlane)isdangerous.Properlydesignedeasementcurvesmakeweavingunnecessary.Itislargelyforsafetyreasons,then,thatease

31、mentcurveshavebeenwidelyadoptedbyhighwayagencies.vRailroadsn.铁v7/9vEasementcurveshavebeenusedbytherailroadsformanyyears,buttheiradoptionbyhighwayagencieshasbecomeonlyrecently.vThisisunderstandable.Railroadtrainsmustfollowtheprecisealignmentofthetracks,andthediscomfortdescribedherecanbeavoidedonlybya

32、doptingeasementcurves.vOntheotherhand,themotor-vehicleoperatorisfreetoalterhislateralpositionontheroadandcanprovidehisowneasementcurvesbysteeringintocircularcurvesgradually.vHowever,thisweavingwithinatrafficlane(butsometimesintootherlane)isdangerous.Properlydesignedeasementcurvesmakeweavingunnecessa

33、ry.vItislargelyforsafetyreasons,then,thateasementcurveshavebeenwidelyadoptedbyhighwayagencies.v8/9vForthesameradiuscircularcurve,theadditionofeasementcurvesattheendschangesthelocationofthecurvewithrelationtoitstangents;hencethedecisionregardingtheiruseshouldbemadebeforethefinallocationsurvey.Thepoin

34、tofbeginningofanordinarycircularcurveisusuallylabeledthePC(pointofcurve)orBC(beginningofcurve).ItsendismarkedthePT(pointoftangent)orEC(endofcurve).Forcurvesthatincludeeasements,thecommonnotationis,asstationingincreases:TS(tangenttospiral),SC(spiraltocircularcurve),CS(circularcurvetospiral),andST(spi

35、raltotangent).v8/9vForthesameradiuscircularcurve,theadditionofeasementcurvesattheendschangesthelocationofthecurvewithrelationtoitstangents;hencethedecisionregardingtheiruseshouldbemadebeforethefinallocationsurvey.vThepointofbeginningofanordinarycircularcurveisusuallylabeledthePC(pointofcurve)orBC(be

36、ginningofcurve).ItsendismarkedthePT(pointoftangent)orEC(endofcurve).vForcurvesthatincludeeasements,thecommonnotationis,asstationingincreases:TS(tangenttospiral),SC(spiraltocircularcurve),CS(circularcurvetospiral),andST(spiraltotangent).labelleb()ln.标签；vt.标注；贴标签于notationnte()nn.符号；Stationingn.驻军v.驻扎（

37、station的ing形式）;布点;定位v9/9vOntwo-lanepavementsprovisionofawilderroadwayisadvisableonsharpcurves.Thiswillallowforsuchfactorsas(1)thetendencyfordriverstoshyawayfromthepavementedge,(2)increasedeffectivetransversevehiclewidthbecausethefrontandrearwheelsdonottrack,and(3)addedwidthbecauseoftheslantedpositio

38、nofthefrontofthevehicletotheroadwaycenterline.For24-ftroadways,theaddedwidthissosmallthatitcanbeneglected.Onlyfor30mphdesignspeedsandcurvessharperthan22(degree)doestheaddedwidthreach2ft.Fornarrowerpavements,however,wideningassumesimportanceevenonfairlyflatcurves.Recommendedamountsofandproceduresforc

39、urvewideningaregiveninGeometricDesignforHighways.vprovisionprovisionprv()nn.v9/9vOntwo-lanepavementsprovisionofawilderroadwayisadvisableonsharpcurves.vThiswillallowforsuchfactorsas(1)thetendencyfordriverstoshyawayfromthepavementedge,(2)increasedeffectivetransversevehiclewidthbecausethefrontandrearwh

40、eelsdonottrack,and(3)addedwidthbecauseoftheslantedpositionofthefrontofthevehicletotheroadwaycenterline.vFor24-ftroadways,theaddedwidthissosmallthatitcanbeneglected.Onlyfor30mphdesignspeedsandcurvessharperthan22(degree)doestheaddedwidthreach2ft.vFornarrowerpavements,however,wideningassumesimportancee

41、venonfairlyflatcurves.RecommendedamountsofandproceduresforcurvewideningaregiveninGeometricDesignforHighways.vFinishLesson 3 Geometric design of highways vText A Alignment Designvalignment lanm()nt n.队列，线形；v课文A 路线设计vText B Gradesv课文B 坡度vText C Sight Distancev课文C 视距v1/9vTheverticalalignmentoftheroadwa

42、yanditseffectonthesafeandeconomicaloperationofthemotorvehicleconstituteoneofthemostimportantfeaturesofroaddesign.Theverticalalignment,whichconsistsofaseriesofstraightlinesconnectedbyverticalparabolicorcircularcurves,isknownasthe“gradeline”.Whenthegradelineisincreasingfromthehorizontalitisknownasa“pl

43、usgrade”,andwhenitisdecreasingfromthehorizontalitisknownasa“minusgrade”.Inanalyzinggradeandgradecontrols,thedesignerusuallystudiestheeffectofchangeingradeonthecenterlineprofile.vNewwordsandexpressionsvGradev1/9vTheverticalalignmentoftheroadwayanditseffectonthesafeandeconomicaloperationofthemotorvehi

44、cleconstituteoneofthemostimportantfeaturesofroaddesign.vTheverticalalignment,whichconsistsofaseriesofstraightlinesconnectedbyverticalparabolicorcircularcurves,isknownasthe“gradeline”.vWhenthegradelineisincreasingfromthehorizontalitisknownasa“plusgrade”,andwhenitisdecreasingfromthehorizontalitisknown

45、asa“minusgrade”.vInanalyzinggradeandgradecontrols,thedesignerusuallystudiestheeffectofchangeingradeonthecenterlineprofile.v2/9vIntheestablishmentofagrade,anidealsituationisoneinwhichthecutisbalancedagainstthefillwithoutagreatdealofborroworanexcessofcuttobewasted.Allhaulsshouldbedownhillifpossibleand

46、nottoolong.Thegradeshouldfollowthegeneralterrainandriseandfallinthedirectionoftheexistingdrainage.Inmountainouscountrythegrademaybesettobalanceexcavationagainstembankmentasacluetowardleastoverallcost.Inflatorprairiecountryitwillbeapproximatelyparalleltothegroundsurfacebutsufficientlyaboveittoallowsu

47、rfacedrainageand,wherenecessary,topermitthewindtocleardriftingsnow.Wheretheroadapproachesorfollowsalongstreams,theheightofthegradelinemaybedictatedbytheexpectedleveloffloodwater.Underallconditions,smooth,flowinggradelinesarepreferabletochoppyonesofmanyshortstraightsectionsconnectedwithshortverticalc

48、urves.vbalanceagainstvTowardtwd;twd;tdprep.v2-1/9vIntheestablishmentofagrade,anidealsituationisoneinwhichthecutisbalancedagainstthefillwithoutagreatdealofborroworanexcessofcuttobewasted.vAllhaulsshouldbedownhillifpossibleandnottoolong.vThegradeshouldfollowthegeneralterrainandriseandfallinthedirectio

49、noftheexistingdrainage.v2-2/9vInmountainouscountrythegrademaybesettobalanceexcavationagainstembankmentasacluetowardleastoverallcost.vInflatorprairiecountryitwillbeapproximatelyparalleltothegroundsurfacebutsufficientlyaboveittoallowsurfacedrainageand,wherenecessary,topermitthewindtocleardriftingsnow.

50、vWheretheroadapproachesorfollowsalongstreams,theheightofthegradelinemaybedictatedbytheexpectedleveloffloodwater.vUnderallconditions,smooth,flowinggradelinesarepreferabletochoppyonesofmanyshortstraightsectionsconnectedwithshortverticalcurves.v3/9vChangesofgradefromplustominusshouldbeplacedincuts,andc

51、hangesfromaminusgradetoaplusgradeshouldbeplacedinfills.Thiswillgenerallygiveagooddesign,andmanytimesitwillavoidtheappearanceofbuildinghillsandproducingdepressionscontrarytothegeneralexistingcontoursoftheland.Otherconsiderationsfordeterminingthegradelinemaybeofmoreimportancethanthebalancingofcutsandf

52、ills.v3/9vChangesofgradefromplustominusshouldbeplacedincuts,andchangesfromaminusgradetoaplusgradeshouldbeplacedinfills.vThiswillgenerallygiveagooddesign,andmanytimesitwillavoidtheappearanceofbuildinghillsandproducingdepressionscontrarytothegeneralexistingcontoursoftheland.vOtherconsiderationsfordete

53、rminingthegradelinemaybeofmoreimportancethanthebalancingofcutsandfills.Depressiondpre()nn.洼地；v4/9vUrbanprojectsusuallyrequireamoredetailedstudyofthecontrolsandfineradjustmentofelevationsthandoruralprojects.Itisoftenbesttoadjustthegradetomeetexistingconditionsbecauseoftheadditionalexpenseofdoingother

54、wise.urbanproject城市项目additionalexpense附加费用；额外开支v5/9vIntheanalysisofgradeandgradecontrol,oneofthemostimportantconsiderationsistheeffectofgradesontheoperatingcostsofthemotorvehicle.Anincreaseingasolineconsumptionandareductioninspeedareapparentwhengradesareincreased.Aneconomicalapproachwouldbetobalance

55、theaddedannualcostofgradereductionagainsttheaddedannualcostofvehicleoperationwithoutgradereduction.Anaccuratesolutiontotheproblemdependsontheknowledgeoftrafficvolumeandtype,whichcanbeobtainedonlybymeansofatrafficsurvey.voperatingcostsv5/9vIntheanalysisofgradeandgradecontrol,oneofthemostimportantcons

56、iderationsistheeffectofgradesontheoperatingcostsofthemotorvehicle.vAnincreaseingasolineconsumptionandareductioninspeedareapparentwhengradesareincreased.vAneconomicalapproachwouldbetobalancetheaddedannualcostofgradereductionagainsttheaddedannualcostofvehicleoperationwithoutgradereduction.vAnaccurates

57、olutiontotheproblemdependsontheknowledgeoftrafficvolumeandtype,whichcanbeobtainedonlybymeansofatrafficsurvey.v6/9vWhilemaximumgradesvaryagreatdealinvariousstates,AASHTOrecommendationsmakemaximumgradesdependentondesignspeedandtopography.Presentpracticelimitsgradesto5percentofadesignspeedof70mph.Forad

58、esignspeedof30mph,maximumgradestypicallyrangefrom7to12percent,dependingontopography.vAASHTO:AmericanAssociationofStateHighwayandTransportationOfficialsv6/9vWhilemaximumgradesvaryagreatdealinvariousstates,AASHTOrecommendationsmakemaximumgradesdependentondesignspeedandtopography.vPresentpracticelimits

59、gradesto5percentofadesignspeedof70mph.vForadesignspeedof30mph,maximumgradestypicallyrangefrom7to12percent,dependingontopography.v7/9vWhereverlongsustainedgradesareused,thedesignershouldnotsubstantiallyexceedthecriticallengthofgradewithouttheprovisionofclimbinglanesforslow-movingvehicles.Criticalgrad

60、elengthsvaryfrom1700ftfora3percentgradeto500ftforan8percentgrade.criticallength临界长度Gradelength坡长criticalgrade临界坡度Substantiallysbstn()ladv.实质上；大体上；大幅度provisionprv()nn.规定；条款；准备vt.供给食物及必需品climbinglane爬坡车道;爬坡道;慢车线v7/9vWhereverlongsustainedgradesareused,thedesignershouldnotsubstantiallyexceedthecriticall

61、engthofgradewithouttheprovisionofclimbinglanesforslow-movingvehicles.vCriticalgradelengthsvaryfrom1700ftfora3percentgradeto500ftforan8percentgrade.vv7/9vWhereverlongsustainedgradesareused,thedesignershouldnotsubstantiallyexceedthecriticallengthofgradewithouttheprovisionofclimbinglanesforslow-movingv

62、ehicles.vCriticalgradelengthsvaryfrom1700ftfora3percentgradeto500ftforan8percentgrade.vv8/9vLongsustainedgradesshouldbelessthanthemaximumgradeusedonanyparticularsectionofahighway.Itisoftenpreferredtobreakthelongsustaineduniformgradebyplacingsteepergradesatthebottomandlighteningthegradenearthetopofth

63、eascent.Dipsintheprofilegradeinwhichvehiclesmaybehiddenfromviewshouldalsobeavoided.v8/9vLongsustainedgradesshouldbelessthanthemaximumgradeusedonanyparticularsectionofahighway.vItisoftenpreferredtobreakthelongsustaineduniformgradebyplacingsteepergradesatthebottomandlighteningthegradenearthetopoftheas

64、cent.vDipsintheprofilegradeinwhichvehiclesmaybehiddenfromviewshouldalsobeavoided.vv8/9vLongsustainedgradesshouldbelessthanthemaximumgradeusedonanyparticularsectionofahighway.vItisoftenpreferredtobreakthelongsustaineduniformgradebyplacingsteepergradesatthebottomandlighteningthegradenearthetopoftheasc

65、ent.vDipsintheprofilegradeinwhichvehiclesmaybehiddenfromviewshouldalsobeavoided.v长v9/9vMaximumgradeforhighwayis9percent.Standardssettingminimumgradesareofimportanceonlywhensurfacedrainageisaproblemaswhenwatermustbecarriedawayinagutterorroadsideditch.InsuchinstancestheAASHTOsuggestsaminimumof0.35%.su

66、rfacedrainage路面排水guttergtn.排水沟；槽roadsideditch公路边沟v9/9vMaximumgradeforhighwayis9percent.vStandardssettingminimumgradesareofimportanceonlywhensurfacedrainageisaproblemaswhenwatermustbecarriedawayinagutterorroadsideditch.vInsuchinstancestheAASHTOsuggestsaminimumof0.35%.surfacedrainage路面排水guttergtn.排水沟；槽roadsideditch公路边沟vv9/9vMaximumgradeforhighwayis9percent.v