公路线形设计-外文翻译

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1、GeometricDesignofHighwaysAAlignmentDesignofaroadisshownontheplaneviewandisaseriesofstraightlinescalledtangentsconnectedbycircular.Inmodernpracticeitiscommontointerposetransitionorspiralcurvesbetweentangentsandcircularcurves.Alignmentmustbeconsistent.Suddenchangesfromflattosharpcurvesandlongta

2、ngentsfollowedbysharpcurvesmustbeavoided;otherwise,accidenthazardswillbecreated.Likewise,placingcircularcurvesofdifferentradiiendtoend(compoundcurves)orhavingashorttangentbetweentwocurvesispoorpracticeunlesssuitabletransitionsbetweenthemareprovided.Long,flatcurvesarepreferableatalltimes,asthe

3、yarepleasinginappearanceanddecreasepossibilityoffutureobsolescence.However,alignmentwithouttangentsisundesirableontwo-laneroadsbecausesomedrivershesitatetopassoncurves.Long,flatcurvesshouldbeusedforsmallchangesindirection,asshortcurvesappearas“kink”.Alsohorizontalandverticalalignmentmustbecon

4、sideredtogether,notseparately.Forexample,asharphorizontalcurvebeginningnearacrestcancreateaseriousaccidenthazard.Avehicletravelinginacurvedpathissubjecttocentrifugalforce.Thisisbalancedbyanequalandoppositeforcedevelopedthroughcannotexceedcertainmaximums,andthesecontrolsplacelimitsonthesharpne

5、ssofcurvesthatcanbeusedwithadesignspeed.Usuallythesharpnessofagivencircularcurveisindicatedbyitsradius.However,foralignmentdesign,sharpnessiscommonlyexpressedintermsofdegreeofcurve,whichisthecentralanglesubtendedbya100-ftlengthofcurve.Degreeofcurveisinverselyproportionaltotheradius.Tangentsec

6、tionsofhighwayscarrynormalcrossslope;curvedsectionsaresuperProvisionmustbemadeforgradualchangefromonetotheother.Thisusuallyinvolvesmaintainingthecenterlineofeachindividualroadwayatprofilegradewhileraisingtheouteredgeandloweringtheinneredgetoproducethedesiredsuperisattainedsomedistancebeyondth

7、epointofcurve.Ifavehicletravelsathighspeedonacarefullyrestrictedpathmadeupoftangentsconnectedbysharpcircularcurve,ridingisextremelyuncomfortable.Asthecarapproachesacurve,superbeginsandthevehicleistiltedinward,butthepassengermustremainvertical