19 Cross Sections

1CrossSectionsCE453Lecture19IowaDOTDesignManual23SeealsoIowaDOTStandardPlans4Objectives1.IdentifycrosssectioncomponentsanddesigncriteriaSee:(Chapter6fromFHWA’sFlexibilityinHighwayDesign)5CrossSectionElements1.Roadway2.Median3.RoadsideRoadwayComponents1.TravelLanes2.ShouldersSource::Volumeandcomposition(percenttrucks,buses,andrecreationalvehicles)ofthevehiculartrafficlikelihoodofbicyclistsandpedestriansusingtherouteFlexibilityinHighwayDesign-Chapter68ConsiderationsforDesignofCross-SectionClimaticconditions(storagespaceforplowedsnow,amountofrain)Presenceofnaturalorhuman-madeobstructionsadjacenttotheroadway(rockcliffs,etc)TypeandintensityofdevelopmentalongthefacilitySafetyoftheusers(speedoftraffic)9TravelLanesFunction:guidancetodriversandvehiclesupportPavementtypes:high(modernstandards),intermediate(surfacetreatments),andlow(unpaved)10TravelLanesSelectionCriteria:TrafficvolumeandcompositionSoilcharacteristicsPastperformanceinareaAvailabilityofmaterialsEnergyconservationInitialcostMaintenancecostOveralllife-cyclecost11CrossSlopeSlopeperpendiculartoflowoftrafficontangentsectionRural–normalcrown–uniformslopefromcentertoedgeofpavement(crossslopebreaktypicallyatcenterline)Urban–normalcrownorparabolicshape(guttercapacity)12CrossSlope•RateofCrossSlope=f(drainage,steering,androlloverorcrossslopebreak)•Driverscrossthecrownlineduringpassingmaneuvers•Difficulttonegotiatesteepslopes•AASHTORecommends•High1.5to2%(0.015ft/ftorm/m)•Intermediate1.5to3%•Low2to6%1314UrbanCross-Sections15UrbanCross-Sections16HMACross-Sections17DrainageConsiderations18DrainageConsiderations19RoadwayComponent–TravelLane•LaneWidthConsiderations•Whatistheimpactofweatheroncrossslopedesign?•Safety:Allowsteeringadjustmentandlateralclearance•Pavementedgecrumbling(deterioration)lesswithwidelane•Cost/Benefit(dependsontraffic)•BicycleUse20LaneWidthMinimumlimitedbyphysicaldimensionofvehicles12ftdesirable11ftacceptableinurbanareaswithrestrictions10ftokayforlowspeed/urbanroadways9ft–okaylowvolumeruralandresidentialroadways14ft–sharedoutsidelanewithbikeTWLTL10–16ft(3.0–4.8m)Auxiliary10ft.(3.0m)ormoreIowaDOTlikes14feet,stripedat12feet21Shoulders•Functions:•LateralSupport•AvoidanceSpace•EmergencyStop•Ped/BikeUse•Turning/PassingatIntersections•MailDelivery,Buses,etc.FlexibilityinHighwayDesign-Chapter622ShouldersShouldbeflushwithroadwaysurfaceSlopedtodrainawayfromtraveledwayShouldbestableenoughtosupportvehiclesinallkindsofweatherw/outruttingShouldbevisiblydifferentfromtraveledway23Paved/Unpaved(earth,turf,gravel)GradedandusablewidthdependsonforeslopeandroundingConsiderfunction,safety,andcapacityimpactsSlope2to6%(paved)4to6%(gravel)8%(turf)Min.2%+laneslopeMaxcrossover8%Width0.6–3.6m(2–12ft)Shouldergeometry24Source:APolicyonGeometricDesignofHighwaysandStreets(TheGreenBook).Washington,DC.AmericanAssociationofStateHighwayandTransportationOfficials,20014thEd.25CurbsControlaccessControldrainageTypeusedvarieswithlocationanddesignspeed26Curbs27Curbs28Iowa’sRoadway-RelatedFatalCrashes52%ofIowa’sfatalitiesarerelatedtoLaneDeparture39%ofIowa’sfatalcrashesaresingle-vehicleRun-Off-the-Road(ROR)crashes29SafetyInvestmentStrategyCandidateSafetyProjectsPavedshouldersMilled-inshoulderrumblestrips2-laneshoulderwideningHighseveritycrashintersectionsHighseveritycrash2-laneroadsHighcrashcurvesExpresswayintersectionsCenterlinerumblestripsCross-medianhead-oncrashes304FootPavedShoulderUS6331MilledShoulderRumbleStrips32MedianFunctionFlexibilityinHighwayDesign-Chapter6►Separateopposingtraffic►Drainage►Aesthetics►Spaceforfuturelanes►Recovery►Accesscontrol►Minimizeheadlightglare33MedianTypes/GeometryDepressed(ruralarterials,6:1preferred,4:1min)Raised(urbanarterials)Flush(urban/sub.somerural)DoubleyellowtolimitaccessTWLTLWidthisdeterminedbyFunctionSafetyNeedforindependentdesignFlexibilityinHighwayDesign-Chapter634IowaDOTUrbanDesignAidsSee*GuidelinesSee*Resurfacing,Restoration,Rehabilitation36RuralDesign-NewConstruction