Slide 1Slide 2Cross Section ElementsComponents of Cross SectionComponents of Cross SectionComponents of Cross SectionComponents of Cross SectionComponents of Cross SectionComponents of Cross SectionComponents of Cross SectionSlide 11Cross SlopeCross SlopeCross SlopeCross SlopeCross SlopeCross SlopeCross SlopeCross SlopeShouldersShouldersShouldersShouldersShouldersShouldersCurbsCurbsCurbsCurbsCurbsCurbsSlideslopesSlideslopesSlideslopesSlideslopesSlideslopesSlideslopesSlideslopesBarriersBarriersCross Section DesignSpring 2017Cross Section DesignLane widthShouldersSide SlopesCurbsTraffic BarriersImportant Definitions:◦Roadway: The portion of a highway, including shoulders, for vehicular use. For instance, a divided highway has two or more roadways◦Traveled Way: The portion of the roadway used for the movement of vehicles, exclusive of shouldersCross Section ElementsComponents of Cross SectionTraveled WayComponents of Cross SectionRoadwayComponents of Cross SectionRight-of-Way: land owned by a government entity for public use (state, local, etc.)Components of Cross SectionClear Zone: Area located between the edge-of-travel way and the location of fixed objects (trees, posts, etc.)Components of Cross SectionUndivided HighwaysComponents of Cross SectionDivided HighwaysComponents of Cross SectionMedianNote: Median measured from edge-of-travel way to edge-of- travel wayLane WidthRange: 9 ft to 12 ft12 ft: most commonly used on rural and urban highways; adequate for most of the heavy vehicle11 ft: acceptable in urban areas (to accommodate pedestrians crosswalk)10 ft: acceptable on low-speed highways9 ft: acceptable on local rural or urban streets (residential)CLUndivided highways (tangent): crown in the middle and a cross slope downward toward both edgesDownward cross slope can be either a plane or a rounded section or bothRounded sections are usually parabolic:◦Advantage: cross slope steepens toward edges◦Disadvantage: difficult to construct; cross slope may be excessive in outer lanesCross SlopeDivided Highways: each one-way traveled way can be crowned separately or can be unidirectional cross slope across the entire traveled wayCrowned roadways have the advantages of rapidly drain water during rainstormsHowever, need to install additional inlets and underground drainage linesPreferred in region of high rainfalls Cross SlopeCross SlopeCrowned for Each DirectionCross SlopeUnidirectional Cross SlopeUnidirectional cross slope provide more comfort to drivers when they change lanesDrainage away from median may effect savings in drainage structures, minimize drainage the inner, high-speed lanesDrainage toward the median will increase costs, but will minimize water on most used lanes of highwaysCross SlopeThe rate of cross slope is an important element in cross-section designTow-lane Highway: 1.5 to 2 percent is acceptable; drivers will have difficulty perceiving this rateFor three or more lanes: start at 0.5 percent and increase by about 0.5 to 1 percent for each successive pair of lanesCross SlopeCross SlopeCross Slope SteeperCross slope steeper than 2 percent for high-speed highways (high type pavement) with a central crowned design should be avoided:◦Abrupt change in centrifugal force◦Trucks may sway (high center of gravity)Exception: 2.5% in areas of intense rainfallThree or more lanes in each direction: 4% max in areas of intense rainfallFor cases where maximum cross slope is used: consideration should be given for grooving and open-graded mixesCross SlopeThe shoulder is the portion of the roadway contiguous with the traveled way that accommodates stopped vehicles, emergency use, and lateral support of subbase, base and surface courses.It can vary from 2 ft to 12 ftTwo types: ◦Graded width: measured from edge of traveled way to intersection of the shoulder slope◦Usable width: actual width that can be used when a driver makes an emergency stopShouldersShouldersShoulders may be surfaced either full or partial width to provide a better all-weather load support than that afforded by native soilsMaterials for shoulders: gravel, shell, crushed rock, mineral and chemical additive, concrete and asphalt pavementsShoulders on minor roads: serves essentially as structural supportNarrow lane width + narrow shoulders are usually associated with higher number of crashes ShouldersAdvantages of well-designed shoulders (rural and urban highways, freeways):◦Space provided for vehicles in the event of an emergency◦Space for motorist to stop occasionally to consult road maps or for other reasons (although illegal in many states)◦Provide space for evasive maneuvers◦Structural support for pavement◦Space for pedestrians and cyclists in urban areasShouldersWidth of shoulders:◦Desirably, provide 1 ft to 2 ft between edge of traveled way and vehicle◦2 ft (low volume) to 12 ft (high speed/high flow)◦Wider may encourage unauthorized use of shoulder◦Shoulders should be continuous ◦Might want to provide wider shoulders every mile or kilometer on elevated structuresShouldersShoulder cross section:◦Shoulder and traveled way must be jointly connected◦Cross Slope:Asphalt/concrete: 2 to 6 percentGravel: 4 to 6 percentTurf: 6 to 8 percent◦Avoid severe cross section break on horizontal curvesDesirable to use different color and texture between shoulders and traveled way (night, inclement weather, etc.)ShouldersCurbs are used for:◦Drainage control◦Roadway edge delineation◦Right-of-way reduction◦Delineation of pedestrian walkwaysThey are mainly used on low-speed roadsThey should be avoided on high-speed highwaysCurbsCurbsCurbsCurbs: defined by vertical and horizontal configurationCurbsVertical curb:-Prevent from vehicles to leave the roadway-Should not be used on high-speed highways-May be used along walls and tunnels6 to 8 inCurbsHorizontal sloping curb:-Mountable by vehicles-Rounded edge allow ease to be mountable during emergency-Will scrap undersides of some vehiclesCurbsHorizontal extruded curb:-Mountable by vehicles-Design to be mountableSideslopes are the area adjacent to the roadway used for drainage purposesThey are also used to ensure roadway stability and allow for recovery for an errant vehicleElements of sideslopes:◦Hinge point◦Foreslope◦Ditch bottom◦BackslopeSlideslopesSlideslopesSlideslopesMay contribute to loss of steering control (vehicle