Figure 4-7.—Cross section.Road NomenclaturePart of the planning and estimating process ismaking sure your crew has the understanding of roadterminology (fig. 4-5). Before any construction isperformed on a project site, the elevation is known asexisting grade. The driving surface of an existing roadthat is to be replaced is also known as the existing grade.The subgrade of a road is a prepared base for theplacement of base course materials. The base course isa select layer of well-compacted soil that is placed incompacted lifts on top of the subgrade. This compactioncan be accomplished by mechanical stabilization orchemical stabilization. The sufrace course and theshoulders complete the road. The surface course isusually concrete or asphalt and is part of the road thatvehicles travel on. The shoulder of the road performs asa retainer on each side of the surface course and allowsfor an emergency parking area.The crown of the road is an established slope fromthe center line of a roadbed to the outside of theshoulders and allows for excess water to drain from thesurface into either a V-type or flat bottom ditch. The areathat covers the entire width of the road project includingthe ditches is known as the roadway. The roadbed is thesection that includes the surface course and bothshoulders, and the travelway is the surface course thatthe vehicle travels on.Slope RatioThe two most common slopes used in roadconstruction are the backslope and foreslope. Thebackslope extends from the top of the cut at the existinggrade to the bottom of the ditch. The foreslope extendsfrom the outside of the shoulder to the bottom of theditch. The amount of slope in a backslope or foreslopeis the ratio of horizontal distance to vertical distance (fig.4-6). This means that for every 1 foot of vertical (up ordown) distance, the horizontal distance changesproportionally. The following are equations used tocompute slope ratio:1.2.3.If the base and the height are knownfactors, but not the slope, use:Base ÷ Height = Slope(B ÷ H = S)If the slope ratio and height are known factors,but not the base, use:Slope x Height = Base(S x H = B)If the base and the slope ratio are knownfactors, but not the height, use:Base ÷ Slope = Height(B ÷ S = H)Cross SectionsA cross-sectional view (fig. 4-7) that is given for aroad project is a cutaway end view of a proposed stationbetween the left slope and the right slope. Typical crosssections are plotted at any intermediate place wherethere is a distance change in slope along the center linewhere the natural ground profile and grade linecorrespond. The cross section displays the slope limits,slope ratio, horizontal distance between centerlinestakes and shoulder stakes. It also shows the verticaldistance of the proposed cut or fill at the shoulder andcenterline stakes.4-7