Road Nomenclature

Figure 4-9.-Area of a square and rectangle.

Equipment Operator Advanced - Advanced construction equipmet operators manual
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Figure 4-7.—Cross section. Road Nomenclature Part of the planning and estimating process is making sure your crew has the understanding of road terminology (fig. 4-5). Before any construction is performed on a project site, the elevation is known as existing grade. The driving surface of an existing road that is to be replaced is also known as the existing grade. The subgrade of a road is a prepared base for the placement of base course materials. The base course is a select layer of well-compacted soil that is placed in compacted lifts on top of the subgrade. This compaction can be accomplished by mechanical stabilization or chemical stabilization. The sufrace course and the shoulders complete the road. The surface course is usually concrete or asphalt and is part of the road that vehicles travel on. The shoulder of the road performs as a retainer on each side of the surface course and allows for an emergency parking area. The crown of the road is an established slope from the center line of a roadbed to the outside of the shoulders and allows for excess water to drain from the surface into either a V-type or flat bottom ditch. The area that covers the entire width of the road project including the ditches is known as the roadway. The roadbed is the section that includes the surface course and both shoulders, and the travelway is the surface course that the vehicle travels on. Slope Ratio The two most common slopes used in road construction are the backslope and foreslope. The backslope extends from the top of the cut at the existing grade to the bottom of the ditch. The foreslope extends from the outside of the shoulder to the bottom of the ditch. The amount of slope in a backslope or foreslope is the ratio of horizontal distance to vertical distance (fig. 4-6). This means that for every 1 foot of vertical (up or down) distance, the horizontal distance changes proportionally. The following are equations used to compute slope ratio: 1. 2. 3. If the base and the height are known factors, 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 known factors, but not the height, use: Base ÷ Slope = Height (B ÷ S = H) Cross Sections A cross-sectional view (fig. 4-7) that is given for a road project is a cutaway end view of a proposed station between the left slope and the right slope. Typical cross sections are plotted at any intermediate place where there is a distance change in slope along the center line where the natural ground profile and grade line correspond. The cross section displays the slope limits, slope ratio, horizontal distance between centerline stakes and shoulder stakes. It also shows the vertical distance of the proposed cut or fill at the shoulder and centerline stakes. 4-7

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