The typical section of a road shows exactly what the road should look like after it is constructed. It includes the type and thickness of the base and surface materials, the crown, superelevation, ditch slope, cut slope, fill slope, and all horizontal widths of components, such as surface, shoulders, and ditches. Since slight deviations will occur during construction, a tolerance in construction is allowed. However, the shape and construction of the road should conform as closely as possible to the typical section. (For general provisions and design criteria, refer to NAVFAC DM-5.5.) Typical sections are prepared for both straight and curved portions of the road. The typical section for a curved portion of a road differs from the straight portion in that the shape of the roadbed is different. In a typical

section for a curve, the pavement is a plane surface instead of crowned and is usually superelevated to account for centrifugal force encountered in curves. The outside shoulder slope is the same as the superelevated pavement slope, but the inside shoulder slope is either the same or greater slope. (Inside shoulder refers to the shoulder closest to the center of the arc, or curve.) Most curves are also widened on the inside to allow for the "curve straightening" effect of long wheelbase vehicles. The back wheels of the trailer in a tractor-trailer rig do not follow in the tracks of the tractor wheels. They run closer to the inside edge on the inside lane and closer to the centerline on the outside lane. This presents a safety hazard when two vehicles meet in curves. Curve widening partially eliminates this hazard. Figure 3-7 is a superelevated section showing curve widening. Specific guidance for curve widening is contained in NAVFAC DM-5.5.

Preliminary cross sections are sectional views of the existing terrain taken at each station point along the center line of the route the road is to take. These sections are usually taken after the roadway has been cleared but may be taken before. If the sections are taken before, the thickness of the sod to be stripped off is normally deducted from the elevations. The preliminary cross section shows the elevations of the natural, or original, ground. These sections, when superimposed on the desired finished roadbed sections, are used for studying various alignments of the road and for preliminary earthwork estimating. Figure 3-8 shows typical preliminary cross sections.

Figure 3-8.Preliminary cross sections.

Figure 3-9.-Subsurface drainage.