Figure 3-4.-Road profile.curves), which will be discussed shortly. The grade linesmay be level or sloped. If the lines slope upward, thegrade is positive; if downward, the grade is negative.The slopes are in reference to the direction of increasingstations. The amount of slope is lettered above the gradeline and is usually indicated as the percent of slope. Infigure 3-4, the slope from station 66 + 00 to 71 + 00 is+2.00 percent. This means the center-line grade rises 2feet in 100 feet horizontal distance. If the slope is -1.50percent, the grade would fall 1.50 feet in 100 feethorizontal distance.At vertical curves, the straight lines are tangents thatintersect at a point called the point of verticalintersection (PVI). This point is comparable to the PIof horizontal curves.Vertical CurvesIf the road is to offer safe, comfortable drivingconditions, the PVI should not break sharply. The lengthof the curve depends upon the steepness of theintersecting grades. In most cases, a vertical curve issymmetrical in that its length is the same on both sidesof the PVI. Unlike the length of a horizontal curve, thelength of a vertical curve is the horizontal distance frombeginning to end of the curve, rather than the distancealong the curve. The station on which the curve beginsand ends is called the point of vertical curvature (PVC)and point of vertical tangency (PVT), respectively.Unlike horizontal curves, vertical curves are parabolic;they have no constant radius. Therefore, the curves areplotted, usually in 50-foot lengths, by computing theoffsets from the two tangents. A vertical curve at thecrest or top of a hill is called a summit curve, oroververtical; one at the bottom of a hill or a dip is calleda sag curve, or undervertical.Drawing the Grade LinesYou should use the same horizontal and verticalscale to draw the grade line as to draw the profile. ‘Ibisallows the amount of cut or fill for a particular point tobe measured. If the grade line is higher than the profile,fill is required; if lower, cut is required.The profile and grade-line drawings also show therelative locations of drainage structures, such as boxculverts and pipe. You use only the vertical scale to drawthese structures. You can plot the heights of thestructures accurately, using the vertical scale. However,because of the exaggerated difference between thevertical and horizontal scales, you cannot draw thewidth of the structures to scale. Therefore, you shoulddraw the width of the structures just wide enough toindicate the type of structure. You should show a boxculvert as a high, narrow rectangle and a round pipe asa high, narrow ellipse.ROAD DIMENSIONSThe type of dimensioning used for road plans is avariation of the standard dimensioning. In roaddimensioning, numerical values for elevations, cuts,fills, and stations are considered dimensions also. Mostroad dimensions appear on the profile and grade-line3-5

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