ROAD DIMENSIONS - 14071

FIGURE 3-5. PROFILE AND GRADE LINE - 14071_68

Engineering Aid 2 - Intermediate Structural engineering guide book
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Figure 3-4.-Road profile. curves), which will be discussed shortly. The grade lines may be level or sloped. If the lines slope upward, the grade is positive; if downward, the grade is negative. The slopes are in reference to the direction of increasing stations. The amount of slope is lettered above the grade line and is usually indicated as the percent of slope. In figure 3-4, the slope from station 66 + 00 to 71 + 00 is +2.00 percent. This means the center-line grade rises 2 feet in 100 feet horizontal distance. If the slope is -1.50 percent, the grade would fall 1.50 feet in 100 feet horizontal distance. At vertical curves, the straight lines are tangents that intersect at a point called the point of vertical intersection (PVI). This point is comparable to the PI of horizontal curves. Vertical Curves If the road is to offer safe, comfortable driving conditions, the PVI should not break sharply. The length of the curve depends upon the steepness of the intersecting grades. In most cases, a vertical curve is symmetrical in that its length is the same on both sides of the PVI. Unlike the length of a horizontal curve, the length of a vertical curve is the horizontal distance from beginning to end of the curve, rather than the distance along the curve. The station on which the curve begins and 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 are plotted, usually in 50-foot lengths, by computing the offsets from the two tangents. A vertical curve at the crest or top of a hill is called a summit curve, or oververtical; one at the bottom of a hill or a dip is called a sag curve, or undervertical. Drawing the Grade Lines You should use the same horizontal and vertical scale to draw the grade line as to draw the profile. ‘Ibis allows the amount of cut or fill for a particular point to be 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 the relative locations of drainage structures, such as box culverts and pipe. You use only the vertical scale to draw these structures. You can plot the heights of the structures accurately, using the vertical scale. However, because of the exaggerated difference between the vertical and horizontal scales, you cannot draw the width of the structures to scale. Therefore, you should draw the width of the structures just wide enough to indicate the type of structure. You should show a box culvert as a high, narrow rectangle and a round pipe as a high, narrow ellipse. ROAD DIMENSIONS The type of dimensioning used for road plans is a variation of the standard dimensioning. In road dimensioning, numerical values for elevations, cuts, fills, and stations are considered dimensions also. Most road dimensions appear on the profile and grade-line 3-5

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