For the first consideration in profile plotting, select suitable horizontal and vertical scales for the profile paper. The suitability of scales varies with the character of the ground and other factors. In figure 14-22, the horizontal scale used was 1 in. = 400 ft, and the vertical scale used was 1 in. = 20 ft (reduced in size for reproduction in this book). Normally, to facilitate the plan plotting, choose scales that are proportional numbers in multiples of ten, such as those given above (H, 1 in. = 400 ft, and V, 1 in. = 20 ft). Write the stations and elevations, as shown in figure 14-22.

Plot the profile, usually from profile level notes, though you may plot it from the elevations obtained from the contour lines. Assume that profile level notes indicate the following center-line elevations at the following stations from 5 + 00 through 15 + 00.

As you can see, an elevation was taken at every full station and also at every plus where there was a significant change in elevation. Can you see now how important it is to follow this last procedure? If an elevation had not been taken at 8 + 75, the drop that exists between 8 + 00 and 9 + 00 would not show on the profile.

Check through the listed elevations, and see how each of them was plotted as a point located where a vertical line indicating the station intersected a horizontal line indicating the elevation of that station. Note, too, that usually stations are labeled where the line crosses highways, streams, and railroads.

Besides the profile of the existing terrain, the vertical tangents of the proposed highway center line have been plotted. The end elevation for each of these (that is, the elevations of points of vertical intersection [PVI]) were determined by the design engineers. Various circumstances were considered. One of the important ones was facilitating, as much as possible, the filling of each depression with an approximately equal volume of cut taken from a nearby hump or from two nearby humps.

The gradient, in terms of percentage of slope (total rise or fall in feet per 100 horizontal feet), is marked on each of the vertical tangents. This percentage is computed for a tangent as follows. For the tangent running from station 6 + 00 to station 18 + 00, the total rise is the difference in elevation, or

The horizontal distance between the stations is 1,200 ft. The percentage of slope, then, is the value of x in the equation

For a tangent running from station 18 + 00 to station 26 + 00, the total slope downward is the difference in elevation, or

The distance between the stations is 800 ft. The percentage of slope then is the value of x in the equation

Figure 14-23.-Typical design cross section.