distance equal to incline distance, reasonable accuracy may be obtained only for slopes less
than 30 percent.
Spot elevation B
Spot elevation A
Road distance from A to B
Calculate the percent of slope:
x 100 = +2.5% = ♂ 3%
x 100 =
Figure 1-3. Map Method to Determine the Percent of Slope
1-2. Curves. Curves are another land feature that must be considered by reconnaissance
personnel as possible obstructions to traffic. The speed at which vehicles can move along a
specified route is affected by curves.
For reconnaissance purposes, curves with a radius of curvature of 25 meters and
less are considered obstructions to traffic flow and are indicated by the abbreviation OB in
the route classification formula. Curves with a radius of curvature between 25.1 and
45 meters are reportable on an overlay but are not considered obstructions.