class.

It also includes any feature that interferes with the crossing of

two or more streams of traffic.

Critical points include every bridge,

overpass, underpass, ferry, ford, road constriction, and sharp turn.

Railroad crossings of any kind are critical points.

Since these items

already have symbols of their own, there is no need to indicate them with an

additional special symbol on your overlay.

As you conduct your recon, you may find areas that you know are

important which do not have a specific map symbol. For example, an ambush

site or an area where there has been a rock slide. In order to indicate

these on the overlay, the symbol for a critical point is used. This is a

number inside a triangle. From the triangle, you extend a line to indicate

the specific location. In the legend area of the overlay, you explain what

the critical point is. Key terrain is always considered a critical point.

e.

Curves.

Curves with a radius of less than 25 meters are considered sharp

curves and are indicated as obstructions (OB). If a curve measures between

25.1 and 45 meters, it must be noted on the overlay, just as a sharp curve

is. It is not considered an obstruction. The wider curves are noted since

they are sharp enough to cause some traffic to have to slow down. In other

words, any curve with a radius of 45 meters (148 feet) or less is noted on

the overlay.

Curves are indicated on the overlay by a triangle.

The point

(vertex) of the triangle is located at the curve. The radius of the curve

in meters is noted outside the triangle. When a series of curves occur in a

short distance, you may indicate it by drawing a second triangle inside the

first.

The vertex of the triangle is placed on the first curve.

Immediately outside the symbol, you indicate the number of curves and the

radius of the sharpest one. For example, 3/24 would indicate 3 curves, the

sharpest of which as a radius of 24 meters.

(1)

Formula Method.

The formula for determining the radius of

a curve is

.

R is the radius of a curve.

The straightline

distance of the centerline of the curve from each outer extremity is

represented by C.

M is the perpendicular distance of the tape to the

centerline of the road.

See Figure 1-17.

If c is 15 meters and M is 2

meters, the formula becomes:

The result would then be that R, the radius of the curve,

is 15 meters. This is a sharp curve and must be indicated as in obstruction

(OB). It has the advantage over the other methods in that it is relatively

quick and

MP1028

1-46

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