f. Road obstruction. Factors which restrict the type, amount, or speed of traffic flow. Examples:
(1) Travel width of roadway below standards (see Appendix A).
(2) Slopes: Slopes percent identified as 7 percent or greater.
This must be identified and
recorded on all overlays.
(3) Curves: Curves of radius of 25 meters or less will be recorded.
(4) Ford crossings. A ford crossing is a location that allows vehicles to travel across a river,
stream, or creek.
(5) Snow blockage (T). This obstruction only applies to areas that have significant snow
problems, otherwise not considered an obstruction.
(6) Flooding (W). These conditions are regular, recurrent, or serious.
17. Curve Formula.
Speed at which vehicles can move along a specified route that is affected by curves. Curves with a
radius of curvature less than 25 meters (100 feet) must be reported. Curves of this nature are
considered an obstruction of traffic. The Army formula is:
C is the distance between point 1 and point 2 (chord). M is the perpendicular distance on the center of
the chord to the center line of the road. (see Appendix A.)
a. Step 1: Once the curve has been identified, team member #1 locates point 1, which is where the
curve line starts. Team member #2 paces off to the opposite side of the curve (30 paces for our
example). Team member #2 turns around and paces halfway back. He does a right face and goes to
the center of the road, center line, or edge of the road. This will give the middle ordinate (9 paces for
our example).
b. Step 2: Take the measurements and put them into the formula. C2 will be 30 x 30 and 8 m
becomes 8 x 9. The m over 2 becomes 9 over 2.
c. Step 3: Multiply 30 x 30 for an answer of 900. Multiply 8 x 9 and this becomes 72. Leave the 9
over 2 at this time. Insert the answers into the formula.
d. Step 4: Divide 72 into 900, for an answer of 12.5. Divide 2 into 9 which will become 4.5.
e. Step 5: Add 12.5 and 4.5. This will get 17 paces.
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MP1007
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