A manual of the principles and practice of road-making: comprising the location, construction, and improvement of roads, (common, macadam, paved, plank, etc.) and rail-roads. By W. M. Gillespie ...

138 THE LOCATION OF ROADS.
move. A certain amount of force being required to produce the entire change in direction, the smaller the radius
of a curve, the less space and time is given for the exercise of this force, and a larger share of it must therefore
be exerted at each moment, with a great increase of labor
and danger.
It is therefore very important that every road-curve
should have as great a radius as possible. It should
never be less than one hundred feet.
When a curve is necessary upon a steep grade, the in
clination should be flattened at that place in order to compensate for the additional resistance of the curve. On
this account a zigzag line up a hill is more objectionable
than an oblique ascent by a straight line.
The curves which are employed to unite straight lines
are usually either circular or parabolic arcs.
CIRCULAR ARCS.
Having given two Fig. 62.
straight lines meeting C
at C, (or which would A...
so meet, if produced)
it is required to mark
out on the ground an
arc of a circle to which \
these lines shall be \
tangents. \
The simplest mode \
for an arc of small radius would be to find the centre, by erecting perpendicu
lars to the tangent lines at-equal distances, A and B, from
their point of meeting C. The intersection, 0, of the
perpendiculars would be the centre, from which the arc