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 ...

APPENDIX B. 393
effect, in the cuttings and fillings; of moving the line to the right
or the left in order to improve its grade or curvature.
The most perfect preliminary location of a line would be made
by first making a topographical survey, and getting contour lines
over all the surface near the proposed line. This can be done
very rapidly with a level provided with extra " stadia hairs."
Preliminary surveys being completed, plots and profiles are
made; curves put in so as to obtain the line of easiest curvature;
a grade line put on the profile so as to nearly equalize the cutting,nd filling, and at the same time get easy grades. (See p. 154.)
Approximate grade contour lines may be obtained from the
cross-sections thus: Knowing at each station the relative heights
of the ground, find where a horizontal line, passing through the
grade point at each station, perpendicular to the line of the road,
would intersect the surface of the ground.
This is most easily done, if the slope is taken in degrees, by a
traverse table. Opening the table to the degree of the slope, calling the depth of the cut or fill the departure, and finding the lati.
tude corresponding to it, which will be the distance of the required
intersection to the right or left. Mark on the plot the places of
these points of intersection, and draw a line through these. This
will be a line on which there will be no cutting or filling, and may
be called a grade contour line.
The located line should approach this as nearly as other considerations (curvatures, etc.) will allow. It should be a compromise
between this line and the straight line.
Grades in railroads should be grouped by bringing the steep ones
together and obtaining some uniformity of them over such a
length of road as would be worked by the same engine; because
no one engine can advantageously work easy grades and steep
ones.
4. Comparison of Lines.
The various lines which have been surveyed and estimated,
betweer two termini, are now to be " equated." One line may be
straight, but have many grades; another level, but have sharp
curves, or be longer than the former; and so on,
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