the general
utility of the earth road system in any locality is dependent to a
considerable extent upon the amount and seasonal distribution of
precipitation. The methods of maintaining earth roads appropriate to
any locality must of necessity be adapted to the climatic conditions,
and the amount of work required to give the highest possible degree of
serviceability will be exceedingly variable from season to season and
from place to place. In regions of great humidity, earth roads may be
expected to have a low average of serviceability, while in arid
regions they may possess sufficient durability for a considerable
volume of traffic. The design adopted for earth roads and the methods
of maintenance followed should therefore be carefully evolved to meet
the soil and climate conditions where the roads are located. These
will differ greatly throughout a state or even a county.

=Cross Sections.=--The general principles of road design were set
forth in Chapter IV. In Fig. 11 are shown typical cross sections for
earth roads adapted to various conditions as indicated. It is not
apparent that one form of ditch is particularly preferable to the
other and since some engineers prefer the V section and others the
trapezoidal section both are shown. It would appear that the V shaped
ditch is somewhat the easier to construct with the blade grader while
the trapezoidal is readily excavated with the slip or fresno scraper.
The ditch capacity required and consequently the dimensions will
depend upon the drainage requirements, as was pointed out in Chapter
III.

[Illustration: Fig. 11. Cross Section for Earth Roads]

EARTH ROADS IN REGIONS OF CONSIDERABLE RAINFALL

In the zones where the annual precipitation exceeds 30 inches
distributed over several months, earth roads will be unserviceable for
a considerable period each year unless they are constructed so as to
minimize the effect of water. This is done by providing for the best
possible drainage and by adopting a method of maintenance that will
restore the surface to a smooth condition as quickly as possible after
a period of rainy weather or after the "frost comes out" in the
spring.

Before the construction of the desired cross section is undertaken,
all of the grade reduction should be completed, except for minor cuts
which can be handled with the elevating grader in the manner that will
be described presently.

Where any considerable change in grade is to be effected,