Wherever the roads are primarily to provide service to the bordering
lands, there are no imposed restrictions on access and all other traffic ser-
vice standards are lower, in varying degree, than on the controlled access
highways. Therefore the class of highway, established by its purpose, must
be kept in mind throughout each of the stages of location and design to prop-
erly, esthetically, and economically fit each highway into the many and vari-
ous complex combinations of the configurations of the ground, its surface
drainage, and man's uses of the land for effective movement of motor vehicles
with convenience, comfort, and safety.
In actuality, as aerial surveys are employed throughout each stage in
highway engineering, the principles just presented are kept in mind by each
specialist on the highway team and are utilized by him, as applicable in whole
or in part, while he performs his particular portion of the work. Therefore,
in developing this paper, aerial surveys could not be separated from the actual
performance of the engineering and other work required. Moreover, in their
broadest sense and extent, aerial surveys can be used beneficially in many
ways, each separate way being chosen according to its applicability and to
need--need for qualitative information, for quantitative data, and for ascer-
taining and demonstrating significant relationships. These needs include
illustrating situations, circumstances, problems, and their proposed solu-
tions; and in obtaining in appropriate form a factual record for review, when
and where essential, to ascertain the completeness and adequacy of solutions,
and to make revisions, as necessary, when or where new requirements and/or
changed situations or circumstances occur.
It seemed pertinent first to discuss the nature of aerial photographs and
of aerial surveys as used in highway work. Next, in an amplification of the
specific working procedures in applying aerial surveys in the stages of highway
engineering, each use-stage is preceded by a statement regarding the objectives
and work accomplished through the advantageous employment of aerial surveys by
the engineer specialists on the highway team. Within each stage there follows,
in somewhat chronological order, the specific procedures which are, or can be,
employed by the highway team in the performance of its engineering work. This
is begun with the preliminary engineering stages--the stages in which the char-
acter, quality, continuity, and lasting utility of a highway are determined by
ascertaining and utilizing position, physical dimensions, and applicable qual-
itative information--and concluded with some uses of aerial surveys in highway
construction, maintenance, improvement, and reconstruction. Finally, a pres-
entation is made regarding the procurement by contract of aerial photographs
and photogrammetrically compiled maps.
NATURE OF AERIAL PHOTOGRAPHS AND AERIAL SURVEYS FOR HIGHWAYS
The uses of aerial photographs and aerial surveys for highway engineering
are manifold. The great number of varied ways in which these means are aids
to the highway team in ascertaining, solving and demonstrating its problems
and their proposed solutions will be more easily understood if the nature of
aerial photographs and aerial surveys for highways is first reviewed.
Aerial Photographs
When obtained at the appropriate scale, as governed by accuracy and detail
requirements, aerial photographs are the basic source of qualitative informa-
tion and quantitative data. The qualitative information is obtained by photo-
graphic interpretation and analyses, and the quantitative data from photogram-
metric measurements and delineations, including maps. Aerial photographs are
records of the status and conditions within an area on a Specific date, and are
easily adaptable and usable, both directly and indirectly, when and where
necessary.
