REPORT OF COMMISSION VII
G VI1-49
of the proposed route with regard to topography, build-up areas, cultivated
areas, estate boundaries, and other factors which appear more or less clearly
from the photograph without the application of special photographic interpreta
tion techniques.
In the forested areas of both Norway and Sweden, photography is used ex
tensively in selecting routes for logging roads.
These photographs are also used as field maps for the personnel constructing
the roads. Since in these areas, aerial photography is regularly taken for forest
estimation purposes, prints are readily available for road planning.
THE HIGHWAY PLANNING PROCESS
In the United States, both photogrammetry and photographic interpretation
are becoming more and more an integral part of the highway planning process.
Many of the State highway departments maintain photogrammetric sections
in which photogrammetry and photographic interpretation are accomplished.
Also the various types of specialist engineers who participate in highway design
and construction are becoming trained in the use of photography as a base for
their various analyses.
Pryor (1954) lists the eight stages in the highway engineering cycle in which
aerial photographic analysis is used:
1. Planning;
2. Reconnaissance of area and determination of route possibilities;
3. Reconnaissance of route alternatives and their comparison in selecting
the best route;
4. Preliminary survey of the selected route for design of the location and
preparation of plans;
5. The location survey staking of the highway on the ground for construc
tion;
6. Condition and inventory surveys;
7. Maintenance and betterment surveys;
8. Surveys for highway improvement and reconstruction.
Mr. Pryor, in the same paper, gives a most concise and informative descrip
tion of the procedure followed in analyzing photography to provide information
for use in these engineering phases. This section of his paper is reproduced below.
Note that while certain photogrammetric techniques are involved, the process
as presented here is basically one of photographic interpretation.
“Sequential steps in the full employment of photogrammetry in each stage will
usually follow a logical pattern. These steps are not rigid. Deviation is possible whenever
situations and exigencies require it. Usually the steps are eight in number. Progressively,
they will provide, in both qualitative and quantitative form, nearly all that is needed
for making most highway engineering decisions.
“The first step is identification or recognition of images on the aerial photographs. The
identification is restricted generally to those images which will have an influence on deci
sions for specific purposes.
“The second step is often inseparable from identification or recognition. It is
interpretation of the images, their pattern, their relationship one to another and to the
highway engineering problems they represent.
“The third step is number. This is the count of all identified and interpreted images
either individually or by groups, which must be considered in making decisions while
solving the highway engineering problems. Like the first and second steps, the third
and fourth are often inseparable.
“Essentially, step four is the measurement of position, shape and size—usually