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13
APPLICATIONS IN RECONNAISSANCE SURVEY OF AREA
The first stage of highway location is the reconnaissance survey of area.
In this stage, the objective is to determine all feasible route alternatives
between the designated termini. The work is accomplished by making such sur-
veys of a broad area as are necessary to determine the controls of highway
route location. These controls may be classified into two categories, those
to be met and those to be avoided. Examples of controls to be met are moun-
tain passes, best crossings of rivers, best sites for grade separations and
interchanges, and specific intermediate areas to be served between the termini.
Examples of controls to be aveided wherever possible are swamps, land slides,
and other poor soil areas, intensely used expensive lands, and specially used
areas as parks and cemeteries.
The feasible routes are determined on the bases of economically achieving
the service standards set by the class of highway to be located, in relation to
the traffic and bordering lands to be served, and the type of topography to be
traversed. Then the probable cost of a highway on each of the various routes
is estimated, including rights-of-way and construction. Should the most feasi-
ble, serviceable, and economical route alternatives not be determined in this
stage, intensified engineering efforts in subsequent stages cannot overcome
these deficiencies, because a superior route cannot be created from one that is
inferior. This, therefore, is the beginning and vital stage in highway location
and design.
Photographic Coverage
For accomplishing the engineering work in the reconnaissance survey of
area stage, aerial vertical photographs are obtained of a broad area 0.4 to 0.6
as wide as the airline distance between termini or the segments extending
between major objectives and intermediate areas to be served. The scales at
which these photographs are obtained and used, as stereoscopic contact prints,
range from small scale in rural areas to large scale in urban areas. As a gen-
eral rule, the scales should be no larger than necessary for efficient and
effective accomplishment of the engineering and other work. Experience has
shown that scales, as follows, will be satisfactory:
1. Rural, rugged regions of little or no land use, between 5,000 and
2,000 feet to one inch (1:60,000 and 1:24,000).
2. Rural regions with extensive land use, regardless of topography,
between 2,000 and 1,500 feet to one inch (1:24,000 and 1:18,000).
3. Urban areas, regardless of topography, between 1,700 and 500 feet to
one inch (1:20,000 and 1:6,000).
Procedures
In conjunction with the aerial photographs, suitable small scale topo-
graphic maps (1:24,000 and smaller scale) are utilized, when available, of the
area of survey. These maps and the photographs constitute ideal companions,
supplementing and augmenting each other in all phases of the reconnaissance
Survey and route location work. When such maps are not available, the photo-
graphs have to do double duty, providing all quantitative data as well as the
qualitative information.
The aerial photographs of the entire area of reconnaissance survey are
examined stereoscopically and are photographically interpreted and analyzed in
sufficient detail and adequate number of times to ascertain the controls of
route location. Depending upon the character of topography and type and inten-
sity of land use within the area, such work includes the determination of con-
trols to be met and controls to be avoided. Among the qualitative controls to
be met are good granular soils on and from which to construct the highway, and
where applicable, mountain passes, sections containing a minimum number of
