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of vehicle operation are estimated and & road-user benefit ratio is deter-
mined for each route.
Regardless of which procedure is utilized in this stage, all work is
concluded with a report presenting details ascertained and conclusions
attained, and recommending the best route for preliminary survey.
APPLICATIONS IN PRELIMINARY SURVEY AND DESIGN OF HIGHWAY ON. APPROVED ROUTE
Once the reconnaissance surveys are completed, a preliminary survey is
made of the selected and approved route. The objectives are to design the best
possible location for the highway on that route and to prepare detailed con-
struction plans. In preparation for accomplishing such objectives, detailed
and accurate surveys are made of a topographic band of sufficient width along
the route to ascertain all of the important positive and negative factors con-
trolling position, establishing the physical characteristics of the highway,
and governing, in certain aspects, its geometric design. Among such factors,
most of which may be determined or ascertained to & reasonable degree of suf-
ficiency by proper use of aerial surveys, are:
1. Data on topography, such as its dimensions (in the form of aerial pho-
tographs, notes on conditions and dimensions, and maps); its degree of rugged-
ness and condition with respect to stability and drainage; its ground struc-
ture and soils by composition and condition; and erosion.
2. Information on land uses, both present and that expected in the future,
by type, quality, intensity, position, ownership, and values, especially as
they are reflected in the costs of rights-of-way.
3. Classes of transportation facilities and their connecting or nonconnec-
ting, and interfering or noninterfering characteristics.
4. Interests of public and directly affected property owners.
5. Extent and physical complexity of property severance.
When such survey-obtained data and information are available in sufficient
detail and usable form, the most feasible and economical location for the high-
way is designed. The several design controls and criteria established in the
planning stage govern in each phase, while the highway is fitted to the topog-
raphy, physically and esthetically in all of its three-dimensional aspects,
and to transportation systems and other developments, both existing and planned
or anticipated. Next, a description of the designed centerline is computed,
including its circular curves, spiral curves, and joining tangents; and plane
coordinates of points of change in curvature and intersection of tangents, and
of points where the centerline intersects property lines. Also computed are
the profile gradients; construction quantities of roadway, drainages, struc-
tures, paving, and so forth; and rights-of-way. Finally detailed construction
plans are prepared, specifications written, schedule of construction items
made, and rights-of-way procured. Thus, every aspect of the highway has been
considered, its dimensions explicitly established, and its position specific-
ally designated for location survey.
This is the stage in which qualitative information must be detailed and
dimensional data exact. In practice, there are direct and indirect procedures
by which aerial surveys are employed. The direct procedure will be given first.
Direct Procedure in Preliminary Survey and Design
The direct procedure of utilizing aerial surveys in preliminary survey and
design is applicable wherever the route was cleared after completion of engi-
neering work in the preceding stage and wherever the ground is not detrimen-
tally obscured from the air by vegetation, regardless of the character of the
topography or the type and intensity of land use. The work proceeds directly
from the setting of photographic targets through aerial photography of the
route, ground control surveys, photogrammetric accomplishment of topographic
mapping and other essential measurements, design, and preparation of construc-
tion plans. Staking of the centerline or other highway stakes is unnecessary.
