22 
Once the mapping is completed, a reconnaissance-type initial design is 
made of the highway to achieve the best possible alinement, gradients, grading 
cross sections, foundation for the highway, and traffic services; and least pos- 
sible rise and fall, grading and other construction quantities, and. interfer- 
ence with or damage to existing land use. This work is accomplished with the 
maps and the aerial photographs which are used concurrently. The photographs 
are stereoscopically examined to ascertain and utilize the pertinent qualita- 
tive information. As an intermediate step, such field checks, as are neces- 
Sary, are made on the ground with photographs and maps in hand (on both of 
which the initially designed location is delineated) to substantiate decisions 
made in performance of the design. Results of this design are determination 
of construction quantities, construction costs, vehicle operation costs, antic- 
ipated maintenance costs, approximate costs of rights-of-way, road-user benefit 
ratios, and the attainment of the best route- for the highway. 
Clearing before preliminary survey 
Wherever, following determination of the best route in the preceding steps 
of this stage, the vegetation-covered route is to be cleared for preliminary 
Survey, an accurate description is computed, utilizing plane coordinates of the 
initially designed centerline. Also a survey tie is computed between each sta- 
tion marker of basic control surveys for the project, as targeted before pho- 
tography, and the nearest alinement point, as a change in curvature, point of 
intersection of semitangents, or & point on a tangent joining circular curves 
where there is a crest in the topography which will provide intervisibility on 
the ground to other alinement points for which such ties are similarly computed. 
Clearing limits are then determined and the designed and computed centerline is 
Staked accurately on the ground, along with the clearing limits. 
When large scale photographs are used 
Whenever sufficient detail cannot be seen on the small scale photographs 
used in the preceding stage, wherever access to routes for inspection of the 
ground is very difficult, and/or wherever it is not intended to do any clear- 
ing, but tall, dense vegetation prohibits attainment of sufficient accuracy in 
the mapping which will be required in the subsequent preliminary survey stage, 
large scale photographs of each route alternative are taken and utilized. The 
photographic coverage of each route is obtained at scales of 1,000 to 500 feet 
to one inch (1:12,000 to 1:6,000) in areas of rugged topography and at scales 
of 500 to 200 feet to one inch (1:6,000 to 1:2,400) for areas of rolling to 
smooth topography and where land use is intense. The width of photographic 
coverage is & nominal maximum of 3 miles (5 kilometers) and usual minimum is 
l mile (1.6 kilometers). 
Each route is transferred from the small scale photographs to the large 
scale photographs as they are examined stereoscopically. The transfer is accom- 
plished by correlating route position on the separate sets of photographs by 
identification of images of the same ground objects or patterns on both sets of 
photographs. In lieu of making investigations on the ground throughout each 
route, the large scale photographs are examined in detail stereoscopically to 
determine the controls of route positioning which should be met to best serve 
traffic, and to take advantage of the topography and land use. The controls 
of topography and land use which should be avoided, wherever possible, are also 
ascertained. Each route location positioning on the large scale photographs is 
adjusted so as to improve the alinement and gradients, and place it on the best 
topography from the standpoint of grading quantities, ground stability, least 
drainage, best exposure, least damage to and/or interference with existing 
land use, and best traffic services. The route is placed on the photographs in 
stereoscopic correspondence with topography to guide the preliminary survey 
parties on the ground. Costs of rights-of-way, construction, maintenance, and