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Ground view of a divided highway with independent alinements at different 
levels for the two roadways. Separation of the opposing roadways eliminates 
headlight glare at night. Such separation along with good slopes and shoul- 
ders, and pleasing alinements fitting the topography, all evident in this 
single photograph, provide year-round safe, convenient, and comfortable traffic 
services. Aerial vertical photographs and topographic maps accurately com- 
piled by photogrammetric methods provide the design engineer with much of the 
information and data he requires to make such highway designs. 
Indirect Procedure in Preliminary Survey and Design 
The indirect procedure of utilizing aerial surveys in preliminary survey 
and design is applicable wherever the ground is covered with timber or other 
tall vegetation, and also wherever it is engineering practice to position, 
stake, and inspect the highway centerline on the ground before undertaking 
detailed design and preparation of construction plans. The work, therefore, 
does not proceed directly from the placing of photographic targets through 
aerial surveys and design. First, an initial survey and design are made. 
Second, surveys on the ground and from the air are accomplished in detail for 
completion of the design. 
Photographic targets 
Photographic targets are placed on the ground before photography. The 
positioning should be such that, wherever feasible, the targets will lie out- 
side possible limits of construction but where they will be within the route 
band to be photographed for initial purposes and again for photography later 
at a larger scale. The positions, shape, size, color and so forth of targets 
used in this procedure are similar to those used in the direct procedure.