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15 
Stereograms Illustrating Route Locations 
The accompanying stereograms, with lines placed in stereoscopic corre- 
spondence with the topography to represent centers of route bands where a high- 
way can be constructed on the ground, illustrate a variety of topographic and 
land use conditions with which highway engineers are confronted. On photo- 
graphs of light color tone, a red wax pencil (china marking) was used to delin- 
eate the route, and on photographs of dark color tone, white acetate tape was 
used. When photographically copied, the red lines appear black. 
To examine a stereogram stereoscopically, either of two methods may be 
employed--a lens-type stereoscope or the unaided eyes. To examine a stereo- 
gram with the unaided eyes, look at the left photograph with the left eye and 
the right one with the right eye. To make this easy, place a 10-inch card 
between the eyes from the face to the line between the pair of photographs of 
the stereogram. By this means, one is prevented from looking first at one 
photograph and then the other. With the card in place, look into the dis- 
tance--like seeing through the paper on which the photographs are printed-- 
until the three-dimensional picture is seen beyond the page. After a little 
practice, the card can be eliminated. 
  
Stereogram l. Segments of two route alternatives through a wooded mountainous 
area for a highway between the same location objectives. More rise and fall is 
introduced into the black route than exists in the white. This is done to place 
the route on moderately sloping topography where greater ground stability exists, 
where less cross drainage is required, and where excavation and embankment yard- 
age will be a minimum. Most of the differences in these route locations and 
their effect on a highway through areas of this type are not easily represented 
on or determined from a topographic map.