45 
CONSTRUCTION ENGINEERING 
Work in construction engineering is governed by the plans prepared in the 
preceding stages. Work is accomplished by setting clearing, slope, structure, 
and other stakes, as necessary, to guide the construction forces. Alterations 
and/or changes are made only where new conditions or circumstances, which 
develop after the location survey and before or during construction, require 
them. 
The quantities of roadway grading, channel changes, slides, waste, and 
borrow are measured by ground surveys and by photogrammetric methods as conven- 
ient. Unusual conditions and unique construction are illustrated by use of 
ground photographs and by use of aerial vertical and oblique photographs. For 
future and archival purposes, the newly completed highway and adjoining lands 
are sometimes photographed. For such purposes and as an aid in maintenance, 
continuous-strip photography taken to permit stereoscopic examination at scales 
from 100 feet to 20 feet to one inch (1:1,200 to 1:240) is especially useful. 
POST-CONSTRUCTION APPLICATIONS OF AERIAL SURVEYS 
Maintenance, and possible subsequent improvement or reconstruction are 
stages following construction in which specific and special uses of aerial sur- 
veys are effective. These are discussed briefly in the sequence in which they 
are applicable. 
Maintenance 
By taking aerial photographs on one date for comparison with those taken 
on another date, as before and after repair of pavement, shoulders, drainage, 
slides, flooding, and washouts, a factual record is obtained for current and 
future use, as necessary. These photographic records are especially useful in 
evaluating the effects of maintenance and to note progressive deteriorations 
and their causes. They are also used photogrammetrically to measure volumes 
of materials moved from slides, for slope protection, and to build up subsided 
sections. 
Improvement and Reconstruction 
  
Aerial surveys are utilized in connection with improvement or reconstruc- 
tion to demonstrate need for improvements and reconstruction caused by increased 
traffic, safety hazards, reduced capacity resulting from intensifications in the 
use of bordering lands, and obsolescence. Also aerial surveys are employed to 
ascertain qualitative information and quantitative data for preparation of 
improvement and reconstruction plans. Aerial photographs are taken to illus- 
trate accrued benefits from completed improvements, and conditions encountered 
during and benefits achieved by reconstruction. Photographs taken on the ground 
and from the air at periodic intervals serve as a photographic record of circum- 
stances and conditions of one date for comparison with those of another.  Appro- 
priate evaluation of this record supplies valuable information regarding changes 
and need for further improvement and/or reconstruction as the cycle evolves to 
a new beginning. 
ELECTRONIC COMPUTERS IN HIGHWAY ENGINEERING 
Some of the advantages in highway engineering of the rapidity with which 
adequate dimensional data could be obtained in greater scope by aerial surveys 
than by surveys on the ground were not realized until electronic methods of com- 
putation were employed. Electronic computation systems enable engineers to store 
in digital form the dimensional data obtained photogrammetrically regarding the 
topography. For example, such data and the basic design criteria, as the highway