ACCURACY OF HIGHWAY SURVEYS 
William T. Pryor 
Chief, Aerial Surveys Branch, Bureau of Public Roads 
Federal Highway Administration, U.S. Department of Transportation 
Washington, D. C. 20591 
Paper for 
The llth Congress of the International Society for Photogrammetry 
Lausanne, Switzerland 
July 8 - 20, 1968 
ABSTRACT 
Highway surveys range from the general to the specific. Where 
the area of concern is large, generalities are acceptable and accuracy 
is less important. Wherever details are required, as for location, 
for design, and for right-of-way and construction plans, precision is 
needed in both dimensions and position.  Accuracies are related to the 
type of topography traversed, the intensity and character of land use 
encountered, and the economic value of the property affected, and for 
rights-of-way needed. The essential accuracies required and now 
feasible when aerial surveys are employed properly and comprehensively 
enough for each particular purpose, according to the circumstances and 
conditions encountered, and to the engineering requirements, are pre- 
sented. 
INTRODUCTION 
Highways have a profound and lasting effect on each area through 
which they are constructed and traveled. Each area served by a highway 
is an area opened to visibility and use. Unless the highway fits into, 
and has the appearance of being an integral part of the topography and 
natural scenery, and is enhancing to the bordering land uses, it is not 
well located, designed, and constructed. 
Highways people remember and seek to use are an eye-appealing 
part of each mile of topography and land use through which they extend. 
Highways must provide adequate traffic services with safety, comfort, 
and convenience, with economy, and with ease, for each driver and all 
other vehicle occupants. Highways should be located and designed to 
serve well the bordering lands. To serve fully, highways must be 
structurally sound, durable, and economical in maintenance. 
None of the foregoing vital characteristics can become the 
initial and continuing elements of our highways unless highway engi- 
neers obtain and appropriately use the qualitative information and 
quantitative data, in the detail, to the accuracy, and of the scope 
essential for achievement. To do so requires surveys--surveys per- 
taining to the topography, soils, ground structure and composition, 
surface and underground drainage, land uses (present and future), 
traffic (its intensity, speed, movement characteristics, origin and 
destination, and purposes of travel), and the legal and economic 
effects of highways and vehicle uses of highways.