INTRODUCTION 
Interest in computer -aided systems for highway design has increased 
quite dramatically in recent years, and computers are now used to some degree 
by all major highway authorities and by many of the more progressive consult- 
ants. This trend should be welcomed by air survey operators because it has 
generated amongst engineersa renewed interest in photogrammetric methods 
of acquiring terrain data. The virtual demise of ground survey methods as a 
source of data for computer -aided systems has come about because in all but 
the smallest projects only air survey can supply terrain data at a speed and 
cost commensurate with the subsequent design process; and because the main e 
body of road engineers has now come to accept that in practice photogrammetric 
methods are no less accurate than ground methods, besides posing fewer 
access problems. Moreover, by minimising ground activity, they awakenless 
public anxiety than location surveys carried out by traditional methods. 
At first sight, the photogrammetrist's role in the computer -aided 
system appears to be limited to the preparation of maps or cross sections or 
digital terrain models, but contact with the system will show that he has 
another equally important function as adviser. This implies no encroachment 
on the territory of the highway engineer; he alone is qualified to direct a design 
project. But it must be remembered that many engineers, although aware of 
the existence of computer-aided systerns, are not yet familiar with the tech- e e 
nique, and others who have ventured into this field only once or twice will have 
found that whilst the experience served to illuminate the problems of the system 
it did not always suggest their solution. Most will need guidance on survey and 
computing matters in general and on many points of technical detail. They 
will wish to draw on the experience of their air survey contractor for some of 
this guidance, not merely in order to demonstrate their independance of rival 
design teams - indeed there is a growing tendency to accept that only by pooling 
resources can engineers hope to keep pace with present developments - but 
because the experienced air survey operator is uniquely placed to give this 
assistance, being already conversant with many of the problems of automation 
applied to surveying and computing. Even authorities which pioneered and are 
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