18.
matical function of higher degree, cannot be used for calcula-
tion of a detailed longitudinal profile of the terrain along
the highway centerline to be used for the final design of the
drainage system, culverts, bridges etc. For getting these de-
tailed information a linear interpolation is so far required.
It should be noticed that there are many other factors than the
earthwork quantities that influence the choice between alterna-
tive highway aligments. The cost of the earthwork quantities
normally amounts to 25-30 $ of the total construction cost. The
forecasted cost of the vehicle operation on the road occupies
in most cases a greater part of the total economic function of
the transportation network than the construction cost.
In practical design work, therefore, the horizontal alignment
is generally fixed during the preliminary design stage and during
the final design the mass-disposition is more influenced by
changes of the vertical alignment. Only smaller changes of the
horizontal alignment must then be made for keeping the connec-
tion between the horizontal and vertical alignment that is re-
quired from the points of view of aesthetics and traffic safety.
The original idea of introducing the DTM in the Highway Design
was to collect better information concerning the terrain for the
first stages, route location and preliminary design. The practi-
cal application today concerns, however, more the final design
stages.
I should also be observed that using a DTM for the calculation
of cut and fill quantities means measurement over the whole area,
terrain corridor, while when longitudinal and transverse profiles
are measured, the data collection is restricted only to a limited
area around the actual horizontal alignment. On the other hand it
should also be stated that such large scale DTM-measurement of
data can be organized efficiently and the cost may be acceptable.
The DTM-system has during the recent years been introduced in
two stages of the Highway Design in the United Kingdom, namely
in preliminary Design and Final Design. In December 1968 the
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