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Ministry of Transport published Phase 2 of the British Inte- 
grated Program for Highway Design. This system included a DTM 
based on a variable interval square grid. The use of this 
suite of programs has promoted the use of the DTM. In the Pre- 
liminary Design stage a DTM is obtained, covering all of the 
possible alternative routes the highway could take. This usual- 
ly presupposes that a certain amount of reconnaissance work has 
already been carried out using existing maps. The photography 
scale for this stage is approximately 1:10000. 
Various horizontal and vertical alignments are compared, usually 
on the basis of optimizing earthwork quantities and one band of 
interest chosen as being the most acceptable one. 
In the Final Design stage a new photography is obtained at a 
Scale of 1:3000 to cover the band of interest chosen in the 
Preliminary Design stage. This band of interest may also have 
been chosen from existing maps. A new DTM is measured and the 
final design of alignment is carried out. The eárthwork quanti- 
ties computed for the final alignment on the basis of levels, 
interpolated in the DTM, often form the volumes on which the 
work to be carried out by the contractor is based. 
There hàve been some problems involved in the practical imple- 
mentation of the DTM in England. These have largely been due 
to the new concept involved, but have now been overcome by the 
use of the system. 
At the Road Research Laboratory in England an interesting work 
is going on concerning the development of methods and aids for 
optimization between alternative highway alignments. There 
exists today a suite of computer programs for optimizing the 
vertical alignment, keeping the horizontal alignment fixed. The 
programs work on the vertical alignment and minimize earthwork 
and bridge cost, while observing geometric standards, level con- 
trol points and phasing. The programs are included in the 
H.O.P.S.-Highway Optimization Program System. 
The further development concerns a suite of programs which will 
try many alternative horizontal and vertical alignments automa- 
tically by using optimization, taking into account those cons- 
traints that can be expressed mathematically.