URBAN ROAD REDESIGN USING COMPUTER AIDED DESIGN SOFTWARE

This article examines the advantages of using computer-aided design (CAD) in urban road redesign. Modern computer methods have done little to change the original manual road design methods, such as template design, but are used mainly to help speed up the design process. With fewer new roads being built and the bulk of road design being redesign, modern CAD packages, targetted at redesign, have been developed. The methodology adopted is the use of 'strings', each defined as a series of lines, arcs or curves, connected consecutively and stored as a series of coordinate points. Modern software also allows the centreline of the new road to be offset from the pegged line, a procedure that has several advantages. Template design is best described in terms of a simple rural road design cross section. In the road's straight sections, the template has a constant width and slope, and a typical section is either the upper driving surface or the lower earthworks design section. The centreline strings' definition defines the master alignment, and the same approach can be used to define secondary strings relative to this alignment. Relative strings can be used in various ways to simplify design. String design is as flexible as template design but more versatile, and can be used for three- dimensional road models, for example for earthworks.