Spline curves for geometric modelling of highway design

The new Road Design Italian Standards (“Norme funzionali e geometriche per la costruzione delle strade”, D.M. 5.11.2001), allows the use of polynomial curves for the design of the road alignment design. Such polynomial curves permit to define effectively road alignment regarding the geometric-dynamic constraint. Really, these curves allow the unitary spatial definition of the road alignment in a numerical form, along an entire road section; these representation methods are very suitable for the design of transport infrastructures (roads, railways, levitation systems, cableways, etc.), when the terrain is represented too through of a three-dimensional numerical model (DTM). For these curves, it is possible to define the characteristic parameters (degree, continuity, shape, curvature, etc.) on the basis of the control of cinematic and dynamic indexes, regarding the vehicle motion. In this paper some kinds of polynomial-parametric curves, proper for the design of road alignment, are examined, making also the performance comparisons with traditional design methodologies. The matrix formulation of these curves is specially appropriate for use in CAD systems and will be implemented in the driving simulation software, currently under development in Roads Department of University of Rome ”La Sapienza”.