The road is a circle described by "radius" and "width". The road surface parameters are defined as:
s: arc length along circle w: lateral displacement of road, perpendiular to circle
The point s = 0, w = 0 has position vector r = {0, -radius, 0};
The functions are defined in such a way that Dymola inlines all the functions. As a result, it is easy to get derivatives of the functions.