Road/Railway design relies on the robustness of road/railway
geometrical computation with four major design elements:
Alignment: The position of the center line of the road, highway or
railway on the ground.
Roadway/Railway: Also called alignment surface. This is the strip of
land over which a road/railway passes. It can also be the part of a bridge used
by vehicles. In the context of road/railway design, it designates the surface
created from the alignment and superelevation. This is the input data for the
road/railway design.
Terrain: In most cases, an alignment surface is associated to a
terrain. It can be an open mesh (surface) or a slab of terrain (volume).
Typical cross section: A road/railway cross section is the result of
the intersection between a plane (usually normal to alignment) and the
road/railway whereas a typical cross section is a profile that is swept
(scanned) along both sides of the road or along the railway to modify the
terrain, and generate excavations and fillings. A typical cross section is an
input for road/railway design, and is represented by a specified sketch.