3. Track layout

Physical geography determines the layout of railroad lines. Built in the 19th century for the most part, and given the power available at the time, railroad lines followed the valleys with their gentle slopes and winding routes. Today's traction power and civil engineering techniques are overturning this practice: a new line is built "as short as possible", allowing for steep gradients and very long tunnels.

The alignment of the track is characterized by the profile representing the geometry of the line in two planes: vertical, i.e. the longitudinal profile, and horizontal, i.e. the plan profile