in figure 1.8. On tangent track, both rails must have the same elevation. In other words, an
imaginary line at right angles to the two rails connecting their tops must be level. Curved track,
however, is banked; the outside rail is raised. The condition of cross level where one rail is
purposely raised is known as superelevation and is discussed fully in Railway Track
Figure 1.8. Proper Cross Level of Track.
The concept of surface is difficult to differentiate from grade and cross level. As
commonly used, surface describes the smoothness of track. Technically, it is the height relation
of successive points along one rail of a track. Proper track surface is attained when the rail is at
the same height throughout its length or when its elevation changes evenly. Proper and poor
surfaces are compared in figure 1.9. Although grade is also a height relation of successive points
along track, this term should be used in referring to large changes occurring over long distances.
The term grade should be reserved for changes of elevation purposely made when the line was
constructed. Surface, on the other hand, refers to irregularities of elevation occurring because of
Figure 1.9. Proper and Poor Surface Compared.