Section I. Roadbed and Ballast
Rail equipment is directly supported by the rails of the track, and each rail is supported at
intervals along its length by crossties. The rail, therefore, acts as a girder between ties. The ties
support the rails and in turn are supported by ballast laid on the subgrade.
A roadbed is a strip of terrain that varies in width from 18 feet for a single track on
tangent to 33 feet for a double track on a curve. The roadbed follows the line of the railroad. It
provides a means of holding the tracks above the surrounding land so that water cannot remain
on them. Ballast laid upon the subgrade distributes the weight of a train over a wide area so that
the ground can support it, as figure 2.1 shows.
Figure 2.1. Spreading Train Weight to Roadbed.
Section I discusses terrain irregularities and how they are compensated for, and ballast--