Design strip segments have a local coordinate system for each internal cross section. An internal cross section is perpendicular to the design strip segment spine and extends from the left tributary boundary to the right tributary boundary. Each internal cross section is treated exactly like a Design Section with its own r, s and z axes (see above).

All of a DSS’s cross sections will have coordinate systems that are parallel, but for certain structure geometries the s-axes of each cross section will not be collinear. This is due to each cross section determining its own "design centroid" (see below).