On the two-dimensional orthogonal drawing of series-parallel graphs

It has been known that every planar 4-graph has a 2-bend 2D orthogonal drawing with the only exception of octahedron, every planar 3-graph has a 1-bend 2D orthogonal drawing with the only exception of K 4, and every outerplanar 3-graph with no triangles has a 0-bend 2D orthogonal drawing. We show in this paper that every series-parallel 4-graph has a 1-bend 2D orthogonal drawing