A set S of lines is universal for drawing planar graphs with n vertices if every planar graph G with n vertices can be drawn on S such that each vertex of G is drawn as a point on a line of S and each edge is drawn as a straight-line segment without any edge crossing. It is known that ⌊ 2(n−1) 3 ⌋ parallel lines are universal for any planar graph with n vertices. In this paper we show that a se...