Two lines or line segments can either intersect (cross) each other or be parallel. In this section, we will be learning how to identify and draw parallel and perpendicular line segments. Parallel line segments never meet, no matter how far they are extended. Two line segments are perpendicular if they form a 90 degree angle where they cross. Parallel and perpendicular line segments are found everywhere in the world around us. For example, city planners often design roads to be parallel and perpendicular to each other. Along with roads, railroad tracks, lines on notebook paper, and bookcases are parallel.