West bound on 580 between Pleasanton and Hayward. As I approached I kept second guessing if it was an X, but as I got closer I determined that indeed it was. A bit of an odd duck though. No roof rack, no lift, stock mud flaps, and a shrock rear bumper. As I passed I looked at the driver, a portly fellow with glasses, who also looked to see who was driving the X that passed him. I exited redwood road, and while waiting to turn left towards Hayward, this fellow exited and turned right towards Castro Valley.