I was flying a traffic watch C-152 along the freeway one day when a Piper Archer flew right over me going the same direction. He was just to the right of the freeway, just like me, but going about 20 Kts faster. He missed me by about 30 feet. It was weird though because it was like it happen in slow motion as he was only going slightly faster. First I heard the engine, then I nearly jumped out of my seat when he appeared just over head. Scary