On my way to an appointment, traveling south on rt. 301 in waldorf, md approaching the intersection with rt. 5 i saw what was possibly an airplane. it was blue but it did not appear to have all features of an airplane. it was traveling in the distance from southwest toward northeast in the air at a distance. it was traveling at the speed that an airplane may travel. when it got closer it banked to the left, when i was able to make out the diamond shape. i would guess it was about 20' x 50' in size. its color/material was a blue-white shimmering metal. i pulled into the parking lot just past the above mentioned intersection. it had turned and was now behind me, it was traveling west - i was then looking north at it from rt. 301. when i went to get a camera and binoculars out of my car it was gone.