After a day in the DC area and suburbs, I was heading home on Pennsylvania Avenue which becomes Maryland's Hwy 4. which is where I was when my daughter, who is 10 years old and quite bright, and I noticed the object straight in front of us but off to the left a bit. I at first thought it was a plane, as this is very close to Andrews AFB, but as we got closer, it had an odd almost triangular shape with some sort of rounded compartment at top center. We are quite used to the planes buzzing everywhere, what struck us about this object was that it was just sitting there in the air above the trees. We saw no exhaust or fumes or propellers. I have no idea how this object was actually flying. We continued to observe it as we drove toward it on a straight portion of the road until finally we passed it and could no longer see it. The whole 15 minutes or so that we observed the object, it never moved, made a sound, flashed a light, nothing. It just hung there in space looking very odd and out of place. There were no markings, flags, symbols or insignia of any kind painted onto the exterior of the craft, it was just covered in a dark smoky gray paint. That's all we recall at this time.The experience was disturbing enough to bring me here and to try to see if anyone else reported the object we saw. I've never seen anything close to a UFO before, and maybe I still haven't, but after a lifetime lived on military bases with planes flying almost constantly, I can honestly say I've never seen anything like that before. The only thing close to that hovering capability would be a helicopter, and this was in no way a helicopter. As I said before, there were no rotors visible, no propellers, no propulsion device visible at all. It just left both my daughter and me with a very odd feeling and a question we couldn't answer, which is something we hate!! Lol!