Traveling south on route 13 with my daughter at 9:30pm when she noticed an object in the sky that seemed to be an airplane with flashing red and white lights. I dismissed it as an airplane for a moment as the object traveled southwest in the direction of d.c. after about a mile or so I could clearly see this object had changed direction and was heading north/northwest towards us. It was quickly plain to see this was a triangle shaped object about 100/150 feet across. I must note the object changed altitude as it traveled north to less than 300 feet at our closest approach from the highway. I pulled over into a parking lot turned off the radio and rolled down the windows looking for an engine sound but we heard none. The object continued northwest moving slowly toward the center of Dover, changing directions to a s/w path and flew away. I’m positive this was a triangle shaped object with 2 red and 2 white lights and this was a clear,bright night sky making the outline of the craft unmistakably easy to see.