I was driving north on I 99 toward east freedom pa. I saw a triangle shaped craft moving from west to east very quickly. It came over the mountain to my left across the valley in a few seconds. It crossed the highway and went over the ridge to my right.it was not moving any faster then a jet. However, it was much lower than normal aircraft would fly to the mountains.It was dark and hard to judge but when I aw it clear the mountain I looked down the ridge to the bottom of the valley and judged the craft was 500 to 600 feet above the ridge line. I looked several times to see if I could see it more but it was gone.The craft had three lights on it. The front light was green. One each side of the side were sevral white lights shaped in a triangle. It happened very quickly and I can not say if it was 5or 6 lights on each side shaped in a triangle on each end of the triangle. I do not know what I saw it happened quickly and I was driving up the interstate.