the most uncommon car i have seen in the past few years was a Vector going the other way on the Interstate north of Charlotte.
But the all time most unusual car, was back about '66 or so, i was driving across Ohio, i think, going from Lincoln to DC, in my TR-4. I had just accelerated away from a toll booth station, and was about up to speed, when this low, red Ferrari slowly went by to my left, blowing lots of blue
oil smoke. I have recalled that sight many times, i believe it was a race 250LM.