I just witnessed 6 or 7 empty charter buses prepositioning - about 40 miles south of DC just off I-95.
Completely empty, they were all turning into a side road with gas, McDonalds, and hotels.
There is no tourist activity going on here.
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Sounds like you are describing one of the ‘pickup points’ for the Virginia Citizens Defense League (Gun rights group) members and guests that partake in the annual ‘Lobby Day’ at Richmond VA Monday.
That could be it.