Buc-ee's is a gas station. It's not a truck stop. And with that in mind, 18-wheelers aren't allowed at Buc-ee's. Buc-ee's is already super crowded and a little hard to navigate getting in and out because of the volume of cars (at all times). Allowing 18-wheelers into the gas station would add to those issues, so Buc-ee's bans trucks.