Size of uk landmass would be a good starter for 10..you can truck one end to the other in probably 12 hours, and very little needs to go one end to the other.
Usa is huge, hence more requirement.
Even if you look at northern europe, in a few hours driving you can cross a few borders, just no need for it. And if you do need it, it goes in cargo for a pax flight of which there are many.