The way around that.
Johnny, I can roll that Merlin in 5.5 seconds!!!!
Make every vehicle not filled to 50% capacity pay an extra fine, or tax. We all need a PU from time to time, and a van would be nice.
However, until we make it too expensive for folks to operate full-time the largest vehicle they might ever want they will do that.
It seems a bit like requiring all the power be on in your house, or none. We agree that's silly. It's silly, but still economically feasible, to have one person putting around in a van or SUV, too.
Arf