If you’re looking to rent for the day, you would never pick 3 cars over 1. And if you already own the 3 cars, you wouldn’t go out of your way to rent another one. I don’t see how a parking charge would change this, unless it was far heavier than this proposal is.

Additionally, think about how many full 9-seat vans there are in Paris. Think about how many single-occupant SUVs there are. I think the benefit here is pretty clear.