Too many, but at least some are directly on vehicles. Transit (in the USA, on the West coast) is funded >90% by taxes on income, property, vehicle registration, fuel, etc not by the people using it.

I cannot speak for every state ever, but I remember that roads in WA were mostly funded by gas/diesel taxes + vehicle registration fees.

Which is also why WA state has been charging an additional significant car registration fee on EVs (on top of the usual annual registration costs), since EVs don't contribute to this normally through gas/diesel taxes.

Everyone uses the roads. You have to reach for very obscure examples to find commerce that doesn't utilize roads. Every bit of concrete and steel to build transit was at some point transported over roads.

Varies from place to place but it's not insignificant