This is essentially a user-based tax. Those that travel more and put more wear and tear on the roads pay a higher amount. Now, I think that a bus wears down a road more than a car so the tax needs to be higher on diesel vehicles. I think it is but I am not sure about that.
The bottom line is that every study seems to indicate we have SIGNIFICANTLY underinvested in our countries infrastructure. Our gas taxes are some of the lowest in the industrialized world so why not increase taxes. This is a NO BRAINER tax that people should just suck up and deal with.....and I HATE higher taxes!