The state currently has a fixed, 19 cent per gallon tax on gasoline and 15 cents on gallons of diesel. These funds are used primarily for road construction. Unfortunately, when fuel prices climb, the tax revenues don't, even though the cost of building roads and bridges is going up. Granholm last week supported a new fuel tax system that would be changed to a percentage rate.
One of the byproducts of Michigan's poor roads is that it discourages the use of smaller cars since they are more susceptible to damage. Changing to a new tax system would potentially raise revenues for road building, as well as encourage the use of more efficient vehicles. Of course a widescale move to EVs will mean yet another change in the road funding process, but that's another story.