The problem with gas taxes is that, as vehicles become more fuel efficient, you get the same road damage but less revenue. The problem with congestion taxes is that they're hard to enforce. Why not combine the two and create a mileage tax? Every time the mileage is reported to the state, a tax would be levied on the number of miles driving since the last time. Whenever a car is sold, wrecked, transferred, or moved out of state, the mileage would be recorded and tax levied. It's not as precise as either the gas tax (at reducing oil consumption) or the congestion tax (at reducing driving in particular areas), but it would both reduce oil consumption and reduce driving in general. It does both things not particularly well, but it makes enforcement easy and unintrusive (particularly since this information is already collected). And in terms of raising revenue, switching up the tax code now and again is a proven strategy.