I found a quick link to an article about taxes and biking. Most every cyclist has heard the old "bikes shouldn't ride on the road, they don't pay taxes" argument. This short, easily readable argument shows why road costs are actually improved by cyclists.
I think there are probably flaws in this argument. The author states that 6-7% of road taxes are paid by motorists, and increasing cyclists wouldn't amount to a significant decrease in this. And the remaining 93-94% is paid by property taxes and the general fund. But later she says that we would need 12 cyclists for every driver to balance the street budgets. Something's got to give. But it's still interesting.