Indeed, most bicyclists in fact also own cars, so they're also paying the licensing fees and gas taxes as well. But by using their bikes in place of cars, the wear and tear (and subsequent maintenance costs) they inflict is exponentially less than that caused by cars and trucks.
A 1995 study titled "Whose Roads?" by cycling advocate Todd Litman laid all this out in detail. The study estimated that automobile users pay an average of 2.3 cents per mile in user fees, including fuel taxes and vehicle registration fees, while they actually impose 6.5 cents per mile in road service costs. Who pays the difference? It's picked up by general taxes and property assessments. So while bicyclists pay an equal share of those taxes, they impose costs averaging only 0.2 cents per mile in road service costs.
The amount bicyclists overpay leaps out when you look at the costs of local roads, the roads cyclists use most. Litman found that only a third of the funds for their construction and maintenance comes from vehicle user charges; local property, income and sales taxes pay the rest. Automobile user fees contribute only about 1 cent per mile toward the costs of local roads but simultaneously impose costs more than six times that amount.
Read the entire article! Some great information to use against those folks who feel that cyclists don't belong on the road because they do not pay for them.
Only a third of construction and maintenance costs of local roads come from "vehicle user charges." Only a third!