Yes, the federal government does subsidize local road expenditures. If I had spent an extra 15 seconds, I would've attached this link first:
Road Spending by State Funded by User Taxes and Fees, Including Federal Gas Tax Revenues | Tax Foundation
The bottom line is that by adding the portion of the federal gasoline tax that is used for roads, the national average is that fuel tax and user fees total about half of the total road expenditures, just like Minnesail said in post #106.
Even if a person does not own a car or buy gasoline, that person still pays fuel tax and user fees indirectly. Those expenses are factored into the prices of every product at the grocery store, for example.