Part of the never-ending debate in the world of transportation policy and urban planning is to what extent (if any) roads are subsidized. Namely: do drivers actually pay the full costs for roads, and/or how much should they pay? The budgets and relative subsidies for transit have been obvious for many years because it's quite simple to pull their data. Roads are a little more complicated to analyze.
Enter the conservative-leaning Tax Foundation. Last year they released an analysis of data from state and local governments to shed some light on the issue. It's a fairly simple numerical look at just how much roads actually are subsidized by general government revenue. From the report:
Nationwide in 2010, state and local governments raised $37 billion in motor fuel taxes and $12 billion in tolls and non-fuel taxes, but spent $155 billion on highways. In other words, highway user taxes and fees made up just 32 percent of state and local expenses on roads. The rest was financed out of general revenues, including federal aid.
The ratios do not change much when adding in all transportation modes. In 2010, state and local governments spent $60 billion on mass transit, $23 billion on air transportation facilities, $1.6 billion on parking facilities, and $5.3 billion in ports and water transportation, in turn raising $13 billion in mass transit fares, $18 billion in air transportation fees, $3.2 billion in parking fees and fines, and $3.8 billion in water transportation taxes and fees. Altogether, states raised about 36 percent of their transportation spending from user taxes, fees, and other charges.
Tables of data available at the link.