The argument at public meetings and in politics always seems to go like this: Highways are practical transportation projects because they pay for themselves, while public transit, bike, and pedestrian projects require exorbitant subsidies.

A new report by the US Public Interest Research Group debunks part of that thinking, showing that roads don't pay for themselves. They're paid for both by users (through gas taxes and tolls) and through substantial contributions from general taxes that non-users also pay.

Wonky graphs showing national subsidies to road projects over time are below the cut for the nerds, but here's the quick version: A lot of the subsidy for highways comes in the form of local spending on streets and secondary roads, which are largely paid for from property tax or general tax revenue. In 2008, local governments spent more than $31 billion on highways raised from property taxes, assessments, and general fund revenues, says the report. That means people who don't drive very often are still shouldering the cost of highways (see related argument: cyclists don't pay taxes).

The report says that the federal government typically covers 80 percent of the cost of highway expansion projects, leaving local or state governments to cover the last twenty percent, while the feds only cover 50 percent of new transit projects on average. "It is not hard to see how this system skews transportation decision-making," says the report.

Lengthy analysis of this report over at Streetsblog DC—graphs below the cut!