Sales taxes on gasoline — like the ones proposed by the governors of Maryland and Virginia to fund transportation projects in each state — aren’t paid directly by consumers like they would be in the sale of other goods, and some claim that’s a political ploy to make them more palatable to voters.

A plan proposed by Maryland Gov. Martin O’Malley would levy a 2 percent sales tax on gas starting in July, but that would be at the wholesale level, before the gas even gets to the local Exxon or BP. O’Malley’s office says that’s because there’s an 18.4-cents-per-gallon federal tax on wholesale gasoline, so if the state taxes gas at the retail level, it would be taxing a tax.