Comes from Edmunds.com:
The median household is spending 11.5% of its income on gasoline, up from 4.6% of its income five years ago.
It’s a pretty basic calculation, which assumes that both miles driven per year and fuel economy have remained constant over time (at 30,000 and 22 miles per gallon, respectively). But to a first order of approximation, it’s probably reasonably reliable. And at 11.5% of income, pain at the pump is certainly more than just psychological: it’s equivalent to a seven-point spike in income tax rates, with the brunt of the tax hike borne by those least well off.