This is only a problem when comparing _disposable_ income PPP, because disposable income has taxes deducted. Disposable income data is harder to collect, and i

This is only a problem when comparing _disposable_ income PPP, because disposable income has taxes deducted. Disposable income data is harder to collect, and is therefore less common. This article uses average income (GDP per capita), which compares pre-tax money. The $10/day value that a US citizen gains from the roads was paid for out of that average income.