"Regressive" and "Progressive" are frequently misunderstood terms around here. I once had someone try to explain to me that paying a toll to use a road is "regressive." A real head-scratcher.
Technically it is if you consider it a tax, because like the gas tax, use of it takes a larger percentage of the income of the poor. Of course, in this case the use of an income-based progressive tax would be patently unfair.
This is one of the main arguments against the sales tax based Fair Tax, except the Fair Tax rebates the sales tax to everyone at a rate that the basic necessities of life effectively aren't taxed. It's neither progressive nor regressive, just fair (hence the name).
It also means that illegal aliens paying no tax on their illegal incomes now will be paying tax whenever they buy something. That's probably one reason why we'll never get the Fair Tax.