It's been 25 years since the federal gas tax went up The federal gas tax is the same 18.4 cents a gallon that was set in 1993. Over the 25 years, the cost of building and maintaining roads and bridges has shot up, leaving the funds that help pay running on empty.

Would a tax per mile driven be more efficient or less efficient than a tax per gallon of gasoline? Which tax would be more regressive? Explain your answer.