Yes, vehicles have become more fuel efficient, but a just-released report by the Institute on Taxation and Economic Policy shows that inflation is 3.5 times more responsible for the decline in the purchasing power of the gas tax.
Jun 25, 2015 Institute on Taxation and Economic Policy
New Hampshire will consider a Republican bill in 2014 to tie the gas tax to inflation, increasing it by about 4 cents next year should it pass. The Senate killed a House bill in May to increase the gas tax by 12 cents over 3 years.
Dec 9, 2013 Concord Monitor
A Freakonomics blogger has trouble finding an affordable bike in Portland, and looks into the reasons why.
Aug 21, 2009 The New York Times: Freakonomics Blog