Decades ago, harkening back to the oil shocks of the 1970’s, the US Congress instituted what would seem to be a reasonable idea of discouraging gas guzzlers. Vehicles below 22mpg are slapped with a special tax, usually referred to as the gas guzzler tax ( the legislation was called: The Energy Tax Act of 1978). The tax is collected by the manufacturer or importer, and is paid by the first buyer.
An economist would refer to such a tax as a disincentive to guzzling gas (actually a disincentive to producing/buying gas guzzling vehicles).
As is usual, what would seem to be a good idea is destroyed by spineless politicians and weaselly lobbyists.
Therefore, SUVs (light truck), of course, are exempt 🙂
In 2005, about 170M was collected. There are untold hundreds of millions of dollars of foregone revenue due to the SUV loophole.
Source: TRANSPORTATION ENERGY DATA BOOK: EDITION 26–2007, Tables 4.20 and 4.21
(a treasure trove of energy data. Also interesting is the studies on speed vs. mpg — generally vehicles peak around 50mph).