NPR's Morning Edition had an interesting story this morning ("High Gas Prices Quietly Welcomed by Environmentalists") about whether gasoline consumption can be better curbed through regulation or through high prices (particularly a tax). Economists feel that gasoline prices would need to double and remain there (i.e. $7-8/gallon) before behavior would really change, and advocate a gas tax to get us there. The externalities (accidents, smog, global warming, etc.) are simply not reflected in the current price of gasoline. Environmentalists, however, feel that a gas tax is a complete political dead-horse, fearing that it would be extremely unpopular with most Americans, and advocated regulations requiring 40mpg automobiles (as exist in Europe). Economists note that the 40 mpg averages in Europe exist, not because of regulation, but because of high prices (through taxes) that have existed for decades.
Unfortunately, it seems unlikely that we are going to get better fuel efficiency (through either taxation or regulation) until we have leadership from either side of the aisle in Washington.
Note also another story on Morning Edition this morning concerning an organization in Indiana promoting car pooling by matching people up using a method similar to online dating ("Carpooling Best Sampled One Day Per Week").