Source: BTS.

Total Motor Vehicle Fuel Consumption and Travel in the United States, 1960-2005

The Oil Shocks of the 1970s and early 1980s were accompanied by increase in the fuel efficiency of motor vehicles. While in 1970, a motor vehicle was consuming on average 760 gallons a year (about 13.8 miles per gallon), in 2005 this figure dropped to 540 gallons a year (about 22 miles a gallon). The system-wide improvement in energy efficiency was consequently around 40%. However, the 1990s saw an increase in the average amount of fuel consumed per vehicle as commuting distances and congestion increased, especially in urban areas.