Energy Efficiency: Potential Fuel Savings Generated by a National Speed Limit Would Be Influenced by Many Other Factors

Gasoline prices are volatile and have increased greatly over the last several years, before dropping again recently. The national average of regular grade retail gasoline prices increased from about $2.24 the week of January 2, 2006, to a peak of $4.11 the week of July 14, 2008, an increase of almost 84 percent, before dropping to about $2.40 the week of November 3, 2008. High fuel prices have focused attention on conservation. Congress previously used a national speed limit as an approach to conserve fuel when, in 1974, it provided for a national 55 mile per hour (mph) speed limit to reduce gasoline consumption in response to the 1973 Arab oil embargo. The law prohibited federal funding of certain highway projects in any state with a maximum speed limit in excess of 55 mph. In 1987, Congress allowed states to raise the maximum speed limit to 65 mph on rural interstate routes. In 1995, the 55 mph speed limit was repealed. Since then, states have been free to set speed limits without the loss of federal highway funds. Congress expressed interest in obtaining information on using a national speed limit to reduce fuel consumption. In response to the request, we reviewed existing literature and consulted knowledgeable stakeholders on the following: (1) What is the relationship between speed and the fuel economy of vehicles? (2) How might reducing the speed limit affect fuel use?