This study is an update of the analysis in Sivak and Tsimhoni (2009). That study examined actual, on-road vehicle fuel economy in the United States from 1923 through 2006. The present study extends the data through 2013, and it also includes retroactive adjustments made to several values by the U.S. Department of Transportation. The data for this analysis consisted of estimated miles driven per gallon of fuel for each year from 1923 through 2013. For 1923 through 1935, fuel economy was calculated by dividing the estimated fuel consumption for highway use (U.S. Department of Commerce, 1957) by the estimated miles driven (National Safety Council, 2007). For 1936 through 1985, fuel economy was calculated from the information in U.S. Department of Transportation (1987). Finally, online versions of annual statistics (U.S. Department of Transportation, annual) were the sources of the information for 1986 through 2013. For 1923 through 1935, fuel-economy information is available only for the entire fleet of all vehicles. For 1936 through 1965, separate estimates are available for cars and trucks. For this time period, “cars” included motorcycles as well. However, the mileage driven by motorcycles represented only a negligible fraction of the total mileage. This is evidenced by the fact that in 1966 (the first year for which separate mileage information for motorcycles is available), motorcycles accumulated 0.3% of the combined mileage for cars and motorcycles (U.S. Department of Transportation, annual). Starting in 1966, the U.S. Department of Transportation divided the truck category into other two-axle, four-tire vehicles (labelled here “light trucks”), single-unit, two-axle, six-tire trucks (“medium-duty trucks”), and combination trucks (“heavy-duty trucks”).1 The light-truck category originally included only pickup trucks, but was expanded to include vans and SUVs when they were introduced. The analysis also examined the combined group of all light-duty vehicles. Prior to 2007, this group included cars and other two-axle, four-tire vehicles. Starting with 2007, the U.S. Department of Transportation changed the division of light-duty vehicles from cars and other two-axle, four-tire vehicles, to short-wheel-base light-duty vehicles and long-wheel-base light-duty vehicles. For simplicity, in the present report we will be referring to these two groups of vehicles as “cars” and “light trucks” throughout. It is important to note that despite the change in 2007 in how all light-duty vehicles were subdivided, the overall classification of the combined group of all light-duty vehicles did not change in 2007. (Author/publisher)
Samenvatting