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Carbon dioxide (CO2) is the primary greenhouse gas emitted by gasoline-powered motor vehicles, and the amount of CO2 emitted depends directly on the amount of gasoline burned by the vehicle. Any reduction in vehicle fuel consumption will also reduce CO2 emissions, and any reduction in CO2 emissions requires a reduction in fuel consumption. In 2004, pursuant to Assembly Bill (AB) 1493, the California Air Resources Board (CARB) adopted greenhouse gas emission standards for new vehicles that would require substantial reductions in CO2 emissions and fuel consumption from light-duty motor vehicles. In December 2007, Congress made significant amendments to the Corporate Average Fuel Economy (CAFE) program with the passage of the Energy Independence and Security Act of 2007 (EISA2007). After the President signed EISA2007 into law, U.S.

This paper discusses some trends and influencing factors in passenger car fuel economy. Fuel economy and fuel consumption were calculated by a carbon balance method from HC, CO, and CO2 emissions measured by the 1972 Federal Test Procedure. The information presented was derived from nearly 4000 tests of passenger cars ranging from 1957 production models to 1975 prototypes. Data are presented for various model year and vehicle weight categories. Trends in fuel economy are discussed on an overall sales-weighted basis and for each individual weight class. Some of the factors that influence fuel economy are quantified through the use of a regression analysis. Particular emphasis is placed on the differences in fuel economy between those vehicles that were subject to federal emission regulations and those vehicles that were not. Three ways to characterize vehicle specific fuel consumption are presented and discussed.

Data from the Nationwide Personal Transportation Study (NPTS) and other sources have been used to generate distributions of vehicle miles traveled (VMT), average speed, and fuel consumption as a function of trip length. Approximately one third of all automobile travel in the U.S. is seen to consist of trips no more than ten miles in length. Because short trips involve more frequent stops and a smaller percentage of operation during warmed-up conditions, nearly half of the fuel used by automobiles is consumed during the execution of these short trips. The typical trip of approximately ten miles in length has been shown to result in a fuel economy that is equal to the average fuel economy achieved for all trips combined.

Concerns regarding U.S. dependence on crude oil from politically unstable regions and the impact of fuel combustion on climate change have led to new state regulations and proposed additional federal regulations requiring reductions in fossil fuel use by passenger cars and light-duty trucks. Significant reductions in fuel consumption can be achieved while maintaining the performance and size of current production vehicles; however, it does not appear that the benefits will be commensurate with the costs. Based on the same model employed by the United Nations Intergovernmental Panel on Climate Change, nationwide reductions in light-duty motor vehicle greenhouse gas emissions of 30% will have no measurable effect on ambient temperature. This calls into question the assumption that the cost of reducing greenhouse gas emissions has corresponding economic benefits related to the moderation of climate change.