VEHICLE FUEL ECONOMY AND THE REBOUND EFFECT – AN ANALYSIS OF EFFICIENCY
Mahoney, James M.
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SUMMARY Understanding and quantifying the environmental impacts of personal transportation is the first step in the management and mitigation process. A life cycle assessment of vehicles allocates a sweeping majority of the lifetime environmental impacts to the use phase. This justifies the strong emphasis being placed on development of fuel efficient vehicles as the chief method used to reduce the environmental impact of transportation. When mandating widespread adoption of efficient vehicles, it is important to consider the rebound effect, a deliberation that is often overlooked. The rebound expresses an increase in consumption associated with an increase in efficiency. A consensus in the literature produces a rebound for improving vehicle fuel economy around 20%, though a fair degree of variability does exist, ranging generally from 5%-65%, with one study presenting value of 1000%. This study investigated how consumers will alter their driving habits in response to changes in fuel price, in the form of both price fluctuations at the pump and improvements in fuel efficiency. Data were also analyzed from four years of the National Household Transportation Survey spanning from 1990 to 2009 and one firsthand survey to estimate the environmental impact of personal vehicle usage, changes in driving behavior over time, and the extent to which a rebound may be exhibited following the adoption of fuel efficient vehicles. The environmental impacts were assessed over the impact categories of energy, water consumption, and emission of multiple different pollutants. Results were obtained for the state of Wisconsin; the Milwaukee, WI, region; and the Madison, WI, area. It was found that there was no difference significant between the groups for annual household miles travelled and for the size of fuel price increase to provoke a change in driving tendencies. There was, however, a difference in how each group would respond to the identified fuel price change. The analysis of environmental impact concluded that in the entire state of Wisconsin, eight of the ten impact categories exhibited a decrease in per person impact between the survey years. In Milwaukee, WI, all ten impact categories displayed an increase in per person impacts. Coincident with a generally increasing trend in annual miles driven per person, improvements in fuel efficiency may not have been the influential factor in decreasing the impacts. The myriad rebound calculations produced magnitudes between 30%-846%, appreciably larger than the 20% approximate average value found in the literature. This suggests that consumers who adopt more fuel efficient vehicles may have a strong propensity to increase their driving activity to the degree that their increase in consumption more than out paces the increase in efficiency, resulting in an overall increase in environmental impact despite improving efficiency.
environmental impact; rebound effect; transportation