Saturday, January 27, 2007

Automobiles: Manufacture vs. Use

This life-cycle inventory of impacts due to the manufacturing and use stages of an automobile was published by Heather L. MacLean and Lester B. Lave of Carnegie Mellon University, in 1998. They based their analysis on a 1990 Ford Taurus, assuming a vehicle lifetime of approximately 14 years and a fuel efficiency of 21.8 mpg.
A car uses 1.2 million MJ of energy over it's lifetime, with 120,000 MJ (10%) in manufacturing and 1.08 million MJ (90%) in the use phase. Since a of gasoline has 131 MJ of energy, an automobile takes the energy equivalent of 916 gallons to manufacture.

Unlike cellphones or computers, most energy used in a cars life cycle is in the usage phase. It takes 19 times more energy to create a car than a PC and Monitor (which takes 6,400 MJ to manufacture) and 86 times more than a mobile phone (1,390 MJ).

With a lifetime of 14 years, the transportation service an automobile provides (10,000 miles) uses 86,000 MJ a year.

Though energy consumption is a fair approximation of overall environmental impact, the emissions of substances that are toxic to humans don't correlate very well to energy. Emissions of toxics tend to correlate more closely to direct human health impacts, rather than environmental impacts. MacLean and Lave report the toxic releases related to car manufacture and use, and these appear in Figure 2. Interestingly, any environmental or health impacts related to toxic releases will be split fairly evenly between manufacture and use, in contrast to energy, which is dominated by the use stage.
via ILEA

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