building a Toyota Prius consumes 113 million British Thermal Units (BTU), while a gallon of gas contains about 113,000 BTU. The 2008 Prius can go 48 miles per gallon (on highways).
A 1998 Toyota Tercel, on the other hand, does 35 mpg and, since it is used, the carbon cost of construction has already been paid.
This would mean that it would take about 129,230 miles of driving before the 2008 Prius surpasses the 1998 Tercel in eco-friendliness.
A more interesting question is what is the marginal cost of building a Prius versus a conventional car?
