http://wwwc.house.gov/international_relations/109/dow072705.pdf
penultimate paragraph:
<quote>
It is relatively easy to narrow down where our oil dependency lies in the US: transportation. Meaningfully reducing demand for transportation fuels is the only realistic way of gaining greater energy independence in the US. The challenge is that the obvious solution, encouraging the use of diesel fuels and the use of more fuel efficient vehicles, is also politically the most difficult. However, the potential is huge. Improving the average fuel efficiency of the US vehicle fleet by just 2 mpg would reduce US gasoline demand by roughly 1 million barrels per day. This is equivalent to all of the growth in US gasoline consumption over the past 8 years.
<unquote>
Michael