It was ME! I stopped driving my Audi A8 and bought a new Prius. The demand for gasoline dropped and we all get lower prices. Hooray for me!
I traded in a Lexus GX470 (18 MPG on the highway) for a 2006 Prius, so it was perhaps both of us. The Prius is awesome, the technology is amazing, I smile everytime I think about the car. I just love it!
His question seems to be *how* did people cut back, not the motivation -- which was obviously price. I remember anecdotal reports of people driving slower. It is much harder to identify cars that stay at home.