In a word: Mileage
Today, my car Yuki the Kia* turned over 208,000 miles. In the previous driving post here, I noted that it had turned over 207,000 miles on December 3, 2010. Since that was 3.25 months ago, that means I drove an average of 308 miles a month. That's half what I drove during the time between 206,000 miles and 207,000 miles. I'm still contributing to the overall decrease in miles driven since the peak in January 2007.
For more, see this post on Calculated Risk.
*There is a very geeky joke behind this name, which one of my daughters is responsible for. That's a story for another post. Originally crossposted to neonvincent on Dreamwidth. Comment here or there, whichever you prefer. http://neonvincent.dreamwidth.org/4600.html