[T]otal traffic deaths declined nearly 9 percent in 2009 — to 33,963. That's the lowest toll since 1954. In 2008, an estimated 37,261 people died on the roadways. The newest numbers fit into a trend of steady decreases since 2005, when an estimated 43,510 people were killed.
Adjusted for population, miles traveled, or any other reasonable factor to reflect how much more driving there is now than there was then, they are probably at their lowest level since the car was invented.
Important factors in the decline probably include increased seat belt use, a decline in drunk driving, better trauma care, recession driven decreased traffic volumes and vehicle safety features.