Interesting sidenote: why did vehicular deaths decline by 25% between 2007 and 2009, without any real decrease in miles traveled? Odd.
My hypotheses:
Older, less-safe cars are breaking down and getting off the road. Newer cars are better able to handle higher speeds and collision avoidance maneuvers. Safety features previously found only in luxury cars are becoming available in lower-end models.
Many roads were widened and/or improved as part of the economic stimulus. More lanes and wider shoulders means more room to dodge a potential accident.
Maybe the weather has been more mild on particularly dangerous roads.
I think it is almost entirely that cars are more safe nowadays than they used to be. And I expect it has less to do with "collision avoidance maneuvers", and more to do with better design and crumple zones, and a significant focus on crash test ratings. There are probably as many accidents as ever, it's just that less of them are fatal.
But my original question was (expanded for clarity): "Why was there a sharp drop from 2007 to 2009 after many years of very gradual decrease or even flatness? Your answer could explain a steady drop as safety features become more widespread, but that didn't happen from 1995 to 2005, even though presumably people bought new cars during this time.
My hypotheses:
Older, less-safe cars are breaking down and getting off the road. Newer cars are better able to handle higher speeds and collision avoidance maneuvers. Safety features previously found only in luxury cars are becoming available in lower-end models.
Many roads were widened and/or improved as part of the economic stimulus. More lanes and wider shoulders means more room to dodge a potential accident.
Maybe the weather has been more mild on particularly dangerous roads.