A lot of the thinking comes out of starting to look at big disasters, you know, like three mile island, nuclear melt downs. And one thing i try and do in the book is extrapolate these ideas out. I bcause those conditions, those layers of safety or lack of safety are different depending on where you live and what kind of car you drive. What happened in your neighborhood 50 years ago? Did they build a highway through it, or did they not build a highwaythrough it that can effect the likelihood of a traffic crash even today.