I think about all the opportunities for collisions to occur during the rush hour.
Consider, say, fifty thousand vehicles trying to get to work in a given city, all at the same time, in stop and go traffic.
There are likely to be a dozen fenderbenders, and one or two worse collisions, during that rush hour.
Now consider all the opportunities for collisions that occurred among all motorists involved during that time. Any one driver must have had a hundred opportunities to cause a crash, and yet only a dozen or two, out of fifty thousand drivers, times at least a hundred opportunities per driver, actually caused a crash!
So, doing the math, that means a dozen collisions caused out of 50 000 * 100, or 12/5 000 000 opportunities, or 2.4 parts per million.
That's almost six sigma performance.
The wonder is not how many accidents happen, but how few.
Agreed. I often think that if aliens were watching rush hour from outer space, they might have the same impression we have as we peer down at a busy ant hill...
Great analysis, btw, from a data geek...:)