Which also tells you something...if there were as many cars in Pripyat, the situation would have been similar. In other words, the two emergency situations differ in most aspects.
But yeah, buses scale far better than individual cars, that's for sure.
(Oh, and btw, given the long-running tinfoil campaigns against federal agencies in general and emergency response in particular, I can totally see how "This is FEMA, everyone get onto our buses, we'll take you somewhere safe" would prompt an orderly evacuation. Not.)
