Zony, Beannie, I really must apologise as I had not dug deep enough to find your interesting post. Oddly, I have just finished a book along similar lines called 'SHIFT' by Hugh Howley, the central volume of a trilogy (WOOL, SHIFT, DUST) which set in the USA has many similar features.
Briefly America has poisoned the air with virulent nano-robots and is forced to save a few thousand of its populations by building huge underground silo's to be kept sealed for centuries until the air purifies itself and the use of drugs to keep the population subservient. It is centred on the success or failure of the 50 silos as the centuries pass and the problems of keeping the knowledge secret. Complex and disquieting.
Anyhow, thanks for thinking about me, I do appreciate it. I am also a great fan of Willie Nelson!
Mike