I mentioned yesterday that the estimated bill for deferred maintenance of government assets is NOT KNOWN, but no knowledgeable source doubts it's enormous. 

The reason it's not known is, current accounting does not require it be recorded as a liability on government balance sheets. Some U.S. state & local governments are recognizing how important it is, though, and are starting to address it without being required to do so. See a few examples here of what they are doing.