I agree completely with posts #3 and #4. Biggest mistake at most airports over the past 50 years was the failure to secure lots and lots of extra land to accomodate the boom in air travel. When DC-3s ruled the skies, almost nobody envisioned the need for a single airport to have half a dozen runways, some nearly nearly 3 miles in length or the need for central terminal space sufficient for 100-150+ gates.

Correcting that lack of foresight will likely cost hundreds of billions over the next several decades. And will necessitate moving some airports out to the middle of nowhere - like Palmdale, CA (instead of LAX) or Peotone, IL (instead of ORD). When ORD was built, the leaders probably thought it was much too big. If we've learned anything, it ought to be that airports should be designed so that 95% of those asked think the new airport is too big, and then the surrounding land should be doubled or tripled (or more).