I don't think we could squeeze enough flights onto the field to make digging down make sense. The terminals we have are nearly sufficient for the runway capacity we have, and we've never fully utilized that. (And may never.) In late TWA days when the airport was planning for growth beyond thirty million passengers annually there was talk of a new terminal as the only economically viable option. Even then, when coffers were more flush and the terminal was legitimately crowded, expanding the historic terminal was seen as a challenge. I suspect there would have been enough hue and cry that a way would have been found had TWA weathered the storm. But that was then.
On a side note, it's worth keeping in mind that air travel as we know it now will probably not always be with us. Transportation will change. There will always be something, but in the future it will be different. We may very well be seeing the glory days of conventional airports right now. It remains to be seen how many large new ones will be built before the next big thing happens. In the US it seems likely the number will not be large. Ours will forever remain one of the first and most ground breaking. (Which, by the way, is part of why it's got a few issues.) And we still have it. And with a little luck we will for a long time to come and it will serve our needs adequately for the immediate future.
This is a bit off topic, but here's a close parallel: in 1892 large unified railroad terminals were still a fairly new thing. There were large central terminals in Europe, where railroads were often state run from the outset. There were some quite large stations in England, where space was tight and cities were large and dense. But few major US terminals boasted that kind of size, in part because most US railroads used their own stations and there were lots of competing railroads, and apart from New York, Philadelphia, and Boston US cities generally didn't face the kinds of constraints European cities did in the middle of the nineteenth century. In the last decades of the nineteenth century, with immigration reaching new levels (and anti-immigrant fervor still twenty years from its first great peak around WWI) US cities swelled. Few cities more than St. Louis. And of the new "western" cities, few others were so dense or geographically constrained. Thus it shouldn't be surprising that ours is among the oldest and largest surviving US passenger terminals. But when I say largest, I mean that only in terms of the number of tracks and trains. The "landside" facilities were quite modest. And the "airside" amenities were abysmal by later standards. The lobby is much smaller than newer terminals half the size (as at Kansas City, say.) The ticket counters were in cramped spaces on the lower level, if I understand it correctly. As were most of the waiting areas. The midway was extremely crowded and very very cramped. The trainshed was dark and dingy. Old hands suggest that Lambert never saw the kind of press of bodies that was once in the midway at Union Station. Which makes sense. Lambert never saw local intracity commuter traffic. No reason to fly from Kirkwood to . . . oh, never mind. And more than half the intercity traffic that once flowed over the rails went to the highways, so while the US population grew, I doubt airports have ever handled remotely as many bodies as major rail stations did in their heyday. So by the late forties, just after the wartime floodtide, but before the highway and airline bleeding, there was TRRA talk of how to deal with the cramped conditions at weary old Lam . . . I mean Union Station. It's probably only thanks to the declines of the next thirty years that we still have the place. That doesn't mean I like the declines. But it sure is neat to have such a grand and groundbreaking old terminal preserved for future generations to gawk.
Imperfect as Lambert is, you know, it's really not too bad a place to fly into or out of. And lord oh lord is it historic . . . and pretty. (To my eye, at least.) I will gladly suffer a quieter and more local airport for the sake of keeping the bit of gorgeous that we've got. Honestly, nothing will bring the traffic back anyway, other than plain old organic population growth. But it's open and doing what it's supposed to be doing. Admirably. Unlike Kansas City's Union . . . oh, sorry. Never mind. Wrong building. (But seriously, much like the airport, Kansas City Union Station NEVER filled it's [much smaller] capacity. And the roof always leaked and it was always a big, empty, echoing barn of a place. Lovely. Beautiful. And I'm always glad to see it. But . . . there are parallels. And for me, I'm quite content to have our more cramped, older facilities that were actually much busier and worked well enough and paid for themselves many times over. I'll take our concourses as the price for the terminal. Even if it means we'll never have so many sexy duty free stores. Who buys stuff at those things anyway? (Glances over at gift box from professor.) Oh . . . yeah, never mind. Priorities. I suppose I have different priorities. Must be because I'm a backwards oaf from St. Louis.
