So you know Lambert has two terminals. Did you know that there was at one point plans for a third?
This is totally stolen
from here, for the record. In it, he shows that the W1W airport expansion built not because of a projected increase in flights, but because of the "crippling effect of bad weather on Lambert operations".
However, they did believe passenger volume was likely to increase. They projected a high-growth scenario, a low-growth scenario (wherein Lambert is de-hubbed, but some other airline eventually steps in to replace some or all of the volume) and a middle ground with some growth. They ultimately based expansion plans off of the middle projection. It explains:
Before the expansion project began, Lambert had 89 aircraft gate positions and about 1.5 million square feet of terminal space. The projected future need (in 2015 with the middle forecast) was about 110 total gates. In order to accommodate these new gates, one option was to relocate the Missouri Air National Guard from its location just west of the main terminal to a site on the east side of the airfield, and to build another concourse to the west of the main terminal.
Another option considered was to build a new midfield terminal. This option allowed for more gates (more than the projected need) and thus allowed for easier future expansion. The satellite terminal would have been located between the new runway and runway 12R-30L, as shown below.
This new midfield terminal would have accommodated an additional 150 gates.
Interestingly, as of the penning of this this report in 2007, the plan hadn't actually been completely discarded, only delayed until volume again justifies considering it:
However, although the option still exists to develop this site, no construction has started on this terminal. Since the demand levels are so far below what was forecasted in 1994, there is no need or justification for the new terminal building. Thus, the terminal expansion plans have been delayed until the passenger demand levels actually require a new terminal building.
Perhaps some day in the (distant) future it will be considered again? One can dream...
-RBB