I think quite a bit of the original Tinminal project was 'cost engineered' out? I recall vividly a meeting where the escalator from the platforms to ticket area was deemed unnecessary at the Parkway, the concession was a disabled lift and only because they had to legally install one!
A grand 'Pullman' plan to have check in off site. In hindsight possibly a visionary idea which probably would have been culled anyway post 11th Sept 2001 (I am not American 9-11).
Anyway, the extra wide lane under the taxiway was to have permitted fast People Mover transit.