I'm going to have to say it's the tram to the various gates. Yes, there is a walkway down to the roadway area, but I think that's just an access way. I have seen that as we use the tram.
It seems to enter the building just outside the Hyatt's ballrooms. I'm guessing that it was originally meant to be a ramp for tradeshow deliveries to the Hyatt.
It's number 1 I think. A connector between the current terminal and a proposed future one. Here are the overall plans. And here is the doc that most clearly shows the intended use of that structure.
I guess I could have Google-ed this in the first place.
If you mean for a rail service connection between the current terminal and the proposed south terminal as GrnMtnMan suggested, then I agree. I think it's less likely to be there for access to any larger rail system unless the airport would be a terminus point for that system.
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