TUP, the two retail spaces are at different levels. The Starbucks is at lobby level, so it's about 4' higher than Canal and a street-level door would be difficult. The "sandwich shop" is at the level of Canal, so it does have a street entrance, and you can see the interior hallway slopes down to link the two retail spaces.
Hines probably thinks the Starbucks doesn't need an exterior entrance because it won't be open outside of 9-5, and it will be mostly patronized by workers who are already in the building (whereas the sandwich shop might draw from surrounding areas). Starbucks still might request an external entrance, and it looks like they could have one that lets out onto that little elevated podium.
Originally Posted by Standpoor
Lake Street itself clears the railroad tracks. As you can see from the second image, the podium clears the railroad tracks and then has a large deck above that. Is this thick deck necessary to carry the load of the park?
The thick deck isn't required structurally, but you need a thick deck to accommodate the root systems of trees. Otherwise, you'll have perpetual saplings.
Sometimes you can make the deck thinner and still increase the soil depth by putting the trees in planters, but this really only gets you an extra 18", because planters any taller than that are unpleasant. Or you can mound up the soil a few feet and make little hills for the trees to go in, but this adds a ton of weight.
Amtrak is also requiring that road access to Union Station be preserved, and the structure has to accommodate a roadway between the tracks and the river. The Riverbend building already has a tunnel through it for this reason. In the future, this could potentially be used for a fourth approach track, since the vertical clearance is high enough.