I immediately liked the idea of the Millennium Line Station at Commercial-Broadway when it was proposed in the late 1990s: an open-air platform sunk into the Grandview Cut, surrounded on both sides with walls of green. To the south, the natural greenery of the slope and, on the north, terraced planters that would serve as a retaining wall.
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At least that was the idea. But the plantings on the north never really took, or were replaced by scraggly vines and weeds. A good idea, but without care and maintenance, a bad result.
That’s changed. Now both slopes are lush with plants that make this one of the greenest places in the city.
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It is nice, unfortunately what will probably be needed as the system (hopefully) grows and this station becomes more of a hub will be double sided platforms for each track (the Spanish solution: http://en.wikipedia.org/wiki/Spanish_solution), the inbound trains already struggle to unload and load all the passengers with the current dwell time during rush hours.
But I’m sure whatever new wall gets created as the old one is push back will eventually become just as green.