Feathers

At Portland's Gateway Transit Center, three giant blue feathers twist in the wind atop 20' poles. Feathers was added as part of the MAX Red Line project, and TriMet's Red Line art guide has this to say about it:

The Gateway "Feathers" by Frank Boyden consist of three 14-18' long painted aluminum feathers that track the wind atop 20' poles. The feathers, which are visible from the I-205 freeway, the bike path and the train, create a landmark for the transit center and signify the start of the airport line with a bright and colorful allusion to flight.

Boyden also co-created the Interactivators along the WES line.

The main problem with Feathers is that it only makes sense if you realize it arrived with the aviation-themed Red Line, and you'll only know that if you Google it. Gateway is really busy most of the day and the feathers are in a fenced-off area, and (typically for TriMet) there doesn't seem to be a sign for it. So it's just going to be a mystery for almost everyone who notices it. Although I often wonder whether anyone other than me bothers noticing this stuff. (I just might be, if Google results are any indication.) Still, transit art is something to look when if your bus is late, I guess, or when the train's out of order again.