I have been traveling frequently btw DCA and Bos on US airways shuttle. I have noticed that the flights are often empty. Does US Airways put the seats up for sale at last minute at reduced rate?

No. The only exception is weekend "E-Savers," for departure on Saturday and return on Sunday, Monday, or Tuesday. E-Savers can save a great deal of money on last-minute weekend trips, especially in uncompetitive markets like PIT-LGA, but I haven't even seen any E-Savers recently for the Shuttle out of DCA.

whoops.