Why do the motorcycles in the guard have sidecars? Was the original idea that one could go scoop up the president if his car blew up? Quick googling didn't reveal the answer.
Apparently very expensive sidecars:
http://www.wtop.com/?nid=25&sid=1557316 And a related little thing I liked in the inauguration: in addition to the variety of vehicles, there were a variety of faces doing the work; I saw women marines, marines of color, all that good stuff.