I was hoping to hear back from the B&O Railroad museum on this issue but 
have not as yet.  Apparently the route referred to as the Baltimore and 
Washington RR exists today as the Capitol Subdivision.  I've attempted 
to map the route using Google Earth and have included a page on my site 
with some discussion of what I have found.

http://twainsgeography.com/content/baltimore_washington_rr