A certain poster, Claude, found this link. Fascinating stuff. Anybody qualified to comment on various subway systems proposed for Detroit over the years?
http://books.google.com/books?id=Yj4pAAAAYAAJ&pg=PA120&lpg=PA120&dq=Detroi t's+underground+subway+passages&source=bl&ots=zTk-ylVFSP&sig=QXzNwmoHodmSTZILEIXYAIAH7X8&hl=en&ei=z1 PGTJLgNMiKnQfDuvWGAQ&sa=X&oi=book_result&ct=result &resnum=7&ved=0CCsQ6AEwBjgK#v=onepage&q&f=false
Bookmarks