> tunneling is monstrously expensive it is even more expensive in parts of Boston known for having the worst problems. The Green Line (which isn't even analyze

> tunneling is monstrously expensive it is even more expensive in parts of Boston known for having the worst problems. The Green Line (which isn't even analyzed) runs through Back Bay, which is largely landfill[1] without very good engineering properties. Combine this with running under many buildings that are National Historic Landmarks[2][3][4] and have shown shifting with bits of construction such as adding an elevator[5], these tunnels are pretty much impossible to expand. [1] http://www.bc.edu/bc_org/avp/cas/fnart/fa267/boston/bos1820.gif http://www.bc.edu/bc_org/avp/cas/fnart/fa267/boston/bos1820.... [2] http://en.wikipedia.org/wiki/Boston_Public_Library,_McKim_Building http://en.wikipedia.org/wiki/Boston_Public_Library,_McKim_Bu... [3] http://en.wikipedia.org/wiki/Old_South_Church_in_Boston http://en.wikipedia.org/wiki/Old_South_Church_in_Boston [4] http://en.wikipedia.org/wiki/Trinity_Church,_Boston http://en.wikipedia.org/wiki/Trinity_Church,_Boston [5] http://www.boston.com/news/local/massachusetts/articles/2008/12/06/historic_church_damaged_by_mbta_project/ http://www.boston.com/news/local/massachusetts/articles/2008...