The blue line and the red line are subways under the elevated loop, but there are free transfers between them when you leave the subway stop and tap back into the elevated stop (or vice versa). It also serves the "loop" neighborhood, which is the area around the physical loop.
niftyjack t1_j65g1ie wrote
Reply to comment by aray25 in I took a 2 1/2 hour flight from Chicago to Boston. It took me 2 1/2 hours to get from Logan to Watertown Square by jenkneefur28
The blue line and the red line are subways under the elevated loop, but there are free transfers between them when you leave the subway stop and tap back into the elevated stop (or vice versa). It also serves the "loop" neighborhood, which is the area around the physical loop.