That tunnel and storage yard were built as part of the TD Garden parking garage, way back in '95.I don't think I ever knew when they buried the Green Line at North Station that the tunnel was built under the Commuter Rail tracks.
It's because the Old Garden + another tall building next door that used to be scrunched across the corner of Beverly were still standing when the New Garden was built. They didn't have any means of curve-easing around the incumbent structures, so when New Garden was built the basement had to bake the tight curve in.Regarding that tunnel, I always thought it was a shame that trains have to slow down so much for the curves. Given it's so new relative to the rest of the green line tunnels, could they have designed it differently so trains could keep up speed? (Or were there already obstacles in the way when they were building the tunnel?)
Also, it seems wasteful that outbound trains from north station to science park usually come to a stop along the curve too (although maybe that could be something we could improve with signal improvements?)