In the original scoping studies >15 years ago it was proposed as a uni-extension to Tufts inclusive with Union as an intermediate stop, using some Fitchburg ROW, some cut-and-cover under (Prospect St.?), and then deep-bore through the base of Prospect Hill to get back on-alignment with the Lowell Line @ the McGrath/Medford St. intersection. That scoping was also mode-agnostic, as one of the Alts. included a Blue Line scheme (obviously eliminated in first cut) where bang-a-right from Charles MGH and trenching under the Charles locks would've set the trajectory. You'd be able to find mention of those early looks way, way at the bottom of the Project Archives on the GLX website. If not in full, then at least in a summary of most-recent previous studies inside the 2005 Major Investment Study archived there.I'm ignorant on the subject, as I wasn't really paying attention to this when they were in the planning, but why did they decide to construct the Union Square branch with this? GLX-Porter makes sense, and I understand all the reasons one would want Green to Porter and beyond, but at completion of this GLX, it seems the catchment area for the two branches will strongly overlap. Those directly in Union Square benefit a great deal, but how, on a cash-strapped project, did they justify adding this single-stop branch on?
Porter CR station bulbs out a little too much inside of the Somerville Ave. cut to fit both modes side-by-side with platforms, as that ADA/MAAB-spec 12 ft. wide island takes up a wee too much real estate to fit them both together via only manicuring the embankments/retaining walls. Therefore the GLX side would have to dip past Beacon St. overpass into a short tunnel. But the roof of said tunnel would literally form the new Fitchburg trackbed, and would probably be no more than a short ramp or 10 stairs down accessed by the current CR egress from the fare lobby. Say...10 steps down at that door for GLX platforms, 10 steps up at that door for the new re-leveled CR platforms sitting on top of the tunnel roof. The build makes even more sense in that if the tunnel ends up allowing the CR level to drop by 3-6 feet it would future-proof the Mass Ave.-Beacon St. cut for a formal air rights capping. Which would serve up any combination of: linear park, exit driveway straight from Lesley U./Porter Exchange parking lot to Somerville Ave., a long-overdue end to the use of cramped Roseland St. as a connecting thoroughfare if other Square traffic patterns were altered with the Lesley/Exchange lot, and so on.Looking at Google Maps, the CR alignment is straight in this location; the curve is simply the CR tracks transitioning to the center of the ROW. If they extend the GL to Porter, the CR tracks will have to be moved to the south side of the ROW and that curve won't be there.
Like a tunnel over the tracks?
Yeah, so not a tunnel, but the path will overhang the trench in this spot.I think it’s just a short stretch approaching the School St bridge, where the proximity to the houses makes even the narrow path untenable.