Sigh. I’ve followed all the GLX shit in great detail for years but not everyone is a railroad encyclopedia. It’s NOT clear. Maps of the GJ show it ending at the junction with the Worcester Line at the foot of the BU Bridge. So either the maps I’ve seen are wrong, or there’s more ROW reserved parallel to the Worcester line on track space I would otherwise just assume IS the Worcester line, and consequently not called the GJ and not just “reserved” for a future extension. So either the maps are wrong and the GJ ROW actually (under that name) goes as far as future West Stn, or the state has just planned ahead to save an additional two track ROW for future use. Given the state of idiocy at the MBTA, forgive me for being skeptical that they are in fact planning ahead. Urban Ring also calls for tunnels la de da thru Kenmore and Longwood with a glaring absence of planning on any of the details or feasibility... so unless somehow the GJ is its own separate thing all the way to West, I would be quite worried it’s not as safe as you say it is... but i certainly hope that’s not the case and there is some foresight here.
The GJ does
not end at the foot of BU Bridge. Never did, never will. You're not looking at the renders in 3 dimensions.
Today the Grand Junction splits off from the Worcester Line
behind Nickerson Field, a full 2000+ ft. west of BU Bridge. The split happens there because the line has to climb a grade of no more than 2% to get 11 ft. off the ground for overpassing Storrow Dr., and make a sharp curve onto that Storrow overpass after it's finished ascending. It takes nearly 2000 ft. of runup to accomplish those tasks.
In the
future with the at-grade Pike option the 2 Grand Junction tracks and 2 Worcester tracks won't meet at-grade until
behind Agganis Arena, barely a block sooner than they do today. The tracks will cross the at-grade Pike on an overpass, but because federal regs require 14 ft. of overclearance for an urban-build Interstate highway the tracks must elevate an additional 3 ft. coming off the water. The new Pike overpass will be diagonal, meaning the line must finish curving when it reaches the Worcester Line side...and only then start descending from 14 ft. to at-grade. Curve would end behind the BU College of General Studies building, and then the incline would stretch from there to Agganis.
However, the actual junction that ties the lines together cannot be behind Agganis Arena, because it's unsafe to have one end of a Grand Junction train crossing switches while the other end of the train is still taking the incline. So they'll wait for enough level running room off the incline to safely contain a max-sized train before placing the junction...meaning:
behind Nickerson Field, same as before. That is the earliest possible spot 2 Grand Junction + 2 Worcester Line tracks can merge into 4 Worcester Line tracks. And it's at the site of West Station on the Babcock-Agganis Way block, so in reality the junction will be a set of crossovers just off the east end of the station platform.
Is this clear yet??? Because I can't possibly dumb it down any further.
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The Worcester Line can't make use of 2000 ft. of tracks that are way up high on a different level, so all points east of West Station they are officially separate ROW's. Thus, if you were to convert the Grand Junction to light rail, you would have a reserved ROW straight to the foot of West Station because there's no other possible RR use for those tracks. If you take any action on the Urban Ring NW quadrant that ends RR service on the line, then West-BU Bridge comes available for mode conversion simultaneous with the UR mainline through Cambridge. The rest of the Harvard spur of the UR would be a separate entity to flesh out with further study, since it is slated to turn north from West and take a reserved path through Harvard's Beacon Park land on a path still TBD. But setting the table as far as West is not in doubt.
It's not necessarily even "planning ahead", so much as this Pike project has to preserve existing service (including the unused 2nd track). And since the ROW geometry is what it is, any revamp that preserves existing service serendipitously maintains a separate ROW to the foot of future West Station, which in turn preserves access to West in the event of a mode conversion.
Of course a project that hasn't been touched in any way/shape/form in 15 years needs a full re-study, but that's not what we're talking here. You asked an if/when question about preserving a light rail ROW to West that could be hooked up to Green and/or UR. ↑↑Here↑↑ it is. It's there....100%. Question answered.