F-Line, isn't there a similar restriction on Blue Line car size from one of the curves on State Street? I have vague recollections of you talking about that in the past.
And my understanding is also that you can't reuse any of the Bowdoin platforms, at least under some of the plans for construction, because the plan is to tunnel under them to go out along Cambridge St. That's why I was talking about construction of a newer station a bit further from GC once the grade levels off. See:
https://www.mass.gov/files/documents/2018/10/19/SummMem_ConstStudy_0.pdf
However, looking at that study, it appears any sort of Bowdoin station is actually, literally impossible. The grade doesn't level off until well past Staniford, at which point you're basically constructing a new station right on top of the Charles switches. I suppose you could argue for attempting to put a lot of the grade change after a Bowdoin station (which seems like it would also minimize the amount of excavation), but that doesn't appear to be in the cards. I'm aware that the grades I'm looking at are for the old study, but I haven't found anything to suggest not doing something basically the same with the new alternatives.
State is not the ruling curve...Bowdoin is. So retention of the loop and the half-loop for thru service locks Blue in at the current car size. State is a MUCH less severe curve, so the cars you would be able to order in the
very next procurement would be able to be considerably longer with Red-Blue constructed with the Bowdoin alignment straightening. The burning question is whether you'd be able to re-standardize the carbodies at rote Orange dimensions (note: the slight difference in platform heights Blue vs. Orange is accommodated in the adjustable air ballast in the cars and does not require any design differences). I've never been able to find an official quote on both the Orange Line's ruling curve and State curve's radius so that answer isn't verifiable without getting very lucky on Google. But State is
close enough to Orange specs that demoing Bowdoin for Red-Blue either allows you a
very nearly Orange-length car with only slight stubbiness...or a "Blue Line Transformation" studies the costs of a State curve-easing and sees if the difference can be made up. At any rate, eliminating Bowdoin as the ruling curve is easily worth 50+ seats per 6-car train for however much longer cars they want to buy for the 0800 series, and that is going to loom large if Suffolk Downs redev and/or Lynn exert their influence on ridership.
More consequential, however, is whacking that speed restriction. You simply can't get the headways down in the neighborhood of what Red and (ultimately) Orange are capable of if the inbound trip to Charles on the half-loop is so extremely slower than the outbound trip from Charles that only has to pass through the far straighter end of the loop. It's silly to get all that precious about Bowdoin station and footsteps-counts from the next-nearest stop when aggregate accessibility is a whole lot worse on a line that could in the future saturate at 6-min. headways and has no way to drop to 5/4/3-mins. because we hand-wrung ourselves into a corner about touching that one misfit station's platform.
As for whether it's rebuildable...yes, that depends on what set of blueprints you're looking at. Originally it was assumed to be cut-and-cover, and at cut-and-cover the rump-of-Bowdoin emergency exit plan with open door for rebuilding was in effect. Then the state said...no, it must be deep-bore. Then there was all the expert push-back saying...no, there's nothing wrong with cut-and-cover except you wanting to tank the project. Then, instead of saying "No, we know what we're talking about" re: the deep-bore plan, this recent backpedalling opening up the door for cut-and-cover again. So we don't know anything for sure, except that there was probably no small amount of thuthiness in the state's last presentation if they were so quick to backpedal. All you can say is that the possibility of a reanimated Bowdoin is nonzero, and we'll know a bit more when this next study takes an engineering crack at it. But again...something is amiss if Bowdoin's fate is keeping anyone up at night. If it's a choice between 50-year capacity gains for the whole line present configuration AND extended each direction, and fear of what a future-redevved Bulfinch Triangle will generate for ridership...what is the higher-leverage proposition? Is it the never-major 'tweener stop taking the same 210-seat cars at middling headways forever, or dual-headhoused GC & Charles being able to take 270-seat cars at as little as 3 minutes a pop when saturation finally requires those headways. This is a pointless one to "yeah, but..." because raw throughput is going to slay the footstep count on-balance (in a way, because of the low-use/'tweener status, that you wouldn't be able to project with this much more controversial "Master Station" consolidation at the downtown transfers). Build Red-Blue for the throughput, hope for sanity and transparency in the study...and if the study ends up matching with the previous C&C scenarios that kept the Bowdoin emergency exit rump know that then there'll at least be the realistic possibility to re-infill if necessary.
