So BLX is providing a crucial amount of load-shifting to do other/better things with other wings of Green.
This is what it all boils down to (emphasis mine). The Green Line/LRT network can do things that no other mode can -- not HRT, not BRT, not mainline rail. Blue-to-Kenmore -- even though it doesn't solve all problems -- frees the Green Line up for new possibilities.
I'd also point out that, even with a transfer, the Blue Line may still be faster for some journeys. In my current maps, I put stops at Mass Ave, Hatch Shell, and then of course Charles/MGH, closing Bowdoin. That means Government Center is 4 stops away rather than 6, and that a Red Line transfer is 3 stops away rather than 5. (With an unusually long straightaway between Mass Ave and Hatch Shell -- nearly a mile, depending on stop placement. So those trains will be flying.)
@Teban54 your point about single-seat rides is well-taken, and probably not given its due consideration in my analysis. As F-Line points out, Kenmore's importance increases if you turn it into an Urban Ring node. Perhaps existing riders will still prefer the one-seat, but the added capacity would create new possibilities.
Another fascinating post, kudos again to you for the dedication you've shown to the topic, Riverside. I'm entirely in agreement you, both in terms of preferred destination and, more importantly, in the need to consider the network impacts as much as (or even more than) just the ridership potential at the chosen node-station.
Kenmore was once actively intended as a transfer node, hence the existence of the turnback loop (which I like to think of as the nameless, less-squeaky western counterpart of my namesake at Government Center); as I understand it the plan at one point was for the C (this predating the Highland Branch's conversion to the D-branch) to loop at Kenmore while the B's tracks would be eaten by the HRT-ified Central Subway. (Ironically, or perhaps poetically, given the clearances in the Tremont Street Subway, it might well have ended up using Blue Line-size HRT stock.) So there's a very good historical argument that Kenmore was supposed to be a LRT/HRT (light/heavy metro) transfer node and that the system's simply been suffering from its never having been built all these years, and that Blue (albeit now via Riverbank) would fix the problem that was intended to have been fixed last century.
This is indeed pretty much how I see it. And yes, the plan would've been for the C to be short-turned and probably also the outer half of the B.
@vanshnookenraggen may know more from his work on his historical track map.
I look forward to these future posts. That said, while I'm intrigued by the three-tier concept, I do have a few thoughts. One's sort-of a nitpick, which is that I wouldn't call things like MUNI Metro's streetcars, New Orleans' streetcars (much as I like them), or even the surface-running portion of the E-branch as proper light rail, regardless of equipment. I wonder if there's room for either stratifying the classification between the systems operating in significantly mixed-modes (like with street running, which is really not that far off from BRT) and those that aren't.
So, with the caveat that I'm still refining these ideas, my response would be that this is exactly why I think the light rail/heavy rail distinction isn't useful for planning or understanding our systems anymore. The "streetcar vs light rail" dichotomy that you're describing isn't really about the equipment -- it's about the infrastructure surrounding the equipment. If you widened the Green Line tunnels, removed the rails, put down pavement, and then did the same on the B and C Lines, and then ran double articulated battery buses on them, how different would that be from today's Green Line? It's not about the equipment -- it's about the infrastructure.
One point to clarify as well -- I think I am possibly using a stricter definition of BRT than you are? To me, mixed-traffic running (which, yes, is not inevitable with street-running, as you can have transit lanes) does not clear the bar for BRT. At the very least, you need segregated lanes with enforcement, and ideally you have as much infrastructure as I described above for the B and C Line.
(I have considered adding a fourth tier: "Feeder Metro". The problem is that, by definition, that tier has minimal infrastructure, and part of my point here is shifting away from vehicle types and toward infrastructure components, so it becomes a bit of a contradiction in terms.)
The Green Line's an interesting example, because a fair number of its problems come from mixing pure grade-separated LRT (D and the Central Subway), two and a half surface branches running in reservations, and half of a branch street running (resulting in the nasty garbage-in, garbage-out difficulty of scheduling the thing to work in the de facto HRT role the Central Subway has been pressed into). (MUNI Metro has some of the same characteristics with its subway, right down to being the other poor fools to suffer the lemons that were the Boeing LRVs.)
Yes, this mixing of light metro and near-heavy metro is I think one of the fundamental challenges stressing the Green Line.
The other point is that as useful as tiered classifications are for discussions like this in forums like this (even if reasonable people can quibble about the specific definitions), part of me really, really hopes that your tiers don't catch on widely, because I feel like they're ripe for misunderstanding and misuse by moronic politicians who'd happily pick up the "light metro" definition to plaster over the fact that they're building BRT when they should be building LRT. (I can just see the MBTA of the era using "light metro" for the Silver Line just to try and add a bit more lipstick to that particular pig.) Hopefully that's just me being unnecessarily cynical, though
Soooooo I mean........ if it's proper BRT -- something like SL3 in Chelsea -- then I'm not opposed to calling it "light metro". You could argue that by putting it into the same category as (say) the B Line, it
raises the expectation for what the infrastructure and service should look like. I'm not opposed to BRT; I'm opposed to
bad BRT. And if it's bad BRT, then it's bad light metro too.
I do share your cynicism, but also the T can spin a frequency reduction with a fare hike as an "enhancement of service", so I think if we let the potential for abuse be a ruling criterion, we'll find ourselves very limited very quickly.
The terms “light metro,” “heavy metro”, and “regional metro” are meant to give us more precise terms to describe the capabilities and roles of different services, deemphasizing a rapidly antiquating distinction between “light rail” and “heavy rail”.
Once we start viewing the T as three overlaid networks (plus a fourth layer of local feeder networks – i.e. most buses), the gap at Kenmore becomes obvious and we can start to plan a more balanced and efficient system for the decades ahead.
Here's where I'd push back a little, referencing what I mentioned above. I don't know that I'd necessarily agree that the Green Line from Kenmore-east is as easily classifiable outside of the heavy metro network as it is west of Kenmore. It's certainly being relied upon to do the work of a heavy metro spine, the stop spacing is not that much more dense than the Orange Line, and on a whole it operates far more like a heavy metro than it does BRT; even one of the most significant differences, the vehicles, will be altered by the Type 10s. (Though, as above, that may well all be able to be chalked up to the Green Line being a unicorn hybrid; that it is such a unicorn is, in my view, a very good reason for some of the pressure to be taken off by BLX to Kenmore.)
Yes, I think this is a fair pushback. Certainly the Central Subway operates (and is asked to operate) like a heavy metro service, though I think it falls short in terms of reliability and capacity. If it is indeed "heavy metro" service, then I'd suggest that it is subpar. But yes, as we've discussed above, the unicorn hybrid nature of the Green Line means that it can't really serve either role fully effectively. I'd like to see Blue-to-Kenmore free the Green Line up to better leverage the advantages of a "light metro" role in the network -- which brings us full circle to F-Line's point above.
(Also, spoiler alert: my vision for the Green Line includes extending the Huntington Subway to Brookline Village-ish, and running the Riverside Line through there. With fully separated ROWs, rapid transit stop spacing, and modern vehicles, that could relieve a significant fraction of the current Green Line's "heavy metro responsibilities.")