Improving service on Warren St
This is an interesting and very relevant thought, which
I've also briefly considered before. Indeed, if we use Delvin's map as a rough measure of density:
View attachment 45047
While there's good residential density (and
job density?) around Nubian, Warren St is arguably even denser. And it nicely fills the gap between Orange and Fairmount, effectively covering most of the area with their walksheds. Even nicer if we can run it to Franklin Park (a recreational destination itself) and/or connect to Fairmount at Four Corners/Geneva.
I'm late to the party here and probably won't be able to respond to everything in the subsequent discussion, but I'll try to layer in thoughts where I can.
Another issue is that while the northern half of Warren St is easily wide enough, the southern half between Quincy St and Blue Hill Ave is narrow and likely cannot not support bi-directional transit lanes. A few solutions:
- Terminate the line at MLK Blvd (not ideal for catchment)
I agree that an MLK terminal is far from perfect, but I would not quite so quickly dismiss its value. (Letting the perfect become the enemy of the good.) MLK is also useful because it's wide enough that you could have an on-street terminal where trains can turn without blocking the (presumably shared bus/LRT) transit lanes on Warren.
- Dig a short, 0.5-mile tunnel that bypasses this narrow section of Warren St ($$)
I can check this again, but my recollection from the last time I looked at this, the problem was actually about where to put the portals, especially at the southern end.
- Run in mixed traffic (lower reliability, not sure if traffic is decent enough)
I think this depends whether your goal is an OSR to downtown, or something else. If the former, then I think mixed traffic isn't ideal.
- Or, this interesting idea that takes 1 lane each on Warren St, BHA and Quincy St: (some deviations from typical route, and may either still run in mixed traffic or turn these streets into one-way)
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Yeah, this is an interesting thought. Yeah, would probably need to be one-way, or obliterate lots of parking -- if you're going to run in mixed traffic, why deviate from Warren at all?
Perhaps this could be somewhat useful post-BNRD to improve reliability on the bus routes? On the other hand, losing northbound service on Warren in favor of a 4-min walk to Blue Hill doesn't sound amazing.
(If we build all of this, Washington streetcar and I-93 subway, I think it's worth looking at letting the I-93 service serve the surface section south of Nubian rather than the streetcar. In addition to avoiding a B branch 2.0, this also improves travel times for points south of Nubian, and lets you dig a tunnel through Nubian onto a portal on Warren St that bypasses several big intersections around Nubian. This point may be more for
@Riverside.)
Yeah, this of course goes back to
my analysis of the strangeness of the B and C Lines. I think there are pros and cons. On the one hand, Warren-via-subway would provide a faster OSR to downtown. On the other hand, potentially you degrade the reliability of the subway portion, which we hope will be used by bus riders from all across Dorchester.
To me, from a network design perspective, the "natural" portal point for a subway would actually be Grove Hall. That's where the network blooms outward in different directions:
Depending how far you go down Blue Hill, that gives you surface segments between 1.5 and 3.3 miles long, which seems much more reasonable.
Of course, it'll be hard enough to build a subway (or viaduct) to Nubian. Doubling it (and along an alignment that I think would need a TBM) makes it all the more difficult.
Anyway, I've wandered far afield from your original question. I still feel that the best option all around to enhance transit access to the Warren St corridor is an extension of the Washington surface line down to MLK, combined with whatever the next generation of the T28 etc will be. It's far from perfect, but it provides benefit without particularly harming other parts of the system, and would not require extreme cost.
The other thing to consider is that there are two reasons to have an OSR downtown: to get to downtown, and to transfer to the other lines. But that second purpose can be achieved without going downtown. A line running out of Longwood would have transfers to Green and Orange at the north, and Red (somewhat less ideally) to the south. If extended further to Kenmore, with BLX, you've got all of them. (I guess except for SL3.)
(A separate line running down Columbia Road from JFK/UMass could enhance the above by providing a Red transfer that doesn't require doubling back.)
I'm not sure 5 min headways are actually unworkable. Some quick digging turned up
this paper which mentions bunching on the Silver Line, pointing out that the biggest problems for reliability are:
- Long boarding times, exacerbated at the time of study by the new fare system. This could be improved with off-board fare collection and by using vehicles with more doors. You can even do this with buses, 4 door articulated buses are a thing that exist. (Although these are slightly longer)
- Because Temple Place is constrained, it doesn't really act like a terminus. The line therefore operates like it's twice as long, with buses having to correct for deviations in headways from both the inbound and outbound trips at Nubian. This would be alleviated by having a proper downtown terminus.
- The biggest factor according to the study, regulation of headways at Nubian is (Or at least was)... crap, to put it bluntly. Not necessarily because it needs to be, but just from poor operations and operations management. The solution here is pretty self-explanatory.
With all of these problems addressed, I don't think 5 min headways are impossible.
My problem is that higher headways become less compatible with transit priority signaling.
@The EGE has much more detailed analysis on this, but it basically boils down to: the more frequent your transit vehicles come, the harder it is to guarantee that they always get the priority at the intersection. Even at simple intersections, you have through traffic, cross traffic, and pedestrian traffic, and you can't make any group wait too long because it'll back up into other intersections.
So, yes, perhaps 5 minute headways are possible, but it may come at the expense of running time and speed. (And to some extent, reliability.)
(That's a really cool paper, though, thanks for finding it!)
Not sure I have much to add on the other topics that were addressed; I agree with
@Teban54 that capacity at Park St is not a concern, and there's definitely no need to turn 3 branches at Park St.
Nothing in particular to add about an LMA subway at the moment. Definitely think you have an interesting analysis about circumferential corridors,
@TheRatmeister!