I’ll try to reply more later, but this idea is extremely similar to the “Red-X” proposal put forth by @F-Line to Dudley and others. I’ll see if I can find direct links.
If the proposal is to begin a Yellow line at Columbia, wouldn't it presume the Braintree branch of the Red Line would merge, but south of Savin Hill, thus preserving a single seat ride to the core, from Quincy and Braintree?I still think it is. Additional frequencies is a service increase, but anyone who doesn't presently have to transfer being forced to now transfer is not likely to see that as a benefit even if the trains on the branch itself run more frequently. It's still an additional inconvenience that doesn't presently exist. Not that it would necessarily mean it's a bad idea to do, mind you, just that the current riders who would be impacted probably wouldn't like it and might get shouty about it. (Which, again, there are tradeoffs in public transportation policy, sometimes people get the short end of the stick, I just tend to flag things where there might be significant political/PR problems that could harm or scuttle a project that perhaps could be avoided entirely. Or, as you suggest, possibly the greater frequencies on-net improve things enough to offset the impact to the people who now have to transfer, which is a selling point but not quite the same as not being a downgrade to those specific passengers.)
If the proposal is to begin a Yellow line at Columbia, wouldn't it presume the Braintree branch of the Red Line would merge, but south of Savin Hill, thus preserving a single seat ride to the core, from Quincy and Braintree?
Wash's original proposal on the previous page said "take over the Braintree Branch" which I interpreted as meaning it would be re-routed into the Congress Street Tunnel (Yellow Line) rather than the Cambridge-Dorchester Tunnel (Red Line) it currently uses. Branching it would solve that problem, but probably leave the headways in the Congress Street Tunnel...sparse.
I’ll try to reply more later, but this idea is extremely similar to the “Red-X” proposal put forth by @F-Line to Dudley and others. I’ll see if I can find direct links.
I was spitballing options for the south end with Fairmount as an idea. My initial idea was just to rapid transit-ify Fairmount, but I'd forgotten about the freight rights, so it couldn't cannibalize the surface ROW. Being Crazy Transit Pitches I'm fine with tunneling under the Fairmount surface ROW.
The Seaport commentary in my original post was unrelated to anything Fairmount. That was purely me looking at various potential places to send a Congress Street Tunnel other than Braintree. Not as ideal a Seaport Transit Pitch as Green + Silver in the Transitway, but that's a different thread.
How wide is the Fairmont ROW? I am terrible at this, but, eyeballing a few places on Google Maps at least looks to me like it could support 3 tracks, which could then be 1 RR and 2 rapid transit (obviously land for stations/etc would need to be figured out).
It would begin at a junction with the Green Line subway west of Boylston Station, continue in a deep tunnel to the existing Silverline Tunnel at South Station
existing Silverline Tunnel at South Station, share that tunnel along Atlantic Ave, and then branch off of it to tunnel under the Central Artery to North Station, utilizing the deep foundations provisioned when the Central Artery was built
The LRT line would continue on the surface to a high level bridge over the Mystic River along the west side of the Tobin Bridge, then descend into Chelsea as a surface line to tie into the Silver Line/Amtrak Chelsea station
Good points all. What I would really like to see is the portion built from North Station to Chelsea. Once the line crosses the Mystic River on a high bridge as shown on the layout i did, it could use the space occupied by the long SB on-ramp that climbs up from Chelsea, which would be removed. There is already another on-ramp to the Tobin a few blocks from there. Once the LRT line reached the northern end of the SB on-ramp (to be removed), space runs out alongside the expressway to fit in an LRT line there, as you pointed out. A couple of options for the LRT to continue north is to tunnel under the expressway for a few blocks until the expressway becomes fully elevated again, or run a short elevated LRT structure along and above Everett Ave to the commuter rail line. All crazy transit stuff, but somehow an LRT line could be threaded through that tight spot.Tunneling under Essex Street, albeit as BRT, was studied for Silver Line Phase III and would be very difficult and expensive. Coming from the Boylston Street Subway makes the problem worse. While there's likely sufficient room in the area of the unused provision for an extension to Post Office Square to shiv a junction there, you then have to underpin potentially both levels of Boylston Station (destroying National Historic Landmarks is generally frowned upon, especially if they're liable to be re-used in a Crazy Transit Pitches world for service to Nubian to replace the Elevated, and even if you can destroy Boylston Under you still have to underpin 1897-vintage Boylston proper) and 1908-vintage Chinatown station. Underpinning these old stations was another problem identified in the SL Phase III study that projected potential cost blowouts so bad it made the Feds run in terror. The Green Line Reconfiguration thread has very-thorough rundowns by F-Line to Dudley and others on the extremely dubious prospects of anything down Essex Street for connecting Green to the Silver Line Transitway. The more-apparently-feasible options all involve re-using the Tremont tunnels, meaning you'd be feeding service in and out of Park with no direct Back Bay/Kenmore access (though a simple transfer).
This would preclude the NSRL from using the Central Artery alignment, which is the only viable four-track alignment that doesn't require the present administrations ludicrous suggestion of Congress Street + Artery NSRL alignments. In my opinion the NSRL should take precedence, but others may have different views. I'm also curious as to the technical feasibility of approaching from under the east side of the O'Neill tunnel, but that probably depends on whether there's enough space for the new tunnel branch to dive under the road tunnel.
While I take no position on the viability of a surface line in Chelsea, the route you've mapped between the Tobin Bridge and the SL3 busway is physically impossible. There are far too many places where the buildings are far too close to the highway structure to be able to fit any type of rail ROW, and it's both extremely unlikely and extremely inadvisable to be able to share space between LRVs and the highway traffic. There's probably enough room for alternate surface routes, but not the mapped one.
This proposal seems to be a mash-up of Silver Line Phase III, parts of the NSRL, and a new Charlestown-Chelsea service. While it would need to be studied again the general consensus in the Green Line Reconfiguration thread was that the reduced tunnel width going from BRT to LRT doesn't nearly help enough to ameliorate the cost and technical difficulty of tunneling down Essex Street (which is the only meaningful way to go if a Back Bay/Kenmore direct run is a project requirement. If it's not, re-using the Tremont tunnels and running via Park Street is likely easier and less expensive overall). There's no specific reason or need for that element of the project to be tied to any of the others; its benefit is in relieving the load on Red and helping deal with the Seaport's transit woes. The Central Artery section fulfills the second-subway function of the NSRL to some degree (and probably with a somewhat less onerous South Station transfer) but without the greater-scope benefits of the NSRL to the Commuter Rail system, which may be in fact precluded (and at the very least would become significantly more expensive). Also not a project that needs to be tied to any of the others. The Charlestown-Chelsea run is not necessarily a bad idea, just one that would need to be studied for cost-benefits on how to do it, but there's absolutely no reason I can see that says that if you want to serve these places it has to be linked to a or this subway, as opposed to, for example, a spur off the Urban Ring or some other route. So there's a lot that's interesting, but I for one don't see much in the way of benefits of aligning these pieces into one single project (and some significant drawbacks, which is unsurprising as the last time the state tried it, they begat the disjointed Silver Line, left permanently incomplete by that same nasty Essex Street stretch.)
Good points all. What I would really like to see is the portion built from North Station to Chelsea. Once the line crosses the Mystic River on a high bridge as shown on the layout i did, it could use the space occupied by the long SB on-ramp that climbs up from Chelsea, which would be removed. There is already another on-ramp to the Tobin a few blocks from there. Once the LRT line reached the northern end of the SB on-ramp (to be removed), space runs out alongside the expressway to fit in an LRT line there, as you pointed out. A couple of options for the LRT to continue north is to tunnel under the expressway for a few blocks until the expressway becomes fully elevated again, or run a short elevated LRT structure along and above Everett Ave to the commuter rail line. All crazy transit stuff, but somehow an LRT line could be threaded through that tight spot.
Good points all. What I would really like to see is the portion built from North Station to Chelsea. Once the line crosses the Mystic River on a high bridge as shown on the layout i did, it could use the space occupied by the long SB on-ramp that climbs up from Chelsea, which would be removed. There is already another on-ramp to the Tobin a few blocks from there. Once the LRT line reached the northern end of the SB on-ramp (to be removed), space runs out alongside the expressway to fit in an LRT line there, as you pointed out. A couple of options for the LRT to continue north is to tunnel under the expressway for a few blocks until the expressway becomes fully elevated again, or run a short elevated LRT structure along and above Everett Ave to the commuter rail line. All crazy transit stuff, but somehow an LRT line could be threaded through that tight spot.
Something I've been tinkering with since the congress st discussion popped up recently: downgrading rt 1 from a fully separated highway south of Squire Rd, and building a new *gasp* HRT line. The new line would run south from there on a RoW that would look very similar to Burgin Parkway in Quincy, cross the mystic along an appropriated deck of the Tobin, bang a left into a tunnel and run parallel to the orange from North Station to Haymarket and follow the Congress St alignment to South Station.
From there, continue south underneath Hudson St, under the pike, and on to Nubian Sq. Connects to all existing lines as well as UR at Chelsea