Green Line Reconfiguration

[TheRatmeister]

Great thoughts from you both. I'll address this part first:

The idea is to set up three completely isolated trunks:

• Nubian - Park Inner
• Huntington - Government Center
• Kenmore - Seaport

Of the three downtown routes, Park Inner is the only one with a capacity constraint (or at least the most likely). Coincidentally, of the three outbound routes, Nubian is the only one that doesn't need "full capacity" of 30-40 tph.

(You can swap the latter two to Huntington-Seaport and Kenmore-GC, which is equivalent and doesn't change the rest of this comment.)

As it turns out, this is the only arrangement that maximizes capacity everywhere without creating a "Herald Square-type merge". Why? The derivation of this is precisely what I'll elaborate in the next blog post.

So if you want three trunks you need two extra tracks between Boylston and Washington St, and that pretty much means doing some form of SL Phase 3 as the easiest link between Boylston Inner and Washington St is probably from the west... somehow. Of the portal alternatives:

• Columbus Ave is in completely the wrong place
• Tremont St is completely unworkable due to the insane loop you'd need at Boylston

Which leaves the Charles St and Stuart St Alts. They could both possibly work, not needing to go nearly as deep should alleviate at least some gradient concerns, but may make construction quite disruptive. Both of these options also involve destroying the buried Pleasant St portal and its flying junction however, which could complicate weaving the Huntington subway into all this.

 

[TheRatmeister]

And we could also go deeper with the "Why?" for the Nubian trunk in the first place. I don't think the corridor really has a lot of branching opportunities, and even with 12 TPH to Nubian, 12 to Needham/Riverside, and 6 to Hyde Sq or Arborway, that's still within the constraints of a single trunk.