No-no-never on thru the Common, as that permitting is what chewed and spat out the Boylston Loop. And the problems to the east with Chinatown underpinning + building foundations + narrow streets are exactly the same. Remember: tunnel depth out of Transitway is totally fixed/unchanging at the threading around Big Dig tunnels with running room to Chinatown unmovably fixing the problematic OL underpin depth. You can avoid Boylston and go deeper to your heart's content west on the Arlington insertion...but the plot was already lost at Chinatown so it doesn't salvage the FTA rating or let you complete design.View attachment 9543
Ok so let's go down this rabbit hole. Instead of Essex, use Avery Pl. That curve buys you an extra 200' (give or take) which maybe buys you enough extra grade to where the performance isn't compromised? Or perhaps it doesn't because now you have to go even deeper to avoid building foundations.
Every "Yeah, but..." about some novel new Essex stab (as if there already weren't a thousand of those officially tried) needs to re-read that last sentence in triplicate. The plot is lost by Chinatown... You have to pick a different Orange transfer station than that one; running distance simply doesn't exist from the fixed Transitway insertion to square the underpin.
That means you have no choice but to alternately target Tufts OL as a replacement for infeasible Chinatown. Which drags you south of Essex by necessity, albeit to universally wider streets that won't be nearly such dog-slow running (thus making crow-flies 2D Google Maps perfectionism the ultimate doesn't-matter waste of time). Any "Yeah, but..." that glosses over this necessity isn't rehabbing the project at all to fundable build, so don't waste any target fixation to the West. If you have to touch Chinatown, you're already dead.
Debate ahoy on Stuart St. Redux as that's wholly enabled by a south jog. But the Orange transfer must target Tufts, not Chinatown. Chinatown is a verified impossibility for achieving 100% Design.