I agree that this has drifted off-topic and should be moved. I'll reply here just to keep things in one place for now. I want to draw additional attention to this:
And, yes, there may be a problem in one of the tunnels. A four track NSRL should provide sufficient redundancy.
In the
latest design, the "four-track NSRL" concept does not provide the redundancy you are describing here. It isn't a NYC Subway-style 4-track tunnel, but rather is essentially a pair of two track tunnels that have a single crossover between them, north of North Station.
Right off the bat, that means that inbound Southside trains will be SOL if there is a blockage in their particular tunnel in the core section -- simply no way for them to access the other tunnel. Northside trains won't be much better off either -- rerouting Tunnel A Northside trains into Tunnel B means that the pairmatched Southside routes need to be able to
receive all that extra traffic, which is no guarantee.
(On my skim through the
2003 DEIR, I also did not see reference to the necessary switches/flying junctions at the southern end of the tunnels.)
The "debate" over whether North Station and South Station would still be needed post-NSRL has always seemed like putting the cart before the horse to me. The reality is that NSRL is going to be
one piece of a much larger transformation, that will include an almost-certainly
gradual electrification of the commuter rail system line by line -- it's not going to be a binary "pre-NSRL"/"post-NSRL" dichotomy. So there will be plenty of time to see how things
actually work in practice, at which point we can have an informed conversation about whether North Station Upper is still needed.
(The damn thing is going to be hard enough to get build as is -- we don't need to add
more Day 1 requirements to the NSRL, e.g. "needs to be able to replace all terminating traffic at North Station.")
In my dream scenario where the 4 tunnel NSRL is complete, the dead head parking at North Station gives way to a new neighborhood, that rail bridge is open to local traffic and that walkway is an at grade connection from the North End to the Esplanade.
However, as with most of our incomplete infrastructure, right now we have to be content with something suicide inducing.
Going back to this -- this sounds like a pleasant idea. Could it be achieved instead with a modest level of decking over the existing North Station platforms?