And the Big Dig took 16 yrs, and NSRL is nowhere near as complex as that.
The Big Dig took something like 15-16 years of construction with another near-decade's worth of planning and politicking to get funding before construction started, and that was before Congress devolved completely into the partisan viper pit that it is now. (Raise your hands if you think a Republican Congress or administration wouldn't try and starve/kill a Massachusetts-centric project out of spite if they got the chance.)
We have, right now, another year and a bit of the Baker administration, which has clearly demonstrated a virulent aversion to doing anything to advance the NSRL (see the NSRL thread's eviscerations of the blatantly-sandbagged NSRL studies). By the time that we even have the
chance of a state administration that favors the NSRL, there's a very real (and quite likely) prospect that Republicans will have taken control of Congress, or at least enough of it to make the snowball have a better chance of surviving hell than the NSRL getting through the much-worse hell that is Capitol Hill. It could easily be ten years before there's even the opportunity to get the money, at which point even if the state did a bunch of prep work in planning you'd still be talking about at least the best part of the decade to get anything done, and that's optimistic. Easily could be worse than that, and that best-case version has the NSRL at least twenty-odd years out. It could easily be twice that, if it's ever even built at all (look at when what's now the GLX was first proposed for an idea of how bloody long it can take even the fairly-obvious projects to come to fruition here)
The degree of uncertainty makes it completely irresponsible (even more than usual) to make design decisions about current projects based on future projects that are completely ephemeral at the present time. It will be
annoying if we build bridges with sufficient capacity and redundancy to serve current and future-expansion North Station capacity demands and then subsequently don't need all of that capacity if and when NSRL comes online, especially if it's sooner than expected, and the same is true for South Station Expansion. On the other hand, if NSRL remains in purgatory for another forty years and the surface terminals choke on unnecessary capacity constraints, that directly harms the existing system for no reason other than God Mode thread perfectionism.
We don't get to make today's decisions based on what we wish tomorrow's going to look like, the best we can do is base them on what we
expect tomorrow is going to look like. The NS bridges need replacing well before any reasonable chance of the NSRL impacting the system if it gets built at all, so we have to deal with the bridges and can't condition how we do that on an NSRL that cannot reasonably be promised to be there when NS would need it to be. That's, unfortunately, the cynical reality of it. I don't like it, I don't accept that it has to stay that way forever, but I also know it's not likely to change overnight and
that we do have to live with.