Re: North-South Rail Link
After looking at the rendering of this, I am a bit confused. Would N/S rail replace north and south station or be in addition to them? Why would this lead to increased frequencies compared to just shortening the turnaround time and expanding south station? Would the fairmount line be able to go through the tunnel even though the portal is at back back station?
It's in addition to. The great mash-up of all lines coming into South Station and the North Station drawbridges are the current limiters for frequencies on the system. For the most part, the commuter rail mainlines themselves have way way more capacity to give for packing trains closer. But they can't tap that capacity because all schedules are still predicated on Cove Interlocking at South Station and Tower 1 at North Station.
Take the NEC, for example. 4 tracks through SW Connecticut manage to carry all Amtrak traffic and dizzying rate of overlapping commuter rail schedules. You would think if we expanded it to 4 tracks here--as is eventually planned all points south of Forest Hills--that there'd be similar capacity to tap here. After all, the station spacing is far less dense than it is on Metro North given how much time the NEC spends in unpopulated wetlands between stops in MA. But then you look at the traffic modeling in the South Coast Rail FEIR and see just how crippled the frequencies are (I'd cite NEC FUTURE's TPH figures too, but their methodology is so faulty as to be useless). Why with comparable track capacity, far less operational complexity, and far less total demand can the New Haven Line absorb that kind of traffic while the Providence Line can't? Not even the 3-track pinch inbound of Forest Hills and Back Bay Station explain the extreme
degree of difference in TPH capacity on the NEC in Massachusetts vs. the NEC on the New Haven Line. After all, the New Haven Line has to merge with the Harlem and Hudson Lines--near-equally extreme on service densities--on the approach to Grand Central.
It's all about the terminal district. The South Station approach is pinched by geography into a very tight mash-up of all lines in a half-mile span where trains are crisscrossing each other to get between mainline and platforms, while the load-bearing NEC/Worcester side has to crawl through one of the system's tightest curves to get there. Metro North has 5 miles of tangent track to sort itself after the last of its three mega-mainlines has merged in, and a much more spread-out set of lead tracks for fanning into the terminal. There's nothing Boston can do about its geography to correct this. The Channel and the Harbor are where they are, and the landfilled soil + all the other tunnels cut through the landfilled soil makes it impossible to realign everything in perfectly orderly fashion. South Station Expansion solves the shorter-term problem of constipated platform assignments imposing a cap
more limited than Cove Interlocking's natural capacity...but fixing that glitch only addresses 20-year incremental growth before Cove itself is the immovable object. Reorganizing stuff by moving the Franklin Line permanently over to the Fairmount routing and trading Needham off to the Orange Line only serves to vacate slots that Amtrak's going to immediately gobble back up; it does nothing for increasing total frequencies. Building NSRL to
replace the surface terminals, like SEPTA did with Center City, ends up a totally lateral move that just sends the same capacity cap underground; there's still a tight mash-up of lines at "Cove Under", still a very space-constrained fan-out into the platforms.
To some extent this problem has been lurking for over 115 years. When all of the mainlines into Boston were built, they each had their own independent terminals limited only by the capacity of the mainlines and the technology of the 19th century. Boston & Albany, Old Colony, New York & New England (Franklin/Fairmount), Boston & Providence (NEC), Fitchburg RR, Eastern RR, Boston & Maine, Boston & Lowell...they each had their own terminal stations spread across the CBD. And they each needed it, because prior to ~1890 there were no motor vehicles or electric streetcars or bicycles or any type of last-mile transport better than a horse on an unpaved, mud-packed city street. So the stop spacing and local passenger + freight frequencies they ran handled all the needs of the modes not yet invented. Basically...RR stations and freight houses packed as close together as express bus stops are today. By the time the two union stations were built the trolleys were out in force, the internal combustion engine was well into its R&D phase and a known-known upcoming game-changer once it got in wide circulation, and roads were starting to get paved with hard surfaces. The RR's were finally able to shed a lot of those hyper-local runs and overdense stop spacing that the streetcars were better-equipped and focus on the more profitable growth markets of suburban and regional service. Which made the concept of catch-all union stations extremely attractive. But the tradeoff for the convenience of consolidating terminals was accepting that Cove and Tower 1 were going to impose a capacity cap.
The post-industrial collapse of the Eastern CBD's, and cars displacing the RR's deferred that capacity cap from becoming a problem for a full century. But now that Boston is bigger than ever and the East Coast megalopolis more saturated than ever we're starting to stare down some real service limits that are going to scrape up against that terminal district capacity cap in the next 25 years. Europe and SE Asia provide the model of 21st century hyper-dense service that the East Coast megalopolis is going to have to implement on wider scale to be able to self-sustain, but we can't do that in Boston because of the capacity trade-off made when the union stations were first built (and then, regrettably, cut in half in the late- 20th century with no means of getting 100% of the way back). It's eventually going to place limits on our region's economic sustainability if we don't plan for a solution to that cap.
So the only solution that restores the true mainline capacity that we'll finally need to tap after 115 years is to create a
second set of terminal district(s) completely separate from the first set that divides up the load before train slots get constrained by the great mash-up. Hence, continuing to use the surface South Station and surface Cove Interlocking to their fullest extent, while shadowing it underground with SS "Under" and Cove "Under". And being able to seamlessly divide traffic between the two by sticking portals a *hair* before the NEC and Worcester Line merge, and a *hair* before the Old Colony and Fairmount merge. By sidestepping the capacity cap of the surface terminal district, headways can now fill out to the tippy-top of the mainline's capacity. And that ends up such an exponential capacity increase that it'll take us 100 years to invent the demand that fills it all up.
The ability to do run-thru service is a nice side benefit (one that gets overrated to the point of confusing the issues). But it's not the reason for doing it. And if retiring the surface terminals (i.e. what SEPTA did) were a goal...run-thru wouldn't be anywhere close to big enough benefit to justify the cost, because it's just trading one capacity cap for a different (and possibly worse) one. NSRL is about a 100-year solve for the RR network's capacity cap, such that New England can exponentially increase its service frequencies across-the-board through the Boston hub.
Including at the firing-on-all-cylinders surface terminals.
How they choose to take advantage of those available frequencies is anybody's guess. It's such a massive gain it'll no doubt take a long time to even sketch out that canvas. It's that total a reboot. But if you want that 100-year canvas at all...you build NSRL, you keep expanded South Station, you keep and eventually expand (with reinstated Drawbridge #3 and more platforms on the ex-Spaulding side of the property) North Station. And then you dream up the system that uses that capacity to the hilt, and sustains the region's economic prowess.
That's the great big promise here. No one expects the full benefits to be realized on Day 1 of the ribbon-cutting, as there is a SHITLOAD of follow-on things to build and investments in service the state and feds have to execute on to make to make the Link pull its weight (and yes, that also means an exponential shitload of rapid transit expansion because the CBD just isn't equipped to distribute several million more annual transit riders pouring into a transfer singularity at NS + SS). But it's the key piece of infrastructure enabling the century-level solve for the capacity cap and the century-level solve for regional sustainability. This is the backbone of your great-grandchildren's mobility, and their economic opportunities in this region. We need to get the ball rolling on it soon, because the effects of the capacity cap are going to be felt in *our* lifetimes, and quite likely while we're still in the workforce.
