With new office towers at Haymarket North Station and Lechmere, it may never again pay to turn short at Park Street.
I'd say anything that currently turns at Park Street should turn at government center. Anything that turns the government center should turn it North Station, and anything that turns at North Station you should probably run to Union square in the future.
Green Line isn't exactly set up to just keep pushing everything forward-forward-forward so every service pattern runs a marathon. The lost art of short-turning that BERy and the MTA did so well and the MBTA almost from Day 1 ran in pants-shitting terror from is arguably a big reason why the Central Subway is a lot more brittle and less flexible than it was >60 years ago when it juggled 8 surface branches with aplomb. Precision turning is where you mesh routing variety and assign headway-boosters to where they're needed. We not only may not have
enough of that, but with the expansion dreams we have it's going to be necessary to get back into the act of hyper-local service supplements and more dynamic pair-matching patterns.
As noted above, stub-end turnbacks are fine at the ends of lines and North Stations where there's a waiting car supply backstopping the somewhat time-consuming end-change, but absent an adjacent yard and in the midst of heavy traffic you need loops to turn fast. Ours unfortunately are on the tight side. So we're in a terrible hurry to tear our Park Loop. Well...what about Brattle Loop which is only a couple feet of radius wider but is most likely going to be needed for rush-hour Medford shorties in a few years because Riverside-Route 16 is too big an ask to sustain at 6 min. headway over that long a distance under peak loading? Are we going to slap artificial restrictions on Brattle for emergency or non-revenue use only and end up running headlong into a problem when Somerville growth goes nuclear?
Or what about ambitous future expansion considerations that the Green Line could handle under GLT traffic management? The Urban Ring is probably going to come with ironclad requirement of turning Cambridge-Lechmere trains @ GC from the north end. What about Kenmore Loop revenue service? If you hook the UR in at BU you're probably going to be running E-to-D circuit service turning at Kenmore to bolster the cross-platform Longwood transfers on all those 66 riders who'll be migrating over to LRT out of Allston, especially since the SW quadrant Kenmore-Dudley Ring will have to be BRT and could use the service augmentation on that first Longwood leg to keep the buses clean for thru-Dudley passengers. Are we going to permit that, or is Kenmore Loop going to be consigned forever to restricted non-revenue use only? Can we answer the question of what patterns might need a Park St. turn in the future before we get too hot to rip it out? Is that where Urban Ring inbound from Kenmore turns on 'circuit' service while inbound from Lechmere boomerang turns at Brattle? Needham and Dudley Sq.: who's the highest priority for a GC-turn slot, but does one have to stand back at Park to do it fluidly? What about Forest Hills redux? If we've made peace with streetcar extension to Hyde Square we're already halfway back to Arborway; does Huntington get fileted Forest Hills-Park and Brookline Village/etc.-Union like the old double-barreled Arborway-Park and Heath-Lechmere peak service of pre-'85? Not all of these are necessarily going to get built, but if you're looking to
delete Central Subway infrastructure that's been there since Day 1 in 1897 you better have your 50-year traffic modeling considerations sorted to absolute confidence.
The hard part here is that the 2 ft. difference in radius between seemingly revenue-expendable Park Loop and seemingly revenue not-expendable Brattle Loop isn't a great enough difference to suddenly get us importing a wholly unmodified world best-seller Siemens S70 Avanto like we're bumming off the assembly line for Seattle's order. It's fairly clear that customization is going to have to make up some of the difference no matter what. What GLT hopes is that it can be customization
within the off-shelf design rather than cutting the other way: another Boston design-build "Type" series of all low-floor that has to lead with another new truck design based from 'our' system and which merely aims to generify the crap out of supply chain to pound the lifetime costs in-line with industry standards. Either scenario would be a massive improvement over today's sustainability, so by no means does having to for-real "Type 10 it" mean we lost. A Boston-first design is clearly the less satisfying outcome for the GLT task force, but one they'll peacefully accept if just no practical alternative because they think they've hit on a formula for doing it way better than ever before.
It would be preferable if the resulting customization were more like a new "Avanto
Tight" flavor that's just a new narrower-turning form factor in the Siemens product catalogue rather than a truck/carbody design that's not organic-Avanto at the root because it had to be led by the nose through redesign by Boston specs. Siemens sells LRV's on three hemispheres of planet Earth. They have legitimately good shot of scoring some follow-on orders from the '
Tight' form factor they just so happen to come up with because Boston's got a kingmaker's 200+ car order up for grabs. It's well worth the R&D of adding a new dimensional flavor to the regular lineup because we happen to be buying in bulk and have some specialer needs to tend to. Somebody on those 3 hemispheres has tight street intersections begging to be marketed to with a flavor that can cut harder corners than the rest but otherwise doesn't have any major design deviations from the rest of the family. The GLT team would much prefer to shop for options "marketed to Boston" from within the family lineup rather than "designed FOR Boston" and fingers-crossed somebody else will like Boston's design.
But no question...if every single loop on the subway other than GC-inbound had to be either ripped up or be slapped with a non-revenue forever restriction for the sake of ordering a generic '
Tight' instead of a "
Type...", the constraints on future service are going to be difficult to swallow and will lower the ceiling on feasible expansion. In that scenario taking a hugely improved "Type" car for Boston with heavy self-policing during design to generify the parts supply chain ends up hands-down the better bet. We can't be
so target-fixated on off-shelf for off-shelf's sake that it's going to make routing patterns too rigid in the face of growth to accommodate dynamic expansion and a full arsenal of headway-boosting tricks. Something has to give, and if "Type"-ing it with a better blueprint this time still ends up a stratospheric improvement over today...the only bottom line that ultimately matters is what a stratospheric improvement over today it is.
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