Just a point to introduce into this debate:
Buses unlike trains can easily be stored, serviced, etc. in vertical structure -- i.e. Parking Garages. For example the MOS garage has one floor on the bottom with a high clearance for -- Buses -- with 3 floors in the middle for cars --- and one on the top [with no real ceiling] although the clearance of the ramps and the lower floors limit the useful clearance.
So why not get a developer to build a complex incorporating a garage for T Buses.
If you're talking distributing storage over
many micro-garage facilities in private dev. spaces like the MOS garage example, operating cost scales defeat that instantly. Each T garage is full-time staffed with Service & Inspection facilities (even the ones where those functions are minimized to just ID'ing a problem on the lift before sending the vehicle to a bigger garage for repair) that impose their own heavy cost premiums on operating the facility and equipping it. The T's ongoing Facilities study bullseyes this as the biggie cost driver. So unfortunately micro-targeting vs. the route layout ends up cutting the exact opposite direction you would hope for running a more nimble system. At least here in Greater Boston. As it is today it is the minor outlying garages--system-smallest Fellsway, perennial out-of-date/"sloppy-seconds" Quincy, Lynn, and North Cambridge TT garage--that are running the most unfavorable on cost ratios and/or falling furthest behind on modernizations. It's all because of poor scalability, and the study has a wealth of info detailing how this needs to change in a big way for future growth to scale without corresponding off-scale cost inflation.
Conversely, if you're thinking stacked single-purpose garages that try to max out the storage density per parcel by going tall, there's simply a numbers game on what parcels are appropriate enough for building that way within-cost fed into local authorities' thus-far complete/total unwillingness to entertain new non-revenue transit land use anywhere within 10 miles of the CBD. The local opposition (witnessed by the ongoing hysteria in Quincy) may be more pronounced here than elsewhere, but there are justifiable reasons why stacked storage facilities are nearly unheard of in other large cities. Ideal cost/benefit matchups are incredibly hard to attain, almost taking fluke luck. For one, moving cumbersome buses from higher floors in/out isn't easy unless the parcel is ideally-shaped for building wide turning-radii ramps that don't cannibalize too much interior space. Second, you instantly subtract a floor from street-level height because presence of so much as one S&I lift on ground floor instantly makes that ground floor two stories tall with proportional increase in the load-bearing costs of the upper floors. Third, ventilation and fire suppression (even in a battery bus -dominated future) have to be orders-of-magnitude tougher in a uniform transit garage vs. a heterogeneous-use car garage of proportionately smaller, lower-powered and self-insured vehicles. Convergence in parcel selection, build techniques vs. resulting capacity, and cost premiums for outfitting end up eliminating all but the flukiest-chance matchups for the scaling metrics they highlight in-study. This sufficiently explains why stacked transit facilities are such an extreme rarity worldwide, and tosses most possible Boston-area site matchups well before engaging hostile locals in all likelihood zeroes out the rest.
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The best cost scalability they found via study was on "super-campuses", mega-garages or multiple garages clustered down the street from each other. Cabot + Albany + Southampton are one such super-campus, system-behemoth Charlestown + centralized heavy-repair Everett the other.
Programmed construction in the ongoing plan to max out Southampton's parcel space with 60-footer storage expansion direct-aids the downtown super-campus. Southampton was initially a quick-and-dirty Silver Line build, a bit small and haphazardly laid out. They are enacting their first real site plan to ramp up its overall efficiency for 60-footers in general, expand on some adjacent parcel flotsam under the City's radar, and in general reorganize land usage more optimally. The expansion comes with advantageous cost-scaling because labor and equipment are there pooled with 40-footer Cabot and Albany garages right up the street, giving Southampton pound-for-pound more value for each additional vehicle it now takes on.
Obviously Widett land-swaps loom huge in the future for scalability. Yes, it's practically the only move that
could make the Albany property available for trade. But being able to stuff 100+ buses on the BTD tow lot also re-shapes the super-campus task distribution such that the
non-expendable Cabot facility can reinvent itself on-footprint to consolidate all 40-footer repair duties from Albany in exchange for trading out some of its space-consuming pure storage underneath the Widett air rights. So even if there ends up not being nearly enough gained new storage to outright close Albany, it's a major cost reduction to be able to consolidate repair functions across the super-campus. It'll make what pure-storage remains of Albany immediately less costly to run and far less impactful to its South End neighbors when it no longer has to retain loud all-day shop functions or stay open for a loud overnight shop shift.
Super-campuses are also what drove the prior study's conclusion to site a 60-footer garage at Wellington (trading Orange Line parking capacity into a garage closer to the parkway/kiss-and-ride so all back acreage could be traded). Wellington would achieve idealized costs by being able to unified-pool staff shifts with Charlestown/Everett, share equipment, and function with parity to Charlestown on non-revenue miles for its routes. It's not in the scaled-back current plan, but is more-or-less the next big pivot after all current optimizations are enacted because Charlestown routes have the largest incumbent potential for 60-footers, all land is agency-owned with Orange Line impacts neutralized by the garage trade, and the acreage in question is very low value for private redev because of its single-point egress is choked off from the outside world crammed behind the the Orange kiss-and-ride + future garage queue. In exchange for building this, (1) Fellsway gets closed and sold off outright, (2) Lynn sheds all heavy-repair functions and slims down just to straight storage + S&I bay, and (3) Lynn closes weekends and couple hours earlier on the late-night shift to be sourced out of Charlestown at lightest-traffic times.
The repurposement of Watertown proposed in the last study (but not this scaled-back current one) was also aided square at serving the super-campuses, even though Watertown in itself was not a super-campus site. Load-shifting some west-leaning routes away from Charlestown is what opens up the extra capacity for Charlestown to reach north and chop Lynn's functions down to part-time. It also allows for immediate closure of North Cambridge TT garage, the tiniest bus facility of all but also one with outsized cost scaling because it has to be staffed 6 days a week to host all repair functions for a very small 28-vehicle fleet. While it's looking less likely by the day that the TT's will be going away for battery-electrics in this immediate next generation procurement because of increasing risk-aversion to BEB's being 100.00% ready for prime time, Watertown being able to absorb the TT's in-full alongside a peeled-off contingent of Charlestown diesels counts as a big win for cost scalability. One that gets better as BEB's are slow-walked into deployment, because the facility will already be servicing the same types of wheel traction motors on the TT's when its BEB assignments start significantly cutting into the diesel ranks. Watertown's also, despite its dense surroundings, an awkward fit for private redev because of the jarring grade difference on its backside wall with Nonantum Rd. There's no street interface to pursue on the river side of anything private mixed-use that could be envisioned there, which tends to cut down any outside interest in it after the most superficial initial look-see.
Now, if we'd been able to double the size of Arborway Garage instead as originally planned Watertown probably would get relegated to un-recommended rating because the West region would be re-shaped in a different direction and Charlestown would be doing more route-swapping with Cabot/Albany to clear its decks for the northern consolidation. But the effect would be very similar:
greater not lesser concentration on the super-campuses, and outer reach of the super-campuses setting the table for any/all secondary facilities. Outside of Quincy, which is simply too far outside the roaming range of any super-campus site to function as a regional quasi-appendage like Lynn, this is 'the' systemwide driver for aligning future capacity. And it's going to trend
more heavily towards the super-campuses than making any pivot away from that to instead micro-targeting bundles of routes at smaller sites. It's not that micro-targeting isn't a valid scheme on-spec...but it's not a
Boston-relevant discussion because the T has already weighed the pros/cons of it for this market through two comprehensive studies and made its existential choice of where future scalibility is headed. Their choice weights way, way heavier to scalability-via-concentration. It's already advanced past that point in actual shovel-ready construction plans to entertain a reversal in distribution.
