1. Branching OL clobbers headways from Sullivan-Malden. Not a good idea when two major bus hubs feel the pinch. I think a better HRT option is available for GLX-Medford now that the NSRL study has ID'd the (bad for NSRL, but potentially good for rapid transit) Congress St. alignment out of SS. NSRL absolutely needs to be built 4-track on the CA/T alignment, but if Congress is a viable (if expensive) dig for a 2-track tunnel you now have open path to build the "Red X" off the RL Cabot Yard leads. Figure this:
- run revenue service off Columbia Jct. via the Cabot leads.
- divert near Haul Road into the disused upper Broadway tunnel--stop at Broadway "Upper"--then up Dot Ave. to SS and conjoin to the existing Red/Silver fare lobby--stop at SS "Under". Depths of all tunnels would be different, but since the NSRL report states both the CA/T and Congress alignments are simultaneously buildable all would fit.
- up Congress. Stops at Post Office Square, State St. (offset by block from Orange/Blue, connected by fare lobby), Haymarket, North Station (upper berth above Orange).
- graft-on portal next to Orange by Community College. Possible slight-offset RL-CC station. Possible Phase I terminus and small turnback yard here to inaugurate service while planning further extension.
- shallow-cut duck under of Boston Sand & Gravel yard, BET commuter rail tracks. Get on alignment with Fitchburg Line, popping briefly above-ground by perimeter access road along BET/Northpoint property line. Probably not any room for a dedicated Northpoint/Cambridge Crossing station here, but the new staircase off Gilmore Bridge pretty much frame CC and Lechmere as their home stops anyway so stick where the frequencies are.
- quick duck under the GLX/Fitchburg spaghetti at Brickbottom, then on-alignment for Medford. Take over all stops from Washington to Route 16, then extend (Phase III) as necessary north to Winchester or Woburn. Northern GL branches become more duty-focused on the Urban Ring NW & NE quadrants + Union branch and further extensions to Porter, Watertown, etc.
- run service on the "X" in rotating fashion: Alewife-Ashmont, Alewife-Braintree, Medford-Ashmont, Medford-Braintree. All route combinations end up getting fullest 3-min. mainline headways for intra-route service, and no worse than 6-min. headways for every permutation of alternating service "X" leg to "X" leg. What this does is:
- outright doubles Ashmont & Braintree branch service (big for exploding Quincy growth) while doing no harm to existing mainline service. This is huge if CBD growth is going to tap out by midcentury and surging south is the only way to go.
- encourages further extension of Ashmont Branch past Mattapan to Hyde Park + Dedham Ctr. New service patterns end up with more headroom/resiliance for slight branch schedule length imbalances.
- SERIOUSLY de-clogs Broadway-Park and saves existing line from always being at the edge of chaos (regardless of Red-Blue, etc. builds) from choking on its dwells in ped-constrained old stations.
- substantially infills an alt-spine to most of the big transfer stations. Provided that Seaport-Downtown Green Line gets built, these stations would have THREE levels of rapid transit transfers: SS (existing Red, "lower" Red, Green/Silver Transitway), State (Red/Orange/Blue), Haymarket (Red/Orange/Green), NS (Red/Orange/Green). Plus both surface + NSRL Purple Line terminals covered in triplicate for RUR and Amtrak. These stops would all have two rapid transit transfers if other formal-proposed builds are complete: Broadway (existing Red, "upper" Red"), Tufts Med Ctr. (Orange/Green likely), Park (Red/Green + OL concourse stet), GC (Blue/Green stet), Charles MGH (Red/Blue), Community College (Red/Orange), Sullivan (Orange/Green-Urban Ring), Porter (Red/Green), Harvard (Red/Green-Urban Ring), Back Bay (Orange/Green if E relocated off Copley and reattached to Tufts/Boylston), Kenmore (Green/Blue if "Riverbank"/Storrow trade-in off Charles built), Logan Airport (Blue/Green-Urban Ring). Plus the outside- fare control Urban Ring Kendall stop a block away from the Red lobby. Holy distributed loads, Urban Planning Man!
- downtown bus load-reshaper. Post Office Square routes (4, 92, 93) can get re-drawn or truncated more advantageously away from traffic. In conjunction with GL-Transitway you can probably deflect the 7 & 11 away from crossing through the Financial District, and obviously the surface Silver Line routes go away. You'd basically end up achieving BERy's original goal of a downtown CBD freed from slow surface transit.
- In a world where Red-Blue, Transitway-Green, Urban Ring, and Green Line Transformation-inspired radial streamlining are already über-priorities the "Red X" recycling the surplus Congress St. alignment ends up contributing 6 more load-distributor transfers to the mix.
I wouldn't really call this high-priority with the project backlog we have to keep moving to keep Boston from choking on its own 2040 growth. But as the
next encore post-2040 to assure we're a sustainable city for the whole second half of the century? This is a potentially big one for the doubling of capacity on existing trunks, contribution of half-dozen more load-spread transfers in the CBD, and 100% compatibility/0% risk to any existing RL service. Payback for the large up-front investment is self-evident in the exponential growth it affords through load-spreading, whether it costs a kajillion dollars or not. If the Congress alignment is as feasible as the NSRL study says it is, we already know this can be built. The only thing "Crazy" about it is how many decades sooner than the next guy do you predict we'll need it.
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2. Let's get the surface LRT spine first, since that can be done in only a few years at reasonable $$$. Washington burial is unfortunately going to be very "hard" tunneling compared to some easier ones like burying the B to BU Bridge to enable Urban Ring NW quadrant, burying the E to Brookline Village to "alt-spine" Kenmore-Downtown, or trading in the Storrow midsection's roadbed for an affordably shallow BL-Kenmore. Harder also than some genuine lower-priority stuff like RLX Mattapan-Hyde Park under River St. And, amongst kajillion-dollar efforts, certainly a lower ceiling benefits-wise than the two biggies: GL-Transitway and NSRL. LRT'ing Washington can be folded in with the GL-Transitway effort if a South End routing is determined favorable over all the structural underpinning problems that killed Silver Line Phase III's Essex St. alignment. In which case the 4-track Tremont St. tunnel can continue 4-track through the Tufts transfer station down Tremont to the corner of Marginal, then split 2 x 2 tunnel to SS vs. portal-up to Washington such that there's total traffic separation everywhere Boylston-outbound. Get the bus terminal properly fed with 6-min. headways flushing downtown, and then since the southern-half Urban Ring is probably going to have to be Kenmore-Dudley BRT + Dudley-Southie BRT from lack of rail ROW's the extra rapid transit spine works hand-in-hand with UR to strengthen the area. Figure also that if the E gets relocated off Copley through Back Bay station and plugs in at this same junction you're probably going to have an E-to-Seaport/Washington underground wye leg providing additionally attractive alternate service patterns later on.
Deep-future you obviously take your best shot at studying burial options, but I somewhat doubt it's ever going to get to the point of pulling the trigger. Construction disruption down Washington is simply too hard for what it's going to chew in mitigation cost, and surface LRT (including TBD patterns that can alt-circuit off the E to re-shape some bus loads) ends up "good enough" long enough that you'll be waiting to midcentury or beyond for any congestion threshold that merits pulling trigger on such a megaproject.
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3. Hard, hard tunneling over extremely hilly terrain, and awkward interfaces with whatever you hope to hook it into. Rather, I think you need to think in terms of what
other builds do to transform this route and ease its congestion. Building Urban Ring LRT with the Harvard spur takes a substantial bite out of the 66 via diversions into Kenmore transfer where hopping across platforms or upstairs onto the UR SW quadrant BRT ends up completing the crosstown trip in two seats faster than it ever took on one 66 seat. This includes more diversions at Harvard Ave. to the B due to the major speedup of inbound schedules from the subway being extended to BU Bridge for the UR interface. The UR studies all saw substantial ridership diversions off the 66 as a result of those new radial gains. Similarly, West Station and Urban Rail-Riverside on the Worcester Line draws a bigger demarcation point in audience turnover at the midpoint of the route. Post-UR and post-West the 66 is going to serve significantly different function, one more easily dealt with in chunks transfer-to-transfer instead of end-to-end Harvard-Dudley. That ends up solving a lot of its issues by recasting most trips on the route to short-hops. It'll always be a radial in need of some BRT-like enhancements, but with other builds in place it doesn't have to act like a miscast singular corridor with intrinsically sucky travel times. Prying off large chunks of ridership to other services ends up accomplishing more than trying to single-task it harder than ever.