Important side note for this project. . .
With all the attention on Green Line Transformation (GLT) and the higher-capacity trolleys they'll be ordering, consider how much elimination of Bowdoin Loop in favor of the extension impacts a future "BLT" and the type of cars orderable for Blue service expansion. Right now the line has to use tiny 48.5 ft. long / 35-seat / 2-door cars, some of the smallest in the world for an HRT line. Orange Line by contrast uses 65 ft. / 58-seat cars and will be gaining a third set of doors on this new order.
Whacking the ruling limit on car length by demolishing the loop will open them up to being able to lengthen trains on the next car order long enough to add that all-important set of third doors for dwell management. That'll be huge for throughput as the line gets more crowded. An old messageboard mention of a previous internal study of outright retiring the loop in favor of stub-end turnbacks said that Bowdoin alone was worth +6 ft. of additional train length...more than enough to net the extra door set. Going the rest of the distance to full Orange Line car length & capacity is TBD and dependent on an engineering study of the next dimensional limiter: State St. curve. State curve is not so much tight--cars would clear the tunnel just fine--, but it abuts the platform meaning longer cars would clip the platform tip closest to the curve.
A "BLT" survey just like the one GLT is doing for Green Line station mods can probably mitigate the State issue to push the achievable car lengths to ~60 ft. and within the ballpark of full Orange Line length. Then it's a matter of itemizing the platform extensions for fitting all 6 cars of that increased length...which shouldn't be a problem because nearly all subway stations on Blue still have some extra slack space behind false walls after their last lengthenings a dozen years ago.
The ongoing Blue climate resiliency study is looking right now at 2 other major changes:
- Converting Airport-Wonderland over to third-rail and retiring the overhead. Blown-down wires are seen as a bigger storm headache than submerged third rail, as turned-off third rail is resilient to rust so long as its feeder cables are kept water-tight.
- Converting the signal system to retire the hardware-intensive mechanical trips and switch heaters in favor of solid-state tech. Could mean Red/Orange-like ATO, could mean Boston's first CBTC installation. But it would be a massive simplification of water-vulnerable hardware and elimination of at-risk copper for water-resistant fiber optic.
These changes would level the only major technical differences between Blue and Red/Orange cars: the pantographs (which would just get taken off the current fleet), and the signaling (now computer hardware instead of mechanical). If the train length "BLT" changes can net a car length equal--or at worst near-equal--then the only remaining difference between Blue and Orange stock would be the +/- 3.5 in. difference in floor height, which does not require any design changes as it can be hard-set on the car's suspension at the factory.
It would then be possible...by the time we're ready to load up for bear for the Lynn extension...to just tap CRRC to produce a large supplemental order of Orange Line cars and 'set' one portion of the order for Blue renewal/expansion and one portion of the order for another round of Orange service densification or expansion. While the makes would still not be able to interline because of the 'hard'-set height-suspension differences and possible differing signal computers, the cars could theoretically change lines during their service lives if they went offline for a height adjustment and computer swap-out. And it would consolidate the two HRT lines under one unified make right during the era when both of them need badly to expand outward...Blue to Lynn and Orange to West Roxbury.
At bare minimum, when the 94-car Siemens fleet is no longer enough to keep up with growth from the West End and Suffolk Downs they'll have immediate vehicle-side options for directly addressing train capacity at-will by taking a gander at achievable train lengths, seating, and door flow. All of that gets technically enabled by Red-Blue being built. It's way more than just a missing link...it's a new and exponential capacity expander to tap for the future as demand projects to soar.