We totally agree that rail through Newton to Needham is a good idea. My argument is simply that demand does not justify the costs to neighborhood aesthetics and cohesion that a surface HRT line would require. This is important, IMO, because the idea of Green Line to Needham isn't as much of a Crazy Transit Pitch as one might think - it's been proposed seriously in both towns and might well happen when Needham St. is developed (will happen soon) and when the T can gets its financial house in order (probably never). My guess is that the CR line will be truncated to Needham Junction at this point, which will provide faster Downtown access to those in Needham who want it, without any need for an Orange Line conversion.
Aren't neighborhood aesthetics and cohesion sacrificed already? The major differences between heavy and light rail would be station presence and trainsets, not too noticeable considering the area is already bisected by a rail right of way.
By the way, the Riverbank Subway is a great idea, and I hope it happens someday. It should be extended under one of the streetcar reservations, though. Those branches have the proper density all the way to termini at the historic limits of Boston's inner transit network.
The B and C may traverse denser corridors, but the B would be incredibly expensive to bury or elevate considering the hills along Comm Ave, and the C is just too short for heavy rail to really make much of a difference. Not to mention, the D is already the second-busiest branch of the Green Line. Like I said, a ~3.5 mile extension to Needham won't be the dealbreaker for whether or not the D is converted to heavy rail. That will be determined by the current D mainline route to Riverside. Riverside, Woodland, Newton Center and Newton Highlands already see decent traffic numbers that would only increase with a reduced trip time into the city.
I suppose, like Riverside suggested, Needham-Newton Highlands could always exist as a shuttle light rail route.
The platform is long enough (they unload deuces back-to-back sometimes), but people would have to get off at the tips of the station behind the faregates and by the inspector's booth. On the rear inbound side there's open access behind the stairs to the abandoned tunnel as an emergency exit. In a blind spot for any station staff, so that's almost daring people to go exploring.
The solution...security cam the place end-to-end...put an alarmed emergency exit door on the behind-stairs passageway. Not hard. If quads are under serious consideration that's probably exactly what they'll do. You wouldn't be talking more than 5-10 grand in cost.
Technically they could even make the outbound side (not sure about inbound) ADA-accessible by sticking an elevator behind the stairs, relocating that electrical box, and fencing off the walkway behind the faregates from the tracks. But...you know...effort.
Would 4-car trains be necessary if they converted the B and D to all 3-car operations and did rush hour 3-car train support on the E to Brigham? I guess logically the B and D may need some 4-car trains as rush hour/special event support.