Speaking of better-than-BRT, check this out. . .
http://www.ameritram.com/
Kinki-Sharyo, maker of our Type 7 trolleys, is demoing a new type of 100% low-floor dual-mode streetcar in Dallas that can run off-wire on stretches using rechargeable batteries that recharge from braking friction just like your Prius. They make 'em in modular length configurations, streetcar or LRV dimensions, and regular electric or battery dual-mode. Don't know if they'd fit the Green Line without modification, but the specs are closer to the T's than most other much wider-body modern LRV's because they're derived from the base Type 7 design. So hopefully it's in the ballpark for being modified to the system and wouldn't have to deviate too far off the cheaper off-shelf specs. Kinki's probably pitching a variant of this for the Type 9 bidding.
Wouldn't it be nice if we replaced the SL1 to Airport with dual-mode LRV's that ran on-wire in the Transitway and around the Logan terminals but off-wire through the Ted? That would solve the whole problem of ever making that part of the Silver Line rail, since pavement rail is OK through the tunnel for Fed regulations but overhead isn't because of exploding gas potential in an auto tunnel. I would love to see this to cure the ridiculous bus speed restrictions in the Transitway. And they could connect it to the rest of the Green Line when they have to temporarily tear up the ground under the NEC tracks from South Station to build the North-South Rail Link portal tunnel to the NEC. Cut-and-cover the trolley tunnel from the end of the Transitway, piggyback it on top of and next to the N-S portal tunnel, cross under the Pike on the Washington St./Shawmut Ave. block, and connect to the unused end of the Tremont St. tunnel. Options for future Southie surface branches that'll do a whole lot better than failed SL2/SL3 and never-implemented SL4. Ability to do a full-circuit light rail Urban Ring through Logan joining the northside leg via Lechmere and alongside the commuter rail tracks.
Hell, if they wanted to convert SL Washington St. to Green Line quickly and cheaper they can do a Phase I with just tracks on Washington, run on batteries from the end of the wires at the tunnel portal to Dudley, and have wires at Dudley to recharge on layovers. Get a second funding appropriation later to infill the wires.
Ditto Arborway restoration. Just throw down tracks and go off-wire from Heath to Forest Hills, wire up Forest Hills from the layover yard, and pay for the wire infill when service is running again for a few years and critics in JP have stopped their "Oh teh trolleys are gonna get stuck behind my God-given right to double-park with impunity!!!" bitching.