That's the problem, though. It isn't superior. Not for what current transit riders in Needham use it for. For the benefits of GL to be obvious, you have to offer frequent connectivity within Needham and build TOD along Needham St. in Newton. Not things you can do with a simple starter line.
This has been studied. Most recently in 2009 by the towns:
http://www.newtonma.gov/civicax/filebank/documents/40881. They went with the starter proposal to get to Heights only, since that sidestepped project dependencies and what-if's with the Orange Line and CR mode for a cleaner study area and less-controversial first step.
This is what they came up with:
-- 15,000 daily riders on the LRT mode at Upper Falls, Highlands/128, and Heights and 6,000 new daily transit riders not taking any current mode.
-- The state PMT methodology severely underestimates the traffic utilization on this corridor and pushes the actual ridership way way up over the last official study. It's a good read...whether it's he-said/she-said or not, the state really has to revisit its metrics because this town-commissioned indie study poked a ton of holes in it.
-- Because the undercounts were so dramatic, Newton Highlands-Needham Heights
alone justifies the build even if no changes are contemplated for the CR mode. It's the areas that have no rail transit whatsoever that float this extension.
-- Heights, with offset GL and CR platforms, would have LRT boardings comparable to the other stops on the extension. The CR boardings might get a slight boost by the transfer, but not much. NORTH is the prevailing demand direction.
-- Center, if CR were shortened 1 stop and the modes met there, would perform almost identical to Heights due to proximity. 2 stops better than one, but basically the profile doesn't change so long as immediate downtown is served by LRT within 1/4 mile of the density center. For that reason they didn't see a need to truncate CR unless external factors (Millis or OL displacement) forced that hand.
-- Growth south of downtown is relatively static because of the low-density residential land use. There's no TOD to tart Junction (and by virtue Hersey/Great Plain) up. They're always going to be quiet areas.
-- Because of the above, displacement of CR is only recommended if something external forces CR to be severed. Millis CR capacity or Orange Line cannibalization in Boston being the only 2 candidates. LRT performs better as a modal displacement because the frequencies obviously beat the pants off CR's best, but it does not grow the less dense south-of-downtown. That area is of entirely different character and land use.
-- A 1-stop CR extension to Highlands/128 was studied previously by the state. The results found almost no new ridership despite the significantly higher parking capacity and surrounding density. It significantly cannibalized boardings from Heights, Center, and Junction and just spread the existing riders out more diffusely. The CR/eastbound/BBY-SS market doesn't expand geographically into other parts of town, and appears to tilt heavier to the lighter-density, non-growing area south of downtown. The higher-density area downtown, up the Highland Ave. corridor, and into Newton that go hog-wild if this GL extension is built appear by and large to not be taking existing transit modes at all.
-- Related to the above...the T's official Millis CR study showed stops in Dover and Medfield cannibalizing ridership at Junction, Hersey, and Center with the bulk of that branch's all-new ridership coming from the Millis area only. Suggesting lower limits still to the natural E-W ridership south of downtown Needham and more dramatic in-town--and very very off-grid--skew for N-S transit demand. Frankly, who cares if Doverites have to drive further...those NIMBY earth-salters fought to get rid of the CR they had while it was still running.
-- Also related to the above...the NYNH&H kept commuter rail service to Highland Ave. and Upper Falls for a couple years after the trolleys came to Riverside. They cut it back to Heights due to low ridership up there. That may have been the correct decision given all the corroborating evidence above. Those areas lost the places they needed to go when the old Newton 'circuit' service got cut by the D.
The big conclusions that can be drawn here are: 1) holy hell is that N-S corridor from downtown to Newton waiting to explode, and 2) CR ridership east and the "convenience" of a Back Bay/SS one-seat has more or less tapped its whole audience. That audience can increase evolutionarily were increased frequencies possible, but it's not going to attract new ridership demographics or travel patterns that weren't already using the commuter rail.
This tidies it up real nice if you don't want to displace CR, or if they can't do it all at once. The Green Line on the north flank more than justifies itself while CR keeps the established pattern static in the static areas of town. But West Roxbury rapid transit is on a whole other level demand-wise, and there is no way to implement that without displacing CR. The Needham study numbers say displacement from Heights--where CR and GL meet--to Junction would faithfully serve the need and incrementally grow the ridership at Center and/or Heights. Good...nobody gets hurt by outright transit loss (not even the Dover freeloaders), and the absorbed ridership at Center and Junction is still league-average for the entire GL. But what about connecting Orange to 128 or Junction?
Where's the extra gear on that ridership when the growth in that part of town is forever static and the local travel patterns don't conform to an E-W direction? Look at Highlands/128...the previous 128 CR extension study pointed to ridership redistribution--not generation--for the BBY-SS oriented trip. The GL studies point to astronomical ridership generation for a Needham-Newton oriented trip at the same place, with the same TOD, and the same parking capacity. That is a hell of a stark difference that frequency alone can't explain.
So when data needs to overpower the lack of connectivity, development, and directional demand that makes that 128 OL stop look iffy and Orange vs. Green boardings at Junction (a non-growth area) looking anemic...these are the kinds of contradictions that need to be overpowered. The official number-crunching ain't showing it. They're arguably not showing much evidence for "Fairmounting" (were those CR frequencies actually possible) the current mode producing much more past West Roxbury than it already is. The un-served demand is all downtown Needham and north, and West Roxbury and Rozzie where they can't throw enough buses out of FH to keep the neighborhood flowing. It does not appear that many for people at Junction or Hersey are going to be inconvenienced if E-W commuter rail gets displaced for the betterment of West Roxbury and Rozzie and they have to 'settle' for light rail.
If there's something missing there that no one's considered, by all means study the shit out of it and find what it is. But the current evidence is lacking, and there are some huge discrepancies in the demand data that have to be squared.