Why not forget about Needham Green Line and Needham Commuter Rail and extend the Orange Line past Forest Hills --> Roslindale Village --> Bellevue --> Highland --> West Roxbury --> "Needham something".
"Needham something" as the terminus of the Orange Line should be enough. Why would they need the Green Line, too? This isn't Somerville - Needham has 2/3 the population of Everett in nearly 4 times the land area.
Transit loss. Needham cannot subsist on the 59 bus/D-line transfer alone...it's a lousy route through godawful Highland Ave. congestion. When the Needham Line was closed for 8 years during the 80's and the T started dropping hints it wasn't so sure it wanted to reopen it, they threatened suit. The T backed off, threw some track gangs at the line, and got it back in service within a year. It's a suit Needham will win if the T tries to shaft them again. They have a dense downtown, and it's their only direct connection to Boston downtown. It's not like "equal or better" could be framed in terms of bus replacement because there's no parallel road route into downtown Boston that would approximate it.
If the line were to be converted to Orange, Green would either have to go first or get a binding (i.e. can't be Arborwayed) commitment to a build. The good news is, it's not so expensive they couldn't swallow both. We're talking a lot less for BOTH than GLX is costing. But what does a "binding" commitment even mean anymore in this state when they've broken most of their binding Transit Commitments.
"Needham-something" on Orange I don't think is worth going for, BTW. It's a long, barren ride across Cutler Park from West Roxbury to 128, there's little room because of all the conservation land to put a station + requisite interstate park-and-ride parking garage on Greendale Ave., little room for TOD for the same reasons, there are NIMBY's around the golf course, there's zero bus connections anywhere, and the accessibility isn't awesome from the Great Plain Ave. exit. The MPO-studied ridership projections on the extension tilt >90% to the Forest Hills-W. Rox stops. There might be a brief rush-hour spike to the 128 park-and-ride, but most hours of the day those OL trains are going to be quite empty. I don't think for the small slice of ridership and very limited hours that ridership would use the line that it justifies going west of W. Rox. That stretch is almost 40% of the entire mileage of the extension, for just 1 stop.
A would-be Green stop (or, hell, 1-stop extension of the commuter rail) at TV Place/128 off the Highland Ave. exit would outslug the ridership of an Orange Needham stop by wide margin. Especially off-peak, when the residential area by the park gets really sleepy and the Highland corridor is still active. Gobs and gobs of TOD potential at that site since it's a major redevelopment initiative for the town (which is why I think the dirt cheap interim CR extension to 128 would have legs).
Needham Jct. is about equally accessible from the Route 135 exit as Hersey is from the Great Plain exit, so they divide the current ridership a lot. Green at Needham Jct. with parking in the middle of the current wye covers Hersey's limited needs just spiffy. Especially if they rail-trail it between Junction and W. Rox through the parks for the locals.
