Boston's bold new transportation plan could include a city-funded trolley network separate from the Green Line

The Boston MPO Program for Mass Transportation did a ballpark estimate of an Orange extension from Forest Hills to Route 128 in 1994, then adjusted it for inflation in the 2003 PMT. $316M for 5.1 miles and 5 stations that outright displaced the inner half of Needham commuter rail (Needham Jct. to Needham Heights then swallowed by a Green Line branch off Newton Highlands).

PMT estimates for many projects that were undertaken are wiiiiiiildly, hilariously lowballed across the board...lowballed below credulity even when you strip out the "MBTA mismanagement tax". GLX, for example, clocked in at $375M in the '03 PMT. That was never going to be sub-$1B even under the best estimates because of the physical characteristics of the build and the later bootstrap of the Somerville Community Path.

You can, however, do some very rough math on the undercount. Let's say the PMT estimates are 3x lower than real-world conditions if using "sensible" project management, such that an idealized GLX should have a floor of $1.2B and the vehicle facility + path extras fleshed-out since '03 and cushion push that to $1.5B. Today's current estimate is $2.3B after the contractor debacle and re-bid [cue "Yakkity Sax" music] as a hopefully final sunk cost premium for project mismanagement. Really really bad, but only a +35% eff-up from "sensible" instead of +50%.

OK...so let's say the '03 PMT's Orange extension x3 = $1B. This is how a Rozzie extension differs:

• Forest Hills to Rozzie is 1.5 mi. instead of 5.1 mi., 1 new station instead of 5. Probably only 1 new or upgraded electrical substation instead of multiple, 1 bridge rebuild instead of 4+. [~25% as costly as the '03 proposal???]
• Probably need both an Orange and Purple platform at Rozzie station. Definitely will need a busway and short-term bus layover parking because half or more of routes 14, 30, 35, 36, 37, 51 will start terminating here instead of duplicating each other to FH. [Bigger/costlier build than the '03 estimate because of CR platform, busier bus terminal than if bus-subway transfers were diffused out to Bellevue/Highland/W. Roxbury and Orange-duplicating bus routes consolidated.]
• Needham commuter rail is staying, so 3 tracks are needed. All bridges along the Arboretum already 3-track width, so need to bust commuter rail down to 1 track from FH and compensate by laying a new passing siding between Rozzie and Bellevue + adding or lengthening another siding further out. [Not needed at all in '03 estimate.]
• Oak Grove-style tail tracks are needed past Robert St., so the 2-track width rail embankment alongside S. Fairview St. & Fallon Field will have to be widened to 3 tracks with retaining walls for 300+ ft. past Robert St. [Not needed at all in '03 estimate.]
• Forest Hills yard (4 storage tracks, with the 2 middle tracks being the "mainline" to Rozzie) has to be lengthened +700 ft. so all of the displaced train storage on the middle "mainline" tracks can slot on the two flanking side tracks instead. Additional surgery as needed if they need to cram couple more trainsets for the extension, as FH storage is tight as-is. ['03 proposal would've done bigger yard on cheaper land in Needham. Somewhat lower-cost???]

$300-350M sounds reasonable. If framed as a down-payment on future commuter rail -displacing Orange service as far as W. Roxbury (if not 128), more reasonable still because Rozzie is the halfway point between FH and W. Rox. Potential cost blowout putting $500M in-play is the station itself. Mainly if they insist on equal or greater parking at Rozzie Orange/CR/bus superstation than today. Rozzie currently has 160 station spaces, not including the 100-space municipal lot behind Citizen's Bank. Bonkers overcapacity for a dense square crawling with buses and too much unnecessary car traffic, but we all know the starting point for City and T will be 1:1 space parity because "always done it this way blah blah...". So there you go: either new land acquisition, or a small/midsize parking garage so they can fit the station and beefier busway capacity on the same parcel. New station = excuse for palatial headhouse even when a utilitarian Malden/Oak Grove job will do. Garage structure = station headhouse must stand out even bigger! Now you're talking $500M or more.

Trade DOWN in parking and make it more bus-centric...lower station cost. Utilitarian headhouse instead of glass jewelry...lower station cost. Offsetting the commuter rail platform to the side by the bank & muni lot via short 100+ ft. walkway and compacting the width that needs to be housed in the station building to just Orange instead of a fatter parallel setup like Malden Ctr. where the longer CR platform would have to overhang Robert St....lower station cost. (Note: CR access still necessary enough @ Rozzie for interzone trips, but overall patronage will be sharply lower so outdoor + offset plenty good enough). Project management competence and how much insistence there is on arbitrary surplus-to-requirement station cruft ends up the probable cost difference between a fairly-rated $300M and a $500M+ wipeout.