Could there be potential savings with an elevated Greenline structure after Dane St up to Porter? Would an elevated structure with sound barriers cost as much as new retaining walls to accommodate four tracks at grade ? The end of the line could potentially be at Somerville Ave grade which would provide a roof over the commuter stop. Would it be a mistake to not rip up and restore the existing rail bed with updated systems because it hasn't been addressed for the last hundred years or so? The retaining wall work and underground drainage (and bridge extensions) of the current extension seems to be a significant amount of cost and time.
Large and unlikely assumption that the residential around here would tolerate an El structure, for one. But also more inefficient on cost. If you're folding the Park crossing elimination into the same structure, that's way too much El structure for the cost accrual to work in your favor. 0.9-1 miles of steel-and-concrete if you're starting past Dane, with a really weird sky-high section where it has to pass over the Beacon St. overpass, up to 2 intermediate stations with pronounced elevator/escalator access in the sky, and a Porter level that may have to awkwardly be up on stilts because of how high the Beacon St. overpass-of-the-overpass is. All while still needing to do the most expensive at-grade punchlist items abutting Union of getting from the station turnout back onto the running ROW, and tapping none of the benefits of the existing quad-track ROW in between. Compared to .2 miles max in tunneling @ Porter and all at-grade everywhere between Webster and Beacon.
There seems to be a few assumptions at work here: (1) tunneling is always equally extremely expensive choice between cut-and-cover vs. deep bore, so Red-Blue's recently disclosed $850M figure is being misconstrued as a likely "floor" cost to run with; (2) the ROW doesn't have room or needs major earthworks retrofitting + total vertical station access because that's how it went with the main GLX; (3) Park St. crossing elimination is going to be some ungainly blowout. I'll address each.
- Cut-and-cover tunneling the likes of which Red-Blue is attempting is always pretty expensive. That's entirely because of the under-street utility 'sandwich' layer and needing to relocate all utilities in it. This is considerable cost on a big-building fronted thoroughfare like Cambridge St. Red-Blue also arrives at its $850M by doing a fairly large HRT-length platform addendum, adding additional egresses to Charles station, and doing a substantial amount of under-street demolition work at Bowdoin Loop to straighten the alignment. When I say there are "no utilities" under the Fitchburg trackbed...there are no utilities, just dirt. No drains, no water, no telecom, no electrical trunks, no nothing. Those all trawl under Somerville Ave.--which we explicitly do not touch--instead, because Somerville Ave. has the "manhole-level" sandwich layer appropriate for installing utilities, while the RR ROW doesn't. The tunnel you dig here is not a cut-and-cover "subway" in the traditional sense; it's a box-tunnel facsimile of the Orange Line Wellington duckunder of Medford Jct., or the collection of Columbia Jct. Red Line duckunders near JFK. A glorified train-sized culvert you dig for the sole purpose of being able to grade separate tracks that run on the roof from tracks that run underneath. In tunneling feet the Porter cost accrual would track like the similar-length 1975 Wellington box tunnel indexed to inflation...plus the Porter platform bulb-out (which, again, only includes the single egress attachment to the CR door of the wholly pre-existing lobby)...and minus the second incline because it's a stub-end. That's an extreme lot less expensive than what Red-Blue is doing. I have a hard time seeing the glorified culvert with outfitted station bulb and CR-level reconstruction exceeding $200M in a "shitty T accounting" universe. It could potentially be in the middle-low $100M+ range under a project team that well-policed its cost controls.
- The ROW has complete quad-track room. If you outright got rid of the CR platform at Porter, it would also have complete at-grade room thru Porter itself. But since this build rakes the hardest on toplines being a Red+Green+Purple+bus integrated transfer, the cost of preserving the CR berth ends up generating a lot of the high-ridership ROI and ends up fully worth doing. You also have side room for the intermediates. If the Conway Park intermediate directly faces the back of Conway Park, there's adequate fan-out room for platforms, at-grade egress straight into the park, and ramp egress to the new Park St. overpass for catching the 83. If the Wilson Sq. intermediate takes the car wash on eminent domain, you have all the room in the world to shave the retaining wall at that property to bulb out for platforms, plunk a Somerville Ave.-facing headhouse, and snake a platform ramp down to the Sacramento St. underpass for accessing the Beacon side of the neighborhood. There's no massive earthworks required to pre-prep the embankment, fit everything in a deep cut, and find room for the Community Path like there is with current GLX. It's largely real-deal pre-existing quad ROW and very close to at-grade everywhere between the Union and Porter cuts, with no Community Path complications.
- Park St. is not a huge crossing elimination production. The only reason it was not eliminated like Dane was mid-20th century is because the ex-warehouse on Tyler St. that it abuts had an active freight siding (track remnants still there) until the early-90's where the switching activity needed back-of-building worker access via the crossing. Were it not for that customer, B&M planned to zap it along with all other Somerville residuals in the mid-50's. Its would-be elimination would be a mirror-image to Dane's 'hump' overpass, inclines, and driveway treatments around the inclines. Could likely be blitz-constructed with an outright road shutdown to save costs because there are adequate paralleling streets for temp-absorbing the volumes for 6 months to a year.
Crazy idea, what if you gave Somerville Ave some approximation of this treatment:
MAX Light Rail, Portland, OR.
Green Line meets surface Somerville Ave somewhere in the vicinity of Beacon Street. From Beacon to White Street, Somerville Ave could be a low-speed, one-way, single-lane, westbound, local-access road on the northern side of the right-of-way.
The southern side of the right-of-way could carry the 83 and Green Line in a mixed bus / light rail reservation. The bus/GL station could be right next to Porter across from White Street, where the street ROW gets wider.
No, never. Somerville Ave. is one of the biggest load-bearing crosstown thoroughfares in all of Somerville. No possible way you can squirrel the native loads off of it. Part of the reason you ever
would consider leveraging the Porter tunnel for air rights featuring is that Roseland St. is already this narrow alleyway being overtasked with masquerading as a thoroughfare for the Lesley/Porter Exchange parking lot and traffic loading profile of Somerville Ave. on the Beacon-Mass Ave. block. And that situation is fucked enough as-is. I don't know where you expect those thoroughfare loads to migrate to for this transit plaza but for creating another 2-3 additional totally inappropriate Roselands around the neighborhood in the process and set the whole neighborhood back a large degree on general livability.
Again...this seems to rely on an assumption that we're doing cut-and-cover tunneling at typical cut-and-cover costs. It's not a cut-and-cover; it's a box culvert. And assumes that it accrues station costs equivalent to building
whole new stations like GLX and/or adding-on
whole new egresses like Red-Blue is doing at Charles. It's not that, either. This is a de facto "adding a room" to full-existing Porter off the same mezzanine, off the same Commuter Rail doorway, with no further adds. Coming down the main-entrance escalators in a GLX universe, you'd simply see the Charlie gates rearranged to put the CR door behind prepayment. Then there'd be a short ramp down at the existing door for the GLX level, a short ramp up for the replacement CR level. That's the sum-total change in station access unless you want to go all optionally hyper-completist with new adds around the neighborhood.
