Hmm that's an interesting thought and seems much more feasible. What about fully integrating it into the south street grid with stop lights and throwing away the express-way qualities entirely? Trim off a lane from each side. Consolidate Back St into it. Slow it waaaay down to a more pedestrian friendly road with crossings. Screw tunnels and weaving lanes.
I realize this is probably screwing over the traffic flow and adding travel time to get across the city...
This is my pipe dream walkable city with a fully integrated waterfront.
The Pike has the Copley exit in both directions and is *slightly* under-capacity between Allston and 93. You need to keep SFR to/from Charlesgate as basically a glorified exit ramp to Kenmore/Fenway because of lack of acceptable Pike ramp options anywhere around BU, but past there Storrow traffic is hugely inflated by induced demand trying to beat the tolls to Copley. There's no load-bearing reason for it to exist. The paralleling surface streets like Beacon and Comm Ave. are not congested at all between Mass Ave. and the Public Gardens, and at least WB on the Pike you have the options (paper-studied to death but state seemingly never in a hurry to enact) to add another 1-2 sets of staggered on/offramps through the Back Bay to further smooth things over. The only compensation you truly must offer is to waive tolls on the Pike *between* Allston and 93 to shape traffic in that direction without getting auto-dinged @ Allston for the minimum-most touch on the tollway.
Unique catchment doesn't restart again until the Public Gardens onramp by Hatch Shell, which is the MA 28 mainline feeding to O'Brien Hwy. and the legit fastest route to/from 93 from Beacon Hill. That stays, but if the midsection thru traffic is gone you might be able to judiciously lane-drop Embankment from 6 to 4 in some non-ramp parts by MGH from the traffic reductions, helping a little more down there.
The home-run value proposition for deleting the midsection--which we've talked about often on aB--is a transit trade-in of Blue Line extension from Charles MGH to Kenmore. BLX-Kenmore is
not in a vacuum anyone's idea of a Top 5 Most Wanted rapid transit build, but the Storrow trade-in presents a unique opportunity for substitution of the roadpack with a mode capable of carrying equal number of commuters within the same project area as the to-be-deleted parkway. Thus, if we have thrashed through the debate and decided that Storrow must go it's a transit build that can "debut at #1" so-to-speak for the funding streams it would attract from being a 1:1 trade-in for the same exact project area. Very situation-specific.
Also not a new idea. Long before Storrow ever ruined the riverbank there was a seriously studied Boston Transit Commission proposal for a Riverbank Subway on that very alignment, where shallow tunneling would've kept the parkland. The idea got shelved by about 1910 because they didn't have a great idea of what trunkline to hook it up to, but transit trade-in of Storrow basically follows what was studied as a high-demand route way back when via Blue Line attachment. With primary upside of load relief for Kenmore and an overstuffed Green Line after all those new Fenway/Pike skyscrapers have saturated the area to the limit...and load transfer of downtown loads to 6-car HRT trains so GL @ Kenmore can absorb way more in the way of branch and radial expansion instead like full-on Urban Ring hookup.
This "Riverbank Subway Redux" would be built in a shallow box tunnel trenching down on the vacated Storrow EB roadpack attached to the Back St. retaining wall. Unlike traditional cut-and-cover which goes about 50 ft. under street with a 'sandwich' layer of utilities, this tunnel would be semi-surface like the Red Line Fields Corner-Ashmont capped cut or the Wellington tunnel on the Orange Line. i.e. No utilities needing to be relocated because it's on the waterfront sitting on the vacant Storrow roadpack with nothing underneath...therefore much cheaper tunneling. In essence, it's a capped box that digs maybe a variable 8-10 ft. below the current Storrow pavement level with a roof that sticks 2-4 ft. above ground. A rebuilt Back St. retaining wall will frame the inbound-side tunnel wall, and it'll be topped off with a dirt hill and plantings almost like a "BU Beach South". Intermediate stops at "Esplanade" (roughly where the current EB road tunnel is), "Beacon" (in the deep cut under Mass Ave.), and Kenmore with cut-and-cover from Beacon St. to Brookline Ave. underpinning the southernmost tip of the GL level at narrow, least-invasive angle. Storage tail tracks then fizz out at start of Brookline Ave., and 100-year future considerations for further extension are provisioned by going further up Brookline Ave. either to Longwood/Brookline Village or bang-a-right under the B&A tracks at the Mass Pike en route to West Station. Nothing past-Kenmore would ever be a part of this build because funding would be constrained to the 1:1 parkway trade-in in the same project area, and we don't today have any consensus ideas on what further to serve. So just FYI that as "future considerations" only, another project for another time.
The very compelling upshot (in addition to the ridership trade-in aspect) is that the very construction of the tunnel framing a new Back St. wall and earthen berm will create enhanced passive flood protection for the whole Back Bay street grid at cut-rate cost, and the extreme-shallow semi-surface nature of the transit tunnel makes it so that the Blue Line stays dry with nothing but full-passive wall and drainage. It actually provides a very attractive/compelling shotgun solution of transit AND an enhanced flood protection solution in one intrinsically cheap-construction build, while giving you enhanced parkland. That's very different from the kind of active flood protection we'll have to be building on things like the Green Line-Transitway connector and NSRL, so cut-rate $$$ FTW.
As for the parkland, the 3-lane Storrow WB carriageway would be more-or-less remanicured into a traffic-calmed 2-lane park access road spanning Charlesgate and Beacon Hill, probably with parking shoulders for Esplanade events. The "more-or-less" part means actual roadway dimensions for the park lane may straddle onto some remnants of the EB left-lane pack in variable spots and serve up some strips of reclaimed waterfront acreage (esp. by the Lagoon), but will more or less be centered on the current WB carriageway. The "BU Beach South" berm over the transit-converted then topped-off EB carriageway adds at least 40 ft. of rec/greenspace on the Back St. side, and you can connect all the N-S alphabet streets on the Back Bay grid directly to it over the roof of the tunnel by doing raised crossings at the intersections. Raised crossings every block (approx. 625 ft.) from Berkeley to Hereford ensures that the park lane provides 'a' retained level of motor-vehicle accessibility to the Hatch Shell while having a de facto enforced 20 MPH speed limit that's physically impossible to abuse as an induced demand shortcut for Beacon/Comm Ave. And, the frequency of the raised crossings w/ grid connections encourages rigorous usage of the "Beach" land along Back St. as an attraction you cross to-and-fro from the riverfront to make recreational use of rather than being one of the proverbial 'bad' examples of static greenspace that's there to look at but not use.
Mind you, a lot has to fall into place to make this work. Starting with the slugfest debate on whether we even want to delete the midsection as a thru parkway, because the highly situational transit trade-in doesn't rate at all without that prereq mechanism. But you can see how all the various interests here...traffic sustainability, transit sustainability, parkland sustainability, flood protection sustainability...dovetail together in a really fucking attractive (and NOT overly expensive!) package if the dominoes fall in the right order.
