[hammersklavier]

VZ's plan is actually really fucking good as far as transit nerdery goes. It solves a number of issues:

- maximal service for minimal cost
- only requires two to four thousand feet of new tunnel
- deletes a flat junction on the NEC
- new stops greatly improve transit access in the eastern Allegheny neighborhood
- dramatically improves transit service to underserved NW Philly

On the other hand, expenses will involve

- major reconfiguration of the 8th Street tunnel between Market and Race (beyond just a new configuration of the 8th Street station complex proper, which with fare unification between SEPTA and PATCO allows for a connection between the "Red Line" and El platform via the PATCO platform -- the second track would also have to be elevated above the PATCO track which in its turn would require*
- reconstruction of the NB platform at Chinatown station to the new track level
- refitting and reopening Spring Garden station
- construction of a new flying junction in North Philadelphia station environs (obviously utilizing the existing North Philadelphia station is cheaper but putting the junction box north of the station box might be a trickier technical challenge than is currently envisioned, since you need to add a grade and there are also support columns associated with the NEC in the tunnel)**
- construction of a 3rd rail distribution system along CHW parallel to the existing catenary, which cannot be dismantled until 3rd rail is active. This includes not just the rail itself but also a power line that links into the existing BSL distribution network and new substations roughly every mile along CHW, amounting to substations in the vicinity of the Budd plant, at Pulaski & Rittenhouse (next to the catenary substation), somewhere around Carpenter station, somewhere around St. Martins station, and next to the substation at CHW proper
- raising the platforms (which might require station relocation due to curvature) at Highland, St. Martins, Carpenter, Upsal, Tulpehocken, and Queen Lane
- procuring additional equipment to provide 15-minute service along this line (though that could be bundled in with a replacement order for the existing -- aging -- BSL fleet)

We're still looking at a complex project with a total cost around $1-$2 bn here.

On the bright side, however, there shouldn't be significant noise issues. Gravel trackbed is a great noise dampener, and none of the CHW curves are sharp enough to induce squealing.
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* The optimal solution might be a double-level tunnel, which is currently not in place. Such a tunnel would also have the advantage of double-tracking PATCO through this curve: unbelievably, there is a single-track PATCO segment between 8th Street and Franklin Square.

** The junction box between the BSL mainline and the Ridge Spur is 1000 feet long (for a 1.5% grade). The North Philadelphia station box ends at Somerset, which means this is where the junction box would have to begin. 1000 feet north of Somerset would be a very sharp curve onto Indiana.

OTOH if we specified a sharper grade, say 3%, we can shorten the junction box to 500 feet: this gets you to Cambria, which nets easier curvature but also requires the rather impressive feat of structural engineering of transmitting the load of the NEC crossing around the new line, which to accomplish would require either (a) greater clearance and hence a longer junction box or (b) a sharper grade. And this assumes the station box ends at Somerset! If it ends further north then you're fucked no matter what you do. Unless, that is, you build the junction box south of Lehigh, which allows you to clear under the existing station box at your own pace, but then that would require constructing an entirely new station box running from the BSL box all the way to the NEC North Philadelphia station. And this would require takings on the 1400 blocks of Somerset and Rush to accommodate! There are also further grade issues linking the new tunnel to the existing CHW infrastructure...

A further thought: Instead one can create a) a junction box south of Lehigh, b) side platforms under the BSL North Philadelphia platforms, and c) a 1300-ft tunnel from the north end of the station box to the CHW bridge over Indiana Ave (again requiring minor takings along the 1400 blocks of Somerset and Rush). This requires a 4.6% grade, however; decreasing the grade will also require increasing the superelevation; by taking the little block of Hicks and Sydenham south of Indiana as well we can extend this to 1600 ft for a 3.75% grade, which looks to be the best we'll get unless we want to extend the tunnel another thousand feet under the CHW ROW.

And another: To make that happen the Red Line tunnel would have to veer west of the BSL tunnel in the latter's north approach into the North Philadelphia station. Since the BSL tunnel occupies the middle 50 feet of Broad Street's ROW this means the Red Line tunnel would have ~25 ft of clearance between the BSL and the building line. And since every foot is precious, it might also be advantageous to align the Red Line North Philadelphia platform as a center platform below the SB BSL platform. In any event, it is clear that the grade must terminate where the Red Line passes under the existing BSL infrastructure.