...Zoo does have a very real time cost, and the only way to ameliorate it is to, well, bypass it. And the only way to bypass Zoo is to build a new Schuylkill crossing.So, now that we have established how to provide high-speed Airport service and augment the 30th Street approaches; so, now that we have established that the existing alignment is operationally superior and that neither speed nor capacity is an issue south of 30th Street, we must take a look at what is the real crux of Philadelphia's rail transportation problems: Zoo.
Before we begin this discussion, keep in mind that (a) Zoo has unused capacity and (b) of all the speed restrictions to address between New York and Philadelphia, Zoo has, or should have, the lowest priority. What this means is that we can compromise on Zoo and still get good or very good service before needing to actually address it as a problem. There is no way to solve Zoo as a speed problem without concrete, and organization and electronics need to be optimized before concrete goes in. What this means is that rebuilding Zoo is a project with a long-term outlook: 2045 or later. It is also the final element of my program of improvements for HSR in Philadelphia (see here).
The least expensive feasible HSR bypass of Zoo is this one: all bypasses will necessarily involve a new Schuylkill crossing, as the existing interlocking is optimized to provide the fastest north-south path from 30th St. onto the bridge. And due to all paths across the river needing to pass through the park, we can assume that all new sections of the alignment will be wholly underground (else we risk regulatory wrath).
The other--straighter--option would be a tunnel under Lemon Hill and Boathouse Row. Such a tunnel would, however, cancel out many of the savings achieved by abandoning Market East for a time gain of mere seconds, and would necessarily involve disturbing Boathouse Row, which lies on top of where the bored tunnel would meet the immersed-tube one. So we will not pursue this option, and instead pursue the option with the least amount of tunneling. Hence the one I provided.
This tunnel has (hopefully) a geometry offering 150 mph service, significantly faster than the 60 mph service we can optimize Zoo proper for; however, if the curvature requires a 120 mph speed limit, that would be acceptable, as the time difference would be infinitesimal. It also maximizes utilization of existing easements, beginning its approach alongside, and then under, the Schuylkill Expressway, and then curving back under the NEC ROW via an immersed tube crossing the Schuylkill under Girard Ave. It would then have to clear under Fairmount Jct.'s approach before returning to the NEC main in the Strawberry Mansion area. Designed for Velaro-, Zefiro-, AGV-, and N700-type equipment (i.e. HSR EMU trainsets) to the exclusion of all else*, this tunnel would allow for significantly steeper max gradients than elsewhere on the NEC as it is strictly a speed bypass of a complex interlocking.
Its expense--though a fraction of the total Market East tunnel's--combined with the relatively marginal improvements it offers is what cements its low priority; as I have mentioned before, upgrading the intercity network to 25kV 60Hz (with the possible exception of bypassable individual terminal systems, if clearance is an issue in urban cores) will single-handedly generate the most time savings, and be the primary mover chopping PHL-NYP time to an hour. The most expensive PHL-NYP improvement needed is, of course, Gateway, which would double the available Hudson tubes and address the choke points on the New York approach. All other projects on the line, such as what Alon Levy suggested, see time improvements of only a few seconds, which, while important, do not get the bang for the buck that addressing the archaic overhead system and the Hudson capacity issue do.
That said, this is my cost breakdown of my program of improvements, in terms of priority:
1. Zoo Interlocking Improvements
has the highest priority, as it costs the least and offers the most significant immediate speed improvement. Let's peg it at $100 million, tied up mainly in incremental track upgrades and path-sorting improvements.
It's followed by the
2. Chester Branch HSR Line, including
2a. Hospital Interlocking,
2b. Grays Ferry Interlocking,
2c. Double-Decked Chester Branch Grays Ferry-Bartram's Gardens,
2d. PHL AirTrain**,
2e. Darby Creek Viaduct (Essington Aerial), and
2f. Eddy Interlocking, along with
2g. Local Stations (a) Bartram's Gardens, (b) 63rd St., (c) 70th St., (d) Eastwick, (e) Airport, (f) Tinicum, (g) Essington, and (h) Industrial Hwy., combined with freight improvements
3. 52nd St. Branch Reactivation, including
3a. Brill Interlocking, and
3b. Baldwin Interlocking,
that is, the integrated and interrelated complex associated with bringing HSR to the Airport via the Chester Branch. This would be the most expensive element of the whole package, as the relatively simple and low-cost interlockings are dependent on the higher-cost line optimizations and reactivations. Of particular note is the Darby Creek Viaduct, extending all the way from proposed Eddy interlocking to Tinicum, essentially a second deck over the freight Chester Branch. The cost of this complex would be in the neighborhood of $2 billion, most of which--that is, all of it railroad south of the Airport--would have to be borne by the Market East Tunnel as well (see why I say Amtrak is dangerously lowballing Market East's costs?).
Finally, the lowest-priority element of my program is
4. New Zoo Bypass,
which, as has been detailed earlier in this post, offers a minute or two time savings, but at a cost of around $1b. The Northeast Corridor is neither congested nor time-optimized enough for this cost to make sense at this time, which is why I stress incrementally improving the rest of the corridor in order to make it viable, if it must be done.
Let me repeat myself. The Northeast Corridor is currently neither congested nor time-optimized enough for a Zoo bypass to be economically feasible.
* Push-pull equipment and motor-based HSR trainsets (like the Acela, KTX-II, and Duck), none of which can achieve the maximum speed EMU-based ones can, would still be routed via the existing Zoo interlocking.
** An automated train along the Airport Line's current fishhook. The Airport Line would be extended to Chester/Wilmington via Tinicum and Essington stations.