I have already spoken about my criticism of Amtrak's proposed Market East tunnel, a cogent enough piece Alon Levy relies on it and The Economist has quoted from it--but I have yet cogently articulated what the alternative is.
Part of it is, it's simple. Really simple. But it's complex. It's not complex in the way the Market East tunnel proposal is--that is, as an engineering challenge--but rather as an organizational one--that is, getting the right players at the table talking the right tones.
There are two, and exactly two, transportation elements to the Market East tunnel proposal; everything else is highly speculative land-use development claims. These are to (1) connect regional/high-speed service to Philadelphia International Airport, and (2) bypass Zoo Interlocking, which, for this proposal, is seen as one of the corridor's major pinch points.
My response to Zoo to begin with. It is true it is a pinch point, but a necessary one. There is no better way to provide a wye junction between the Northeast and Keystone Corridors, two high-speed lines, without egregious tunneling and investment. Much better, then, to simply optimize Zoo for 100 kph (~60 mph) traversal, particularly since one goes directly from it into the 30th St. yards and station throat.
Certain transit proponents claim Zoo traversal takes 45 minutes; this is demonstrably false: a much more accurate time penalty can be ascertained by comparing the commuter rail times from North Philadelphia to 30th Street and North Broad to Market East, respectively, to one another. This is approximately four minutes, and for local services; express trains can run the same route more quickly. The reality is that, for the fastest services (the Acela and Northeast Regionals), the time penalty is more like 45 seconds, and can be reduced to 30 with an optimized interlocking. Besides, there are improvements elsewhere on the corridors that can ameliorate Zoo's impact--switching to modern 25kV 60MHz constant-tension catenary (the most advanced currently available), for example, will effectively double speed limits throughout the corridor.
So, because (a) it's a junction between two high-speed lines, (b) no form of restructuring is economically feasible, and (c) far greater speed (and thus time) gains are available through a far less expensive project, I urge ignoring the, er, urge to bypass Zoo. Keeping structures like Zoo in place are one of the major compromises one has to make when implementing a high-speed system on top of an existing medium-speed one, as the Italians, French, Germans, Belgians, Dutch, Koreans, Russians, and (soon) British have all found out*.
The second problem this proposal purports to solve is bringing intercity rail to the Airport. The proposed route would break off the existing NEC in the Eddystone area, follow I-95 or the Chester Branch into the Airport area, provide a new station, and then delve under the Schuylkill and the tunnel, coming back out around Frankford Junction--but this is not really the most optimum way to bring passenger rail there.
The Chester Branch is arrow-straight. Don't be fooled by the SEPTA line, which comes off the NEC following the 52nd St. Branch and then curves onto the Chester Branch; look on Google Maps. It diverges from the NEC right under the Grays Ferry bridge and extends past the Airport with no noticeable curvature whatsoever. It continues this pattern, though now with minimal curvature to avoid geographic obstacles, all the way to Eddystone. SEPTA's line makes use of a part of this alignment, but to put it bluntly, it is about as tailored to high-speed rail as you're going to get. Ignoring it is thus foolhardy.
The big issue the Chester Branch has is its mixed traffic. This comes in two flavors: local traffic to Chester (well, duh) and through traffic using its uppermost mile as a cutoff linking the CSX (ex-B&O) main with the (ex-PRR) High Line; this latter section is pretty important for double-stacks originating from the Ports of Baltimore and Wilmington, particularly as the Charles Street Tunnel down in Baltimore and Fairmount Tunnel up here are too squat for them.
This is, however, mostly an organizational issue that can be solved with limited, but judicious, application of concrete (and concrete needed to provide grade separations, anyway). In this case, this involves (a) grade-separating the line through Essington and Tinicum--this will involve an aerial due to the shallow water table and Darby Creek crossing--as well as flying over Industrial Highway to meet the NEC (the existing freight line would be retained underneath this aerial), (b) re-activating the rather more circuitous 52nd St. Branch for freight traffic with a new junction with CSX about a football field north of the apex of the existing SEPTA flyover, a reactivation which would service industrial development along Essington Ave. and parts of the Industrial Hwy. near the Penrose Ave. bridge, and any potential Port expansion around the mouth of the Schuylkill, and (c) a double-deck railroad between the CSX line and the High Line, with the passenger section underneath and the freight section on top. At the NEC, the freight line would veer onto the High Line right-of-way and the passenger one would integrate with the NEC main via either flyovers or duckunders.
While this slate of improvements is not insignificant, keep in mind that the Essington/Tinicum aerial would be necessary anyway, due to the Darby Creek crossing, and that each improvement utilizes existing rights-of-way with technically minimalist solutions for handling passenger/freight traffic separation and the grade separation necessary for true high-speed rail. Costing isn't too hard: I do not believe double-stacks move along the Chester Branch and so undercutting shouldn't be necessary, and the two-level box structure between the NEC and CSX puts Plate K clearance (the double-stacks) up on the highest level. Total costs shouldn't be more than $100 million to $250 million.
There are significant operational advantages to this alignment. Firstly, trains not calling at the Airport can use the existing NEC alignment to bypass it completely, which means that the line can be (re)built to handle lower capacity than the tunnel proposal (which would shove all trains through the Airport station, whether they stopped there or not).
It also offers a new local alignment to Chester, allowing for stops at Tinicum and/or Essington, as well as 70th, 63rd, and Bartram's Gardens in the city. The Airport fishhook can then be repurposed into an AirTrain-type setup.
And finally, there are concrete land-development advantages.
Biggest of these is that the 52nd St. Branch alignment offers freight access to a large swampy area across the Schuylkill from the Navy Yard--an area which, with the completion of the current Port expansion (called Southport, I believe), will become the next logical place for a new Port terminal to handle growing Northeast port traffic. A natural terminus, it lies between a large industrial area and the Airport, and would make the Navy Yard a natural place to handle the Port's administrative (office) functions, lying, as it would, between two of Port's three largest termini.
More importantly for passengers, local stops can be leveraged for transit-oriented development. This is particularly useful around 63rd and 70th Sts. and Bartram's Garden.
Finally, with the speed boost from catenary modernization, PHL would lie about an hour from Midtown--the same time, coincidentally, that JFK is on the subway. Instead of attempting to use less and less tenable suburban airports to handle NYC's congestion, PHL's roomy international terminus can provide necessary space.
This is the alternative vision I have: Airport service provided along a natural corridor, Zoo improved inasmuch as is geometrically feasible, and none of that asinine Market East tunnel proposal--which, I may remind you, would be a bored tunnel through alluvial soil under the water table in a heavily-urbanized area, which can be read as f(x) = Extreme Cost Overruns. There is no way on this earth, or any other, that that project will cost "merely" $3 billion, as Amtrak is attempting to sell us on; peg it more between $10 and $15 billion, and that is at its technical cheapest: a 300%-500% cost increase.
By contrast, my proposal will add in reasonable intercity PHL service for $250 million (note m) on top of the flat cost of modernizing the NEC--that is, catenary conversion plus the costs of Gateway and the Great Circle tunnels under the Hudson and in Baltimore, respectively.
* The Japanese, Taiwanese, and Spanish high-speed networks are all of a completely different gauge standard than the existing systems, and so don't run into this issue. China, meanwhile, has the resources and attitude to ignore this issue.