Northeast Corridor, 95% Cheaper: Frankford Junction
Amtrak’s plan for high-speed rail on the Northeast Corridor, at a cost of about $290 billion depending on the exact alternative chosen, is unacceptably costly. I went into some details of where excess cost comes from in an older post. In this post, I hope to start a series in which I focus on a specific part of the Northeast Corridor and propose a cheaper alternative than what the NEC Future plan assumes is necessary. The title is taken from a post of mine from four years ago; since then, the projected costs have doubled, hence the title is changed from 90% cheaper to 95% cheaper. In this post, I am going to focus on untangling Frankford Junction.
Frankford Junction is one of the slowest parts of the Northeast Corridor today south of New York. It has a sharp S-curve, imposing a speed limit of 50 mph, or 80 km/h. While worse slowdowns exist, they are all very close to station throats. For example, Zoo Junction just north of Philadelphia 30th Street Station has a curve with radius about 400 meters and an interlocking, so that superelevation is low. The speed limit is low (30 mph, or 50 km/h), but it’s only about 2 km out of the station; it costs about 2 minutes, and with proper superelevation and tilting the speed limit could be doubled, reducing the time cost to 25 seconds. In contrast, Frankford Junction is about 13 km out of 30th Street Station; an 80 km/h restriction there, in the middle of what could be a 200 km/h zone, makes it uneconomic for trains to accelerate to high speed before they clear the junction. This impacts about 4 km, making it a 108-second slowdown, which can be mitigated by either more tilting or a wider curve. In reality, a mixture is required.
The NEC Future plan for high-speed rail, the $290 billion Alternative 3, avoids the Frankford Junction S-curve entirely by tunneling under Center City and building a new HSR station near Market East, a more central location than 30th Street; see PDF-pp. 19, 20, and 78 of Appendix A of the environmental impact statement. This option should be instantly disposed of: 30th Street is close enough to the Philadelphia CBD, and well-connected enough to the region by public transit, that it is no worse a station choice than Shin-Osaka. The Tokaido Shinkansen could not serve Osaka Station as a through-station without tunneling; since Japan National Railways wanted to be able to extend HSR onward, as it eventually did with the Sanyo Shinkansen, it chose to serve Osaka via a new station, Shin-Osaka, 3 km away from the main station. Given the expense of long tunnels under Philadelphia, the slightly less optimal station today should be retained as good enough.
A lower-powered plan providing some HSR functionality, Alternative 2, does not include a new tunnel under Philadelphia, but instead bypasses Frankford Junction. On Appendix A, this is on PDF-pp. 19, 20, and 70. Unfortunately, the bypass is in a tunnel, which appears to be about 4 kilometers. The tunnel has to cross under a minor stream, Frankford Creek, adding to the cost. Instead, I am going to propose an alignment that bypasses the tunnel, with moderate takings, entirely above ground.
In brief, to minimize trip times without excessive construction, it is best to use the highest superelevation and cant deficiency that HSR technology supports today. The maximum superelevation is 200 mm, on the Tokaido Shinkansen (link, PDF-p. 41); there were plans to raise superelevation to 200 mm on the Tohoku Shinkansen, to permit a maximum speed of 360 km/h, but they were shelved as that speed created problems unrelated to superelevation, including noise, pantograph wear, and long braking distances. The maximum cant deficiency on existing trainsets capable of more than 300 km/h is about 180 mm, including the E5/E6 Shinkansen and the Talgo 350 and Talgo AVRIL. Tilting trains capable of nearly 300 mm cant deficiency exist, but are limited to 250 km/h so far. With 200 mm superelevation and 175 mm cant deficiency, speed in meters per second equals square root of (2.5 * curve radius in meters); the minimum curve radius for 200 km/h is then 1,235 meters.
An S-curve requires some distance to reverse the curve, to avoid shocking the train and the passengers with a large jerk, in which they suddenly change from being flung to the right to being flung to the left. If you have ridden a subway, sitting while the train was decelerating, you must have noticed that as the train decelerated, you felt some force pushing you forward, but once the train came to a complete stop, you’d be pulled backward. This is the jerk: your muscles adjusted to being pushed forward and resisting by pulling backward, and once the train stopped, they’d pull you back while adjusting back to the lack of motion. This is why S-curves built a long time ago, before this was well-understood, impose low speed limits.
With today’s computer-assisted design and engineering, it’s possible to design perfect S-curves with constant, low jerk. The limits are described in the above link on PDF-pp. 30 and 38. With the above-described specs, both sets of standards described in the link require 160 meters of ramp. For a single transition from tangent track to a fully superelevated curve, this can be modeled very accurately as 80 meters of straight track plus the circular curve (half the transition spiral is within the curve); the displacement from an actual spiral curve is small. For an S-curve, this requires double the usual transition, so 160 meters of tangent track between the two circles; bear in mind that this distance grows linearly with speed, so on full-speed 360 km/h track, nearly 300 meters are required.
Here is a drawing of two circles and a tangent track between them. The curve of course consists only of a short arc of each circle. The straight segment is a little less than 700 meters, which permits a gentle spiral. The curves have radius 1,250 meters. Takings include a charter school, a wholesale retailer, an auto shop, and what appears to be industrial parking lots, but as far as I can tell no residences (and if I’m wrong, then very few residences, all very close to industrial sites). The charter school, First Philadelphia Preparatory, is expanding, from 900 students in 2012-3 to an expected 1,800 in 2018-9. School construction costs in Pennsylvania are high, and $100 million is expected for a school of that size; see also table 5 on PDF-p. 7 here for national figures. The remaining takings are likely to cost a fraction of this one. Even with the high cost of takings, it is better to realign about 2 kilometers of track above-ground, at perhaps $150 million, than to build 4 km of tunnel, at $1.5 billion; both figures are based on cost items within the NEC Future documents. This represents a saving of about 83% over Alternative 2, which is projected to cost $116-121 billion excluding rolling stock (PDF-p. 42 of chapter 9 of the EIS).
Given the long spiral length, it may be feasible to avoid the charter school entirely. This would probably require shrinking curve radius slightly, permitting 180 or 190 km/h rather than 200 km/h. However, the travel time cost is measured in seconds: with about 11 km from the end of Zoo Junction to the northern end of Frankford Junction, of which 1 is required just to accelerate to speed, the difference between 200 and 180 km/h is 20 seconds. Further savings, reducing this time difference, are possible if the speed limit without taking the school is 190, or if trains accelerate to 200, decelerate to curve speed, and accelerate again to the north. This option would improve the cost saving over Alternative 2 to about 90%.
The correct way forward for affordable improvement of the Northeast Corridor is to look for ways in which expensive infrastructure can be avoided. If a tunnel can be replaced by a viaduct at the cost of a few extra takings, it should be. If an expensive undertaking can be avoided at the cost of perhaps 10 seconds of extra travel time, then it probably should be avoided. There should be some idea of how much it’s acceptable to spend per minute of marginal travel time saving, by segment: the New York-Philadelphia segment has the heaviest traffic and thus should have the highest maximum cost per unit of time saved. But even then, $100 million for 20 seconds is probably too high, and $100 million for 10 seconds is certainly too high.
This is neat.
It would be cool if there was some sort of tool that would allow you to draw a line on google maps, specify the rolling stock and some constraints (like super-elevation and dwell times), and then it would give you the curve radii, a speed graph etc.
I thought about it! Apparently building in a rolling stock performance calculator is trivial; integrating everything with Google Earth or another mapping tool is the hard part.
While working at ReThink Studio, I have developed a pretty reliable method for calculating trip time estimations for existing and proposed rail lines. Let me know if you’d like to discuss this in more detail sometime.
Can you talk a bit more about your method? What I normally do for travel time estimation is plug in train performance parameters to get the acceleration and deceleration penalties for a slowdown from speed x to speed y.
In this post I didn’t really do that, because a slowdown near a station doesn’t quite work this way – instead, it delays the train’s acceleration. Heading north from Philly, a train goes at the maximum speed of the Zoo Junction curve, and then at the maximum speed of Frankford Junction (unless Frankford is so low that it’s useful to accelerate, decelerate for the junction, and accelerate again), and then at maximum line speed east of Frankford. The difference between 180 km/h and 200 km/h is then equal to the difference between running between a point north of Zoo where an accelerating train reaches 180 km/h and the north end of Frankford at 180 and running between these points at 200. No acceleration penalty needs to be computed, because the train is accelerating from 0 at Philly to line speed north of Frankford anyway, so it’s just a matter of whether this stretch of about 10 km is done at 180 or at 200.
The idea that a station in Market East would be more centrally located is also outdated. At this point, the CBD is steadily moving west towards 30th St., and much of the major construction in Philadelphia is either in West Philadelphia, near the current station, or right across the river from it.
So, not only would your idea likely save money, it probably also creates a more optimal outcome regardless of spending.
Most interested local lay have suggested using the Erie-Torresdale alignment as a bypass. The advantage to this is apparent: about a mile with a taking at either end. The disadvantages are Frankford Creek for a tunnel and the Erie-Torresdale el stop for an aerial, where the gradient required for clearing under the creek is much more trivial than any attempt at either clearing over the el stop (whose highest point is, I’d guess, ~60 ft in the air) or squeezing a clearance box between the street and the el.
But even a limited cut-and-cover tunnel with no station boxes would be expensive. Fixing the junction with a perfect S-curve and minimal takings is almost certainly the best available option.
The market in Philadelphia is big enough – when you can get to Washington in one hour, Boston in two, Cleveland in three or Montreal in four- that there can be a train that serves Suburban and Market East once or twice an hour. For instance Boston to D.C. and Harrisburg to N.Y. via West Trenton. They would be used by people coming and going to metro Philadelphia.
Alon, great piece! This is exactly the topic which your analysis is most valuable. Looking forward to reading the coming ones. Just a side note, IIRC you said a couple years ago that $1 Billion would be enough for constant-tension catenary from NY to WAS. Do you think this is still the case? I struggle to see Amtrak making such a project work given their engineering track record and the complexity of the high tension (utility) wires high above much of the NJ section. On my last trip, I noticed that even the short/simple doubletrack from Secaucus Jct to NYP lacked constant-tension catenary. That seems like a terrible place to have a catenary problem due to heat.
Would the Septa local trains require reduced superelevation (that is, would the superelevation for high-speed trains be too much for trains traversing the curve at, say, 80 mph)? If so, is there a problem with mixing different degrees of superelevation on the same right of way?
No. At a radius of 1,250 meters, 200 mm superelevation perfectly balance at 147 km/h. At 130 km/h, there are 44 mm of cant excess. Railroads and regulatory agencies dislike cant excess, but in truth it’s equivalent to cant deficiency; 44 mm is no big deal for passenger trains in either direction. If the curve is tightened to 1,120 meters, with 190 km/h intercity trains, to reduce takings, then at 130 km/h cant excess is reduced to 25 mm.
I’ve heard some arguments about passenger comfort requiring some amount of cant deficiency – i.e. if you look out the window and see the train turning but don’t feel any turning it can induce motion sickness. But at such a large curve radius it might not matter anyway – you’d barely be able to see that the train is turning.
That’s for when there’s zero cant deficiency, not for when there’s cant excess. When there’s cant excess, you see the horizon rise and fall and notice a small difference in gravity pulling you in the downward direction.
The freight going over the Delair bridge is going to be slower. the local that stops at Bridesburg will be going slower. And if they build a station to connect to the El, that local will be stopped. The local tracks are going to be different.
Of course. But intercity trains have no business using the local tracks, so it’s fine to fully superelevate the express tracks, which are to be used only by intercity trains and express regional trains (assuming SEPTA chooses to run any).
Last time I looked, before the current meltdown, there were express trains on the Trenton Line. Very likely on the local tracks because they made stops other than Trenton. Unless automobiles get banned the frequency is never going to high enough that they need to use the express tracks.
In your opinion, is there any advantage to setting a time goal, such as XX minutes for HSR travel time between Phila and NYC and then using that goal in an attempt to determine a budget? That way I could see that 50 minutes would cost 50 Billion$$, but 60 minutes might only cost 30 B$, and likewise 45 minutes might only be 5 B$ more then a 50 minute trip. I have often thought it would be a good idea to ‘deal with’ the Zoo Junction, but I understand your real world point about the cost of fixing that, whatever the actual dollar cost, would have only a very slight benefit in actual travel time. Thanks
Yes, very much so. Time goals are of especial importance when planning rolling stock requirements and service patterns: for example, if a railroad is expected to run hourly service, then the travel time goal should be an integer or half-integer number of hours minus turnaround time, to use rolling stock maximally efficiently.
Neat idea, this would make a lot of sense, particularly combined with Zoo reworking.
If Amtrak wanted to run trains through downtown Philadelphia, running them through the City Center Tunnel would make much more sense, especially as that tunnel is at about 60% capacity. The southern end of the tunnel is already connected to the NEC and the northern section could be connected at North Philadelphia via short cut/cover tunnel segment. Trains would have to slow way down to access the tunnel and travel relatively slowly through it but the additional ridership might make up for it, particularly if it ran express throughout the rest of its journey. This would also allow Trenton Line trains to access downtown faster and avoid Zoo.
It’s much cheaper to just leave it the way it is and let the trains use the West Trenton line to get back to New York.
Just as illustrated here. I’ve assumed both NEC HSR tunnel and North Philadelphia connection tunnel, combined in a single project. But this isn’t absolutely necessary https://drive.google.com/open?id=1JZm-iXGZhlM_MX1W4ivjU8rH6cw&usp=sharing
How’s this square with the Amtrak plan of putting PHL on the new NEC mainline?
Two independent issues, really. One is north of 30th Street, the other south. I’m ambivalent about putting the airport on the mainline (but if it’s done, it should be above-ground, without a tunnel under airport grounds), but that can be done without any Frankford tunneling.
Why would anybody in their right mind take a train past BWI or EWR to get to PHL?
Using SEPTA’s commuter trains as PHL’s people mover sucks. Having Amtrak stop there doesn’t solve that problem. Two car trolley cars, like JFK’s airtrain…. might be excessive. But they could run more often than twice an hour. Either a new station out on the existing mainline where Regionals stop or all the way to University City where the train from New York to DC via West Trenton stops. Or something. …and there would be one station at the airport. Most people would have to get on a people mover anyway.
adirondacker12800- That’s not the problem it’s meant to solve. It’s meant to allow air-rail connectivity primarily for regional rail, like PVD, BWI, and EWR, to varying extents, already have.
PHL is closer than the other two major airports for anyone between the Susquehanna and Delaware rivers. That’s right around 7 million people.
PHL also has recently attracted budget airlines (I’ve taken $29 flights between Orlando and PHL to go to DC and NY, recently), but honestly that’s neither here nor there.
As far as the people mover between terminals, that’s not what an intercity or regional rail train should be doing, you’re certainly correct that people would have to get on a people mover.
As to what technology- I think using the airport line right-of-way for the 36 trolley would be fine; it runs every 5 minutes currently. Alternatively, a dedicated airport trolley going solely between eastwick and the terminals. Basically whatever ends up being all-things-considered cheaper for similar levels of service.
I would suggest a single airport station (which could also serve as an intermodal center, consolidated rental car facility, same idea as the one at MIA).
Alon, I agree on a value-engineered above-ground solution.
PHL is worth serving, but not at all costs.
They have regional connectivity at Temple, Jefferson, Suburban, 30th Street and University City. Every half hour. It sucks. Changing the destination on the train from “Airport” to “Wilmington” doesn’t change that all that much.
Click to access air.pdf
Drag the people mover all the way out to the existing mainline and a new station, six tracks like Newark Airport would be nice, or all the way to University. Two car trolleys can run more frequently.
First off, if you remove the split from airport line and Wilmington line, you increase frequency. Wilmington trains serving the airport double the service, already. Second, you’re forgetting this service called “northeast regional”, which adds another train an hour. That’s going from service every 30 minutes to about every 10, if everything is scheduled accordingly.
That is certainly an improvement.
That’s to say nothing of how much better service south- remember that PHL is Delaware’s airport. Currently it takes roughly as long to take SEPTA from Wilmington to PHL as it does to take Amtrak from Wilmington to BWI. Despite the fact that PHL is 60 miles closer. Most people drive. Some take a cab.
As far as whether the NEC should move closer to the airport, or the people mover closer to the NEC, I don’t have a strong preference. If amtrak is correct that it would save time between DC and Boston to serve PHL more directly, I’m definitely in favor of that.
I believe we can agree the current situation is inadequate.
Not to judge or anything, but Delaware doesn’t have a lot of people in it. Might as well talk about the need for a dedicated airport connection between Southern Brooklyn and JFK. It’s really hard to get there – a bunch of transfers, and a really circuitous path.
Amrak doesn’t stop at all at Providence, Acela doesn’t stop at Newark and not every regional. I’m not in the mood to go parse BWI. And people who are not going to the terminal where the station is will still have to get on a people mover.
…and BWI is a bus transfer….
People in Brooklyn, if they have more than a backpack….. know how to call for a cab. Ya are spending 300 bucks to go see Granny in Florida a 30 dollar cab fare ain’t gonna break you.
Literally the only time I took a cab between Brooklyn and an airport, a) it was LGA and not JFK, and b) I tried taking the subway but due to train delays was worried about missing the flight. (I missed the flight anyway – I got to the airport in time, but boarding wasn’t announced and I got to the gate too late.)
A train or even a bus on a Triboro RX-ish route to JFK wouldn’t have helped much if at all with a trip to LGA. Since the A shares it’s Manhattan route with the D there’s probably capacity for something in Brooklyn and Queens. I don’t know if there would be much demand. Two car shuttles screwing up the schedule of Triboro, running mostly empty most of the time from Sunset Park to Howard Beach? I don’t know if NYC subway cars can run as a single car anymore…
It’s not so much that Delaware is important (it’s not particularly so), I reckon that was a bit distracting to mention. It’s more that there’s something on the other side of the airport if you route regional rail through it, as opposed to the current dead-end turnaround.
Looking at station rankings, Amtrak’s BWI station is just ahead of Newark Penn, and just behind Wilmington in annual Amtrak ridership. Seems like it’s doing okay (and Wilmington has a surprising number of amtrak riders).
It takes getting on a people mover to get between terminals and the rental car center or parking in many airports. That people mover isn’t (to the best of my knowledge, ever) 4+ miles long. Some people movers are a bus. I deboarded an Emirates A380 at Dubai International Airport and they put us on a bus to get to the terminal. It’s part of travelling.
I hadn’t realized that there were regionals that skipped EWR. I did know that acela does. BWI gets the level of service I would figure appropriate for PHL.
As I said before, As far as whether the NEC should move closer to the airport, or the people mover closer to the NEC, I don’t have a strong preference, PHL is worth serving, but not at all costs. If amtrak is correct that it would save time between DC and Boston to serve PHL more directly, I’m definitely in favor of that, especially considering the positive effects it would have for airport service levels and increasing the service area and population where transit to the airport is effective.
I believe we can agree the current situation is inadequate, can we?
It is definitionally impossible to save time by serving the airport. The airport is a detour compared to the legacy route, unless the trains only serve Eastwick, in which case it’s a wash. You can save time by building a long tunnel under Center City and avoiding 30th Street Station, but for the same cost you can save a lot more time elsewhere.
Is belt parkway one of those Robert Moses specials where buses physically cannot fit, or is there just not demand to make the 12-mile jaunt a regular bus service from Coney island to the Howard Beach/JFK station?
Either way, I’d agree there are other, more significant transit (and broadly social) needs in that area and that laying rail from south brooklyn to jfk would be folly.
Except maybe, just maybe, for a few peak hour trains on weekdays, everything will be stopping in Philadelphia.
How many billions of dollar would it take to dig a tunnel from Frankford Junction to the airport. How many billions for the deep cavern under Jefferson. How many minutes would it save versus improving the existing a bit? So that the fraction of SEPTA riders that are on the Trenton-Wilmington line …. can change to the people mover on the airport instead of a few minutes away off the airport?
There aren’t a whole lot of people living in Coney Island, there isn’t enough demand. . . there isn’t enough demand in all of Brooklyn….
Again, Alon and I are advocating a surface solution, not a megabucks tunnel.
Somewhere in the vicinity of Eastwick is decently close for a people-mover station (it’s under a mile, rather than 4 to Darby or 6 to University city) the 36 trolley could terminate there, Amtrak and Wilmington/Newark trains would serve it.
Put the consolidated rental car facility, some long-term parking, intercity bus service there, and put it on whatever people mover could use existing airport line track at a frequency of every 10 minutes (matching train service), or every 5 minutes.
That seems like the ideal solution to me.
Eastwick isn’t near where Amtrak and other SEPTA trains run. Not even on a SEPTA rail map.
Eastwick (current station) on the airport line. Last stop before the terminals. Eastiwck (36 trolley terminus) is a loop a few hundred meters from it. Eastwick is 2.5 km South of the current NEC mainline. Track to it from Eddystone runs parallel to current NEC. Similar distance, maybe a bit straighter.
One benefit would be being able to upgrade it to best-possible specs without having to allow for Amtrak/SEPTA trains to operate on the track during the process.
Alon thinks it’s a wash. I’m inclined to agree- but the station provides benefits. I think bringing service every 10 minutes to the city center from the airport, more destinations in fewer transfers and less time, and travel time comparable to driving from Wilmington, make it worth investigating.
What’s the significant difference between changing to a people mover on the existing mainline and changing to the same people mover in Eastwick? I come with “there isn’t any”. Standard gauge trolley cars, they have have to raise the tracks some inside the airport and build some platforms out on the existing mainline. Everybody gets to keep their frequency and mostly empty trains don’t have to wander through the airport.
Alon has previously argued for running future NEC HSR/Amtrak via Eastwick and the old B&O ROW to Eddystone/Chester before rejoining the PRR/current NEC ROW, I think because it’s less curvy than the current route. HSR trains shouldn’t stop at the airport, but improved service to the airport (with a people mover to Eastwick, etc) could come with the HSR project (assuming the ROW is wide enough for four tracks; it looks like it). (I guess then regional rail trains from Wilmington would run via Eastwick-Airport with a timed transfer at Chester to local trains via Sharon Hill etc?)
What makes BWI worth stopping at (not only for regional, but also Acela) that doesn’t apply to stations to busier airports at EWR or PHL? I haven’t gotten an answer so far.
Potentially unpopular opinion, but I’m not so sure that a service for the existing stations that would be bypassed would be necessary; between where the airport line separates from the Wilmington/Newark and where it would reunite; total daily ridership is about 16% of the Newark/Wilmington line, over 60% of that is from the 4 busiest stations, all are within 3 mi of eachother, and they’re just the stations with the biggest parking lot, it’s only about 2 mi from where new stop(s) would be located on the Airport/Wilmington/Newark line and where the to-be-closed stations are.
A single stop within the largely-vacant industria of Essington could host more parking and replace 9 stations of fairly minimal ridership. I’d probably go with that over any “timed transfer at Chester to local trains via Sharon Hill” type solution. But that’s just me.
It seems to me like a major reason for making the expenditure to stop at BWI or any other airport on the NEC (PHL, EWR, BWI, Harrisburg, Bradley, others?) is that the tracks already run very close to the airport and that air traffic, particularly in the Northeast, is frequently snarled by congestion and Mother Nature. If a snowstorm grounds flights, the airlines and passengers benefit by having another option to get to their destination.
PHL is off the mainline. EWR is on the mainline, but extensive commuter rail traffic means that scheduling intercity trains to stop there is a chore – that’s why even the Regionals skip Metropark on weekdays. I’m not even sure HSR should serve BWI, depending again on train scheduling, but that’s at least plausible.
BWI is Baltimore’s New Carrolton/Metropark/RT128 that happens to have shuttle bus service to the airport terminals.
Just because there are platforms at a station doesn’t mean all trains must stop there. The NEC isn’t BART. The Nozomi can blast through and some if not all of the Hikari and the Kodama once an hour. Just for laughs I asked the Amtrak reservation system to look up trains between Washington D.C. and Metropark N.J. There are 21 of them on the two weekdays in July that I picked… that’s adequate.
Yeah, and I don’t think any HSR should stop at Route 128; let the MBTA handle it. Save the Kodama stops for things like New London, Stamford, New Rochelle, Trenton, and Wilmington.
It’s busier than Trenton, New Rochelle or Stamford.
And since straighter railroad tracks are going to cause the hens to stop laying, make the dough go flat at Mystic Pizza etc. New London can settle for the train that toddles through on the old alignment six times a day. It’s much less busy than Rt.128.
Hey, at least straighter tracks will make it easier for the people of Mystic to visit New Haven and get better pizza.
Moving a tie will cause the fabric of the universe to rend. Amtrak will end up putting the straighter tracks someplace else. Their only hope in getting level boarding so M8s can go to New London.
First of all, PHL’s terminal layout is not at all conducive to a people mover, at least on the Airport Line ROW. From gate to gate there are frequent shuttle buses between the terminal arms, and since all terminals are already connected airside walking is the quickest option most of the time. What the Airport Line succeeds at doing is providing 1-seat or cross-platform regional access to PHL, and the terminal-level granularity avoids excessively long walks.
As far as intercity goes, the Chester Branch does not appear any faster than the NEC given the same number of curves. And without costly tunneling and multiple stops at the airport, the walking distance between an Airport HSR station and a gate is subpar. Keeping legacy service with a free transfer connection at 30th is perfectly fine enough. And the easier solution to serve south-of-30th riders is to build an airport transfer station on the NEC at 54th St, with the added benefit of an infill city station; Amtrak doesn’t have to serve it if the market’s not there. The bottom line is that 1) PHL operates in a constrained market, 2) PHL isn’t in the situation to require a frequent people mover; a 4TPH airport line suffices, 3) It’s not easy for an intercity train to serve the airport as conveniently as the Airport Line does.
Interesting discussion. I don’t know much about this, and I’m probably about to make that obvious. Based on the current Airport line schedule, couldn’t you save 8 minutes per 46-minute round trip by stopping all the trains at Terminal A and installing a covered moving sidewalk over the existing tracks to take people to the escalators for the other terminals? Would that allow for more frequent service or is the bottleneck somewhere else?
Nice drawing experiment. Your numbers, however, are somewhat off.
First, a radius of 1250 m or 4100 ft gives you a maximum speed of about 130 km/h (80 mph), or somewhat more if you allow for a higher centrifugal force. This is, IMHO, way too little for an expenseive rerouting of such an important railroad.
Then, you need an ADDITIONAL tangent track between the two transition curves, of maybe 100 m or 300 ft.
Last, the tangent tracks after the curves are offset by roughly L²/24…48R, depending on the transition curve used. This typically means more area needed for the curves. In your case, with R=1250 m and a roughly 60° curve, i.e., L approximately equal to R, that would be about 30 m or 100 ft offset, thus probably touching different buildings and tracts of land.
Maybe it could still be done with only a little money …
(130/3.6)^2/1250 = 1.04 m/s^2. This is really low – 156 mm total equivalent cant, where non-tilting trains in Germany do 310 every day on the Frankfurt-Cologne line. With the right cant and cant deficiency, this is 180 km/h. Moreover, using the limit value of cant (200 mm) and the cant deficiency of active suspension Shinkansen (again, hundreds of times per day), you can squeeze 380 mm, which is 200 km/h.
Now repeat this throughout the line. This is how you speed up trains without the massive tunnels that Amtrak and its consultants think are necessary.
Another aspect of this curve is to disentangle Amtrak (express track) from SEPTA (local tracks) here, rather than at Zoo interlocking, allowing faster speeds between North Philadelphia and 30th Street station for both. Also allowing SEPTA to add infill stations and both SEPTA (Chestnut Hill West line) and NJTransit (Atlantic City Line) more scheduling flexibility. See this map (https://firstname.lastname@example.org,-75.097818,14.97z/data=!4m2!6m1!1s1mkVoIHSHuzx2Xb9bTKlxO6pClnlWOuVo) by @benshe_.
In Germany it would give you 170kmh (180kmh with direct fixation track, 210kmh with tilting trains)
(Balancing superelevation 180kmh = 11.8 180^2 / 1250 = 306mm; regular design superelevation for 6.5 180^2 / 1250 = 168mm rounded to 170mm; cant deficiency 136mm)
Actually no, you don’t. Immediately adjacent transition curves — it’s actually the superelevation transition ramps that are the limit — can have a quite nice geometry, where the inner and outer rails smoothly (not in the C∞ sense, yoyur non-engineering freaks) go from positive to negative height over the centreline without the bump of a mandatory intermediate straight (and zero superelevation) section. The German term for this is “Gleisschere” but I can’t find an English one.
Plenty of examples here:
Normal German curve transition (“Bloss” spiral) length 4.5 * 180 * 136 / 1000 = 110m
Superelevation ramp length 7.5 * 180 * 170 = 230m, but design exceptions allow 6.0 * 180 * 170 = 184m.
So 184m — the required transition length for superelevation nearly always exceeds that for horizontal curvature. Your 30m is optimistically low, unless I’m making mistakes.
Y-axis offset (again “Bloss” spiral) of end of transition spiral from the circular cuves = 184^2 / (42.23 * 1250) = 0.64m