Rockin' and Rollin' on the NEC

Trains Magazine Passenger
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We took NEC Train 93 south from Rt 128 to Richmond on 25Nov and back on Train 174 on 1Dec, riding Business Class. With the car on the rear of the train I noticed a lot of lateral rocking and jolting as we passed over the many switches, especially in NJ and CT. It got a lot worse as speeds increased (to c. 120mph).

Now this was common on a Superliner trip we took to Arizona and back in 2022, but I kinda expected it on the freight roads, riding in the upper deck sleepers (though it did make sleeping difficult). But on Amtrak’s own tracks in the NEC? Is it getting worse? Even with the Business Car in the front, as on the trip south, it was pretty bad.

I’m wondering if it’s a problem with aging Amfleet cars, or poorly-maintained switch points—or something else. Are there improvements Amtrak can make to the switches that would make travel over them smoother? I don’t remember near as much jolting on trains in Spain, back in 2006. This was our first NEC trip since before the Covid craziness; has the road gotten worse, or are my aging bones just complaining more?

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Perhaps more a function of overly sharp switches rather than poor maintenance?

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In my experience Amfleet was always somewhat poor at absorbing the lateral-motion equivalent of ‘jounce’, and I associated that with the relative lack of over-center stability of the airbag secondary suspension. This in turn could be associated with exciting the ‘giggling’ vibration of some of the interior plastic pieces that I found so annoying at times.

One of the things Nystrom found out analyzing high-speed passive suspension in the late 1930s was that ‘suitable’ compliance for high-speed shocks could make for a harsh ride at lower and more common speeds, and this is likely true for lateral as well as vertical excursion. If there is an effective ‘deadband’ for the first few inches of lateral from centered, it may be easy for momentum to build up and produce both a sense of horizontal acceleration and a perceived lack of compliance as the lateral damping or snubbing or whatever comes into effect.

I know when I was looking at 225mph peak in the early 1970s that some form of active lateral suspension would likely be needed, especially with ride-height-correcting airbag or hydraulic secondary suspension, to eliminate this concern on ‘legacy’ track alignment. Current LGV solves it, but with relatively colossal expenses on civil and, in early cases, similarly colossal expenses on things like line and surface.

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Interesting to hear from an expert, if somewhat over my head. Do you suppose that the replacement coaches for the Amfleet cars will incorporate LGV-style improvement in suspension? And whether there will ever be significant improvements in “things like line and surface”? And what’s in the offing for non-NEC intercity rail? Makes me wonder whether the limitations of steel wheel on steel rail might be best superceded one day by maglev—but that’s a topic for another time.

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Keep in mind that LGV means ‘lignes a grande vitesse’ and refers exclusively to track and signal design, not trains (which are ‘trains a grande vitesse’ or TGV.

All the replacements for Amfleet I have seen (and the associated RFP) have implicitly followed PRIIA (which is 125mph ‘HrSR’ as maximum expected speed. The current ‘state of the art’ for something like the Airo trains is “better” than the Pioneer III derived trucks and suspension on Amfleet, but I have not studied the particular physical systems they intend to use for peak-speed lateral compliance. I am almost 100% sure it would not be active even if the trains are given ‘negative cant deficiency’ tilt.

That is a function of track maintenance, and up to recently involved considerable ‘human’ operation even where advanced European or Asian track equipment or TLMs were available. If you look at the history of the ‘zeroth generation’ of Shin Kansen from the early 1960s, line and surface were beat to death in less than about six weeks’ time, and some large number of hundreds of millions of yen were reported as necessary to maintain track geometry even remotely to support that (now pathetically slow) ‘high speed’ operation.

More modern LGV track with internal shock absorption (for example pads and elastic fixation) can work with low-unspring-mass suspension to reduce chronic maintenance… but it will still be ‘more necessary’ to monitor and PROMPTLY adjust any anomalies. Naturally this is easier on properly-engineered high-speed lines with 12-mile-radius horizontal and vertical curves that are not subjected to freight loads…

Meanwhile there remains that alarming study of the first-generation ‘porky’ Acela on the section of the NEC maintained by Metro-North, where vertical shock in excess of 189g (!!!) was recorded. I would doubt on first principles that any railroad producing that level of acceleration – whether from transient negotiation of switches or some other overlooked cause – is going to have necessary care for lateral acceleration, particularly in curves where you already need two more orders in your track-mechanics differential equations for the jerk in curving accommodation.

As you probably know from reading the interminable ‘second-spine’ discussions, it is well-recognized and accepted that a great amount of the existing NEC trackage will never be suited for speeds much in excess of 165mph… ‘speeding America into the Fifties’ indeed – and achieving even remotely suitable geometry in much of New England would only be possible on extensive viaduct construction. How likely do you think that will be?

[quote]
And what’s in the offing for non-NEC intercity rail? Makes me wonder whether the limitations of steel wheel on steel rail might be best superseded one day by maglev—but that’s a topic for another time.

Non-NEC intercity rail will mostly be either 79mph (on routes shared with freight traffic) or 90 to 110mph kludgery. The care involved in going from 90 up to 110 is enormously expensive, but sealed-corridor alone to get to 125mph is enormous by comparison… all of it needing to be paid for entirely by the passenger entities whatever they may be. Above 125 there can be no grade crossings of any kind… which I just don’t see happening here in my lifetime.

Maglev outside dedicated corridors is a cost nonstarter here, particularly when high-speed rail even to 350 km/h involves less grading and careful alignment. It’s an interesting technology, but essentially nowhere near as flexible as two-rail, and it requires full decicated guideways and usually intrusive support structure everywhere. Its only real ‘proven’ use is point-to-point bridging between airports and perceived city or traffic centers, with the ‘speed’ advantages largely squandered by internal airport and city ‘last-mile’ circulation and transport; it might have some role as connection to a putative HSR backbone but that role is much better filled by HrSR and hybrid air taxis.

The Chinese say they are working on a dynamically suspended alternative to maglev that will operate in a partially-evacuated tube, a bit like a less-goofy version of Hyperloop. They claim to be working up to over 1000 peak mph. Do not expect me to ride it.

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Thanks for your authoritative responses; apologies for the delay in acknowledging.

Re Maglev: Some years ago I read a book by James Powell and others entitled Maglev America: How Maglev Will Transform the World Economy (2013). The authors claimed that emerging maglev technology would make it possible for maglev trains to share existing rail roadbeds with conventional trains. Obviously this would not be high-speed, but presumably ML trains could be diverted to dedicated track where feasible for faster runs. And ML could be used for freight as well. I don’t remember details, but wonder if you’ve ever heard of this approach.

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I’ve only ridden the Shanghai maglev that was built by the Germans. It’s not exactly a smooth ride. Jittery. More like the subway than the TGVs I’ve ridden which ride better.

Maybe maglev tech is better today?

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I rode that line from Pudong in 2006 when it was quite new. Smooth. I wonder if it has deteriorated since?

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You can probably figure out the ‘ringers’ in this claim with a little reflection. Maglev on an ‘existing rail roadbed’ implies complete replacement of the existing track structure and some of the subgrade, probably replaced by slab track without a raised ‘fin’ or reaction rail that would be a clearance hazard for conventional equipment. The running rails would then be provided in the slab with top-down fixation, probably similar to the ‘winning’ system in that Railroad Research report on slab track.

The problem is that maglev even with modern cryogenic magnets is only really cost-effective over modern LGV/TGV at sustained speeds higher than current rail practice. Almost by definition any ‘legacy’ conventional route would have unsuitable lateral and vertical curve profile. The maglev technically shares the TGV’s relative insensitivity to nominally very steep peak or ruling grade (greater than 8-10% even for wheel-on-rail) but the vertical curves required often involve as much civil work as substantial tunneling.

Most of the maglev proposals I looked at back in the day were built as some kind of pier-supported viaduct, the thing the Chinese have so thoroughly evolved for rapid LGV construction. Outside Asia, I don’t think anyone has the stomach for the extensive tunneling and cutting that would be involved closer to grade.

This leaves open the economics of scheduling maglev ‘fast’ segments with more conventional HSR at other times (including HSR’s ability to use legacy last-mile traffic or conventional line segments during construction). There are terrible dangers inherent in maglev collisions where some form of electromagnetic braking fails to be applied correctly.

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And yet the Japanese keep at it.

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Yeah, it seems as though the Japanese are more adventuresome than we have been, but we have put our marbles all on airways for intercity travel, and highways for everything else. Then, our nationwide distances are generally longer.

Still, DC-NYC on the NEC has shown that trains can be competitive with airplanes on medium-distance routes (given center-city origins and destinations), so it can be argued that some adventure would be warranted. But for HSR or Maglev you’re still talking about dedicated infrastructure, tunneling or viaducts, as WH says. You’d need a lot of demand before the costs could be justified.

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I’m curious if the outside swing hanger trucks would have offered an improvement.

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The bags would still have been between the bolster and the carbody, not down at the spring plank. An OSH would only add an additional degree of freedom in the secondary suspension, requiring additional transverse damping, although it might permit a design of air bag with much higher lateral stiffness that would still level and have indeterminate spring rate in vertical accommodation and carbody roll.

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I was thinking more along the lines of the OSH trucks made in the 1950’s, though the metal springs may give a harsher ride than the air springs used on the Amfleet cars.

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Are the coming replacements for the Amfleet cars (whatever they’re called) going to have trucks with better lateral (‘jounce’) control? And the sleeper replacements, too?

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I think all the Siemens single-level stuff uses the same general truck approach, which is PRIIA compliant (to 125mph, tested 10% over). I have not ridden anything with that suspension, but it was my impression that a lot of the lateral wobble and roll induction was taken out of track on the Corridor over the years. Pictures and diagrams I have show long springs for secondary; I don’t know how they implement variable load or tide-height accommodation. I have noted that magnetorheological proportional lateral damping would be very effective (and not too expensive) at controlling the over-center float from big or long air-bag secondary (e.g. for the Mexican rebuilding of Amfleet as needed if they actually start getting to any high peak road speed).

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The US built Siemens Venture trainsets are based on Siemens Viaggio Comfort design, which uses SF400 bogies (a trailer bogie with electro-pneumatic disc brakes, 3 per axle).

For the North American Venture version, Siemens adapted this platform to meet FRA truck-to-carbody attachment requirement, and operational standards.
SF400: https://assets.new.siemens.com/siemens/assets/api/uuid:aa0e2fb5-6a54-4a86-83a5-66c37a356936/mors-b10027-00-datasheet-bogies-sf400-deenus-144_original.pdf
Regards, Volker

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Very large flat airbags for vertical. I cannot read from the diagrams provided by Volker how lateral accommodation is damped. Presumably very well.

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For damping of lateral and vertical
movements, hydraulic dampers are
installed.

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Keep in mind that ‘hydraulic dampers’ may refer to conventional ‘shock absorbers’.