Alstom claims tilting train can solve HS2’s speed conundrum
French TGV-maker says its design can run fast on high-speed line and tilt on corners on existing routes
Robert Wright and
Gill Plimmer
SEPTEMBER 20, 2016
Alstom claims tilting train can solve HS2’s speed conundrum French TGV-maker says its design can run fast on high-speed line and tilt on corners on existing routes Alstom said trains based on those it's making for the US Amtrak network could be ideal
SEPTEMBER 20, 2016 The builder of France’s TGV trains is hoping to persuade officials planning the UK’s high-speed HS2 line that it can resolve one of their biggest conundrums: that on some of the lines new trains may run more slowly than existing rolling stock. Alstom, one of the world’s biggest train makers, has been telling engineers it could offer a train capable of running very fast on the dedicated high-speed line that could also tilt on corners on existing routes. Without tilting capability any new train would likely be slower over some sections of the existing network, such as the route from Preston to Glasgow, where Alstom’s tilting Pendolinos operate. However, HS2’s planners have long doubted that a train would be able to fulfil both functions. The discussions have been taking place at a time when HS2, a government-owned company, is considering a change to its rolling-stock strategy. It had looked set to place an initial order for trains capable of running only on the new high-speed line and for another group designed to run on the new line and on the UK’s existing “classic” network. It now looks set to order only trains compatible with the existing network at first, before ordering high-speed-only trains when more of the high-speed network is open. Transport ministers will decide shortly which strategy to pursue. Henrik Anderberg, Alstom’s director for HS2, said trains based on those it is making for the north-east corridor of the US’s Amtrak network could be ideal for the “classic-compatible” order because they would be capable of 300kph and also designed to tilt. “The [Amtrak] tilting technology is the same tilting technology that we have on our Pendolinos but we have refined that,” Mr Anderberg said. The technology was constantly evolving, he added, and any train offered to HS2 might have a higher top speed than 300kph.
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https://www.ft.com/content/77ba6e10-7c36-11e6-b837-eb4b4333ee43
The Physics of High-Speed Trains
By
Patrick Di Justo
July 25, 2013
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But banking the tracks isn’t a cure-all—a passenger train can tilt only so far before people fall out of their seats. So the minimum curve radius comes into play. Imagine that a curved portion of track is actually running along the outer edge of a large circle. How big must that circle be to insure that a train’s centrifugal force can be managed with only a reasonable amount of banking?
It’s relatively easy to calculate these forces and the ways to counteract them, so it’s relatively easy to set a safe maximum speed for a certain kind of track. Yes, badly maintained tracks, trains, or signals can sometimes contribute to a derailment. Historically, however, many of the world’s worst train accidents on sharp curves—the 1918 Malbone Street wreck in the New York City subway system, which killed at least ninety-three people (figures vary), or the Metro derailment in Valencia, Spain, in 2006, which killed forty-three—were simply caused by the trains going too fast.
That seems to be the case in the Santiago de Compostela accident: tracks rated for fifty miles per hour need almost no banking and can have a curve radius of fifteen hundred feet, while a train traveling at a hundred and twenty miles per hour needs a track with significant banking, and a minimum curve radius of more than
a mile and a half. The laws of physics all but insured that in this particular battle between gravity and centrifugal force, the latter would win.
https://www.newyorker.com/tech/elements/the-physics-of-high-speed-trains
Not brought into this article is superelevation (cant). Given enough velocity, you can go almost vertical with the tracks. Think of motorcyle velodromes. The problem comes with lower speed trains having to share the same track. This is even a concern for rail and flange wear on regular tracks. The cant angle is optimized for weight, speed and centre-of-gravity. It is compromised for the rest.
In the event, the cant for a line like the WCML in the UK, and for the Peterborough route if built, is well within acceptable design latitudes for both *higher speed tilting passenger* and premium express freight.
Addendum:
Excellent examination here:
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Why Tilting Trains Necessary Often train operating companies face a decision for building a high speed railway transport system. In order to eliminate the problem with corners we have to either build high speed railway tracks or by introducing tilting mechanisms. When we are choosing the 1st option we have to construct tracks on the corners with higher radius of curvature. In passive tilting on a curve, under the influence of centrifugal force, the lower part of the car body swings outwards. It should be noted that passive tilt has a negative impact on safety due to the lateral shift of centre of gravity of the car body. The active tilt relies on active technology controlled by a controller and executed by an actuator. Tilt as such has normally not an impact on safety on actively tilted train.
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https://www.irjet.net/archives/V4/i12/IRJET-V4I1296.pdf
