I've seen term "reverse curve." What does that mean?
Still in training.
I believe it's the same thing as an S-curve. Where it starts going in one direction and then goes in the opposite.
PS--I just typed "railroad reverse curve" into Google and that's what it is.
IF you don't have several hundred feet between those curves turning in opposite directions, you have a potential nightmare on your hands.
mudchicken IF you don't have several hundred feet between those curves turning in opposite directions, you have a potential nightmare on your hands.
I new you'd go off on a tangent, there.
ChuckCobleighI new you'd go off on a tangent, there.
You know MC - always on the straight and narrow...
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
The sharper the curve in degrees the greater the distance needed. Also, the speed which trains operate is involved.
BNSF (former Santa Fe) constructed a new line through the mountains of Arizona in 1959-1960 which allowed passenger trains to operate at 90 MPH. and had one degree (or less) curves. The minimum distance between curves was 500 feet of tangent.
Would one of the reasons for needing 500 feet of tangent be dealing with transitioning superelevation? For model railroads where track isn't canted, allowing for the length of the longest car should be enough.
Superelevation follows the "spiral easement" entering or exiting a curve. The tangent between curve allows the center lines of equipment to line up straight before starting a new curve.
rcdrye, you are correct.
I believe Santa Fe used 570 foot spirals with a gradual step up to three and a half inches of super elevation. But the 500 feet of intervening tangent still applied.
Thank you, gents.
rcdrye The tangent between curve allows the center lines of equipment to line up straight before starting a new curve.
The tangent between curve allows the center lines of equipment to line up straight before starting a new curve.
That's pretty much what I thought could be the reason for the 500' tangent. Since the purpose of superelevation was to balance out "centrifugal force", the amount of superelevation would increase with the increase in curvature of the spiral.
(1) Before you get into the superelevation, you have an unstable situation with trucks turned in opposite directions.
(2) Track liners, given enough time and iterations, will overlap the spirals.
(3) Speed will have to drop mui-pronto or the gods of centripital force will induce some severe rock and roll. (think wheel lift) Cars and locomotives leaning in all directions. Sometimes you have no choice and train handling gets iffy. (time to get absolution from the boss and the Chief Engineer)
(4) If anything in the consist has centerbound or stuck trucks - GAME OVER
(5)and yes, your superelevation will accentuate the rock and roll.
(6) having seen what happens on Raton, Glorietta, Tennessee, Moffat and Cajon, grade and braking only makes the issues worse when added to reverse curves. (bad enough in some yards)
mudchicken" - Track liners, given enough time and iterations, will overlap the spirals.
MC, with his many years of latest experience, knows that the original engineering construction design disappears with changes in train operation and maintenance procedures. I probably would not recognize the engineering I participated in creating in 1959-1960 if I were revisit Williams-Crookton, Arizona.
Erik_Mag rcdrye The tangent between curve allows the center lines of equipment to line up straight before starting a new curve. That's pretty much what I thought could be the reason for the 500' tangent. Since the purpose of superelevation was to balance out "centrifugal force", the amount of superelevation would increase with the increase in curvature of the spiral.
Makes sense, as traversing into or out of the spiral requires changes in angular momentum along the long axis of the car (ie. changes in rate of roll). I would perhaps naively assume that easing into a spiral from a tangent with the corresponding easing into changes in superelevation as well easing out of the spiral's increase in curvature to the constant curvature portion of the curve would reduce some of these dynamic effects. In flying terms, this would be equivalent to smoothly move the yoke or stick in changing the bank angle as opposed to a sudden movement of the yoke/stick.
Similar thing with straighline acceleration - a perfectly rigid body would not have any dynamic effects of "jerk", were as non-rigid body would show sigficant differences between a given acceleration applied instantly versus applied gradualy.
Fun to see a lot of interesting info in this thread.
One only need observe a Lego train to appreciate the spiral...
Or a model train running on snap-track.
I'll be interested to see the rules diningcar used in incrementing superelevation (which is also entry- and exit-spiraled) in his 570' curve spiral. My somewhat naive preference is to commence the superelevation after the car has settled into the spiral in yaw, and then have it fully relieved before the lateral spiral goes back to tangent. A major point of superelevation is to decrease overturning load on the low rail, so both speed and degree of curvature factor into how much is used -- this is different from 'passenger' use of superelevation which I'd expect to be coordinated with actual lateral angular acceleration in the spiral.
I shall try to remember; Santa Fe had a standard plan for spirals that was in a printed format which each Party Chief carried.
The curves were staked (in those days) every fifty feet as the 570 foot spiral was created and deflections for the transit operator were calculated to those points. The 570 spiral point was established from which a one degree curve was the established every fifty feet until the spiral at the other curve end was created back toward the (at least) five hundred feet to tangent.
Superelevation was calculated to coincide with the fifty foot centerline locations and was increased incrementally to the 3-1/2 max, which then continued until the reversing spiral was reached
OvermodMy somewhat naive preference is to commence the superelevation after the car has settled into the spiral in yaw
For a given speed, the amount of superelevation in a curve should be based on the radius of that curve. The tighter the curve, the greater the superelevation.
If the radius is infinite, no superelevation is needed. If the radius is "huge", very little is needed. If the radius is "sharp", much more is needed.
At any point in the easement for a curve, there is a particular radius. And there is an appropriate superelevation. It starts from zero, because of the (near) infinite initial curve radius, and increases as the radius gets tighter, reaching its maximum in the "true curve".
Thus, all changes in superelevation should happen in the easement of the curve.
If you're going to do something different, you better have a VERY good reason. Do you?
Ed
7j43kFor a given speed, the amount of superelevation in a curve should be based on the radius of that curve. The tighter the curve, the greater the superelevation. If the radius is infinite, no superelevation is needed. If the radius is "huge", very little is needed. If the radius is "sharp", much more is needed. At any point in the easement for a curve, there is a particular radius. And there is an appropriate superelevation. It starts from zero, because of the (near) infinite initial curve radius, and increases as the radius gets tighter, reaching its maximum in the "true curve". Thus, all changes in superelevation should happen in the easement of the curve. If you're going to do something different, you better have a VERY good reason. Do you? Ed
The intended speed that the curve is to be negotiated has a big effect on how much superelevation is necesary to be built into it - if the intended speed for a curve is 90 MPH then more is needed than if the intended speed for the same curve is 30 MPH.
Is the curve on a high speed passenger line or a slow speed maximum tonnage freight line? Different neighborhoods have differeing requirements.
Never too old to have a happy childhood!
BaltACDThe intended speed that the curve is to be negotiated has a big effect on how much superelevation is necesary to be built into it - if the intended speed for a curve is 90 MPH then more is needed than if the intended speed for the same curve is 30 MPH. Is the curve on a high speed passenger line or a slow speed maximum tonnage freight line? Different neighborhoods have differeing requirements.
Yes. That is why I started with "For a given speed..."
And if you're running both slow coal trains and fast passenger on the same track, there'll be some compromises involved.
In Earl J. Currie's books on the BN, he noted that they relaid track with less superelevation because they weren't running any more high-speed Zephyrs and such anymore. I believe he even attributed some derailments for the coal trains to excess superelevation.
CWI had a curve just south of 130th Street that was superelevated to handle Erie and Monon passenger trains. In 1969, an EL intermodal train had a bad slack run on the curve and several TTX flats toppled toward the inside of the curve. Surprisingly, none of the track was torn up. A similar incident occurred about a year later. Since the last passenger train (El "Lake Cities") had been discontinued, a track gang turned up a while later to reduce the superelevation.
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The wear on the lower rails created a need to transpose them with the higher rail which was easy before welded rail.
I have been gone too long (30 plus years) and Amtrak has replaced railway companies' passenger service so I cannot comment about today's issues.
BaltACD The intended speed that the curve is to be negotiated has a big effect on how much superelevation is necesary to be built into it - if the intended speed for a curve is 90 MPH then more is needed than if the intended speed for the same curve is 30 MPH. Is the curve on a high speed passenger line or a slow speed maximum tonnage freight line? Different neighborhoods have differeing requirements.
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The new fly-over near Truxton, AZ in an interesting example.
Before the rehab of the Adirondack Division over the past few years, we had a curve that was designed by NYC for probably 50 MPH. When I started, we were limited to 15 MPH on that section, and it caused us no end of problems with our HEP gensets, as the tilt was enough to effect the low oil sensors on the gensets.
While there's still some cant there, it's not as much.
Not to mention that it's not far from "Rule 98" territory for us (10 MPH), so even if the speed limit was 50 MPH, we'd just be working on getting up to speed or slowing for same. It does mean that NYC must have been really sailing coming in to Thendara station from the north...
The Truckton flyover was completed in the past year or two. My understanding is that its purpose is to allow eastward trains use of the lesser gradient toward the Yampai summit 26 miles away.
The original line was constructed in 1882 and a second track was built in the 1920's utilizing lesser gradient. The lesser gradient was sought, at this time, so that power could be assigned to heavy eastward trains that would then allow one less locomotive between Needles and Belen, 460 miles away.
There is perhaps more to this story, and my understanding may be flawed, but that's what I have now.
If an eastward train wants the lesser grade east from Truxton, they'll stick to right-hand running until past Seligman.
timzIf an eastward train wants the lesser grade east from Truxton, they'll stick to right-hand running until past Seligman.
The 'train' doesn't call the shots - the Train Dispatcher routes trains in accordance to how he wants to run 'his' railroad understanding the physical characteristics of his territory and the trains under his control.
Balt, not so on the double and triple track 725 (approx.) mile route through the mountainous BNSF line between Belen and Barstow. While the dispatcher has considerable discretion, he is also subject to operations management plans to minimize the power required. There are frequent 50 mph crossovers (and to my current knowledge) no sidings utilized. Lower priority trains may be held where crew change occurs.
Also,
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