I know that most mainline curves were eased. I am wondering how far that concept extended into yard trackage.
In particular, I am wondering if it would have been applied to a wye used to turn passenger cars. I know that prototype passenger cars could generally take a 48" curve equivalent. But I'm wondering if that 48" was eased or not.
I think it's fine to have opinions, but what I'm after is info from someone who KNOWS.
There used to be a guy who lived across the street who would have known. Sadly, he's "gone". Nice guy, and missed.
Anyway, if there's a railroad guy here who DOES know, I'd appreciate the sharing.
Thanks,
Ed
do you understand the purpose of easement leading to curves?
greg - Philadelphia & Reading / Reading
Several sources of prototype information I have suggest that almost all railroad curves are layed out as parabolic segments, not as constant curves.
The smaller the change in direction, the more likely the curve will never actually reach a constant radius situation. Think of them as two easements back to back, or a segment out of the small radius end of an elipse.
The NMRA data sheets have drawings and formulas for laying out such a curve.
I can't post any supporting documents right now, not home and all my documents on this are in those silly old fashioned things called books.
Sheldon
gregc do you understand the purpose of easement leading to curves?
I believe I do. And I think "purpose" should be plural.
7j43kI believe I do.
then you undetrstand that there's no need for any in a yard
gregc 7j43k I believe I do. then you undetrstand that there's no need for any in a yard
7j43k I believe I do.
No, I do not understand that.
Easements and super elevation are used on mainline tracks to ease trains into and through curves at speed. Yard limits restrict train speed to very low speeds and neither one is of any advantage at slow speed.
Rails, by their very nature, will have a natural eased length on either side of any curve. It would take a determined road crew to craft an uneased, Bachman EZ-Track 18" radius-type, un-eased curve. Why they would bother is beyond me, in-yard or outside of one.
ndbprr Easements and super elevation are used on mainline tracks to ease trains into and through curves at speed. Yard limits restrict train speed to very low speeds and neither one is of any advantage at slow speed.
I disagree. An eased curve at very slow speeds will create less offset between cars, and lesser sideways forces. That may or may not be something that is desired in any particular place. Hence my question.
I do agree about superelevation. In fact, superelevation is more problematic the slower a train is going.
7j43k ndbprr Easements and super elevation are used on mainline tracks to ease trains into and through curves at speed. Yard limits restrict train speed to very low speeds and neither one is of any advantage at slow speed. I disagree. An eased curve at very slow speeds will create less offset between cars, and lesser sideways forces. That may or may not be something that is desired in any particular place. Hence my question. I do agree about superelevation. In fact, superelevation is more problematic the slower a train is going. Ed
Ed, you are correct.
Despite what Mike thinks, civil engineers and the crews they direct have no trouble putting rail exactly where they want them.
As I explained, almost all curves on the prototype are spiral in design and nature, even slow speed trackage for reason you suggest.
So, I think I'm done here because I will not debate Greg or Mike.....
CALTRAIN DESIGN CRITERIA CHAPTER 2 - TRACK SEPTEMBER 30, 2011 2-11 3.0 HORIZONTAL ALIGNMENT The horizontal alignment of track consists of a series of tangents joined to circular curves and spiral transition curves as measured along the center line of track. Track superelevation in curves is used to maximize train operating speeds wherever practicable. In yards and other non-revenue tracks, spiral transition curves are rarely required.
CHAPTER 2 - TRACK
SEPTEMBER 30, 2011 2-11
3.0 HORIZONTAL ALIGNMENT
The horizontal alignment of track consists of a series of tangents joined to circular curves and spiral transition curves as measured along the center line of track. Track superelevation in curves is used to maximize train operating speeds wherever practicable. In yards and other non-revenue tracks, spiral transition curves are rarely required.
While about transit track specifically this article notes that turnouts/switches/points can be and are made with either a circular or an eased curve in the diverging side, https://www.masstransitmag.com/rail/article/10770680/rail-switch-design-for-optimum-performance
And as with a number of things in railroading the answer to "what is the best thing to do?" is, "It depends."
Summary The parametric studies identified design features that contribute to the good performance of early 1900s vintage transit switches. A comparison was made to an AREMA-style nontangential, circular curve alignment turnout. The study showed that the SEPTA switch turnout is predicted to outperform the replacement switches significantly for the range of operations used (i.e., 5 to 15 mph). Key factors in the better performance were the tangential switch entry and the spiral alignment. Other features, such as a cast AMS switch point, do not improve performance over modern rail steels. The particular circumstances of the line operations will affect the results of any such study. Key operating parameters include the desired operating speed, the percentage of diverging traffic and the length of the vehicles.
The parametric studies identified design features that contribute to the good performance of early 1900s vintage transit switches. A comparison was made to an AREMA-style nontangential, circular curve alignment turnout. The study showed that the SEPTA switch turnout is predicted to outperform the replacement switches significantly for the range of operations used (i.e., 5 to 15 mph).
Key factors in the better performance were the tangential switch entry and the spiral alignment. Other features, such as a cast AMS switch point, do not improve performance over modern rail steels. The particular circumstances of the line operations will affect the results of any such study. Key operating parameters include the desired operating speed, the percentage of diverging traffic and the length of the vehicles.
KitbashOn30's response would apply to mainline track.
The OP specifically asked about yard trackage. I posted the link below in another thread related to yard track centerline spacing. It's the FRA Yard Design Manual.
https://rosap.ntl.bts.gov/view/dot/32572/dot_32572_DS1.pdf?
There are numerous references through the document related to horizontal curves. All references are for simple circular curves - no spirals (correct term for easement). Based on this document I would conclude that curves in yard tracks generally do not have easemeets. As with everything, there may be exceptions.
Ray
KitbashOn30 CALTRAIN DESIGN CRITERIA CHAPTER 2 - TRACK SEPTEMBER 30, 2011 2-11 3.0 HORIZONTAL ALIGNMENT The horizontal alignment of track consists of a series of tangents joined to circular curves and spiral transition curves as measured along the center line of track. Track superelevation in curves is used to maximize train operating speeds wherever practicable. In yards and other non-revenue tracks, spiral transition curves are rarely required. Sourced: https://www.caltrain.com/assets/_engineering/engineering-standards-2/criteria/CHAPTER2.pdf
Sourced: https://www.caltrain.com/assets/_engineering/engineering-standards-2/criteria/CHAPTER2.pdf
Not required by one particular modern mass transit system and never used in the history of the industry are two dfferent things. It woud be interesting to know what their minimum curve is.....
Each railroad, in the long history of railroading this country, has set most of their own standards, and as such there are bound to be various approaches, depending on railroad, time in history, and situation.
Agreed, small changes in direction on slow speed trackage are generally not "over engineered" in terms of radius or easement. A wye to turn whole trains or passenger cars, or large locos would be a different sitiuation. A substantial change in direction, even on slow speed trackage may very well be eased BECAUSE it involves the sharpest practial radius for the equipment in question.
Easements, separate from superelevation are about coupler aligment and side "jolt" entering curves.
Radius, amount of change in direction, types of equipment, would all effect the choices made in laying out trackage, even in a yard.
But connecting two tangent tracks with parabolic curves is standard railroad engineering practice, as is similar practice with highways.
Colorado Ray KitbashOn30's response would apply to mainline track. The OP specifically asked about yard trackage. I posted the link below in another thread related to yard track centerline spacing. It's the FRA Yard Design Manual. https://rosap.ntl.bts.gov/view/dot/32572/dot_32572_DS1.pdf? There are numerous references through the document related to horizontal curves. All references are for simple circular curves - no spirals (correct term for easement). Based on this document I would conclude that curves in yard tracks generally do not have easemeets. As with everything, there may be exceptions. Ray
The way I read most of that, they are refering to small changes in direction within yard ladders and such, which I agree, would not be complex in their layout and engineering.
But the OP specificly asked about a wye for turning passenger cars? I have to think, based on what I have read, there is a high likelyhood that trackage of that nature, would be built with spiral easements or as a complete parabolic curve to get the best preformance in the smallest space.
It seems to me, a lot of these responses did not take into consideration the WHOLE question asked by the OP?
But I could be wrong.....
Sheldon, the standard practice of connecting two tangents with parabolic curves would not have to apply to yards and industrial trackage. Several years ago I designed an industrial spur to serve an acid unload facility I was designing off of Union Pacific's mainline across northern Nevada. Following the UP's guide for industrial trackage, I used simple curves.
As an interesting aside related to your highway reference, I recall one state where they don't use spirals and all curves are simple or compound curves. I believe it might be Washington state. Driving on their roads was definitely different.
Thanks to all for your thoughts and data.
Indeed, the prompting for my question was for turning passenger cars. Passenger cars have diaphragms, and a whole lot of other "stuff" that MAY not be thrilled with suddenly being asked to go sideways a foot.
It seems to me that the closer you get to true minimum radius, the more useful easements are (in the slow-speed sense).
I can SEE how much an easement lessens offset when I compare my passenger cars going through a 48"/tangent to a 60"/long easement--NIGHT AND DAY!
I know mainline curves are "always" eased, but I got to wondering about the "other" trackage.
So I thought I'd ask how the big guys do it.
Colorado RayKitbashOn30's response would apply to mainline track.
Even where Caltrains says that? ... " In yards and other non-revenue tracks, spiral transition curves are rarely required."
Colorado Ray Sheldon, the standard practice of connecting two tangents with parabolic curves would not have to apply to yards and industrial trackage. Several years ago I designed an industrial spur to serve an acid unload facility I was designing off of Union Pacific's mainline across northern Nevada. Following the UP's guide for industrial trackage, I used simple curves. As an interesting aside related to your highway reference, I recall one state where they don't use spirals and all curves are simple or compound curves. I believe it might be Washington state. Driving on their roads was definitely different. Ray
Ray, I understand.
A few thoughts.
I agree that freight trackage, especially modern industrial trackage, would see little benefit from easements.
Being someone who models a time period 68 years ago, I always think more historically rather than only considering current/recent prototype practice.
70-80 years ago, railroads where still operating steam, and a lot more passenger equipment.
Much of that passenger equipment still had six wheel trucks and hard sprung diaphragms.
A great many of the switchers working yards were 0-8-0's, some of which were converted from mainline 2-8-0's, so they had slightly larger drivers.
All of this equipment reacts differently to curves than modern diesels and lightweight passenger cars on four wheel trucks with rubber tube diaphragms, or especially modern freight cars with their long coupler shank cushioned draft gear.
Here in the Baltimore region wye's are everywhere, and mainline or part of the verious industrial belt lines, their arial views generally give the impression of parabolic curves.
And of course many of these are routes that have generally been in use for 100 years or more.
I understand trackage get redone, and things change, so it is hard to say for sure exactly what was done in every case.
I think there are no absolutes here, but in my study of historical railroading there is good evidence to suggest most larger changes in direction were/are eased.
why would there be passengers on passenger cars being turned? aren't those cars turned only at some final destination for the car?
gregc why would there be passengers on passenger cars being turned? aren't those cars turned only at some final destination for the car?
Back in the day, a great many stub end passenger terminals existed, and arriving passenger trains were in many cases backed around wyes and into the terminal.
This allowed locos and head end equipment to uncouple and head to engine terminals, post offices and railway express loading docks while passengers disembarked and boarded.
In other cases, newly boaded passengers were backed around wyes for trains to head in the desired direction after pulling out of stations.
Passengers were backed up around what is effectively yard trackage wyes all the time back in the heyday of passenger service.
B&O's Camden Station in Baltimore was just one of many such stations.
And in old eastern cities, space for this trackage was often tight.
ATLANTIC CENTRALBack in the day, a great many stub end passenger terminals existed, and arriving passenger trains were in many cases backed around wyes and into the terminal.
i'm not questioning whether passenger cars or whole trains need to be reversed,
i'm questioning whether they are reversed with passengers on board?
So, while it has changed a lot since the days when it was a major passenger terminal, the Camden Station wye still exists. Looking at it on Goggle maps it is a wye with one side completely straight and has nearly equal curves on the other two sides. The radius appears to be about a 400', or a 14 degree curve in railroad terms, pretty sharp, about 56" radius in HO.
And it is clear in the aerial photo that both curves are eased.
gregc ATLANTIC CENTRAL Back in the day, a great many stub end passenger terminals existed, and arriving passenger trains were in many cases backed around wyes and into the terminal. i'm not questioning whether passenger cars or whole trains need to be reversed, i'm questioning whether they are reversed with passengers on board?
ATLANTIC CENTRAL Back in the day, a great many stub end passenger terminals existed, and arriving passenger trains were in many cases backed around wyes and into the terminal.
In the case of terminals like the one I just described, there is no other way to get the people to the platforms? Is that so hard to understand?
And there were lots of passenger terminals like this.
gregci'm not questioning whether passenger cars or whole trains need to be reversed, i'm questioning whether they are reversed with passengers on board? Add Quote to your Post
If the passenger terminal is on the tail of a wye, then no train, inbound or outbound gets into the station without transiting a wye. St Louis Union station as an example.
Dave H. Painted side goes up. My website : wnbranch.com
Greg, so do your own research, find out I'm right, because I'm not going to argue or spend time looking up the proof for you.
If a PRR train leasve New York with 500 people on board going to St Louis and the the St Louis station is build on the tail of a wye, then the ONLY way to get to the station is to go around a wye leg. So yes, the train has passengers on it.
In San Diego trains arriving on the ATSF went to the depot. When they departed the train was backed out of the station to a wye, shoved around the wye, and then departed towards Los Angeles. The trains had passengers on them.
Thank you Dave....
Colorado Ray wrote
"As an interesting aside related to your highway reference, I recall one state where they don't use spirals except when the lane width is less than 12ft and all curves are simple or compound curves. I believe it might be Washington state. Driving on their roads was definitely different."
California Department of Transportation (CALTRANS) generally does not use spirials easements and recomends against using compoind curves.. The thinking is that easements add unnessarycomplication in design, layout and construction. The lanes are wide enough that drivers will naturally ease the curves and still stay within them.
"203.5 Compound Curves Compound curves should be avoided because drivers who have adjusted to the first curve could over drive the second curve if the second curve has a smaller radius than the first. Exceptions can occur in mountainous terrain or other situations where use of a simple curve would result in excessive cost. Where compound curves are necessary, the shorter radius should be at least two-thirds the longer radius when the shorter radius is 1,000 feet or less. On one-way roads, the larger radius should follow the smaller radius. The total arc length of a compound curve should be not less than 500 feet.
203.6 Reversing Curves When horizontal curves reverse direction the connecting tangents should be long enough to accommodate the standard superelevation runoffs given on Figure 202.5A. If this is not possible, the 6 percent per 100 feet rate of change should govern (see Index 202.5(3)). When feasible, a minimum of 400 feet of tangent should be considered.
203.7 Broken Back Curves A broken back curve consists of two curves in the same direction joined by a short tangent. Broken back curves are unsightly and undesirable.
203.8 Spiral Transition Spiral transitions are used to transition from a tangent alignment to a circular curve and between circular curves of unequal radius. Spiral transitions may be used whenever the traffic lane width is less than 12 feet, the posted speed is greater than 45 miles per hour, and the superelevation rate exceeds 8 percent. The length of spiral should be the same as the Superelevation Runoff Length shown in Figure 202.5A. In the typical design, full superelevation occurs where the spiral curve meets the circular curve, with crown runoff being handled per Figure 202.5A. For a general discussion of spiral transitions see AASHTO A Policy on the Geometric Design of Streets and Highways. When used, spirals transitions should conform to the Clothoid definition. "
https://dot.ca.gov/-/media/dot-media/programs/design/documents/chp0200-a11y.pdf
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
The PRSL had reverse loops at Cold Springs Harbor south of Wildwood Crest but no passengers. The Toltec and Cumbres has a loop in Antonito Colorado that is used after the passengers detain but the Durango and Silverton backs around the wye in Silverton before letting people off and stops on the leg so people are closer to town