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.
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.
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.
A quick google suggests rails are commonly bent in situ and there would be no particular reason that an easement would normally result. Rail lengths are much too short for this to be permitted. You cannot build a proper curve in a real railroad if each rail has an eased radius at both ends because it’s too hard to bend it to a smooth curve. You can’t build a smooth curve with rails that have easements at both ends.
Model railroad flex track won’t curve easily at each end of a piece but real rails are bent to fit the surveyed alignment.
It would be handy to have a flex track bender like the Aristo device.
Real railroads have access to tools and power needed to bend rail to the required radius.
So, yards wouldn’t need eased curves and it isn’t a necessary part of bending rail.
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.
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.
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.
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 choic
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?
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.
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.
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.