This now ancient conversation needs a sort of definitive tie-up. I'm going to go with the video posted by Euclid above, which I'll repost here:
https://www.youtube.com/watch?v=ZuR5QTlfOzk
It's at 4:33 that the narrator calls it a "Slip Diamond." I don't like the word "slip" confusing it with single or double slip switches, but I'll go with the name anyway until I hear better.
The problem is the usage of that word "slip." A slip implies that there is an alternate route, not just a crossing. If track AB crosses track YZ, it normally would have a diamond with 4 frogs, often with replaceable elements for repairing the wear encountered from thousands of wheels bumping over it at any speed. However a crossing with a slip, called a single slip switch, would still allow AB to cross YZ, but would provide for an alternate route, AZ. A DOUBLE Slip would allow not only the alternate route AZ, but another alternate route, YB.
The Slip Diamond Crossing sounds like it would have alternate routes, but it does not. If you're coming from point A, the only place you can go is point B, or get derailed. Likewise, from point Y you can only go to point Z. So the word 'slip' seems ambiguously applied here, and yet I have no other word for it.
Actually, I do. I'd consider calling it a movable point diamond crossing. It's not perfect, but it doesn't imply there are alternate routes, and it DOES describe exactly what's going on there. However, it appears that "point" is used outside of North America to refer to "frog," so a movable point becomes a movable frog. That muddies up our definition, so that may not work.
I guess we're stuck with "Slip Diamond Crossing" for now, but everyone who reads it will think "double slip switch." [or single] And we've certainly established that it's NOT THAT!
Enough for now. But I'm going to be looking for a better explanation of that thing for a long time to come.
Shooshie
CSSHEGEWISCHThe hammering that occurs from crossing the flangeway is no small matter and it can be felt from inside the train even at low speeds. The hammer blows also put a lot of stress on the casting that makes up the crossing frogs.
Spend a few hours near a diamond and you'll hear all the proof you need.
Like trying to sleep in a tent at Deshler...
For that matter, look at how often one sees the welders at work at Rochelle.
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Both routes through Grand Ave. were routes of the Hiawatha's. The Hiawatha trains moved pretty fast and I would imagine that train speeds through there were 30-40 mph at the time. They didn't waste time from the depot to Grand Ave.
Randy
The hammering that occurs from crossing the flangeway is no small matter and it can be felt from inside the train even at low speeds. The hammer blows also put a lot of stress on the casting that makes up the crossing frogs.
Curved crossings are not that unusual, especially in an interlocking such as at 21st Street, where the former Alton two-track main line diverges from the former PRR main, also double track.
I do not see why this type of crossing would be better for higher speeds. Crossings have no fundamental curvature that limits speed like switches do. Most crossings are located where straight tracks cross each other. I recall a Milwaukee Road crossing of the conventional four-frog design that allowed the passenger trains to go over it at 79 mph. There must have been lots of other examples. The photo of the mystery crossing posted by Shooshie does not appear to be on particularly fast track. The Milwaukee did run trains over 100 mph, but I doubt they ran that fast at the location in the photo. In any case, I do not see any advantage for a higher speed with this type of crossing.
It would eliminate bumping impact as wheels cross the flangeway of the other track. However it would only eliminate the bumping of two frogs while leaving the other two frogs to bump. Besides, I would roughly guess that at least 99% of crossings were the conventional four-frog diamonds where the bumping was deemed perfectly acceptable. Bumping does add maintenance cost, but so do switch points. So I cannot see why the reason for this crossing design would be the elimination of the gaps that cause bumping.
EuclidSo what is the point of this mystery crossing design?
I think that was mentioned early in the thread - to allow for higher speeds through the diamond.
Norm48327EuclidThe one great remaining mystery question is this: What is the purpose of this crossing design? Um, get to one track from another maybe? Think so?
EuclidThe one great remaining mystery question is this: What is the purpose of this crossing design?
It does not lead form one track to another. It only enables one track to cross another. Most of the time, that is accomplished with a so-called "diamond" crossing having four rigid frogs. That type of crossing is always open to passage from all four approach directions.
This mystery "slip diamond" crossing has two sets of movable points that must be lined for one track or the other. If a train enters it against being lined, it will act as a derail. It does eliminate the maintenace of two rigid frogs, but it adds the mainenance of movable points.
So what is the point of this mystery crossing design?
Euclid The one great remaining mystery question is this: What is the purpose of this crossing design?
The one great remaining mystery question is this: What is the purpose of this crossing design?
Um, get to one track from another maybe? Think so?
Norm
So far, we have distant photos, a highly detailed freeze frame in a video, highly detailed photos of a precision scale model, and a highly detailed engineering plan view. We also have a name for this type of crossing which is "Slip Diamond." It has two rigid frogs and four movable points. So it is clear how this crossing operates.
Excellent description and explanation.
Here is a modeling sequence for what certainly seems to be the type of switch in question in this thread. There are close-up shots that show it perfectly. On the second page, there is an engineering drawing that shows it perfectly. At the bottom of the first page, people question what the point of this crossing is. The author might be answering the question on the second page when he talks about what is allowed for crossing angles, but I am not sure.
http://model-railroad-hobbyist.com/node/7561
A good idea to separate this into three categories, or more.....
Hoping I'm swimming at the beach where the party rocks, "the reason for the design."
The "inside" will be the area, side, of the wye that the tracks surround, and the "outside" will be the track on the periphery. Very high traffic volume here. Double track joins with traffic that goes thru in both directions. That can be said for all wye legs.
All double track at this junction requires that each inside track cross or join its opposing inside track. If directional, a track for "East" and "West" would work, and joining, wouldn't be necessary but "crossing" would....so the track with the closed point crossing makes sense versus the battering conventional frogs take.
The tower controlling these joining moves: in Sacramento: on the San Joaquin, (Stockton) route and the Cal-P (virtually Oakland to everywhere East) was Elvas Tower.
This video seems to have found its way to me by Google association due to my writing about the topic of this thread. At exactly 4:33, it shows a still shot of what they call a “slip diamond.” This appears to be the same type of crossing as the one Shooshie has inquired about and posted the photos of. However, it does not explain the reason for the design:
Frogs in Curves vs. Curved Frogs
The curvature issue raises another question. Even with a switch on straight track, the diverging rail of the switch passing through the frog is curved. But is that curvature built into the frog itself? Or is the frog straight with curved rail merely adjoining each end of it? There would not be much curvature direction change in the short length of a frog if it were curved. It is a question I have never considered, but my guess is that the frog is straight even though set in a curved rail.
Perhaps in most switches, the rail adjoining the frog is actually straight as the curve of the turnout reverses to come back to parallel with the track with the switch. But in the photo you show, the curvature definitely continues through the frog. So is that frog itself actually built rigid with that curvature built in? Or is that frog straight?
I guess the same questions would apply to the crossing with the unusual switch. I can’t really tell if the curvature is built into the two frogs or not. But in any case, if they can run the curvature of the track through two frogs, why can’t they run it through two more?
Interestingly, if you ran into that switch when it was lined against you, it would not just split as normal with a trailing point move. Instead, it would act as a derail. And it would be quite a disruptive derail at that.
When I opened the piece I saw line drawings of interlocking types and not pictures and drawings of switches. In other words, each line depicted a track thus what was depicted was a double track railroad at a junction with one track crossing over another track with a switch or turnout to a diamond to the branch track. Discussion led to the idea that the diamond did not have to be, that a staggered turnout could be used instead which also afforded the idea of trains continuing in the direction of movement either to the branch or to the continuing second track. This further led to the talk of slip and double slip switches are are found usually in passenger terminals and in rapid transit (subways) interlockings. where the appliance can divert a train to two or more tracks from two or more tracks or be simply a diamond. My point is that the switches...slip and double slip switches are or can be part of the interlocking as presented in the first place but the interlocking as presented in the first place did not have to be slip or double slip switches. To confuse things even more was that the diagram first presented was for left hand running indicating that the situation as presented was English. If anyone unfamiliar with the different switches and uses I recommend a visit to NJT's Hoboken station where there are dozens viewable from the ends of the platforms. I wouldn't be surprised if such were also visible at some of the Boston and Chicago or other large commuter stations. NYP and GCT are difficult to see being underground and away from the platforms, same with the NYC Subways...LIRR's Jamaica station, both ends, has a good array, too. It is important to remember, too, that each interlocking, junctions, and yard is individually designed to accommodate the expected moves to be made.
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Euclid Considering that both tracks are curved, I am not sure if a rigid diamond could have been used. It seems like that would require curved frogs.
Considering that both tracks are curved, I am not sure if a rigid diamond could have been used. It seems like that would require curved frogs.
Your point is well-taken, but they wouldn't be the first curved frogs in the world, nor the first curved crossing. But this might have been the simpler solution over machining those curved frogs, which was my original point in calling it a "poor man's diamond crossing." It may simply have been easier to do it this way than to engineer and build the 50 foot curved diamond. Smoother, too.
Nevertheless, I've seen a lot of crossings on curves, and they didn't choose this method. Example:
I do not know the photographer's name, and once again I use this picture to further a discussion. Clearly, curved frogs pose no problem to the C&NW in 1953, four years after the other picture was taken. There's a curved crossing that uses a simple diamond with four frogs. In contrast, the one under Wisconsin Avenue Bridge in Milwaukee was essentially a double-slip switch without the "slip." That is, without the outer rails that would give it directional options.
Does anyone else find this intriguing? It's as if there must be a story behind it — probably a mundane one — but it's going to bug me until I know that story!
Henry,
The thread started with a description of a crossing and a photo that people could not see unless they were a subscriber to Trains. So that led to differing interpretations of what the OP described. At this point, it is 100% clear what the OP was describing based on the photos he posted on the previous page. The only questions now pertain to the reason for using such a crossing design and how common it was. This is a crossing that needs to be lined for the route and has two frogs and four movable points.
This thread is talking about at least three different things as if they are one! First, it started out with a situation involving interlocking styles followed by diamonds and types of switches inside an interlocking, and about slip and double slip switches. Get the three concepts separated because there is a lot of misconceptions and misinformation and confusion going on right now.
As I mentioned on the previous page, I assume that this design is necessitated or preferred due to the fact that both tracks in the crossing are curved. I don’t think it is based on a need for high speed.
It is a crossing that requires tending operation if trains do not stop, but so do lots of switches, and the presence of a tower indicates the ability to operate the crossing along with other switches there.
It appears that we're looking northward, toward the Michigan Upper Peninsula on the Milwaukee Road. The tracks curving to the left head to the Pacific Ocean. In the immediate few miles ahead lie some of Milwaukee's heavy industrial areas, so this certainly isn't high-speed in the northbound leg of the crossing.
Could the explanation be as simple as not wanting frogs at those middle-points of the diamond? When you consider what we're looking at, it's simply a crossing with about a 50 foot diamond. All points in the diamond could have been done with fixed frogs, but these two points they chose to do with movable rails. Thus, only one route over the crossing is physically possible to pass at any given moment. Attempt crossing from the non-aligned route, and you'll have a derailed train.
I don't literally think that the movable rails are stubs. They appear tapered the way all switch points are tapered for a smooth transition to the fixed rails. But if you think deeply about how those joints were engineered, you will perceive some tricky problems in designing and building an arrangement like that.
On the up side, it eliminates the bump of a long frog on both sides of the middle of the "diamond," but at the expense of greater mechanical complexity and the constant need for an operator in that tower to set the crossing properly.
I just haven't seen one of these before, and I was wondering if there is some story pertaining to this particular location. This view, by the way, is currently found at 43.038776, -87.967455. Or, by address,
Shooshie,
That is a very interesting track device detail. I am not sure how unique it is, but I have never seen a crossing like that before. As you say, it is actually two switches facing each other with no space between them. Each switch has its frog and two points. The frogs are not movable. I assume that the two switches are linked together, so when you line up for either direction of the crossing, both switches move simultaneously.
In the picture, the trailing points nearest the viewer are lined to the left, and the facing points are lined to the right. So the crossing is lined for the track coming out from under the gondola and curving to the left. When you "throw" the crossing, the near points move to the right, and the far points move to the left.
I assume that this design is necessitated or preferred due to the fact that both tracks in the crossing are curved. I don’t think it is based on a need for high speed.
From the photo, I cannot tell what the points look like. The gleam of the rails in the photo and the distance may just make them look like stub switches. Although as switches go, they turn out relatively sharply, so I am not sure how points might be configured to work there. A photo or plan detail of the points would be most interesting to see.
Is this switch owned by the CMSTP&P?
Shooshie Actually and to my surprise , wilkapedia has a good explanation. http://en.wikipedia.org/wiki/Switched_diamond#Switched_diamond Not a slip switch for there is no divergent route and as was stated slip switches are LOW speed devices rarely found outside of terminals. Randy That's not it. Notice that in the wikipedia diagram, only the frog area moves, that is, the inner X between two outer rails. This example on the Milwaukee looks like two switches, back to back. No frog. All movable points are on outer rails. There is no inner frog or diamond. At first glance, I thought it was a pair of opposing stub switches, and I wondered why anyone would ever design them such that you were having to line up TWO pair of movable stubs, rather than the usual pair. Then I noticed that there were no "slip" curves for the alternate routes. This was not a switch. It's a crossing without a frog/diamond. I hope that sheds some light on why I consider this a unique crossing.
Actually and to my surprise , wilkapedia has a good explanation. http://en.wikipedia.org/wiki/Switched_diamond#Switched_diamond Not a slip switch for there is no divergent route and as was stated slip switches are LOW speed devices rarely found outside of terminals. Randy
http://en.wikipedia.org/wiki/Switched_diamond#Switched_diamond
Not a slip switch for there is no divergent route and as was stated slip switches are LOW speed devices rarely found outside of terminals.
That's not it. Notice that in the wikipedia diagram, only the frog area moves, that is, the inner X between two outer rails. This example on the Milwaukee looks like two switches, back to back. No frog. All movable points are on outer rails. There is no inner frog or diamond.
At first glance, I thought it was a pair of opposing stub switches, and I wondered why anyone would ever design them such that you were having to line up TWO pair of movable stubs, rather than the usual pair.
Then I noticed that there were no "slip" curves for the alternate routes. This was not a switch.
It's a crossing without a frog/diamond.
I hope that sheds some light on why I consider this a unique crossing.
Just behind the tender of the steam locomotive is the Tower that controls this interlocking and provides the 24 hour supervision of it's operation. A signal maintainer would normally be stationed at the tower to perform all the required maintenance operations on a daylight Monday-Friday basis and being subject to call for any repairs required after those hours.
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DwightBranch, the purpose of the "guard" rails at a switch frog is more aptly put in the word "guide" rails. The frog theoretically allows an opening for a wheel flange to go a different way. The guide rail prevents that from happening by holding the other wheel as close to its designated path as possible. Of course, it would require a sudden lateral force for the flange ever to go the wrong way, but no doubt it happened.
The movable frog closes that gap, eliminating the need for the guide rails. This (the top photo) is truly a high-speed switch.
No, it's not a slip switch of any sort.
It doesn't have a movable frog. Ahhh!!! I just figured out how to insert photos in this forum. Sorry for not figuring out that it's just a matter of using the [ img ] and [ /img ] tags.
Anyway, you can see here that this is an unusual kind of crossing. Maybe high speed, but it sure doesn't look it. Looks to me that someone decided to delay the construction of a diamond, then forgot about it. It would have a pretty long frog/diamond length due to the shallow angles between the tracks, but that shouldn't be a problem. That's why it mystifies me. Why'd they make it this way? Or why'd they leave it this way?
For now, the best candidate seems to be the fast-crossing explanation. It would eliminate the diamond and the corresponding bump that invariably goes with diamonds. But it requires someone on duty 24/7 to be sure it's set right. I guess that's normal on railroads, anyway.
I'll bet some of you know the real story of this particular location. Tell us all, if you do!
I hope that Kalmbach will forgive me, but for the sake of all those who cannot access the picture, I've copied it and put it in my dropbox so that we can have this conversation:
https://dl.dropboxusercontent.com/u/75122252/MilwaukeePoorMansCrossing.jpg
It's been so long that I don't remember how to turn that into a link using HTML, so forgive me also that you have to copy the URL physically, and paste it into your browser. Seems that we all have to be members, anyway, right? So it shouldn't be a problem for us to see this switch and talk about it.
This isn't a double-slip switch. I'd never have asked about such a thing. This looks like two back-to-back stub switches, until you realize that there are no alternate routes. You can only go straight through on the route on which you're approaching. BUT... the other points... er... stubs... have to be lined up or you'll go flying off into oblivion, taking the approaching trackwork with you.
So, some say it's a high-speed crossing. That's believable, but that doesn't look like a high-speed area. Were it in a cornfield in Iowa, yes, but not under a bridge in industrial Milwaukee. Still, it may be the truth. The westbound line (curve to the left) could be a high-speed route.
Sorry to be just now returning to the conversation, but I've been too busy for the past few days.
Thanks,
BaltACD Moveable point frog Standard Frog
Moveable point frog
Standard Frog
The one I saw on BNSF was a bit different, but the point was like that. I notice in the photo of the movable point frog there aren't any guard rails on the outside rails, they seem to be part of the frog. The one I saw actually had guard rails like the bottom photo, elaborate things with narrow guard rails, unlike normal frogs which usually have guard rails made from normal rails bent to shape.
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