Atlas Model Railroad Co. - The Dreadful " S " Curve
Atlas Model Railroad Co.
Username:
Password:
Save Password


Register
Forgot Password?
  Atlas Model Home   Forums   Events Calendar   Rules   FAQ  
Active Topics | Members | Online Users | Forum Archive | Basic Forum (Mac / Netscape Users) | Search | Statistics
[ Active Members: 0 | Anonymous Members: 0 | Guests: 28 ]  [ Total: 28 ]  [ Newest Member: jjbern ]
 All Forums
 Atlas Model Railroad Forums
 HO Scale Model Railroad Forum
 The Dreadful " S " Curve
Next Page
 Forum Locked |   Topic Locked |   Printer Friendly
Author Previous Topic: Why are Branchline freight cars such a crap shoot? Topic Next Topic: 2009 Springfield Show
Page: of 2

High Ball

Posted - 2008 December 23 :  11:34:00 AM  Show Profile
Hello;

I've got a boxcar full of How To HOMRR books. I've often read about the dreadful S curve and reasons why it should be avoided. But all the reasons have escaped me because I was certain not to ever be in that position. Well, it looks like I am. And now that I need to know why, I cant find the books I need.

The situation is I forgot to add a second crossover from the main to the sub main. I've got one going off but forgot the one going back on. I have two choices. One, tear up quite a bit of track. Move it out 3/8". Install an " X " crossover, 2 RHTO and 2LHTO. Or, tear up only a little bit of track. Install 2 RH #6 TO for a crossover that would have the train coming out onto the start of a 28"R curve. Or have it coming off the 28"R, going through the crossover and out onto a straight main.

I'm thinking that if the train is operated at prototypical speed going through the crossover there should be no problem.

I've looked an many track plans in MRR and see this situation appearing often. thanks.
nicholas

Country: USA | Posts: 688

graftonterminalrr

Posted - 2008 December 23 :  11:57:16 AM  Show Profile  Visit graftonterminalrr's Homepage
Okay, simple reason for why you want to avoid an S curve.

It is because you want to keep the train on the track through the curve. Couplers are ideally suited for operation when they are at track centerline. We give movement allowances to the couplers so that they can stay coupled around a curve, but the problem with the S curve is that you are combining curves in two directions and it's often not possible to allow sufficient coupler movement to keep cars on the track and coupled.

Push a car through an S curve. The end of the car will swing from one direction to the other rapidly at the point where the track pieces join. If you have another car coupled to the first car, this movement will cause a derailment.


Owner/Operator of the Grafton Terminal Railway, set in the 1978-1984 period

Country: Canada | Posts: 871 Go to Top of Page

charlief

Posted - 2008 December 23 :  12:12:19 PM  Show Profile
Somewhere I read that the problems associated with S curves can be eliminated if you put a short straight section in the middle between the two opposite curves. Ideally the straight section should be as long as your longest car.

As to the turnouts, I have used curved turnouts very frequently due to limited space. I have found there isn't the jerking about with them as there is with regular turnoouts.



Country: USA | Posts: 762 Go to Top of Page

CP9125

Posted - 2008 December 23 :  12:24:19 PM  Show Profile
We have 2 or 3 S Curves on our layout and we have no problem hauling 100 car freights at Scale Speed (Usually around 35MPH). We bumped up the outsides edges a bit, not that its super elevated by just helps it lean a bit.


Country: | Posts: 39 Go to Top of Page

cp6027

Posted - 2008 December 23 :  12:32:59 PM  Show Profile
Many S-curves cannot be avoided and they are everywhere on layouts and the prototype. Any crossover, the typical yard ladder or typical parallel industry siding is an S-curve, so issuing a blanket statement never to have them is a bit misleading.

As the poster above suggested, leaving a short tangent between the two curves mitigates the effects of the S-curve. On the prototype, the minimum tangent distance varies between 100 and 500 feet depending on the design/operating speed of the track. We don't have that much space on our layouts, so aiming for a tangent a bit longer than the length of the longest car or locomotive should alleviate most problems with an S-curve, probably around 70 to 100 scale feet (9 to 12 inches) depending on your era and exact equipment. The somewhat broad 28" radius on the curve will also help to lessen the severity of the S-curve.

Another option, depending on exactly how the track is configured, would be to run the 28" radius curve into a LH #6 turnout with the through route of this turnout leading into the diverging side of a RH #6 to complete the crossover move. This would save the 9-12 inches of tangent required in the scenario above and eliminate any S-curves. However, it would have one of the main tracks normally operating through the diverging route of the turnout. This is usually frowned upon at most locations, but can be prototypical in a larger interlocking with multiple crossovers, particularly near a yard where operating speeds are lower.

Both of these options are more prototypical than the "double crossover with diamond" that is rarely found on the prototype with the exception of transit systems and some major passenger terminal trackage. It does, however, save a lot of space on a layout.



Edited by - cp6027 on 2008 December 23 12:34:52 PM

Country: USA | Posts: 459 Go to Top of Page

detroitterminal

Posted - 2008 December 23 :  1:45:47 PM  Show Profile
I believe two "double crossover with diamonds" existed (They may still be in operation) in the Great Lakes area. One example is in Toledo, Ohio at C&O coal docks (Presque Isle?)and the other I believe is in the Grand Rapids, Michigan area (CSX's Wyoming yard?).


Country: USA | Posts: 204 Go to Top of Page

Brakie

Posted - 2008 December 23 :  3:49:36 PM  Show Profile
"Many S-curves cannot be avoided and they are everywhere on layouts and the prototype. Any crossover, the typical yard ladder or typical parallel industry siding is an S-curve, so issuing a blanket statement never to have them is a bit misleading."
-------------------
Exactly! This is why one should take any thing the layout "experts" say with a grain of salt.

The BEST solution is to use a straight section as long as possible between the curves and with crossovers-slow speed restrictions just like the prototype.
-------------------
Both of these options are more prototypical than the "double crossover with diamond" that is rarely found on the prototype
-------------------

I have no idea who the "expert" was that started that myth.
There are many examples of the prototype using these where needed.



Larry
Summerset Ry.

Country: USA | Posts: 7537 Go to Top of Page

cp6027

Posted - 2008 December 23 :  4:32:13 PM  Show Profile
quote:
Originally posted by Brakie


-------------------
Both of these options are more prototypical than the "double crossover with diamond" that is rarely found on the prototype
-------------------

I have no idea who the "expert" was that started that myth.
There are many examples of the prototype using these where needed.




Droege was probably that expert.

Yes, double crossovers with a diamond (aka universal with diamond), movable point crossings, lap switches, slip switches, crossovers in curves etc all exist somewhere but I still maintain they are rare. These non-standard items are only used where, due to numerous constraints, there is no possible way to configure the tracks otherwise. The two examples cited are in terminal and yard areas where such constraints are more likely. These items do save space but at the cost of increased maintenance compared to an equivalent layout of standard track components, especially when introducing a diamong that is not needed if the universal crossovers are spaced apart. Not that maintenance cost matters in our scale world!

It is just my opinion (and I'm probably a bit more picky about it since I make my living designing prototype track arrangments) but when somebody drops one into the middle of their double track mainline for no particular reason it just seems toy-like to me.



Country: USA | Posts: 459 Go to Top of Page

jrbernier

Posted - 2008 December 23 :  4:35:55 PM  Show Profile
Nick,

You will get a 'sort of' S-Curve with a crosssover. If you are using #4 turnouts - there could very well be an issue. They 'key' is the amount of straight trackage from the tip of the frog to the other frog facing it. It should be about 1 car length. That is why many folks suggest using at least a pair of #6 turnouts for a crossover. Also, if you are going through a RH curve, the crossover you encounter at the end of the curve should be a RH as well - It keeps the 'flow' moving in the same direction. A survey of most prototypes will bear this out(and yes, there are exceptions).

Jim


Modeling the Milwaukee Road in SW Wisconsin - In the 50's!

Country: USA | Posts: 931 Go to Top of Page

umtrr-author

Posted - 2008 December 23 :  5:02:09 PM  Show Profile  Visit umtrr-author's Homepage
quote:
Originally posted by cp6027

(snip)

Another option, depending on exactly how the track is configured, would be to run the 28" radius curve into a LH #6 turnout with the through route of this turnout leading into the diverging side of a RH #6 to complete the crossover move. This would save the 9-12 inches of tangent required in the scenario above and eliminate any S-curves. However, it would have one of the main tracks normally operating through the diverging route of the turnout.



This is what I was thinking as well. There are track plans I've seen that have this arrangement.

quote:

This is usually frowned upon at most locations, but can be prototypical in a larger interlocking with multiple crossovers, particularly near a yard where operating speeds are lower.



True in terms of the prototype, but there are often so many compromises on model pikes that this one doesn't seem too bad, particularly versus the double crossover with diamond as you noted.

At some point Rule #1 has to be applied.


UMTRR, A1G, W&NY and more...
http://www.irwinsjournal.com

Country: | Posts: 2164 Go to Top of Page

Luther Brefo

Posted - 2008 December 23 :  5:44:04 PM  Show Profile  Visit Luther Brefo's Homepage
S curves are everywhere on the real railroads though less common on passenger only routes and much less dramatic as they are on many model railroads. Sometimes it is easier to use superelevation and flange lubrication to move equipment through curves than it would be to fill and stabilize an alternative route. The wieght of the prototype equipment also reduces the potential for cars to pull off the track due to coupler overswing. It can be an issue on the real railroads but trackwork on the prototype is designed to suit the situation. There is no blanket solution just as there is no one size fits all solution on model railroads. These areas on the real railroads also have restrictions when it comes to operating practices. If you are into prototypical operations, you may consider adopting a simplified form of these rules for your model railroad.

Luther Brefo
www.lalrailfan.net

Country: USA | Posts: 1362 Go to Top of Page

OkieBob

Posted - 2008 December 23 :  8:42:07 PM  Show Profile
straight section in the middle between the two opposite curves must be as long as the longest car you are going to run.

O.T.S.F.

Country: | Posts: 173 Go to Top of Page

midwestrailroader

Posted - 2008 December 23 :  9:04:28 PM  Show Profile
quote:
Originally posted by detroitterminal

I believe two "double crossover with diamonds" existed (They may still be in operation) in the Great Lakes area. One example is in Toledo, Ohio at C&O coal docks (Presque Isle?)and the other I believe is in the Grand Rapids, Michigan area (CSX's Wyoming yard?).



http://upload.wikimedia.org/wikipedia/en/d/d6/Ttc-keele-crossing.jpg

http://www.trainsarefun.com/lirr/bayridge/crossover.jpg

http://www.dpanda.us/project/23a.jpg



Salt

Edited by - midwestrailroader on 2008 December 23 9:13:39 PM

Country: USA | Posts: 623 Go to Top of Page

John Mock

Posted - 2008 December 24 :  01:15:07 AM  Show Profile
quote:
Originally posted by cp6027

quote:
Originally posted by Brakie


-------------------
Both of these options are more prototypical than the "double crossover with diamond" that is rarely found on the prototype
-------------------

I have no idea who the "expert" was that started that myth.
There are many examples of the prototype using these where needed.




Droege was probably that expert.

Yes, double crossovers with a diamond (aka universal with diamond), movable point crossings, lap switches, slip switches, crossovers in curves etc all exist somewhere but I still maintain they are rare. These non-standard items are only used where, due to numerous constraints, there is no possible way to configure the tracks otherwise. The two examples cited are in terminal and yard areas where such constraints are more likely. These items do save space but at the cost of increased maintenance compared to an equivalent layout of standard track components, especially when introducing a diamong that is not needed if the universal crossovers are spaced apart. Not that maintenance cost matters in our scale world!

It is just my opinion (and I'm probably a bit more picky about it since I make my living designing prototype track arrangments) but when somebody drops one into the middle of their double track mainline for no particular reason it just seems toy-like to me.



Just to add on a bit to CP6027's excellent response: It is also very possible to design yard ladder tracks without S-curves, and the track plan books by Armstrong illustrate how to do it with commercially available turnouts.

Regarding special trackwork on the prototype: double slip switches were only very rarely used outside yard limits. The only known mainline location (according to a Morning Sun Books author) was on the Erie at Leavittsburg, Ohio, at/near a junction with the B&O where a single track crossed a double track main. A friend of mine and I drove out there in the 1990's and were able to see where the turnouts had been, but he forgot his book had said the double slip switches had been removed in the late '70's. Oops!

John



Edited by - John Mock on 2008 December 24 01:17:47 AM

Country: USA | Posts: 1480 Go to Top of Page

Beavis

Posted - 2008 December 24 :  09:38:03 AM  Show Profile
I completely agree with cp6027's assessment-while we can all name a few points where goofy track arrangements like these were used, they're pretty rare, and avoided if possible. However, I can think of these just off the top of my head:
Marion, Ohio-two double crossovers with diamonds, along with a mainline double slip (all gone),
Alliance, Ohio-double crossover with diamond in the plant between mains at CP Tower (all gone),
Pittsburgh, Pa.(Pennsylvania Avenue Interlocking)-double crossovers with diamond, between mains Two and Three (gone),
Union City Ohio/Indiana-single slip on main #1 (removed around 1968),
Terre Haute, Indiana-Haley Tower-single slip on main #2(unsure if it is removed),
Toledo, Ohio-Swan Creek interlocking (CP 289), single slip on Main #1, still in service

The Pennsylvania had a few mainline double slips in the electrified zone East of Harrisburg prior to the mid fifties, as well.

Still, I see a lot of these type switches used on model railroads, and while interesting, really don't need to be necessary, and do look pretty toylike. I think just the fact we can name spots where they were on the prototype goes to show how rare they really are. Three way switches are another example of a rare switch used a lot on model railroads.



Edited by - Beavis on 2008 December 24 09:41:08 AM

Country: | Posts: 131 Go to Top of Page

Brakie

Posted - 2008 December 24 :  09:46:19 AM  Show Profile
John said:The only known mainline location (according to a Morning Sun Books author) was on the Erie at Leavittsburg, Ohio, at/near a junction with the B&O where a single track crossed a double track main.
--------------------------
John,That's a mighty wide paint brush that the author of that book use since it leaves out every other railroad in the US.Such a blanket statement should be taken lightly and held to Erie's trackage.

Of course a lot of the old track has disappeared through mergers.I am sure some of those long abandon track contained double crossovers.


Larry
Summerset Ry.

Country: USA | Posts: 7537 Go to Top of Page
Page: of 2 Previous Topic: Why are Branchline freight cars such a crap shoot? Topic Next Topic: 2009 Springfield Show  
 Forum Locked |   Topic Locked |   Printer Friendly
Next Page
Jump To:
Atlas Model Railroad Co. © 1709-2011 Atlas Models Go To Top Of Page
This page was generated in 1.48 seconds. Powered By: Snitz Forums 2000