# Are Transition Curves necessary?



## drooniem (Jul 24, 2013)

Hi all,
Reading a lot about transitions curves and have a few questions. Are they prototypical? Are they necessary on model layouts. If so, why? Would they be recommended on all radius curves? I understand the concept and the how, but am fuzzy on the why. I'm guessing they might help reduce derails.
Second question: What exactly are single slip and double slip turnouts? I understand why they are used, but not how they work or how they are installed. I'm a bit of a newby, but I can always count on this site to steer me in the right direction.
Thanx, Dan


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## gunrunnerjohn (Nov 10, 2010)

They are prototypical on some curves, but they're not necessary for a model layout. A vast majority of model layouts do not use transition curves.


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## D&J Railroad (Oct 4, 2013)

Transitions will help reduce trains flying off the rails on curves. A transition on a railroad is pretty much the same as how you would steer a car into a curve. You don't jerk the steering wheel, you gradually turn it as you get further into the curve and the same coming out of the curve.
Also, transitions help larger locomotives negotiate tight radii. Using a transition or easement you can get a loco into a curve that is tighter than the minimum radii recommended for the loco.


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## DA Cookie (Jan 6, 2014)

So a transition turn is the same as a banked turn on a highway or racetrack?


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## ZebraCakez (Mar 26, 2011)

Transition curves and banking are two different things I believe. Obviously we all know that banking is achieved by lifting the outer rail in relation to the inner rail, thus causing the train to lean into a curve.

Transitions are the act of slowly working a curve up to its sharpest point. Picture a curve with a 22" radius at the apex. Now, instead of the entrance to that curve being a straight section of track that breaks into a 22" radius curve, you start off slowly and gradually work down to the 22" radius apex. Maybe when the train first starts to turn the curve is 36" radius or something. As the train moves through the curve it is gradually getting tighter until at the apex it is down to the 22", then as the train exits the curve it gradually straightens out (instead of just going from 22" radius to straight instantly.

When driving your car you make all your turns in smooth, linear motions. Imagine if when taking a left hand turn, instead of gradually turning into it, your wheels just went from going straight to full left - lock instantly. It would be a rough ride. 

That same smooth, linear motion is what transition curves accomplish. They ease your trains into a curve rather then just throwing in into the curves sharpest radius from nothing.


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## DA Cookie (Jan 6, 2014)

Gotcha. That makes perfect sense. I should have been able to figure that out on my own. Duh. 

Thanks a lot.


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## Hutch (Dec 19, 2012)

They take up a lot of space on a model layout that some of us can't afford. This is why we have some small curves in the first place.


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## D&J Railroad (Oct 4, 2013)

The banking of a curve on a railroad is called, "super elevation". There is an engineering formula of how much super elevation you would need for a certain degree of curve. Though it works well for the prototype railroad, it's difficult to build into a model railroad. Most modelers who do employ super elevation do it with a strip of card stock type paper under one side of the track before the ballast goes down. It may not seem like much but when ya put a tall rolling stock on the track, you will see it. I did super elevation on most of my curves by adjusting the benchwork after I had installed the track. Using a bubble level I could adjust the SE to exactly where I wanted it and the trains look very cool with the slight bit of lean.
Here is a video clip from my empire I did when I was installing the signal system. You can see a bit of the super elevation as the train roles by. It's more noticable when you can see the end of the train.


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## DonR (Oct 18, 2012)

The guys have done a bang up job of explaining
the transition curves. Nobody mentioned your other
question about single and double slip turnouts.

Wikipedia has a good explanation: http://en.wikipedia.org/wiki/Railroad_switch

The single slip switch would be used on a passing siding. It would enable
a Northbound train to move to the passing siding without the need to have a
man throw the points. An oncoming Southbound train's wheels would press the points
back to 'straight' and continue on again no one need actually throw the switch.
The train on the siding then can proceed again without switch activation
as it's wheels press the points to 'curve'. The old single track trolley
lines used these turnouts every few blocks to afford ability to run cars
in both directions on a single track. 

You see the double slip turnouts in major yards where a track such as
a lead passes through a number of yard tracks, yet there is a pre planned
route that would be used without anyone throwing the turnouts.

These are very interesting turnouts that are not used as often on model
layouts. I had a double slip on an N layout that worked well, but you can
imagine the potential difficulties of depending on loco or car wheels to
push the turnout points without derail. Atlas turnouts, among a few
others actually permit this on some of their models.

Don


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## hirailer (Oct 24, 2013)

This is an explanation of transition curves taken from Track Planning for realistic operation by John Armstrong.

Transition curves take out that "jerk" that you see when model trains are entering a curve like you see on sectional track. I like to run a lot of passenger equipment which really benefits in appearance and I'm sure they reduce derailments. A lot of my friends with larger layouts use transitional curves which do use a bit more real estate but is worth the effort.

My third layout is under early construction stages which incorporates transition curves the same as the prior two. All my track and turnouts are handlaid in an effort to represent the prototype the best I can.

Respectfully,

Mel


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## SSBN743 (Dec 30, 2013)

I have been trying to understand easement as well in recent history. While I have no problem understanding the concept, I’m having some trouble with the application. I just bought John Armstrong’s book yesterday that has this exact diagram in it – frankly, what is he talking about?

I think I understand, I think, but I’m having trouble visualizing it. Now, I am not actually trying to lay the track, and maybe that’s the problem, but, rather I’m using AnyRail to plan a layout.

So here is a picture of sectional track with straight sections going directly into 18” curves:









Ok, so I want to make an easement for these two curves and I have a hard time following John’s instructions. Take step 1 for example, “Extend to circular curve well past the point where it is closest to the straight track.” What does that mean? It doesn’t seem too exact to me to say “well past”.

So if I just do it like I would do it based on his drawing and table I get the following:

Now if I simply figure the offset in of 3/8” (I set the grid size to .38) for HO scale and 18” curves, I get this:









From the table I know that transition curve should be 12”, or 6” on either side. So I adjust the last straight sectional piece to be 3” instead of 9”.

I also do the same for the curved piece.

Since the curved piece is 30 degrees of a circle at its’ current length I can figure the amount that it should represent at its’ 3” length.

Circumference: 18”R * 2 * Pi = 113.094 inches
Inches per Degree: 113.094/360=.31415 inches

My sectional track covers 30 degrees in its length so first figure its length and 30 degrees is 1/12 of 360 degrees. So I can take my circumference and divide by 12 to get a length of 9.4245”; which AnyRail already does for me by the way.

Therefore we can do the same calculation to figure out how many degrees a 3”, 18” radius piece would cover and we get about 9.5 degrees. So we can use AnyRail to create a piece of flex track 3” long and then curve it to 9.5 degrees and an 18” radius. In real life we would simply cut a piece of flex track or just cut a sectional piece to 3 inches of radial distance.

Using a piece of flex track to make that special curve piece I end with the following:









This accounts for the length of the easement and now for the angle. AnyRail will automatically create a spiral curve of known dimensions. Since we know we have 20.5 degrees of the circle left to cover and we have 12” to cover that we can create a piece of flex track and use AnyRail to create a spiral curve spanning 20.5 degrees and ending in an 18” radius.

I’m no mathematician, but AnyRail makes that piece 10.3 inches in radial length and it looks like this:









I don’t know or understand why it is not 12” but it is. After everything is said and done this is what I end up with:









Now in real life I’m sure I can make this work by just stretching the flex track to a “natural curve” just has Mr. Armstrong describes. But shouldn’t this be more exact? Here’s how it would look:









Is this the right idea? It looks kind of weird to me but I can certainly see the difference.


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## hirailer (Oct 24, 2013)

You got the right idea. When you are working with the actual track, the transition looks much better. When I am laying out an easement, I find that the factor of 'x' being 1/2 inch for ALL curves results in a visually acceptable transition. In actual practice, the difference between 3/8" for sharp curves and 1/2"is hardly noticeable.

The results are worth the effort.

Mel


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## D&J Railroad (Oct 4, 2013)

If you are trying to create a transition by piecing together parts of sectional track, you are going to drive yourself crazy. Use flex track and let the natural bend of the track build the transition.


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## Southern (Nov 17, 2008)

DonR said:


> The guys have done a bang up job of explaining
> the transition curves. Nobody mentioned your other
> question about single and double slip turnouts.
> 
> ...


That is not correct. Single and double slip turnouts still have switch machine or hand throws.

A double slip is a cross over that has two turnouts built into it. A single slip has only one.


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## SSBN743 (Dec 30, 2013)

D&J Railroad said:


> If you are trying to create a transition by piecing together parts of sectional track, you are going to drive yourself crazy. Use flex track and let the natural bend of the track build the transition.


I am defineatly learning that sectional track creates some problems. One question though; are you saying that the whole curve should be flex track, or just the transition curve?


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## Southern (Nov 17, 2008)

I use mostly use all flex track. It is just easier to put it were you want it.


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## D&J Railroad (Oct 4, 2013)

SSBN743 said:


> I am defineatly learning that sectional track creates some problems. One question though; are you saying that the whole curve should be flex track, or just the transition curve?


Yeah, if you're going to use flex track at all, use it for the whole curve.


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## drooniem (Jul 24, 2013)

As always, great answers in a timely fashion. I'm hoping to use transitional curves on most of my layout. And I've got 3 passing sidings that I might try out some single slip turnouts. If they work well I might add a few doubles in a yard. Peco makes both, so I'm gonna try them out. Thanks again, guys.
Dan


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## D&J Railroad (Oct 4, 2013)

I think you will be happy with easements in your curves as it adds a bit of interest to the operation of trains as they glide into a curve rather than suddenly jerk into a right or left turn.


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## DonR (Oct 18, 2012)

Southern said:


> That is not correct. Single and double slip turnouts still have switch machine or hand throws.
> 
> A double slip is a cross over that has two turnouts built into it. A single slip has only one.


You are right, Southern.

I didn't mean to imply they had no switch motor. What I wanted
to get across was that
their point springs are 'weak' enuf to permit the wheel flanges
to move them.

Don


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## drooniem (Jul 24, 2013)

To SSBN473: Model Railroader has printed a couple of articles that explained transitional curves and easements. I thought the authors did a good job making it understandable. It would be difficult to come up with a formula for figuring the curve as the radius changes every fraction of an inch. Such a formula would most likely take knowledge of advanced calculus... way beyond my old brain. But they included a chart that gave various easements as they related to the transition of various radius curves. They suggest using a flexible metal yardstick to transition the curve from the offset of the easement... seems sensible to me. I could find out the issue months if you need.
Dan


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## SSBN743 (Dec 30, 2013)

D&J Railroad said:


> Yeah, if you're going to use flex track at all, use it for the whole curve.





drooniem said:


> To SSBN473: Model Railroader has printed a couple of articles that explained transitional curves and easements. I thought the authors did a good job making it understandable. It would be difficult to come up with a formula for figuring the curve as the radius changes every fraction of an inch. Such a formula would most likely take knowledge of advanced calculus... way beyond my old brain. But they included a chart that gave various easements as they related to the transition of various radius curves. They suggest using a flexible metal yardstick to transition the curve from the offset of the easement... seems sensible to me. I could find out the issue months if you need.
> 
> Dan


Ok, thanks guys. I’m just having a hard time getting it to work in AnyRail, but I think that when I actually do this it will be much easier.

I did find the NMRA guide that spells out 4 or 5 different methods of getting the easement correct. They even go on to describe super-elevation and run-offs, each with their own crazy formulas. One of those guides does have a template, unfortunately, it doesn’t look like it will work too well – they even state that they think other methods are better because you would need a template for each and every situation.

Thanks for the help though; I guess I’ll know more, for better or worse, when I actually lay the track. Right now I’m just winging it AnyRail; from the start AnyRail was just a guesstimate anyway, I’m sure I’ll learn a great deal about the accuracy of AnyRail when I lay the track!


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