Turnout geometry in US and Canada

obirek

New member
Hi all,

I would like to build a route according to railway standard in US and Canada and I would much appreciate if someone help me with basic geometry of turnouts used in these countries. I know what type of turnouts are used in East Europe and I can built them in Surveyor easily. For each turnout I need to know two properties:

1/ The radius of the curved section joining straight and diverged track.
2/ The angle at which straight and diverged tracks intersect. This angle can be given in degrees or as the tangent of the angle, e.g. 1:9, meaning for 9 measurement units forward, diverged track moves to the side one measurement unit.


I looked into number of web sides and I found very detailed blue prints of various turnouts, but I could not derive these two simple properties.
 
It's probably not as technical as all that, no offense intended. A reasonable radius would probably work just by eyeballing it.

Cheers

AJ
 
I'd suggest grabbing an animated (and therefore fixed) turnout from the DLS or out of the game. Lay regular track over it so the rails line up. Then delete the fixed turn out and use the tools in surveyor to measure the radius and so forth.

And, if you can find Blueprints (they are on the net, I've seen them, though I can't recall where) you can use a ruler on your computer monitor to check ratios since they would be scale drawings.
 
Use Google Earth ruler to measure a crossover interlocking ... apply that same measurement to your Trainz turnouts ... do the same ithe curve radius
 
If you can manage to get your hands on Paul Mallery's "Trackwork Handbook for Model Railroads", you will find all the prototype info you could ever want. It's old...my copy is from 1974. It is the ultimate track layers bible.
 
Many thanks to all of you for your tips! See my comments below.


If you can manage to get your hands on Paul Mallery's "Trackwork Handbook for Model Railroads", you will find all the prototype info you could ever want. It's old...my copy is from 1974. It is the ultimate track layers bible.

A second hand copy is $5 only, but postage to Australia costs $47.60, which is bit too pricey just for finding two lucky numbers, especially if there is no guarantee the numbers are there.

Use Google Earth ruler to measure a crossover interlocking ... apply that same measurement to your Trainz turnouts ... do the same ithe curve radius

I'm afraid this method isn't too terribly accurate... It can be used to confirm where different turnouts types may be used, but to build turnouts in Surveyor you need +/- 0.05 m and +/- 0.05 degree accuracy. Say, 5 meters is not much in Google Earth, but it can make a turnout with radius of 300 meters calculated as one with 209 meters, almost 100 meters shorter! 100 meters is a lot, even in Trainz.


I'd suggest grabbing an animated (and therefore fixed) turnout from the DLS or out of the game. Lay regular track over it so the rails line up. Then delete the fixed turn out and use the tools in surveyor to measure the radius and so forth.

And, if you can find Blueprints (they are on the net, I've seen them, though I can't recall where) you can use a ruler on your computer monitor to check ratios since they would be scale drawings.

The problem with this method is that I would need to built a turnout out of a template and then use "show curve radius" tool to find out the radius. The tool is terribly inaccurate. It produces several different readings, varying by as much as 50 meters or more, which can be 25% or more of radius length. There is no tool to measure angle, other than laying fixed track in the diverge direction, as in the template and reading angle by turning the fixed track. Some authors, like Natvander, were thoughtful and gave hints what is the turnout angle, for instance "Turnout 1:9", <kuid2:61119:28995:1>, but there is no mentioning of turnout radius. There is set of US turnouts by martinvk, but no turnout properties in the description. As to the blueprints - some turnouts have radius of 1200 meters (about 4000 ft) and I don't know if they will ever build screen big enough to measure such distance in real scale.

Few days ago I came across this document - "CN Engineering Specification for Industrial Tracks". There, on page 33, there is a plan of right hand turnout, for types #8, #10, #12, #15, #20. I think the angle I am looking for is the value of F angle (FROG). This is approximately 7.2, 5.7, 4.8, 3.8, 2.9 degree respectively for the turnout types. But I can't find the radius of the arc at which the straight and diverged tracks are connected. I guess it can be calculated from other properties, but how?

turnoutgeometry.jpg


It's probably not as technical as all that, no offense intended. A reasonable radius would probably work just by eyeballing it.

Cheers

AJ

If I can't build a turnout exactly as they do it in Canadian railways and within the limits of Surveyor, it is not a big drama. But I hate this word "cannot". It is often said that the beauty is in the detail and I believe there is some true in this saying. You can read simplified version of "The Great Gatsby" and find out what the novel is about, but you will miss all the style, color and what great literature is about. As to "reasonable" radius - there are strict guidelines on most railways. You can't use the same turnout for a factory siding, where permitted speed is 20 mph or less and for a main line where a train can diverge at speed of 60 mph. So, how to tell the two apart?
 
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I added this reply to update the table above. I will keep editing this part as I gather all required data. Please send me your feedback.

First, I learned that the turnout angle is "encoded" in its number, e.g. #8 has ratio of the opposite and adjacent side 1/8, #10 has ratio 1/10 and so on. I can hear my math tutor comment: "Modesty, simplicity, elegance". Taking arc tangent of this ratio and converting to degrees gives the angle I was looking for. The only discrepancy is in #8 turnout: DEGREES(ATAN(1/8)) = 7.125 = 7 deg 07' 30", while most specs shows 7 deg 09' 10" (about 2 minutes difference). But angles for all other turnouts reconcile.

Second, I read that the part called "curved closure rail" is not an arc with constant radius, but a parabola with variable radius, presumably followed by arc. If so, it is not possible to build such turnout in Surveyor, using two splines. But in AREMA Conference document, http://www.arema.org/files/library/...her_Diverging_Speed_in_the_Same_Footprint.pdf, on page 14, I found that radius of #20 turnout is 3289.29'. Unfortunately, there were no radii for other turnouts in this documents.

There are many pages about turnouts beginning with # (hash), but most of them are concerning model railways. The figures shown on these pages are adjusted to suit model railways, so I am not sure if I can use the scale to reverse to the prototypical value. For instance, in http://bellsandwhistles.us/modelrailroading/Clinic08_handout.pdf, it is written that radius for #10 turnout is 117" in HO scale. 117" x 87.1 = 10191" = 849'. Is this value correct?

I also miss the information what is the maximum permitted speed when moving in diverged direction and general guide lines where to use each turnouts, i.e. main track crossover, connect main and additional track. I need this information to build realistically looking routes for USA and Canada. The sad thing is that everything I built so far is rubbish, because I built according to East European standard, which is much different from North American standard.

TURNOUT PROPERTIES FOR NORTH AMERICAN RAILWAYS
Turnout Type
Radius (ft)
Angle (degrees)
Max. speed (mph)
Recommended Use
#8
?
7.2
?
?
#10
?
5.7
?
?
#12
?
4.8
?
?
#15
?
3.8
?
?
#20
3289.29
2.9
?
?

 
According to Mallery a #10 turnout is as follows: Lead Curve(from toe of point to point of frog), 7deg,15',18". Length 790.25ft
 
According to Mallery a #10 turnout is as follows: Lead Curve(from toe of point to point of frog), 7deg,15',18". Length 790.25ft
Length 790.25ft ! ! ! Thats way too huge of a switch ! That might be proper for a 300mph TGV rail line.
Most US 2 track crossover interlockings are @ 400' point to point.
Some yard switchs are @ 80 foot point to frog.
 
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I am using the CN template as above and using some math. In this illustration I am using the #12 switch which is 140' in length and the frog is at 98'. The first thing I do is measure out 140'. I then measure out the lead length and point length and mark those on the map too. Then I do some math: at the end of the switch the angle F (for a #12 switch) is 3.3 degrees which is .0576 feet, I then multiply .0567 X 140 (length of switch) to get the distance between the two inner rails, 8 feet. So at the end of the switch the two inner rails should be about 8 feet apart.

0d8dbb9523swtich 1.jpg

I then start my track and drag the track straight to the point end, then shift+click and drag the track to frog length, shift+click and bend it to the switch end at 8 feet offset. I will then add a couple of splines to smooth things out.

83756bfa4cswtich 2.jpg



I find this is making my switches much nicer and smooth as I didn't have a lot of nice results using the templates, but that is just me.
 
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