Tony Koester talked about the

Tony Koester talked about the spacing in "2 inch" in his book Building Multideck layouts. He said as long as it is over 30" radius (example  30" and 32"), he had no problems with it even with his really long freight cars. He said it was close, but he never had a swipe. My minimum is 30" and I am going with 2" spacing with easements on my main line.

Hope that helps.

Jim

Fractional inch radii

Ken,

Why are even numeric radii important? If you were in the metric system then 2" equals 2 x 2.54 = 5.08 cm.

As far as requirements for radii go, if you're planning to run brass articulated locos 2" won't be nearly enough on curves although it will be fine.

Do you have the longest equipment you'll be running on hand?

Mock up a 30" and 32" segment (or what ever you min mainline radii will be) and see if two of your longest, fattest equipment can get by each other.  Full length passenger equipment, 85' hi cube box cars, tri-level racks are all good for testing for side swipe avoidance.

Think about anything you might ever want to run on your layout for checking.

MRH issue #1 has an "Insights on curve radii" article by Joe F. in it that iirc addresses the track spacing on curves issue (but maybe I'm remember wrong).

Charlie

 Nope. 2" center-to-center on

Nope. 2" center-to-center on straight track. Center-to-center on curves needs to be a little wider - how wide is determined by what kind of stuff you run on it.

Smile,
Stein

The modular club runs a 36 inch minimum radius.

I did not see a standard set for spacing on curves, but since the corner modules are club owned, the standard does not address spacing on curves.  I think we follow NMRA standards for track spacing on curves.  What spacing you wish to run on your railroad will be determined by what equipment you want to run.  A few years ago we had a meet at a local shopping mall and a friend of one of the members asked to run his brass challenger on the layout.  As Charlie said, brass does not like either our radius or track spacing.  The problem with brass articulated locomotives is that they are hinged just like the prototype.  When going around our "tight" 36 inch radius curves on the inside main, the Challenger's smoke box swung past the outside rail on the outside main by at least 1/2 inch!  I think brass articulated locomotives would probably consider a 72" radius as a minimum standard for reliable operation.

2 inches works with diesels and 30" radius

We used minimum 2 inch centers on our mainlines.  We use 30" minumum radius and run diesels and 89 foot flatcars and autoracks.  There is barely enough clearance on curves, but the equipment does clear.  We do have wider spacing in various places for prototypical reasons as well, and will sometimes allow some extra room on curves if it doesn't look too bad.  Hidden track is often wider spaced as well, since appearance doesn't matter there.

Steam era mainlines typically used 15 foot track centers.  Yard and spur tracks went down to about 13 foot.  Rolling stock and locomotives were allowed 10' 6" wide carbodies and some appliances were allowed to extend a bit further; you can say the rolling stock can be 11 foot wide.  This allows 4 feet of clearance on mainline tracks and about 2 feet in yards.  It doesn't sound like much, but that's the way it is on the prototype.  We use 1 7/8" spacing on our yard tracks to represent the narrower spacing there, and it doesn't cause any issues on straight yard tracks.

Fifteen feet works out to about 2.067", which is a hair above 2 1/16", so the NMRA is correct for steam era standards.  Modern mainlines use wider spacing where they have been upgraded to handle excess width loads more easily.

If you run steam, you run into the problem that most models are made too wide to accommodate the excessively wide wheel treads and lateral movement in the wheelsets to make it around the model curves.  You will have to adjust your center to center on curves for sure to take that into account.  Articulated locos also have the boiler swing to contend with, as someone else mentioned.  

As I read the NMRA S-7 and S-8 standards...

Looking at the charts published on the NMRA website, the 2 1/16th minimum track center in HO comes from the fact that the metal gauge is 1 1/32nd inch wide from the center to either edge.  2 inches is just too close if the cars and locomotives you run are close to maximum allowable width.  Additionally, S-8 requires that center-to-center distance be increased on curves to allow for overhang.  If you're running what the standard calls Class I, which includes longer steam locomotives, typically with two-wheel trailing trucks, larger four and six-wheel truck diesels, and equivalent rolling stock (which I believe would include what you call "Classic" gauge), then the center-to-center distance increases to 2 5/16th inches as the radius DECREASES to 23", and it doesn't recommend operation of this equipment on any radius less than that.  If you're operating Class Ia trains, that Includes the largest steam locomotives with four-wheel trailing trucks, articulated locomotives, those with rigid wheelbases in excess of 20 feet, full length passenger cars and other long rolling stock, the minimum radius recommended is 32" and the track centers are at 2 1/2 inches.  I read these charts before designing my layout, and decided that 36" would be a suitable minimum radius, since I have the room for it.  I keep the track centers to 2 1/2 inches, as this allows me to get my fat fingers around the cars without knocking the cars on the next track onto the ground.

Now, I designed my track layout about 5 years ago, and these diagrams haven't changed at all.  I don't know where the 2" minimum came from, unless it's just old folklore, which in this case is just wrong.  If you run older, smaller cars and locos, then you can get away with fudging the clearances, but if you run bigger stuff, just go with the correct numbers.

It all depends.

Ken - it will all depend on the equipment you will run on your tracks.  Doesn't depend on anybody else's equipment or their experiences.

Long cars hang over toward the inside of a curve.

Locomotives with a long overhang in front or back will project outward away from a curve.  If you combine the two, you need to have the tracks far enough apart so they don't hit.  It doesn't matter whether the locomotive is brass or plastic, steam or diesel.  The overhang is the whole issue.  Some long freight cars might do this also.

If you run short stuff all the time then it's not an issue.

Straight track is not an issue.  You can actually go a lot closer than 2 inches without operation problems.  In fact the real railroads are a lot closer.  The straight track spacing is really only to allow a little bit of finger room for poking cars or other unprototypical actions.

The needed spacing will depend on the radius of the curves you would like, combined with the equipment you will be running.  (Or ever will run at any future time.)

All these standards arise from issues that affect the operation of our models.  If you want to design your trackwork to avoid all problems, go with the "worst case" using the "Class 1a" values in S-8.  At my club, one friend was running long flat cars on the outside and I had a long steam engine going the other direction on the inside, on a 30-inch radius curve with 2-1/2 inch spacing.  (The outer curve is 32.5-inch radius)  The two JUST BARELY had clearance to pass.  The NMRA chart would indicate that something larger than 2-1/2 is needed.

Although it seems that even-inch dimensions might be easier to lay out, the final operation is more important.  You may want to make the outer track have a constant even radius except for the easement zone.  Then the inner radius could be the odd dimension, and just rough-in a much larger easement zone to blend the tracks back to whatever your tangent track spacing is.  This would keep rolling stock from colliding yet allow a pleasing appearance of the track lines.

Well, that's just my 1.1 cents.   (That's 2-cents after taxes.)

Kevin

Highly recommend 3" Center to Center Spacing

I have 30" R. curves. I run articulated locomotives that must pass each other and I STRONGLY recommend 3" center to center track spacing if you have the room. Even on larger radii it sure can't hurt. I seem to remember 3" minimum being a very common recommendation for this situation for many years now. I thought it was NMRA but perhaps not. Anyway, 3" gave me a large "comfort zone" and room to play with scenicing trackside a bit more.

Jim

How close can a spur be to a

Not a problem

I have seen spurs so close to the main line that the ties on the main line side are completely buried in ballast, and the rail appears to be holding the ballast back.  Prototype track spacing varies widely, as is clearly demonstrated when I read a high & wide profile.  Some tracks are so far away from the main line that I can run past them at full speed, while others are so close that I either cannot pass, or only at walking speed.  So I would suggest that you not worry about that track at all.

How wide do you NEED it to be?

All depends on what you're modeling...

Or just ask the UP:

http://www.uprr.com/aboutup/operations/specs/track/index.shtml

Phew!

Ballast

Not only would I not worry about it, I would embrace it and call it prototypical!

Ballast is typically (at least today) dumped from a ballast car, either between or outside the rails and on top of the ties.  If/when the RR gets around to finishing the job, here's a brief description of some of the machines they'll use:

• Tamper - this has vibrating fingers which reach down between the ties.  Some can also lift the ties at the same time, allowing the track gang to adjust the track level.  This will do a lot to eliminate the ballast on top of the ties.
• Spreader/sweeper - This thing looks like the love child of a snow plow and a street sweeper.  It pushes the ballast off the tops of the ties, and a large rotating drum with rubber fingers sweeps the track clean.  The result is a very smooth surface with ballast up to the top surface of the ties, and with the track looking fresh and neat, lots of ballast dust making it look bright.  I can always tell when the track gang has been working, which makes it easy to see where the slow orders are on the main line!

Of course, these jobs can all be done by hand as well, and would have been before the '50s.  Incidentally, Southern Ry. was one of the early adopters of mechanized track gangs, developing a number of the machines themselves in an effort to save labor costs.

That new ballast you see might never be spread out, or they might be leaving it until the track needs more work.  Passing trains will slowly spread the ballast by their vibrations.  It might well be a situation where the track foreman had some extra ballast and needed to use it somewhere.  He knew that spot would need some ballast eventually, so he dumped it there and will come back some time in the future to finish.  This way he doesn't have to get a ballast train loaded and brought in, and he doesn't have to get as much track time when it's time to tamp and level the track.

I once over ballasted flex

Track Spacing

I went and check the track spacing on my prototype and the tracks are 15' centers on passing sidings and in the yard.

Good to know Bill.That works

" passing sidings like runaround tracks? "

Pretty much the same thing. Both have switches at each end. What they are called is more based on their operation function than on their configuration. If it's at the end of a branch line or long industrial spur it is called a run around because they would not be passing another train there but they would be running around their train to come back home. If it's out on the mainline somewhere it's called a passing siding because that's what they do out there. If it's in a town with industries to switch and trains meeting it's likely called both :> ) .......DaveB

Interesting video barr. Made

Sideway Clearances

So if I want to run long articulates, and long passenger cars, and auto carriers on either 30" radius helix tracks, or on as small as 24" layout curves,  I need to give a clearance of at minimum 1.5 inches from the center of the track to any obstacle, either inner or outer one?
Is that how you see it??
 

John Armstrong recommends 2

John Armstrong recommends 2 inch centers on straight train in his book Track Planning for Realistic Operation, but wider spacing on curves and that spacing depends on how tight they are.

I would never recommend 2 inch centers on curves unless they are very broad.  I personally don't like to live "on the edge" with regard to minimums.  I've used a least 2 1/4" centers on my curves which are above 32-inches radius.  For say, 24-inch curves and below, 2 1/2" centers area a good idea.

 "I personally don't like to

Great advice, add the bit of cushion and get to work :> ) ......DaveB

Check NMRA RP-7

Track centers and clearances are covered under NMRA Recommended Practices RP-7.  The latest data is in draft form dated May 2017, which is about as up to date as you'll ever get.  The data covers various scales, radii, and equipment eras.

The only deviation that might be worthwhile to explore is finger clearance in limited access areas such as between the levels of a multi-track helix.

HO track spacing and curves

This may be a little off but there is a very good article titled "How to plan concentric curves with easements" in Model Railroad Planning 2011.  The article provides graphics and formulas to determine track centerlines and easements for concentric curves.

ed

Helix Clearance for dbl-stack container cars, and auto cars

 What would you figure the best clearance to have on a helix that wants to run modern cars,....3.5", 3.75", or 4" ??

What would you figure the best clearance to have on a helix that wants to run modern cars,....3.5", 3.75", or 4" ??