Yard Track Spacing and Radius...

Model Railroader Layouts and layout building
21

Mike, somewhere in all this most of us are trying to build a “model” of a railroad. Yes, that is full of compromises.

But looking to the prototype for operational standards is a good place to start.

The NMRA gauge is 2-3/16" wide BECAUSE, it is not a double track clearance gauge, there are pages of information in the NMRA Standard and Recommended Practices on double track spacing.

The NMRA gauge is a bridge and structure clearance gauge, and any simple reasearch will reveal that the prototype uses more generious clearances for trackside structures and bridges than it does for double track minimum spacing.

The pioneers in this hobby many decades ago adopted 2" track centers as a good compromise because it looked acceptably close, provided some extra clearance, and would work at least with larger curves as a single standard.

This allowed manufacturers to make lots of “compatible” products, double track bridges, turnouts, crossovers, tunnel portals, signal bridges and more.

You are obviously welcome to build your layout however you see fit. I personally would want no part of your seat of the pants, hook the flex track together before fastening it, way of doing things.

And I have been doing this successfully for a long time…

I will stay with my universal 2" track centers, I will keep engineering the path of my trackwork before I install it, and I will likely leave you to it for a while, I have more important things to busy myself with.

And my 100 plus Atlas turnouts work just fine - maybe because they are properly fastened down…

Sheldon

22

You do realize that posting “I do the same thing” isn’t very useful. Only differing views can be useful.

I post “my version” to provide workable options to others.

It’s frankly bizarre the way these threads go off on tangents amounting to arguments that my way is the best way.

Nope, my way is the best way. Always. That’s why it’s my way.

Readers are then free to try the different alternatives and discover which is their way. For them that will always be the best way.

As an aside I’m not sure I understand the remarks about the NMRA gauge not working for curves. Whatever works for any trackside obstruction has to work for passing trains. That’s just geometry. Things either overlap or they don’t. It can’t matter if only one of the things is moving or both are.

This really isn’t a very complicated hobby. There are lots of different ways to achieve an enjoyable result.

23

[Y] +1

Anyone can read my posts, copy and paste them, and then claim that they are an expert.

Unfortunately, they are using my posts, which are not a good place to start.

[(-D]

-Kevin

24

There is an NMRA RP (RP-7.2) to provide some guidance on this. The RP assume very large locomotives and 85’ rolling stock, so it is probably a bit overconcervative. They recommend around 2.5" spacing for 36" curves.

They do provide a tool to calculate the recommended spacing for your specific rolling stock.

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/curved_track_center_and_obstacle_clearance_assistant_jul_2017.html

Just playing with your rolling stock may be the easier route. However, for someone like me who is still planning and has limited rolling stock, these tools may be more helpful.

25

The issue is that parts of the cars overhang inboard and outboard on curves, so the effective clearance between adjacent tracks becomes the most extreme ‘worst case’. You could build gages that would at least approximate this for particular types of car and particular ‘sharpest’ radii.

PRR discovered at some point that clearances on Horse Shoe were a bit tighter than the ones used for clearance in the J1 2-10-4 design, with the result that passing engines started trying to knock parts off each other.

There were some yards in the East with so little room between tracks that there would be damage if cars on adjacent tracks had plug doors left open.

It does if the thing tips due to ‘centrifugal force’ far enough to make contact with another thing… or rocks with side-bearing clearance or offset weight… etc.

Part of the fun is that the force of contact (and many of the effects) increase greatly with relative speed. At some point there might be aerodynamic effects that could induce deflection or rock.

26

Overmod

back when I started on RR about 197? worked at Robert Young Yard in elkhart before I got on the GTW anyway some of the tracks off of the hump were off limits to people they were so close together If the cars rocked a bit they would hit I think they finally fixed them long after I was there

27

And again, tapered wheels and and tapered axle ends do NOT insure that the car is ALWAYS centered on the track…

Sheldon

28

To answer the OP’s question directly: yes yard tracks on 2" centres will work fine.

29

To answer the OP’s question indirectly the NMRA recommends wider track centres than 2" for reasons not clear to me.

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-7.1_tangent_track_centers_and_clearance_diagrams_2019.01.pdf

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-7.2_curved_track_centers_july_2017.pdf

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-7.3_curved_track_obstacle_clearances_july_2017.pdf

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-7_track_centers_and_obstacle_clearances_july_2017.pdf

One wonders why the NMRA gauge is set at 2 3/16" for measuring clearances. The clearances to track centres are 2.5" minimum for a pair of parallel tangent tracks. That’s 5/16" wider than the gauge!

30

Your model cars and locomotives should not be rocking. That’s a defect.

Centrifugal force would act on trains travelling on both the inside track and the outside track so the only effect of that would be the delta resulting frim the differing radii. Pull the other one.

The Venturi effect of passing model trains must be pretty small also, and doesn’t scale anyway because the viscosity of the air doesn’t scale.

If your locomotives or rolling stock are rocking into each other or sucking each other off the rails at yard speeds then track spacing ain’t your problem.

Whether it’s the ends of the cars or the middles that encroach into the space between the tracks matters not if both sets of cars each clear their own track obstacles. If the car passes through the templated clearance on any single track two trains can’t hit each other on parallel tracks each of which gives that same clearance.

31

The NMRA RP actually says tanget (straight) tracks can have a spacing of 1 25/32" for cars of the “classic” era. (which fits the OP 1950s.

The 2.5" spacing is for curved tracks. This is to account for the overhangs in the corner. They are assuming you have a big boy pulling 85’ passenger cars so that is probably excessive.

The standards gage is for straight tracks and is actually more for structures. Which have different clearence needs.

32

There are few things sadder than when you try to help a dog and he tries to bite.

That would be true unless, um, the train on the outer track wasn’t moving. Which is where the concern is if you actually think about it a moment.

As we say in skeet, PULL!

33

Good lord, Mike…why not read and think a bit instead of scurrying over to your keyboard at every opportunity.

34

[quote user=“richhotrain”]

selector

To the OP, I suggest deriving empirical data. You have certain items of rolling stock. They gotta work. Right? So, find out if they’ll work down to a certain limit. Get out a sheet of plywood or drywall, fix some track radii…nested to duplicate the conditions in your yard…and run a good sampling of your locomotives and rolling stock around them to see what happens. You’ll find an empirical ‘lower limit’ above which you’ll know to craft your curved yard ladders, and you’ll construct them with confidence knowing your product will be satisfactory.

Agreed, and this is why I wrote my earlier response to the OP.

richhotrain

Years ago, I got some good advice from my LHS guys about spacing of tracks on curves. They recommended that I buy a pair of 85’ boxcars and test them on actual track to be sure. I wouldn’t blindly rely on the advice of others unless they can say with certainty that 2" on center spacing for 36" radius tracks will work based upon their actual experience.

If this were my layout, I would use 2 1/2" spacing on curves and, since it is the yard, I would step down the radius on curved tracks to something like 32" radius. In fact, that is exactly what I did on my old layout where I installed a yard on a curve on my layout.

Don’t act on the advice of others unless they speak from personal experience. Try it out for yourself by putting down some track

35

Nope. Sorry.

You are wrong. Wronger than Overmod said.

The whole point of bringing up centrifugal force here is that the train tips at a certain angle. If it DIDN’T tip, what’s the point?

For trains 1.5" wide, on parallel tracks at 2" centers, when the tipping angle from vertical is 42 degrees, they will touch. I just did an experimental setup to find that number.

You, of course, will say that this is silly, among other reasons because they’d have derailed already. Yes. Quite true.

But:

My POINT is that they WERE 1/2" apart when they were stopped. To get to the above silly point, they have to move closer and closer as they tip further and further. So, although they won’t touch for sure until 42 degrees, the possibility that they MIGHT touch increases, too.

Let’s see what happens when we close the track centers down to 1.6". Standing still, they don’t touch. They’re separated by .1" But if they were to tip from centrifugal force, both going at the same speed, that .1" would DISAPPEAR at 21 degrees (experimental result again) from the vertical. And, as pointed out above, the possibility starts increasing at earlier tip angles.

This effect is in addition to the difference of lean angle caused by differing radii.

Overmod, I trust you are getting my point. Note that the trains are traveling at the same speed.

Ed

36

My 2-8-8-4 will need to be restricted to the outermost of my hidden return tracks. The cab overhang is so excessive on the outside of the curve that this is necessary.

-Kevin

37

Mmmm. Me like! Good!

(Sorry about letting my inner kid appear–it happens.)

Ed

38

It just goes to show, Crandell, that great minds think alike. [Y]

Rich

39

I do recognize it. You might draw a couple of diagrams to show why the interference develops as cars of roughly rectangular cross-section tip progressively around points corresponding to flanges on outside wheels, and then show the ‘worst case’ for sections at interfering ends on various car lengths, overhangs, and curve radii.

I didn’t go into that detail as I was only concerned with potential momentary contact of a (potentially wobbly) car with a standing adjacent train with its now-fixed overhangs. I think by the time we get to Unstoppable-grade levels of tilt, we’re no longer in the realm of advice to the OP on reasonable track spacing for his purposes. Even modeling of negative cant deficiency in passenger models (which Hornby did, and I presume Rapido did with their APT model) is on the esoteric side for typical modeling concerns – although not for Amtrak on the NEC north of New Haven…

The other point in question is the wobble. Yes, good models shouldn’t wobble, but a good three-point side-bearing arrangement implies that the ‘stiff’ truck can prevent any roll of the carbody including when the ‘far end’ leads into what may be sharp curves and its angular momentum change is accommodated via the center pin of the ‘tiltable’ truck. Long practical evidence with good model railroading practice certainly indicates this doesn’t rise to the level of a chronic derailment cause, but in some cases, especially with sprung or ‘articulating’ sideframes, it might prove to increase the effective upper-outer ‘critical contact radius’ enough to matter if the situation were already critical.

All this palaver is fun but I don’t think it’s getting the OP much closer to what he was asking to know… [:$]

40

Here’s a bit more on the subject:

On a 38.5 inch radius curve, the tightest in the yard, a 65’ long freight car (the potentially most troublesome) will project an approximate additional 1/8" inwards. It will not project outwards that much. Since there is 2" between track centers, and a freight car is about 1.5" wide, there is 1/2" available for clearance WITHOUT accounting for increased curve overhang.

1/8" is dramatically less than 1/2", so I say clearance in the curves in the yard for the type of cars and locomotives that will be in it is more than adequate.

IF projection outward in the curve were to also be 1/8" (which it will not), and two of these cars were passing, there would still be 1/4" clearance.

Note that no road engines nor passenger cars will be in this yard.

Now, the arrival/departure tracks might be different. I see a 37" and a 39". If an articulated is planned on being operated there, overhang outwards for the boiler front should be considered. And perhaps outward overhang on each end of a 4-8-4. Articulateds could be limited to the outer track, and likely things would be fine there.

I also note that two of the three A/D tracks don’t have much straight near the switches, perhaps generating difficulties adding/removing engines and cabooses.

It would be wise if the OP were to do some overhang measurements and calculations for the “biggest” motive power and passenger cars on specified radii before locking things in.

I took a few minutes and found that the outward swing of a Big Boy’s front would be a half inch