# Double Track spacing



## HOSP4449Fan (Dec 2, 2013)

I'm running my loop through a wall into a closet and back out. It's 3.5" spacing enough with 1 track straight and 1 072 curve into a straight? Chances of 2 trains passing here are pretty slim










from my Galaxy S7


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## Lehigh74 (Sep 25, 2015)

NMRA standard S-8 calls for 3-7/8” track center for a 36 ½” radius curve for class II (for small engines with short overhangs). I would go with at least 4”… or 4 ½” if you can.

http://www.nmra.org/sites/default/files/standards/sandrp/pdf/s-8.pdf


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## bluecomet400 (Sep 13, 2015)

3.5" is pretty tight--probably too tight if you're running larger locos like Hudsons, Mohawks etc. I went with 4.5" spacing on mine. The chances of trains passing there may be slim, but what if they did??


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## PatKn (Jul 14, 2015)

I use 4/5 inch minimum center to center for two straight sections. I prefer 5.5 inches. A curve needs more space to allow for overhang. 3.5 inches is too close.


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## cole226 (Feb 8, 2013)

beware of the overhang on the inside of the turn too. where your radius comes into your wall cutout.


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## phillyreading (Aug 25, 2015)

I am using 4 & a half inches(center rail to center rail) on my curves that are side by side and am using 031 & 042 track. Sometimes the 4 & a half inches can be tight if I run 16 inch long passenger cars on the 042 track and another train on the 031 track. I would go up to 5 inches if I had the room to do so.

Lee Fritz


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## Guest (Dec 7, 2016)

4.5" minimum, and better at 5.5". Don't take chances at this point when you can do something about this easily.


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## gunrunnerjohn (Nov 10, 2010)

I can tell you with certainty that 4.5" spacing isn't nearly enough for O99 curves and large articulated locomotives or 21" passenger cars!  I'd do some trial runs for your setup. The good part is the straight track is pretty easy to simulate, so part a passenger car there and run your locomotive with the biggest overhang round the curve and see if it clips the car.


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## Lee Willis (Jan 1, 2014)

I understand the pressures to squeeze things down, but the "chances of two trains passing here are pretty slim" only means collisions will be rare, but they _will _happen. And given they will mostly happen when big engines and long rolling stock with significant overhang are running, probably they will be both rather spectacular and expensive.

I have no idea what is around the end of the curve you show in the picture. It it leads into any type of straightaway, I would cut down the straightway's length and use flextrack to start the curve earlier and at a lighter angle, as I show below, then once the spacing has opened up, go to 72". If this curve is part of a 180 degree curve back around at the end of a loop, and you don't have room to make it an inch or two wider on the other side, then I would still recommend doing this and using flex track on the rest of that 180 degree curve. It would mean the rest of the curve would be around 70" or 71" inch radius instead of 72", but I have only one loco, out of about two dozen rated at 72", that will not make it through a 70" inch curve (I've tried). That is the Lionel 4-12-2 UP 9000, which frankly, doesn't seem to even like 72" curves much. You could set this up and experiment with your engines before doing it permanently if in doubt. Keep in mind that almost all 72" locos (except that irksome 9000) seem to be happy enough with slightly tighter curves, even 66" in many cases. The 72" rating is usually limited by 72" switches, and as long as you have them in the loop, I think you could get away with 70" curves. I've done something similar myself, actually.


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## gunrunnerjohn (Nov 10, 2010)

From all appearances here, enlarging the hole a bit on the left doesn't seem all that traumatic, and would solve the clearance issue very easily.


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## balidas (Jun 3, 2011)

HOSP4449Fan said:


> Chances of 2 trains passing here are pretty slim


That just makes Mr. Murphy laugh diabolically while dancing with glee.


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## HOSP4449Fan (Dec 2, 2013)

I've managed to get the space to 4.5 - 5 inches and could probably get a little more if needed. Trains will be running in from switches off the main line. I need to get my bench work done and check the clearance with my engines/rolling stock. I don't have much O scale stuff and this is the top level to a 3 level layout with HO on the lower 2 levels. I'm sure down the line I'll invest in some O scale stuff, but not in the near future. I also had to tie back a condenser line from the HVAC unit in the attic.


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## Lee Willis (Jan 1, 2014)

Looking good now. This is way better.


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## gunrunnerjohn (Nov 10, 2010)

Since the one track is straight, I suspect you'll have no clearance issues with that spacing.


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## Laidoffsick (Sep 20, 2015)

You'll have to make that hole bigger for more space. Even if you don't have big engines or cars now, you may want some down the road. We run 072 inside and 080 outside and went with 6" spacing. We can run anything without clearance issues. Prototypical? NO... neither is our center rail. Make the room now so you don't have to go back and re-do it later.


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## HOSP4449Fan (Dec 2, 2013)

Laidoffsick said:


> You'll have to make that hole bigger for more space. Even if you don't have big engines or cars now, you may want some down the road. We run 072 inside and 080 outside and went with 6" spacing. We can run anything without clearance issues. Prototypical? NO... neither is our center rail. Make the room now so you don't have to go back and re-do it later.


Well it turns out my loop in this room is going to be started with 072 and then 063 in the middle and 072 on the exit (4 pieces) due to width restraints. The room is 73.5 wide so I'm a few inches short of a full 072 loop. This will leave me limited to engines I can run on it. I went with a lil over 4.5" center spacing on the opening. Should clear 18" passenger cars fine. 



















from my Galaxy S7


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## Lehigh74 (Sep 25, 2015)

I was going to suggest that since you are using Gargraves track, you can use flex track to make the diameter greater than 63”. Many engines will negotiate smaller than rated diameters. My Lionel 751E for example is rated at 72”, but will do 68.5”.

But then I started thinking you could remove a section of drywall from the wall opposite to the opening / whole you already have, install a header with jack studs to support the stud wall above and buy yourself another 4” of diameter. Gotta keep your priorities straight.


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