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Still moving forward. Am using Scarm now and really enjoying it. One thing that keeps comming up is what minimum radii to use on mainline and in yards? Also the same question for switches I guess,,,size turnouts for yards and mainline? Era; 1940, hoping to use some diesel and maybe passanger cars from that era. Any help will be appreciated. Q


Certified Great Northern Nut
What scale? :)

For HO I would say absolute min radius is 18". I used 20" for all my curves and when I move and do it over I'll use 22".

I would use 22" on the main and min 18" in the yards personally.

#5 switches in the yard, you could use #4 if you have to.

Min #6 on the mainline.


BN Modeller
I’d say it all depends on your available space.
No matter what the scale is, generally the biggest radius you can fit the better.
And I agree about #4’s or #5’s in yards, on mains I’d stick with #6’s or #8’s.
Again depending on your space and type of cars.


Well-Known Member
Staff member
As you will be, by the 1040's, getting into the era of the lightweight 85' passenger cars, which I think even the earlier heavyweights were as well, radii of 22" min will be essential. Turnouts in yards would be tight at #6. And the rule where you have turnouts back to back forming an S between parrallel tracks is to have a straight length of at least a car, between turnouts so you don't have the ends of coupled cars swinging in opposite directions


Well-Known Member
I was under the impression that you were doing N scale.

As far as track the only thing I would add is I would use either #6s or #8s in the staging yards , engine facilities ...anywhere a road locomotive might go.

I don't know how close to the prototype you want to stay but , 1940 diesel power is going to be pretty limited, mass production of diesel locomotives didn't get really get going until 1939 , so not many would have been delivered by 1940 ., The choices are some what limited in that era for diesel , EMD FT s and VO 1000 s . Post war period is when diesels begin to take hold . Most FM and EMD prime movers were used by the Navy for submarines , early Alcos were "requisitioned" by the Army ,Baldwin built a few VO 1000 s and 660s .

The lions share of EMD FT road diesels were allocated to the ATSF , but other roads were allocated some , but not everyone got some ( the PRR > 0 and the NYC >4 ?).

Basically the ATSF was allowed to switch to diesel during the war , everybody else pretty much got screwed .

Things eased after 1946 , orders and production took off . GPs and SDs start showing up in 1950 . Steam is fully phased out by 1960.

Cars shouldn't be a huge problem . Just look for the BLT date on the sides .


WOW as usual I got much more information that I could have hoped for and Thanks to all. I am sorry I forgot to include N scale is what I am using. Now it is back to the drawing board to get allot more questions. Thanks again for the informative answers. Q


Well-Known Member
Minimum radius. Really broad rule of thumb, minimum radius of 3 times then length of your cars.

Remember minimum radius is a MINIMUM, that is the bottom below which you aren't going to go. Standard radius is the one you shoot for for most applications. The minimum radius recommended by the manufacturers is a harder bottom. That is the radius below which the model starts to not work well. The risk with going with the minimum radius is if you aren't really consistent with your track laying, its possible to end up BELOW the minimum and that could result in the track not operating well.

Your track will be more reliable if you set a minimum and then try to stay above that, for example saying 18 is the minimum and trying to stay at 19-20 in radius will end up being way more reliable.

As far as switches go, a number 6 will handle about 95% of all the model railroad equipment. A number 8 looks really cool, but takes up a lot of room. Figure a switch in HO is as long as twice the frog number. A number 6 switch is nominally a foot long. A #6 crossover is about 2 ft long.

Another thing to watch is track centers. The tighter the radius, the more "swing out" and "overhang" cars will have. With 2" track spacing on 18" + 20" radius, running long cars (passenger or auto racks) may result in the cars hitting each other on the curves. For really tight curves allow an extra 1/4 to 1/2 inch of track spacing (ex. 18" and 20 1/2" radius) to make sure your cars won't sideswipe each other. Once you get over 24-27" radius its not as critical, or if you are only running 40 ft or shorter cars its not as critical. For example I model 1903 and the longest cars I have are 50-60 ft passenger cars and most freight cars are in the 34-36 ft range. For me having 2" spacing on 20" radius curves, not a problem. However if I tried to run 89 ft piggyback cars, auto racks and SD90's by each other, there could be issues.

(OOPS, just noticed you are in N scale, completely changes the numbers, but the concepts are the same.)

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