HO Track Angles

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New Member
Can anyone help me find angles and radii for common HO track? I plan on using mostly Atlas Track, so I would like to know that a Custom Wye comes in straight and branches at 15 degrees left and right (example - guessing on the actual?). Another example, a right Snap switch is actually a 9" straight + 1.5 inches, overlaid with 2/3 of an 18" radius turn covering 60 degrees.

I have templates, etc, but would like to be able to do the math, geometrically speaking...:) I would like to "see" the dimensions so I could better understand the various turnouts and their advantages.

Thanks in advance!


I have an Atlas track layout book, and in the back it has drawings of all the track Atlas makes with that type of info. I think it's the mid-size layout book, but I'm not sure. I'm pretty sure any of their layout books would have that info.
Check your LHS. They probably have one. BTW it's very inexpensive.


Fun Lover
Typically turns some in radii, 15", 18", 22", etc. But turnouts are given by number. 4,5,6, etc. What the number stands for is the ratio of distance to divergence.

If you think of the move of a knight in chess. It moves two forward and one over--and if it were a turnout it would be a #2.

So a #4 turnout would be four units foward and one over. An #8 would be eight units and one over, etc. I don't know what the angles of divergence would be because I just think of them in the terms above, but you could could get them with your good old Texas Instruments trig calculator.


Milw Road in SW Wisconsin
Atlas Track Geometry

Atlas has basically 2 different geometries for their track:

o - The 'Snap Switch' has a constant 18" radius curve through the divirging leg and leaves the tangent at a 20 degree angle.

o - The 'Customline' trackage uses prototype configurations and use the '#' system. Basically the #4 divirges at a 12.5 degree angle, the #6 at a 9.5 degree angle, and the 'wye' divirges at a 9.5 degree ange to each side. Understand that there is no 'constant' radius through the turnout, so it is hard to calculate a 'replacement radius' here. Trains(real or model) will run better through these turnouts due to the straight section through the frog.
BTW, the Atlas Customline #4 is really a #4.5 turnout. A #4 is really tight, and the Atlas turnout is great for industrial spurs. I use the Atlas Customline #6 turnouts for all of my passing sidings, and yards. I use the Customline #4 for industrial spurs and some house tracks.


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