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In North America, equipment for unlimited interchange between railway companies is built to accommodate for a 288foot (87.8 m) radius, but normally a 410foot (125.0 m) radius is used as a minimum, as some freight carriages (freight cars) are handled by special agreement between railways that cannot take the sharper curvature. For the handling of long freight trains, a minimum 574foot (175.0 m) radius is preferred.[3]

Link to Wiki
https://en.wikipedia.org/wiki/Minimum...

To translate that into model railway terms, 288 feet becomes 3’ 3 ¾” or 1.09 m in HO Scale
410 feet becomes 4’ – 8 ½” or 56.5 inches or 1.436 m in HO scale
I did not calculate 574 feet