There is a track radius tab to find the radius of track...but when I lay track I like to have a full circle of "FT 15 Degree 250 Meter Radius" Fixed Track. I keep this on all layouts, and never delete it...when I need it, I slide it across the route, and lay track on it using the "Hold Shift" key method of laying track. Then when I am done laying track, I slide the circle of track out of the way, and put it asside on my "Painters Pallet" of often used assets, that I have on a out of the way on a unused baseboard.
The PRR Horseshoe Curve is the equivilent of "FT 15 Degree 200 Meter Radius" Fixed track. Some branch lines use much tighter fixed track equivilents. It seems that this is the only way to get a perfect circle of track in Trainz.
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