John et al -- Turnouts are in fact eased. If you consult the AREA (American Railway Engineering Association) dimensional standards for turnouts, you will find that the curved closure rail is eased, then straightened through the frog. AREA tables also provide the effective radius of the curved branch; these radii are generally quite a bit larger than the typical model curves. There is no standard for No. 4 turnouts; the tables start with No. 5 (closure radius of 178 feet, 33 actual inches in S). (PRR has different standards -- Their smallest is a No. 5.289. Go figure.)
That said, I have standard turnouts only in my terminal/yard area. These are No. 5 for freight yard, No. 6 (259-foot radius, 48.5 inch actual inches in S) for the passenger terminal and coach yard. Elsewhere, I drew centerlines using heavy O scale (.172) rail to draw easements between tangents and curves, and I built the turnouts to follow the centerlines. The result is smoothly-flowing trackwork. You might ask where one purchases turnouts manufactured to AREA standards. Well, I don't know and don't care. I have scratchbuilt all of mine. I'm not recommending that in general; it's just that constructing trackwork is my first love in model railroading, and I am somewhat sad that I have no more trackage to construct. Dick Karnes Mercer Island WA
