Radius isn't the only aspect of track planning for instance there is also switch angle or size I use exclusively N°8 points or over because we europeans run engines and cars with buffers, under that size you will have buffer lock on the reverse curve. A minimum radius often found on engine terminal trackageand on wyes or interchange tracks on prototype railroads is around 11'6" radius, as John Armstrong used to explain in Model Railroader magazine, every engine or just about, can negociate that at very restricted speeds. My Accucraft T1, which is probably the longest rigid wheelbase engine you can find, negociates that. The beauty of Johns philosophy is that if real engines pass through those kinds of curves, gingerly, because the side play in real engines is practically identical to the one in our models (that is: not scaled down) and there aren't the dynamic forces that come into play with real size locos, ours can negociate these types of curves at cruizing speed. This is real good news to us modelers. however I can confirm from more than 30 years of operation in the garden, these kinds of curves do offer a big rolling resistance to the train. So bigger is adviseable. Also another important factor to consider in layout planning is the size of your sidings and yards. As long as I was modeling continental trains, an 8-9 meters siding was a going proposition, I could fit a7 coach passenger train in it when most pacifics handled 8 and about 25 continental size freight cars. Going american (and Pennsy to boot) means 40', 50' up to 70' freight cars and up to hundreds of them. Suddenly my siding looked ridiculously short... On the other hand I confirm that one has to keep things in reason very large layouts means that your train starts to look like N gauge once they are far away. And depending on your climate the maintenance can easely get out of hands. my track is about 50 meters in circumference. Because of my US modeling, I am contemplating replacing the 11'6" curve by one of17'6" radius which should lengthen the main to around 60 or so meters. But I will also lengthen a siding considerably. The larger the curve and the pointwork the smoother the operation and the better trains look, this is the most important factor for me. When I look at some videos of GG 1 or big boys going over some 4foot cuves it makes me sick. These weren't rapid transit equipment at all. So why have them run on rapid transit type of right of way? If you must use that type of curves go narrow gauge or Rapid transit. Especially out of doors. I mean that, after years of beying limited by the size of indoor space available to my hobby, coming out of doors was like discovering freedom after years in jail. There are limitations out of doors also, my terrain for instance is on an average ten percent gradient: Too steep to climb. But I took advantage of that to have the track at ground level on one side and at table top height on the other. Great for manual controling of our steamers, on the fly. Think and plan carefully, you will be happier on the long run.
