prrjim posted:ON30 and ON3 are both valid track gauges. However, very little common carrier, if any, was built to 30 inch gauge in the USA. I think there has been quite a bit of industrial narrow gauge at 30 inches. 3 Foot gauge (36 inches) was used a lot for common carrier shortlines in the 1870s and so. There was a major movement to build "narrow" gauge lines because they were cheaper to build and maintain in every way. Colorado had over 1700 miles of narrow gauge at one time. The East Broad Top in Pennsylvania is another famous 3 ft line. There was also the Ohio River and Western which ran from near Wheeling to Zanesville OH and the Washington and Waynesville which ran between the namesake towns. The B&O was involved in the Pittsburgh Southern which was built to 3 ft and then standard gauged in a few years. Maine had a small system of 2 ft gauge common carriers.
so could you use ON30 track to model ON3? Probably that would work as well as using 5 ft gauge to model 4 ft 8 1/2. Some people will not like it and some wouldn't do it.
Thanks for the explanation. I knew Colorado had narrow gauge, but I didn't know which size it was. I've heard of the Broad Top, but did not know it was narrow gauge. Also didn't know about any of the others you mentioned. My LHS has some On30, but I am not sure I have ever even seen any On3? (Pretty sure I have those correct here?). Maybe I'll ask them about that one.
I really am 'prototypically challenged', wasn't kidding about that. 
If it looks like a train and runs well on my Atlas track I am happy. I do like the more detailed models they have these days and also command control, but have no idea if they are correct or not. The correctness doesn't bother me as I don't know the differences. I started out with RailKing when I got back in the hobby in 2011, but have now moved up to to the actual O-scale sized trains. I like the looks of the larger, actual correctly sized items over the smaller ones available. I actually like 3 rails though, from what I had as a kid it just looks right to me. The postwar trains I had as a kid really look small to me these days. 
Maybe I am being slowly converted to the more prototypical items as I go along? Anyway, thanks for the info, it was interesting and I always learn something! However, remembering it all is the tricky part these days, as I get older.
