Prototypically this was a common practice in years past. Depending on the era the ratio of home road, interchange (generally adjacent and/or partially owned by the home road) roads, distance roads, and other has changed. It is also effected by the commodities primarily carried by the home road, the actual routes, typography, etc. Read about the Clinchfield, Bangor & Aroostook, or the D&H. Anyway i'm sure others here will be more specific and detailed in their answers.
To answer your first question succinctly: Yes, it was common. I'll leave the rest of your questions to those who are more knowledgeable. I used to have a listing of the ratios (in 1950) published by the American Association of Railroads; if i can find it i'll post it.
