> The tracks at Tobin, Twain, and Quincy Jct. connect to the main on both ends, like a siding. But for operational purposes, they are not sidings nor are they controlled track. UP refers to them as "Business Tracks".

Good examples. For a track which connects to the main track to be a "siding" it must be specifically designated as such in the timetable. Stub sidings have only one switch, although these are virtually unknown on the class 1 RRs. From the GCOR: A track connected to the main track and used for meeting or passing trains. Location of sidings are shown in the timetable. The SP referred to business tracks as "additional stations", and I dimly recall the AT&SF referring to them as "tracks between stations".

In other words, just because a track is connected to the main track at both of its ends doesn't necessarily mean it's a siding.