I'm a bit confused on the rules and restrictions for laying track.
For example if I already have 2 cubes from Chicago to Kansas City, would these situations be legal for a 3 track lay.
1. Would I be able to lay between Tulsa, Springfield, and Omaha? I assumed no because it is a fork and not continuous.
No. Fork and not continuous.
2. Can I lay Rock Island, Springfield and Memphis? It is one line, but the the 3 cubes are not directly adjacent.
Not sure what you are trying to do here. Go through Saint Louis?
In any event: not legal.
3. What about a loop like Tulsa to Springfield back to Kansas City?
No. Each track you add must (1) be directly adjacent to the previous one you just laid and (2) connect to a city which that color's track had not previously connected. The loop clearly does not satisfy #2 as you already had track into Kansas City when you built the last piece of track to go there.
As always, the mailing list is a better source as John will answer your question and his rulings are definitive.