The ICG has been developed to be an operations based layout. If you are not familiar with what protype operations is all about, then go to the OpSig site and read up. When I first learned of "operations" it did not interest me at all. It sounded like maybe some people were taking this hobby a little too seriously and just needed to relax and enjoy the trains some more.
Boy was I in for a surprise. My first exposure to operations was at the USRA layout that was located at Union Station in Indy. A couple of the members talked the rest of us into "operating", and it totally changed my perspective on the hobby. Building layouts, trains, kits, etc... is fun. Running trains is fun. After a while though, I think you need some purpose to all of the work, and for me, that has become ops. Not only does it give the layout purpose, it is another aspect of the hobby with its own sub-set of topics and interests, and it is a very social part of the hobby.
Since I joined the OpSig, I have been to prototype operations weekends in Chicago, Ft. Wayne, and Detroit, and have operated at a few conventions. These have all been great learning experiences, getting to see how so many other layouts accomplish this lofty goal. It takes layout planning, quality track and equipment, and a well though out operations plan for the whole thing to flow well, and I find that challenge to be motivating.
I am not the prototype stickler like some, so I am not concerned about mimicking the traffic that "ran over the line on March 11th, 1977", nor am I even that concerned at this point with just modeling specific industries that were on the ICG in the era that I model. I do what I like within reason and what I can justify in my own mind. My operations plan will look like ICG traffic for the most part, but definitely not 100% accurate, and that's ok with me.
As of March 2010, I am still tweaking my op plan, but I have held a few formal op sessions using RailOp to generate traffic, and using CATS to dispatch although I do not have signals on the layout yet. Here is a list of the trains that I run based on an A.M. and P.M. session. The ICG actually ran all trains as extras in this era (except Amtrak) so there is no real time table.
Learn more about operatons related software on the software page.
There are some great articles on model railroad operations on the Gateway NMRA site.