I currently have my model layout in storage, however I model GTW (with DTSL), BN, DM&IR, (shortlines AA and D&M), with B&O and Amtrak passenger service. I don't believe in a paticular time frame or following a prototype, except for the industries. I run SD70s with F-units and have a FP45 painted in GTW. I do run a few steam engines but they are mostly for excursions or rail fan trips. I follow Michigan railroading, and do apply many of the same industries to my model layout.