My current and more than likely last layout is N Scale and models Santa Fe mainline from Kansas City to Hutchinson, KS. on the lower level and an upper level that continues from Chambers, NM, to Flagstaff, AZ. (Photo is of diesel facility in Argentine Yard - taken 4-10-00, by J. Stephen Sandifer, Houston).
Originally, layout time period was mid 1950's. From the beginning it was planned to be an operating layout, handling up to seven people. Unfortunately, good running N Scale steam engines are few and far between (IMHO). Gradually, I have converted over to modern engines and rolling stock. The modern Kato, Atlas & Life/Like diesels run SO much better than steam and early diesels (again IMHO). So I gradually updated layout to the current date. I will convert the roundhouse into a museum with a few steam engines around along with some of the early diesels and passenger cars. This gives us an excuse to run an excursion train from time to time. I am currently designing a small version of Kansas City's Union Station and plan to continue on with the construction. (I know KC is currently renovating the old station into a Science Center). I am building it as a station, slightly reduced - will cover only 8 tracks instead of 16-18. I am also lucky where mine is situated, I don't have to (can't see it) model the front of the station. My only explanation for having the station still standing/ operating in current day, is 'cause I want to!
Every Friday we have operating sessions with 4 engineers, yard master and dispatcher. Sessions last 3-4 hours, with car/cards. Unfortunately the layout was built just before DCC was popular, so it is analog, with 50 blocks controlled by rotary switches.