My dads dad (and his dad lol) and all his bothers and sisters have all been working for the 'Deutsche Bahn'. ( my generation stopped that none of us is working there lol) so they are all model train obsessed.
I have no idea what brands are there in the US for that stuff but in Germany Fleischmann and Märklin are the 2 main brands.
My dad has (spend wayyyy too much money on that stuff) a ton of different sizes, as kids we use to have mainly LGB (which is 1:22.5 , so rather big) then my dad added HO and O stuff.
He has a ton os special, and rare engines (such as the https://en.wikipedia.org/wiki/Crocodile_(locomotive))
He also upgraded his stream engines to actually steam and make noises and such lol
He even had like train ports with a 'drehschleife' (like that thing the engine drives on and it has a peice of track just long enough for the engine and it can turn it around? no clue what that is called in english lol) but in LGB size those things weight a ton and were no cheap lol We usually build it up for christmas. laster when me moved from a condo into a house he build a huge mini landscape in the basement.
I did not care too much about it though lol but my neighbor, who is my age was really into it and had a ton of native stuff from Märklin that could control and program multiple trains (I think it was called Märklin Digital). And I know there are several museums dedicated to that, having models trans and landscapes and cars and all that automated. http://www.modellbahn-im-museum.de/ but the last time i looked into that , that was years ago, I am sure nowadays woth the Pi and arduino it should be easier and cheaper to get stuff like that automated, though it is still pretty technical as for the cars, you either have to have electric cars and program the route in them, or have like a magnetic track under them they can follow. Many options.... if you are into that stuff, you can dump a LOT of money and time. lol