There are trainspergs, we know them, we giggle at them. Such as my ex's old man. He was a trainsperg par excellence and had been all his life. I'm pretty sure his entire career and family (he was a lawyer also) was secondary to his main passion in life, which was the collection and assembly of increasingly excessive model railway layouts.
I tried to get into this and understand for the sake of familial harmony but the barriers to entry in railway modelling are enormous. You need space, carpentry skills to put together the baseboards and scenery, huge disposable income (even entry-level OO/HO scale models are not cheap, and at O scale you can spend thousands on a single locomotive), endless time, endless patience, an autistic level of research into exactly what was where (and yes, you WILL be sneered at by your fellow trainspergs if you put a type of loco or carriage on a recreation of a line that it was never run on in real life), and, for truly advanced trainspergs, the ability to design custom electronic circuits and programming for the signals.
Then there are track bashers. I only met one of these once when I was at university. They will go on endless tours of the railway network to try and get into a particularly unusual or odd bit of rolling stock, like a BR Mark 1 carriage or behind a Deutsche Bahn class 103 for the continental track basher. (Allegedly Deutsche Bahn digs out its older locomotives when trainspergs are in town to attract them.) Steam engines give them erections and make them declare that things are "dreadful" or "hellfire" (both compliments) and they thrash about and proclaim, "MY LORDS!" when particularly, erm, excited. (Contrary to popular belief, going into a tunnel at 100mph while in a carriage behind a Class 47 doesn't make them spunk their pants, but it might as well.) If they were actually to pull the whistle on a steam loco they would probably die there and then, their life complete.
I don't know what it is about railways that attracts spergs that other forms of transport don't. Yeah, there's planespergs but they just gather in small groups at the borders of Air Force bases and tick off the fast jets as they come and go. They don't have conventions too much, and the hardcore ones engage in the comparatively harmless hobby of playing endless hours of IL-2 Sturmovik or MS Flight Simulator X or suchlike. There are carspergs, but that's understandable considering a fancy or fast car is generally an adult toy if that makes sense, or a status symbol. There are bus spotters but they're considered :autistic: even by railway enthusiasts. And boat spotting requires going to a harbourside or wharf and most of the really big boats spend their time out at sea away from the autism.
But trainspergs, they are serious and numerous. They have conventions. They give courses on how to model their layouts in ever more autismal detail. They go on heritage railway rides. They buy old bits of signalling and trackside paraphernalia. They artificially weather their models to make them look like they might have looked at the time. Railway companies and operators will actively engage with them and cater to them. This does not happen with busspergs, boatspergs, or planespergs.
Any ideas anyone?