train spotter

noun

1. a person who collects the numbers of railway locomotives
2. informal.
   a person who is obsessed with trivial details, esp of a subject generally considered uninteresting

Example Sentences

If you’re a train spotter, you’re going to hate it, because it’s not in the timeline, but whatever.

From New York Times

Forney was a cousin of 19th century steam locomotive designer Matthias Forney, so the museum is a train spotter’s dream.

From Washington Times

Unless you're paid to follow these things, or are an amateur political train spotter, you might struggle to put a name to every one of the seven faces - try naming the leader of Plaid Cymru if you're not living in Wales.

From BBC