Four different methods for counting trains passing by:
- with (normal) signal
- with chain signal
- with gate
- with rail
Use the signal method where you already have a signal or can place it without influencing your train network. It works perfect (no false positives).
Use gate method if you don't want to place additional signals in your existing setup. Could cause false positives when players passes by and gate is opening not for the train but for the player.
Use rail method for a counter with no additional signals (at least no active signal, because it is on its own 1-tile track) and if you want perfect counting (no false positives).
The chain signal method is a bit wanky because it counts not only for the track it is places on, but also for the other tracks/blocks which affect the chain singal.