Factorio Forums

I got a idea for the game what about under grown trains? Like how the under grown belts work I like to see a train in the same way.

I guess you mean underground ?
It has been asked many times before, but there is no clue the devs plan to add this to the game (and I don't think it will).
It would remove almost all the interest of rail signaling.

It would make a lot more sense to have a bridge than a tunnel, but like stated I don't see it being implemented.

Main problem is what to do with trains stuck in the tunnel or people leaving trains while in the tunnel.

The OP's suggestion has already been suggested in the following threads:

viewtopic.php?f=6&t=46978 Underground Rail
viewtopic.php?f=6&t=44338 Underground rails

I kind of like the idea of under grown trains. Little mini trains darting around your railway, sounds cute.