ELI5 Trains - how do they grip slippery rails?

How do trains maintain traction on the tracks, especially during rainy or icy conditions? How do the wheels not slip off? Why do we always see stone or gravel on train tracks? How did early trains in the 1800s make sure they didn’t collide into each other? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: leprechaun2me, lblluke, kuddemuddel, toxiclayishimura_mjd, darthartero and dcsantonio To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]