Players are separated into groups ahead of time. Which group you end up in depends on how actively you play the railroad game, and what level you’ve made it to. If you’re already taking part in a marathon, you can’t change groups during it. That said, you can end up being sorted into a higher-level group when the next marathon rolls around. To do so, build more train stations, upgrade your trains, and actively play the game.

Have fun playing the game!