"Sometimes near the last turn, I can't build a route, even if I'm sure I have the right number of cards."

> Make sure you have enough plastic trains left!
At the beginning of the game you are dealt 45 trains.
Each time you build a route, those plastic trains are laid out on the map.
When you don't have any trains available anymore, you can't build a new route.
The number of trains you have is displayed on the bottom right corner of the screen next to your player icon and alongside your score.