The clock runs to the end
Each level asks you to deliver a number of trains, shown at the top of the screen, before the clock runs out. When you reach it, the level is won, but the clock keeps going: the time left is a bonus round, marked Bonus.
During the bonus round, every delivery scores double and a mistake costs nothing. The win is already yours.
Points and streaks
A delivery is worth 100 points. Deliveries in a row are worth more, up to 180 points from the fifth in a row. A mistake ends the streak.
Your score is your points: it does not depend on the level number. A level's best score is the best of your wins.
Stop when you want
Pause during the bonus round and choose Finish — keep the win to end the level at once.