There are 4 action cards. When one is turned over, its effects are applied immediately, then it is discarded. This reduces the kilometer counter by 50. Discard it along with 50 points of positive km cards. All players remove the most recent card from their runs, and toss them on the discard pile.
All players immediately place one extra card on thier run.
All players add 2 cards to their run. Then the Start Player card passes to the next player. If you've burned through the draw pile, shuffle the discards and make a new one. End of a Stage A stage ends when the kilometer counter reaches a certain value at the end of a round. If the number is reached before all of the km cards are turned up, keep going.