Here are some rules clarifications and answers to frequent questions on the game:
Question: Can you add more than 1 level to a bunker in a turn?
Answer: No, you can only 1 level (the next one) to a bunker in your turn.
Question: In the example on page 4 only 2 cards are use to upgrade that bunker. Why is that different?
Answer: The example is wrong. You need 3 cards (1 face up and 2 face down) to upgrade a bunker to level 2.
Question: Is there a hand limit?
Answer: No, you can have an unlimited number of cards in your hand.
Question: When you move a train/truck are the cards you pay placed in the new location (where it is being moved to)?
Answer: Yes, its says in the rulebook: "place them in the new region where trucks/trains are departing from".