If you take a Locomotive from the face-up cards, you can only draw one card that turn instead of two. If the replacement card that gets flipped up is also a Locomotive, you cannot take it as your second card.

No, one player cannot claim both routes to the same cities. In 2-3 player games, only one of the double-routes can be used by anyone - once someone claims one route, the other is closed to all players.

If at any time three of the five face-up cards are Locomotives, all five face-up cards are immediately discarded and five new cards are turned face-up to replace them.

No, you are never required to connect to any of your previously played routes. You may claim any open route on the board, even if it's completely separate from your other routes.

No, gray routes can be claimed using any one color, but all cards in the set must be the same type. You cannot mix different colored cards together, even for gray routes.

You lose points equal to the value shown on any Destination Tickets you fail to complete. These points are subtracted from your final score at the end of the game.

When drawing Destination Tickets (either at setup or during the game), you must keep at least one card but may keep two or all three. Any returned cards go to the bottom of the deck.

If the deck is empty and there are no discards (because players are hoarding cards), you cannot draw Train Car cards. You can only claim a route or draw Destination Tickets on your turn.