Can I play on other players trains or the community train - if I haven't started my train?

It's very frustrating when you don't have the opening tile to start your train ....

But don't worry - you can still play on any open train or on the community train - 

even if you haven't started on your own train.

You must always answer a player's double even if you haven't played.

 In fact, many people have won the game without every playing on their own train.  

This leads us into the discussion of how many tiles you need to answer a double ....

Many people answer a double with just one tile.  We prefer answering a double with three matches.

This creates a chickenfoot.  The three tiles look like a chickenfoot.

This forces other players to answer your domino before playing a tile on their own train.  It's a very strategic play, you can do it early in the game, so you create three opportunities, for you to place tiles.  Additionally, you derail your opponent's train by disrupting their hand.