Track trains are brush-based entities that move forward and backward along a path . The path that track trains follow is made up of linked point-based path_track entities. Track trains come in two main varieties: player-controlled and automatic. Player controlled track trains, when used, override the player's forward and backward movement keys to control the train movement. These trains can be ridden and have the ability to switch the path they take with external triggers. Automatic track trains are controlled with external triggers and have no direct player control. An example of an automatic track train could be a platform with more than one movement direction or, as we'll soon see, an invisible box acting as a camera's target.