File Extension TD4 File Format Saved track design (Roller Coaster Tycoon) TD4 stands for Saved track design (Roller Coaster Tycoon). This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question E-Views: Riding the roller coaster to recession Ariba to change operating model Will stock market instability incite IT strain?