Coupler Track and Decoupler Track are two tracks designed to be used to join or separate trains of carts. They must be powered by redstone to function. When you run two carts over a Coupler Track, one after the other, they link. If 2 linked carts move over a Decoupler Track, they unlink. Trains are useful for subway systems in SMP, as you can build a subway between houses and other buildings.
|Coupler Track:||Decoupler Track:|