Minecraft wiki entry for Minecart_booster, associated text: Minecarts behave in a unique manner when running alongside one another - they accelerate rapidly. This effect is used to create boosters. A booster consists of a short track with another minecart placed next to the track you want to boost. The two tracks must have one or more blocks of contact. When your minecart is next to the other cart, they will both accelerate. There is a maximum speed (8 m/s, 1 block = 1 meter), but the internal value from which speed is derived is not capped, allowing the cart to maintain the maximum speed for much longer than it would normally be able to. However, if a minecart is repeatedly accelerated this way for a long period of time, it may suddenly stop, most likely due to an integer overflow resetting the value to zero. To avoid this, make sure that no cart is continuously being boosted over a long period of time.