Minecraft wiki entry for Minecarts, associated text: With simple switching, a minecart can be temporarily diverted into a small loop of powered rails and left there to accelerate. After a delay, which can be achieved with either repeaters or a hopper timer, a second switch can be activated to set the minecart loose down the track. Using this method, with fairly modest delays (in the range of 10-20 seconds) a set of four powered rails can be used to propel a minecart at full speed for several hundred blocks, thus vastly exceeding the efficiency of placing powered rails along the track.