Minecraft wiki entry for Activator_Rail, associated text: Activator rails (and other rails) can be used as "roads" for minecarts. A minecart that enters an activator rail's space from either end of the activator rail continues to move, losing only a little velocity (which can then be increased again with powered rails). A minecart that enters an activator rail's space from the side turns east or south (depending on the activator rail's orientation), or in the downward direction for a slanted activator rail.