Wye tracks are a good mean to adjust a minecart's travel direction.
They are placed in the world by right clicking a spike maul on a flex track and cycle through possibilities. By default, wye track kit is the second possibility, after turnout track kit.
They can be controlled by an switch actuator, either lever (manual), motor (signal/redstone based), or routing (routing table based).
When a player break the track kit, it drops nothing and becomes a piece of flex track.