The Disembarking Track is used to eject a rider from a Minecart. If the cart is being ridden by an entity, it will eject that entity when it passes over one of these rails. If the minecart is empty, there is no effect.
It must be powered with Redstone to function.
One use is to set up an automatic ejection system to remove mobs and animals from your carts. Place an advanced detector under the rail, pointing up, and program it to detect mobs and animals. This will eject them from the cart, but not you.A system like this combined with gated track can make an automatic mob/animal sorter.