Minecraft wiki entry for Minecarts, associated text: When an empty cart is detected, generally it's a good idea to send it into an overflowing pile. An overflow pile is a drop of two or more blocks with a rail at the bottom. When carts are boosted into the hole, they snap to the track, regardless of how many carts are already on the track. This pile should be placed where the carts can be collected, either close to a station or in a maintenance area. It is important to boost carts to full speed just before they are dropped to ensure they don't become stuck on the end of the track and eventually back up the system.