Imagine your four-way shuttle AS/RS is running at full speed. Orders are coming in, shuttles are moving, and the warehouse control system is assigning tasks as expected.

Then you notice something strange: throughput starts to drop.

Some shuttles are waiting near lifts. Others are taking longer routes than expected. A few tasks remain unfinished even though the equipment appears to be working normally.

What's going on?

If you're designing or operating a multi-shuttle warehouse, this is a problem worth understanding. Adding more shuttles may seem like the obvious solution, but congestion is often caused by how equipment shares resources, how tasks are scheduled, and how the system handles conflicting movements.

Let's look at what causes these problems and what you can do to prevent them.

1. Why Does a Four-Way Shuttle System Become Congested?

A four-way shuttle can travel horizontally and change direction at compatible intersections, depending on the rack and rail design.…