Factorio Train Signals: Diagnose a Blocked Junction

That Sinking Feeling When Your Entire Rail Network Freezes

You are deep into expanding your factory, setting up blue circuits or launching a rocket, and suddenly power flickers. You zoom out on the map, only to see fifty cargo trains frozen bumper-to-bumper across a single busy crossroads. A 2-4 hauler is nose-to-tail with an oil tanker, both waiting on each other in an infinite standoff. Welcome to the classic Factorio train deadlock. It is a rite of passage for every engineer, but fixing it does not require tearing down miles of tracks or starting your base over from scratch.

Most rail jams boil down to one simple misunderstanding: the difference between regular rail signals and chain signals. Regular rail signals only look at the single block directly in front of them—if it is empty, they let the train roll forward, even if the train will immediately get stuck halfway through an intersection. Chain signals, on the other hand, look ahead to the next signal down the line. They tell the train: 'Do not enter this intersection unless you have enough clear track on the other side to fit your entire train.'

The 'Chain In, Rail Out' Golden Rule and Spotting the Bottleneck

Diagnosing a locked junction is all about reading rail blocks. When you hold a rail signal in your hand, Factorio lights up your tracks in colored blocks (red, green, cyan, magenta). Every junction must be carved into its own isolated block. If a single block crosses over multiple conflicting paths, only one train can ever occupy that entire zone at a time.

The golden mantra every player swears by is 'Chain in, Rail out.' You place chain signals before every entrance and crossing inside the junction, and only place a regular rail signal at the final exit where there is a full train length of clear track waiting. In this guide, TuTu has gathered the clearest visual breakdowns and live debug sessions so you can trace block occupancy, spot missing chain signals, and keep your trains running smoothly forever.