Railways use track circuits to detect the presence of trains on a section of track. A track circuit works by sending a small electrical current through the rails, and when a train's wheels and axles bridge the two rails, they short-circuit the current, signaling to the signal box that the section is occupied. This information is used to control signals and prevent trains from entering the same section, which could cause a collision. If a foreign object, such as a piece of metal, is placed on the rails, it can also create a short circuit, causing a false 'occupied' signal and bringing trains to a halt.

In the Dutch incident, Prorail said that materials deliberately placed on the tracks caused track-circuit failures. This means the objects likely created a short circuit, making the system think a train was present when there was none. The result was that signals turned red, and trains were stopped or delayed to avoid potential collisions. Understanding this mechanism explains why a small object on the tracks can cause such widespread disruption.