1909

This type of line blocking, the Webb-Thompson rod system, was very common in Great Britain right up to our days.

The principle is that the two stations bordering a "rod section" each have a container with a certain number of rods. The two containers are electrically connected to each other. When a rod is taken out from either of them, it is not possible to take out another until the withdrawn rod has been returned to either of the containers.

Since a train is not allowed to proceed without a rod, two trains cannot simultaneously be on the same rod section. The rods are differently designed for different sections and only fit into the "correct" containers.

The device was in use from 1909 to 1922 on the single-track lines Djursholm Ösby–Täby and Djursholm Ösby–Djursholm Sveavägen at Stockholm–Roslagens Railways.