3. Signage principles

The basis of signalling is the dialogue between the "ground", which manages operations, and the train – or "traffic" – driven by man. This dialogue assumes that the traffic program is known and accepted: timetable, stops, speeds.

This is the "march" of the train.

The dialogue covers the following information exchanges:

• the train's position in space and time, i.e. its coordinates relative to the planned schedule;

• commands for adapting the walk to degraded situations that may arise during the walk.

The framework for this dialogue rules out any kind of improvisation, and is therefore subject to extremely rigorous "regulations", generally certified by the government authorities in charge.