The Pulse of the TGV: How TVM Signals Work Without Lights

TVM (Transmission Voie-Machine), which translates to “Track-to-Train Transmission,” is the dedicated cab-signaling system developed in France for their high-speed TGV network. It was designed to solve the same problem as the German LZB: drivers cannot see lineside signals at 300 km/h.

How It Works: The “Singing” Rails

Unlike the German LZB (which uses a separate cable loop) or ETCS Level 2 (which uses GSM-R radio), TVM utilizes the rails themselves.

The system sends Coded Track Circuits—electrical currents with specific frequencies—through the running rails. Antennas mounted under the train’s nose pick up these pulses. The onboard computer decodes the frequency (e.g., “Frequency A means go 300 km/h,” “Frequency B means slow to 270 km/h”) and displays it on the dashboard.

No More Traffic Lights

On a French high-speed line (LGV), you will not see traditional Green/Red traffic lights next to the track. Instead, you see specific marker boards:

• Block Markers (Jalon d’arrêt): Blue boards with yellow triangles. These mark the boundary of a block section.
• Cab Display: The driver sees a digital number (e.g., “300”) on the dashboard. If the limit drops to “000”, the train must stop at the next marker.

TVM Versions