High-Speed Rail in France Signalling

High-Speed Rail in France Signalling

Because TGVs on LGVs travel too fast for their drivers to see and react to traditional lineside signals, an automated system called TVM, "Transmission Voie-Machine" (track-to-train transmission) is used for signalling. Information is transmitted to trains by electrical pulses sent through the rails, providing speed, target speed, and stop/go indications directly to the driver via dashboard-mounted instruments. This high degree of automation does not eliminate driver control, though there are safeguards that can safely stop the train in the event of driver error.

An LGV is divided into signal blocks of about 1500 m (≈1 mile) with the boundaries marked by blue boards with a yellow triangle. Dashboard instruments show the maximum permitted speed for the current block and a target speed based on the profile of the line ahead. The speeds are based on factors such as the proximity of trains ahead (with steadily decreasing speeds permitted in blocks closer to the rear of the next train), junction placement, speed restrictions, the top speed of the train and distance from the end of the LGV. As trains cannot usually stop within one signal block, which can range in length from a few hundred metres to a few kilometres, drivers are alerted to slow gradually several blocks before a required stop.

Two versions, TVM-430 and TVM-300, are in use. TVM-430 was first installed on the LGV Nord to the Channel Tunnel and Belgium, and supplies trains with more information than TVM-300. Among other benefits, TVM-430 allows a train's onboard computer to generate a continuous speed control curve in the event of an emergency brake activation, effectively forcing the driver to reduce speed safely without releasing the brake by displaying the Flashing Signal Aspects on the speedometer. When the flashing signal is displayed, the driver must apply the brake and target speed will be more constrained at the next block section.

The signalling system is normally permissive: the driver of a train is permitted to proceed into an occupied block section without first obtaining authorisation. Speed is limited to 30 km/h (19 mph), and if it exceeds 35 km/h (22 mph) the emergency brake is applied. If the board marking the entrance to the block section is accompanied by a sign marked Nf, non-franchissable (non-passable) the block section is not permissive, and the driver must obtain authorisation from the PAR, "Poste d'Aiguillage et de Régulation" (Signalling and Control Centre), before entering. Once a route is set or the PAR has provided authorisation, a white lamp above the board is lit to inform the driver. The driver acknowledges the authorisation by a button on the control panel. This disables the emergency braking, which would otherwise occur when passing over the ground loop adjacent to the Nf board.

When trains enter or leave LGVs they pass over a ground loop that automatically switches the driver's dashboard indicators to the appropriate signalling system. For example, a train leaving an LGV for a "ligne classique" has its TVM system deactivated and its traditional KVB "Contrôle de Vitesse par Balises" (beacon speed control) system enabled.

The most recent LGV, LGV Est, is equipped with European Train Control System Level 2 signalling together with TVM-430. It is equipped with GSM-R radio communications, one component of the European Rail Traffic Management System: the communications-based ETCS Level 2 signalling system is the other component, which makes use of the radio network. Trains can operate using either signalling system. Domestic TGVs use TVM-430, while TGV POS trainsets that operate into Germany use ETCS Level 2. ETCS Level 2 and TVM-430 use the same block sections, but use different means (radio links for ETCS, and track-to-train transmission for TVM-430) to transmit signal information to trains. Since ERTMS is mandated for eventual adoption throughout the European Union, similar installations including ETCS signalling are expected on future LGVs.