It’s what you might call a high-speed medical auscultation. Even at very high speed. The patient is both monolithic like a rail and electric like a catenary. Welcome aboard the SNCF Iris 320. Iris as “Quick inspection of security installations”, and 320… like 320 km/h! This train is the only TGV entirely dedicated to monitoring the state of the rail network.
1,500 km traveled every day
It systematically covers 1,500 km of high-speed lines every day (160,000 km per year). “Each kilometer of a high-speed line (LGV) is inspected every two weeks, explains Alain Thiébaut, head of the LGV division at SNCF Réseau, the branch of the rail group that owns and manages the infrastructure. If this frequency could not be respected on a section, the speed could be lowered there as a safety measure. » At the risk of consequences on the regularity of traffic.
The classic tracks are examined less frequently, with slower trains. Why this difference in treatment? “The faster a train travels, the faster defects appear on the rails and tracks,” replies the SNCF Réseau specialist.
Two glazed turrets on the roof
The Iris 320 began to circulate in 2007, but its project is much earlier. “We knew that new high-speed lines were going to be built and that the number of trains would only increase there, recalls Alain Thiébaut. It was therefore necessary to have a surveillance train capable of traveling over many kilometers and as quickly as the TGVs so as not to interfere with traffic. »
On this Thursday in October, it is a little after 1 p.m., and the Iris awaits its departure for Paris at the edge of a platform at the Le Mans station (Sarthe). From the platform, nothing distinguishes it at first glance from a classic TGV train, except for its livery which bears the inscriptions “Vigirail” and “Network Monitoring”.
Observing it better, we notice two glazed turrets emerging from the roof. They house cameras that film the state of the catenaries, the overhead cables that power the train electrically. Other details are less obvious to notice for a neophyte, such as multiple boxes fitted with sensors placed near the wheels or under the chassis… For the rest, the eight cars seem to be waiting for their passengers, except that they do not carry usually only a handful of SNCF network technicians.
Data every 25 cm
It is 1:25 p.m. and the Iris 320 leaves for Paris Montparnasse station. No travellers, therefore no seats, if not about fifteen who make up a kind of VIP lounge. A little further, there is a meeting room, a space for the meals of the technicians with a tiny kitchen.
If the sensors are distributed along the train, most of the screens and computers are in the first three cars. The data collected is considerable because no less than 75 sensors scan the track… every 25 cm, at 320 km/h and without contact, thanks to its cameras and lasers.
Accelerometers, force, displacement and pressure sensors, electric arc detectors… The measurements accumulate in the form of curves on countless screens that the technicians scrutinize, measurements precise to the nearest millimeter.
Watch out for the slope
The spacing of the rails is thus scrutinized, as well as their horizontality (the leveling) or even the “cant”. The cant is, to simplify, the difference in height between the two rails in curves. “You sometimes meet people who think that train drivers have a steering wheel, says Alain Thiébaut. But the train is only guided by the rail and it is the difference in height between the rails that allows it to engage in a curve. »
In France, the maximum cant is 18 centimeters. It is found in Burgundy, on an LGV line that crosses the Yonne. If, by bad luck, a TGV broke down at this precise point, travelers would lean to the side…
When certain anomalies detected are significant, they give rise to immediate reactions with alert messages which can cause the speed of all trains to slow down while waiting for the dispatch of maintenance teams. Otherwise, the data will be processed within 48 hours. Arrived in Paris, the Iris 320 will leave for Saint-Pierre-des-Corps, near Tours. And continue his long wandering as a rail watchman.
2,700 km of high-speed lines
28,000 km. This is the total length of the railway lines of the French network, where 2,200 signal boxes are installed, and of which 16,000 km are electrified.
2,700 km. This is the length of high-speed lines (LGV). That is more than 5,000 km of tracks since the LGVs have two. It should be noted that some are the result of public-private partnerships and possibly maintained by companies other than SNCF Réseau. This is the case of the South Europe Atlantic Line, between Tours and Bordeaux.
From 800 to 900 TGVs circulate every day on the 15,000 daily SNCF trains. The Paris-Lyon line, with the 230 TGVs that travel there daily, is the busiest high-speed line in Europe.