By the way, how are the train times determined? Answer with SNCF timetable planners

If you take a train today, you will undoubtedly notice: your line’s schedules have often changed by a few minutes, sometimes more radically. And for good reason, every second Sunday in December corresponds to the approval of a new timetable (or, to use the technical term, “annual service”) in France and Europe. It includes all TGV, Ouigo and TER traffic scheduled for the coming year. But who decide to leave the train at 8:07 a.m. instead of 8:09 a.m. And how do you explain certain curiosities, such as the difference in travel time from one day to the next?

The design of these timetables is the responsibility of SNCF Réseau timetable planners. The subsidiary of the SNCF group, which is responsible for railway infrastructure, has 300 in the country and around a hundred in the regions. “The timetable planner is in a way the railway watchmaker. 15,000 trains in circulation every day, about six million hourly trains per year will be allocated.emphasizes Figaro Camille Fluteaux, technical support expert for schedule planners. Among these movements are obviously the passenger trains of the national operator (TGV inOui, Ouigo, TER, etc.) as well as those of its competitors (such as Trenitalia) as well as freight convoys or works.

Train timetables are drawn up two years in advance

“Hourly service is planned at least two years in advanceCamille Fluteaux continues. It all starts with requests for train paths from the nearly forty railway companies operating in the French network. A train route is a time slot on which a train is authorized to run between points A and B at a specific time. “On our design software, schedules are represented as a graph, with each line equivalent to a groove. The whole challenge is to respond fairly to these requests, ensuring that they do not conflict with other traffic.What follows is a Tetris-like puzzle that requires careful thinking and precision, especially on rush hour routes with busy stations. Thus, it may happen that the allocated train routes end up being different from the requested ones, as this SNCF Réseau technical document reminds us.

The length and mass of the train, the material used, the speed limit, the geographical profile of the line, the opening hours of the station, the availability of works… Many criteria are taken into account when distributing the timetables. “A train that works as a single unit [rame seule, NDLR] does not have the same features as a double unit train [deux rames accrochées l’une à l’autre, NDLR]just as a freight train traveling through the mountains does not have the same limitations as a commercial train traveling over flat terrain», Details Camille Fluteaux. Once the timetable is validated, the timetabler assigns the train number that appears on your ticket and on the station boards.

For the 2023 timetable (which therefore applies from this Sunday, December 11, 2022), train route requests were submitted at the latest last April. For cross-border routes, timetable planners coordinate with their counterparts in neighboring countries, which also break their timetables in December, as required by European regulations. Year-round services also include trains that run occasionally, such as services to mountain resorts in winter, to the coast in summer, to Strasbourg during year-end celebrations and even pilgrimage trains to Lourdes.

And in case of unforeseen events.

Once the schedule has been approved, it is not approved. After “construction,” the schedule planners move into the “adjustment” phase to adjust the schedule in the event of unforeseen events. A strike or technical incident forces a review of the transport plan. Similarly, traffic can be added at the last minute, for example in case of bad weather. “Timetable planners also contribute to the regularity of autumn trains by placing already installed railway washing trains in circulation, whose role is to remove dead leaves.“, recalls Nicolas, a schedule planner in the northern Paris chain, who passionately shares all the nuances of his profession. on his Twitter account @HorairisteSNCF.

To avoid a grain of sand in the gearbox, a pattern limit is sometimes added to the timing calculation. It makes it possible to absorb traffic vagaries such as long parking or signal failure. On a classic line, it corresponds to 4 or 5 extra minutes per 100 km. Thus, even with a delay of a few minutes, the train stays on its path and does not threaten to disrupt other traffic.