“Our network was not built to work with such heat,” said transport minister Elisabeth Borne during the June heatwave, when trains were delayed or stopped.
Steel train tracks expand and contract with temperature changes. They get longer when they heat up, which puts stress on the fasteners that keep them anchored to the ground. Once they get above 45 degrees Celsius, they can expand enough to buckle, which can derail trains.
In direct sunlight, tracks can get up to 20 degrees hotter than the ambient air, so temperatures over 30 degrees are a concern.
Other hot weather problems for involve the overhead electrical wires that also can expand in the heat and touch the tops of the train carriages. High temperatures can also damage electrical components along the tracks, and even cause fires.
Managing the heat
The French rail company, SNCF, has a high heat plan that goes into effect once temperatures hit 35 degrees. It provides support to passengers, including water distribution. Once track temperatures hit 45 degrees, workers start conducting close inspections.
On Thursday track manager Adrien Bobillot was taking the temperature of a stretch of track near Paris: 56 degrees at 3pm. He said it was likely to get to 60 degrees, which “might be our record”.
He and a team were walking slowly up the tracks in the afternoon, during the hottest period of the day, to check on tracks and fasteners. Some team members joined conductors in the locomotives “to look at the track’s movement” from the train, said Bobillot.
If these inspections find that tracks have expanded too much and are starting to move, they will call for slowing down the trains. Slower trains put less force on the tracks, which can avoid derailments and other problems.
The SNCF asked travelers to the heatwave-hit regions on Thursday to cancel or postpone their trips, offering free ticket exchange or reimbursement. It warned that some trains would have delays, especially high-speed TGVs, which would be running at 280 to 300 kilometers per hour, rather than the usual 330 kilometers per hour.
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Paris metros and commuter lines were running at reduced speeds on Thursday, when temperatures hit a record high 42.6 degrees. The RATP said the outdoor infrastructure, in particular, was “sensitive to variations in temperatures”.
Some cancelled their trains altogether. Thalys, which connects Paris to Belgium and the Netherlands, decided to close ticket sales on Thursday and Friday because of heat-related infrastructure problems.
Finding a balance
French rail infrastructure may not be adapted to high heat, but adapting requires finding a balance between extreme hot and cold, taking into account climate change and weather predictions.
Currently tracks are laid when they are at the average temperature of an area, to accommodate expansion in the heat or shrinking in the cold. Studies in the Paris area have set the reference temperature to 24 degrees, taking into account the region’s climate.
Increasing the reference temperature would accommodate hot weather, but it would also mean increased stress when the weather is cold, causing tracks to contract so much they break.
Some mitigation efforts include painting tracks white, to reflect sunshine; increasing plants around train lines; or using concrete to anchor the tracks.
Some lines in France use concrete slabs instead of ballast, the loose rocks that are packed around the base of tracks to keep them in place. Concrete can help stabilize the tracks, but it costs more than ballast.
(Additional reporting by Mathilde Warda)