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As temperatures have risen in France, the duration of some journeys by train is long. Trains have been slowed down or canceled as tracks can buckle under extreme heat. The French railway infrastructure was not built for such high temperatures, but it will have to adapt as heat waves become more common due to climate change.
"Our network was not built to work with such heat," said Transport Minister Elisabeth Borne during the heatwave in June, when trains were delayed or stopped.
Steel railroads expand and contract with temperature changes. They heat longer, which puts stress on the fasteners that keep them anchored to the ground. Once over 45 degrees Celsius, they can expand enough to deform, which can derail trains.
In direct sunlight, the slopes can reach up to 20 degrees Celsius warmer than the ambient air. Temperatures above 30 degrees Celsius are therefore a concern.
Overhead electric cables can also expand under the effect of heat and hit the top of the cars. High temperatures can also damage electrical components along the tracks and even cause fires.
Manage heat
The French railway company, SNCF, has a high heat plan that comes into effect as soon as the temperature reaches 35 degrees. It provides support to pbadengers, including the distribution of water. As soon as the track temperature reaches 45 degrees, workers begin to perform thorough inspections.
On Thursday, track manager Adrien Bobillot took the temperature of a stretch of track near Paris: 56 degrees to 15 hours. He said that it was likely that he would reach 60 degrees, which "could be our record".
He and a team were walking slowly on the tracks in the afternoon, during the hottest time of the day, to check the tracks and bindings. Some members of the team joined locomotive train drivers "to observe the movement of the track" from the train, said Bobillot.
Slow down
If these inspections reveal that the tracks have grown too much and are starting to move, they will require a slowdown in the trains. Slower trains exert less force on the tracks, which can prevent derailments and other problems.
The SNCF asked Thursday travelers going to the regions affected by the heat wave to cancel or postpone their travel, offering them a free exchange or refund of their tickets. He warned that some trains would have delays, especially TGVs, which would run between 280 and 300 kilometers at the time, instead of the usual 330 kilometers.
Paris subways and suburban lines were running at a slower pace on Thursday, when temperatures reached a record high of 42.6 degrees. RATP stated that outdoor infrastructure, in particular, was "temperature-sensitive".
Some canceled their trains completely. Thalys, which links Paris to Belgium and the Netherlands, has decided to end the sale of tickets Thursday and Friday because of infrastructure problems related to heat.
Find a balance
The French railway infrastructure may not be suitable for hot weather, but it requires a balance between extreme heat and cold, taking into account climate change and weather forecasts.
Currently, tracks are laid when they are at the average temperature of an area, to accommodate thermal expansion or cold. Studies in the Paris region have set the reference temperature at 24 degrees, taking into account the climate of the region.
The increase of the reference temperature would be appropriate for heat, but it would also mean an increase in cold weather stress, resulting in a significant contraction of the tracks that break.
Some mitigation efforts include painting tracks in white, to reflect the sun; to increase the factories around the train lines; or using concrete to anchor the tracks.
Some lines in France use concrete slabs instead of ballast, loose rocks that pile up at the base of the tracks to keep them in place. Concrete can help stabilize the tracks, but it costs more than ballast.
(Additional report by Mathilde Warda)
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