When a road has to close, “the socio-economic impacts can be considerable with disruptions in service, access to health, communication…”, lists Sophie Cahen, of the National Federation of Public Works (FNTP), which brings together construction companies.
The exceptional floods which hit Pas-de-Calais, showered by torrential rains several times this winter, cut and damaged up to 10% of the department’s roads, she notes.
Elsewhere in France, heavy rainfall has cut off several roads this winter due to landslides in Nice, Dordogne, Cantal and Calvados. Each time the roads, parts of which collapsed, had to close for several weeks, isolating certain hamlets.
“We know about torrential floods and forest fires, but they are becoming more frequent. (…) Territories that were once protected are no longer so,” explains David Zambon, deputy director general of the Center for Studies and Expertise on Risks, Environment, Mobility and Development (Cerema), a public research institute.
Reduced road lifespan
With nearly 1.1 million kilometers of network, the road is the “backbone” of transport in France, far ahead of the train and its 33,000 kilometers of railway tracks. Around 75% of home-work journeys are made by car, by road.
If rain and floods constitute the main threats, greater temperature amplitudes reduce the lifespan of roads, says Idrrim (Institute of Roads, Streets and Infrastructure for Mobility).
Another threatening phenomenon is drought, the “extent of which has been observed significantly over the past ten years with the shrinking swellings of clay” which crack and deform the roads, notes Mr. Zambon.
Marine subversion is another major concern: 1,765 km of structuring roads are threatened by coastal erosion due to rising sea levels by 2100, according to a Cerema study published at the beginning of April.
Region particularly concerned: the Mediterranean basin is considered a climate change “hotspot”. The Provence-Alpes-Côte d’Azur region has implemented an innovative method to precisely assess vulnerabilities in its territory.
22 billion euros to invest
“We have just started the vulnerability study infrastructure by infrastructure. From what moment we have ruptures, from when we have deterioration… We test these infrastructures in different scenarios”, explains Jean-Pierre Serrus, vice-president of this region still marked by the tragedy of the valley of the Roya devastated by storm Alex in 2020.
Adaptation is increasingly on the agenda of local elected officials – only 20,000 km of road falls within the national network.
“The economic model is insufficient,” recognizes Mr. Serrus. “The way we collect revenue and spend cannot resolve all the areas of our ecological transition strategy,” he admits. Hence the idea of establishing a precise diagnosis and priorities: an absolute necessity if we follow the scenario envisaged by the government of a France at +4°C by the end of the century (compared to 1850-1900), estimates Mr. Serrus.
According to a 2021 report from the Carbone 4 firm, roads would require 22 billion euros in curative investments to be made between 2035 and 2050, “when the physical consequences of climate change will be more clearly felt”. For bridges, 12 billion in preventive investments must be made before 2035, according to the same Source.
“Today, due to climate change, roads must allow more water to circulate. When they are in an urban environment, they must help make the environment more livable and avoid heat islands,” explains Bernard Sala, head of innovation at Colas (a subsidiary of Bouygues), a specialist in road and railway works.
All this costs more but if we don’t invest now, “decisions will be deferred to the future”, he says. “And we haven’t found much other than road support to accommodate all mobility. »
