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Hot danger on the highway: when blow-ups cause the road surface to crack

Blow-ups destroy concrete roadways, asphalt roads become soft, rain washes out routes. Germany is looking for solutions to protect its infrastructure from climate change. And what is the situation in Saxony?

Reading time: 3 Minutes

Man sieht einen Blow-up auf der Autobahn
Blow-ups can occur on highways in hot weather - a risk for everyone, but especially for motorcyclists. © dpa/Rene Priebe

From Hanna Gersmann

No, that shouldn't happen in summer. The highway, or more precisely the road surface, should not bulge and then burst open. But such so-called blow-ups can occur when everything heats up at temperatures above 30 degrees Celsius. Like the weekend before last on the A15, where five vehicles were damaged when driving over it. This is dangerous, possibly even a deadly trap. If a car or motorcyclist notices the huge cracks too late and drives over them at speed, they can lose control of their vehicle.

Is the threat of road deformation more frequent when the summers get hotter? And more fundamentally: how is Germany preparing its infrastructure to withstand climate change, which is also bringing more and more rain from the sky?

Markus Oeser is the President of the Federal Highway Research Institute, or BASt for short. This federal research institute, based in Bergisch Gladbach in North Rhine-Westphalia, advises the Federal Ministry of Transport and works on "solutions for the effects of climate change". The professor of civil engineering explains: "Older concrete road surfaces in particular, which are not as malleable as those made of asphalt and already have previous damage, are more susceptible in extreme heat." However, there are not many of these older road surfaces left. And the majority of freeways, main roads and other routes are made of asphalt anyway.

According to Oeser, "The concrete sections of highway that are older are now heavily monitored. On the one hand, sensors help, and on the other hand, the highway maintenance departments go out with measuring vehicles during longer periods of heat. If damage occurs or becomes apparent, countermeasures are taken quickly."

Light and dark streets

Are there no problems with asphalt? "Yes," says Oeser, "dangerous ruts can form in asphalt roads in extreme heat, which become particularly treacherous in heavy rain." However, the deformation depends on the recipe, the material mix. For example, there are asphalt surfaces that can cope with temperatures of up to 60 degrees Celsius because they are particularly hard. However, these cannot withstand cold winters: The hard asphalt then cracks because it cannot contract. So "a compromise" is needed in the composition of the asphalt. Work is also being done on brighter roads that can reflect sunlight better but do not dazzle.

One person who is working on brighter roads is Lutz Weiler, Managing Director of Offenbacher Asphaltbau und Mischwerke. He has developed "KlimaPhalt". The pavement not only has a light-colored surface, it can also store water in its cavities.

Doesn't a road like this sag slightly? The loads transported by trucks are getting heavier and heavier. Cars also weigh significantly more than they used to. "This is not intended for freeways," says Weiler, "but it is for the hard shoulder and for the many other less busy roads in cities."

The special surface has already been tested in a residential area in Offenbach since 2020. Weiler says: "Klimaphalt can absorb up to 100 liters of rainwater per square meter and partially store it, meaning it can also buffer heavy rainfall." This creates evaporative cooling and acts like a natural air conditioning system. "This also relieves the sewer system and prevents flooding."

Climate change costs

It's not just about heat. Increasingly, the infrastructure also has to withstand torrential downpours. That is why, says BASt President Oeser, studies are currently being carried out throughout Germany to determine where water, which is particularly unpredictable, can accumulate. There, drainage pipes are being made larger and the foundations of bridges are being redesigned. In general, bridges should span a river completely rather than resting on pillars in the river. The piers disrupted the flow, could lead to turbulence and increase the speed of the water. The masses of water would then rush down into the valley even faster.

What will all this cost? "We have to make the infrastructure resilient to climate change and we are well on the way to doing this," says Oeser, "it is not yet possible to put a figure on how much we will have to invest." But doing nothing would be particularly costly for the economy, which is also dependent on exports.

"There is no general protection against blow-ups," explains the Allgemeiner Deutscher Automobil-Club (ADAC) and advises: "On affected stretches of road, drive carefully and attentively. Increase the distance to the vehicle in front of you. Observe the speed limits. Damaged roads without signs should be reported immediately to the police or highway maintenance department."

The situation in Saxony from the perspective of those responsible

  • In principle, no heat damage is known from Saxony's highways, according to the eastern branch of Autobahn GmbH in response to a SZ inquiry.
  • Heavily damaged concrete pavements in the area of the Dresden-West highway authority and between Glauchau-Ost and the state border have been renewed or are currently being renewed. In particular, ASR-damaged concrete carriageways ("concrete cancer") have been fundamentally renewed in recent years and asphalt has also been installed instead of concrete in some cases. The joints and edge areas of the existing concrete carriageways have been and are increasingly being renovated. As a result, blow-ups on concrete carriageways have been significantly reduced or completely prevented in Saxony in recent years.
  • At present, it can be assumed that the concrete roadways are safe to use even in very hot weather.
  • The Autobahn GmbH maintenance depots are aware of their responsibility against the backdrop of high temperatures, and not just during the daily route inspections that take place anyway. They check the routes even more intensively at high temperatures. If measures are necessary, they are initiated immediately by the operations department. (SZ)

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