Why is Germany building roads for yesterday's climate?
As heat waves buckle its Autobahn, Germany is still paving roads for a past climate. Engineers know how to fix it — so what's the
As heat waves buckle its Autobahn, Germany is still paving roads for a past climate. Engineers know how to fix it — so what's the holdup? Multi-day European heat waves with temperatures topping 104 degrees Fahrenheit (40 degrees Celsius) are increasingly leaving their mark on Germany's famed Autobahn — buckling concrete slabs, deforming asphalt, and forcing temporary speed limits. In early July alone, seven stretches of the country's highways had to be shut down completely for a time. "The cause often lies in the bitumen — the petroleum-derived binder in asphalt. It's elastic and can soften at high temperatures, from around 60 degrees Celsius," a spokesperson from Autobahn GmbH, the company that manages Germany's highways, told DW. Bitumen is a component in most of the country's roads. When outdoor temperatures climb above 30C, the surface of dark asphalt can quickly heat to double that or more in the sun and then deform. Using modern, bitumen-free asphalt mixes lowers the risk of such damage, according to Autobahn GmbH. So, as heat waves intensify and traffic volumes rise, are Germany's roads built to last? Autobahn need to be prepared for the heat German roads are "not designed for these stresses at all," said Nina Stelzenmüller. The engineer heads the road construction technology division at the Karlsruhe Institute of Technology (KIT) in southwestern Germany. "The composition of the road surface is based on experience from the last 30 or 50 years," and not on the increasingly noticeable shifts in the climate, explained Stelzenmüller. Older concrete road surfaces in particular are especially vulnerable to heat, like this section of highway in eastern Germany Image: Michael Bahlo/dpa/picture alliance At present, road surfaces have to be designed for a temperature range of minus 30C to plus 45C, according to Autobahn GmbH.
They are built, the company said, to withstand "the climatic stresses from heat and cold to be expected in Germany." Yet in some regions of eastern Germany, temperatures could exceed that 45C maximum on certain days by at least 2040. That's according to climate models from Germany's Meteorological Service (DWD), which assume emissions will remain high in the coming years and that global warming will continue to intensify. A study involving the research institute of Germany's federal transport ministry (BASt) likewise concludes that climate change is already pushing existing road materials to their limits, and that action is needed. But these findings have not yet translated into binding requirements for updating street surfaces. Resurfacing as an opportunity: Climate-ready asphalt for the future Every road resurfaced today needs to withstand temperatures that may only become reality decades from now. But there are plenty of ways to make Germany's vital road infrastructure heat-resistant for the medium to long-term. A 2019 study, also involving BASt, found that dark asphalt heated up by 7C less when light-colored quartzite was mixed in. The researchers recommended applying reflective surface layers to roads and building in other cooling materials as quickly as possible. The study did not examine the cost or durability of such heat adaptations. According to Autobahn GmbH, lighter-colored stone is already being used in construction in some cases. The regional availability and cost of such stone also play a role in its use, said the company. A truck sprays water on the road during the June heat wave. This is meant to cool the asphalt and prevent damage Image: Jacob Schröter/dpa/picture alliance Individual states and cities are also testing and planning light-colored road surfaces, including in the western German cities of Oberhausen and Stuttgart, as well as the eastern state of Brandenburg.
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