Why are some French roads turning white during the heatwave?
White streaks have been spotted on roads from Brittany to Lyon
As the mercury rises authorities are taking steps to protect roads. Inset shows photos from Jura of the spraying of roads with lime milk
Marc Bruxelle/Shutterstock/ Departement du Jura/Facebook
Drivers across France may have noticed streaky white lines appearing on roads across the country in the past week.
Appearing from Lyon to Brittany and in several other areas facing the hottest temperatures, drivers have been perplexed by their sudden appearance, with some wondering if they are related to the heat.
These lines are indeed linked to the current record-breaking heatwave, but are not directly caused by it.
Instead, the mixture is being deposited by local authorities to cool roads down and prevent traffic accidents at a time where hospitals are reeling from an intake of patients suffering from heat-related illness.
What is the mixture and how does it work?
The mixture is lime milk (sometimes called milk of lime or lime slurry), made from diluting calcium hydroxide into water. It is largely water-based, containing up to 85% water and only a small amount of calcium hydroxide, or lime.
The mixture is sprayed onto roads by trucks, and can help rapidly cool down road surfaces by around 10C.
Simply spraying the mixture and allowing it to rest over the road is enough – it does not require anything else.
In turn, this reduces the risk of road surfaces becoming so hot that they start to disintegrate, tearing up asphalt and gravel. As roads get hot and particles get dislodged they can also become slippery.
The lime milk acts as a cooling agent, keeping the road intact and preventing gravel or other debris from dislodging.
The mixture eventually evaporates, requiring a truck to come round and unload a new layer on the route.
Is it safe for vehicles, and does it impact the environment?
One of the main reasons local authorities are choosing lime milk is because of its ecological credentials.
Studies show that the mixture poses little to no risks to human health nor biodiversity in the areas where it is used, either when it is laid or evaporates.
“Lime milk is not harmful to the environment or human health… It is a chemically inert product, formerly widely used as white paint. It therefore poses no toxicity risk and is perfectly suited for this road application,” said the Rhône department to local media Actu.
In addition, the solution does not pose any risks to vehicles driving on it.
