the freezing point of water. An array of pipes embedded in the road surface is used to collect solar energy in summer, transfer the heat to thermal banks and return the heat to the road in winter to maintain the surface above . This automated form of renewable energy collection, storage and delivery avoids the environmental issues of using chemical contaminants. It was suggested in 2012 that superhydrophobic surfaces capable of repelling water can also be used to prevent ice accumulation leading to icephobicity. However, not every superhydrophobic surface is icephobic and the method is still under development. Trains and rail switches Trains and rail switches in Arctic regions can have significant problems with snow and ice build up. They need a constant heat source on cold days to assure functionality. On trains it is primarily the brakes, suspension and couplers that require heaters for deicing. On rails it is primarily the switches that are sensitive to ice. High-powered electrical heaters prevent ice formation and rapidly melt any ice that forms. The heaters are preferably made of PTC material, for example PTC rubber, to avoid overheating and potentially destroying the heaters. These heaters are self-limiting and require no regulating electronics; they cannot overheat and require no overheat protection. Aviation Ground deicing of aircraft On the ground, when there are freezing conditions and precipitation, deicing an aircraft is commonly practiced. Frozen contaminants interfere with the aerodynamic properties of the vehicle. Furthermore, dislodged ice can damage the engines. Ground deicing methods include: Spraying on various aircraft deicing fluids to melt ice and prevent reformation Using unheated forced air to blow off loose snow and ice Using infrared heating to melt snow, ice, and frost without using chemicals Mechanical deicing using tools such as brooms, scrapers, and ropes Placing an aircraft in a warm hangar In-flight deicing Ice can build up on aircraft in flight due to atmospheric conditions, causing potential degradation of flight performance. Large commercial aircraft almost always have in-flight ice protections systems to shed ice buildup and prevent reformation. Ice protection systems are becoming increasingly common in smaller general aviation aircraft as well. Ice protection systems typically use one or more of the following approaches: pneumatic rubber "boots" on leading edges of wings and control surfaces, which expand to break off accumulated ice electrically heated strips on critical surfaces to prevent ice formation and melt accumulated ice bleed air systems