France's Wattway is a solar roadway that was built outside Tourouvre-au-Perch in Normandy in 2016. It has proven to be an expensive failure. The 1 kilometer (less than 1 mile) road in Normandy cost 5 million Euros to build, which is around 5.5 million US dollars for a single lane of a two-lane highway!
The solar roadway has a photovoltaic surface constructed from panels with a silicon resin used to protect the driving surface. The designer, a company called Colas, claimed it would stand up to a heavy trucks and tractors, but farm trucks and tractors have caused the silicon layer to flake and crack, damaging the delicate solar panels underneath.
There is also the problem of noise pollution when traffic passes on the road. The noise is so loud that the local government has limited traffic to just 70 kilometers per hour (around 43 miles per hour) to cut down on the sound.
The Wattway also is a failure at generating solar energy. According to the designers of the system, it was meant to capture 790 kilowatt-hours per day. That sounds good, but that part of Normandy averages only around 44 days of strong sunlight per year; too little to reach the designer's anticipated levels of energy.