Potholes are the £14.4 billion problem blighting Britain’s roads and leaving behind many a frustrated motorist.Now engineers believe “self-healing” roads may be the solution. Research suggests that asphalt roads could be made far more durable by adding a new ingredient: recycled cooking oil.Potholes typically appear when water penetrates cracks in the asphalt over the winter. When the water freezes, it expands, making the cracks larger and forming fresh ones. When the broken-up material is washe...