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Today’s road surfaces are created by mixing hot asphalt with sand, gravel or crushed stone before it is spread over the road surface. The Goodyear Tire and Rubber Company has patented a way to extend the lifetime of this surface (US 2003/203997). The asphalt, which binds the aggregate together, tends to be brittle and so breaks down over time. Goodyear says that adding sulphur and a polymer that combines styrene with butadiene rubber to the mix makes the asphalt more flexible and less likely to break down, so the road surface lasts longer.