A California highway project found an unusual use for thousands of discarded tyres. In 2009, the California Department of Transportation completed a road repair project at Confusion Hill on US 101 in Mendocino County, where longstanding rockslides had repeatedly threatened the highway. The new route bypassed the unstable area using two bridges, but engineers faced another problem, adding conventional fill would have placed too much weight on an underground drainage structure beneath one bridge embankment. Instead, they turned to tyre-derived aggregate (TDA), made from shredded waste tyres, as a lightweight fill material. The project ultimately used about 270,000 waste tyres, giving the discarded rubber a structural role beneath the road.
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