The 1930s-vintage Sixth Street Viaduct Bridge in Los Angeles, which has been featured in several movies, is weakened by widespread alkali-silica reaction, and needs to be replaced. The new $401 million bridge will have a cable-stayed design with a double steel-arch center span and two prestressed-concrete viaducts. Several old bridges over the Los Angeles River have ASR. "We now know how to proportion the concrete mixture so you don't get ASR," says Rachel Detwiler, an engineer and editor-in-chief of the Precast/Prestressed Concrete Institute Journal. "But at the time that the bridge was built, they did not know about alkali-silica reaction."