dioxide that entails. now hs2 is trying to make amends with the help of a sandwich — a very big sandwich. here's an animation showing what a stretch of the raised track will look like. it will be made with an innovative sandwich of cement and steel. the design enhances the properties of both materials, so building the viaduct uses less of both. so we're saving 7,500 tonnes of embodied carbon in this i structure, which approximately - halves the embodied carbon compared to a conventional box girder. that's fantastic. it's extraordinary. i mean, i would say that it's not only because of this structural l form, but it's largely because of it. - we're also doing some other things with the design of this viaduct - to minimise the embodied carbon. in the uk, we have a law which says that we are committed to having zero emissions in 2050.