Civil Engineering is concerned with the construction of roads, bridges, tunnels, dams and other structures, and their relation to the natural and social environment. It is a diverse discipline, uniting subjects such as the design of structures, materials, surveying, modelling of how schemes will effect the wider world, as well as construction itself. Just as their 19th Century predecessors had criss-crossed the country with canals and railways, in the latter half of the 20th Century civil engineers adapted Britain to mass use of motorised road transport. Britain’s first motorway,the Preston-By-Pass, opened in 1958, and was followed by an immense effort to construct over 2000 miles of motorway around the country, requiring developments in planning, construction and materials use. Meanwhile, bridge design was transformed by design innovations and new materials tobuild lighter and stronger structures, such as the 1966 Severn Bridge, whose box girder design concept is used in most of the world's longest suspension bridges. More recently, civil engineers have increasingly turned to addressing environmental concerns, developing schemes to help to alleviate the impact of climate change.