The viaducts carrying the A38 over the River Plym, which after the construction of the Marsh Mills flyover became the Exeter bound sliproads, were built in 1969-1970 as part of the Plympton bypass. They were replaced in the 1990s due to suffering from Alkali Silica Reaction, and the project, completed in February 1996 at a cost of £12.25million, involved the world's largest sideways bridge slide at the time for the , 5,500 tonne bridge. This required the road to be closed for only 48 hours, winning it an AA National Motoring Award in 1996 for innovation and minimisation of traffic congestion.