Taylor Woodrow will increase capacity from two tracks to four between Dr Day's Junction and Filton Abbey Wood Station.
As well as doubling the capacity of the rail line, the three-year contract includes the replacement or enhancement of 17 structures along the 15km route, including four bridge reconstructions for electrification clearance and the refurbishment of two stations.
Taylor Woodrow is the civil engineering division of Vinci Construction UK
Taylor Woodrow project director Richard Hogg said: “This scheme is essential to deliver Network Rail’s vision of improving the Great Western Railway Network to help boost the local economy and will enable passengers to commute more easily around the Bristol area.
“The improvements to the infrastructure will make rail transport even more efficient and help reduce journey times; we are greatly looking forward to working with Network Rail on this important scheme.”
Councillor Brian Allinson, chair of the West of England Joint Transport Board, said: “This four tracking is vital for our MetroWest plans to improve the local rail services and it’s a real milestone getting it started.”