The £9.3m project will see a footpath on the three-lane bridge deck removed to lay a new road section for two lane traffic in each direction.
A new cantilevered 3m wide steel structure will be bolted to the side of the existing Countess Wear Bridge in Exeter for cyclists and pedestrians, running to 170m in length.
Around £2m has been previously invested on installing concrete piled foundations in the piers of the historic Grade II listed bridge to support the walkway.
The widening is the next priority along the Bridge Road route, which is critical to help unlock major developments of 6,000 new homes in Newcourt and south west Exeter.
It is being funded using a combination of developer contributions and, as one of the priorities of the Local Transport Board, it has received £5.3M from a Department for Transport grant for major local transport schemes.
The project also includes a 4.8 m extension to the reinforced concrete Countess Wear Flood Relief structure, including strengthening and refurbishment works to the remaining structure.
Work will start within weeks on the 14 month long job.