Widening of national road 176

Doubling the lanes of the Chateaubriand bridge

In order to remove a bottleneck well known to users, responsible for regular slowdowns and traffic jams, Brittany’s regional directorate for the environment, planning and housing (DREAL) decided to proceed with the 2×2-lane upgrading of the last remaining single-lane section of the RN 176. It has entrusted Artelia with the supervision of the project, the main challenge of which lies in widening the Chateaubriand bridge.


The purpose of widening this 3.5 km section to two lanes is to improve traffic flow and safety on one of Brittany’s major roads, thereby enhancing the comfort of users on a daily basis. The project involves widening the carriageways along the entire section and carrying out a number of associated improvements (creating water collection and treatment basins, installing berm and noise barriers, building access ramps and gyratory roundabouts, etc.). The main difficulty, however, lies in widening the Chateaubriand bridge, a 424 m-long arch spanning the River Rance.

As project manager, Artelia is giving its full attention to the widening of this structure, which is the most complex and technical element, both in terms of design studies and construction. This remarkable structure, which was brought into service in 1991, has left its mark on the contemporary history of arch bridges, with its large 261 m opening. Widening its deck will be a first for this type of structure in France. There are also environmental challenges, as this infrastructure crosses an exceptional site, the Rance estuary, which is part of the European Natura 2000 network. Particular care will also be taken to limit traffic disruption and the nuisance caused by the works, which are scheduled to start in 2025.