Commissioned in 1974, the Vennes-Chexbres section of the N09 highway is subject to major maintenance works. In addition, to overcome the difficulties caused by the traffic overload of the section, it is planned to implement a dynamic lane that enables to use the emergency lane as a temporary traffic lane during the high traffic load periods (temporary PUN) between the junctions of Vennes and Belmont. Lombardi SA, leader of the LIG-A JV, oversees the project management and most of the tunnel- and geotechnical studies. The Belmont tunnel, double tube with one-way traffic (L=about 350 m), will be extended with the help of a protective cover that guarantees a separation of the construction area from the traffic space along its entire length, thus maintaining 2 lanes with reduced width (2x3.50 m) during the enlargement of the tunnel. The construction method chosen and adapted for the Belmont tunnel is pioneering in Switzerland and represents a significant technical challenge, but also a great opportunity for the other numerous Swiss tunnels that in the coming years will have to be repaired or enlarged under traffic. All works will be carried out under traffic (DMT of 65,000 vehicles/day) with the upkeep of the 4 lanes at peak times. This traffic management and the implementation of the PUN are associated with important civil works, including the enlargement of the Belmont tunnel and the expansion and strengthening of other structures in the section.