Opened in 1974, the section Vennes-Chexbres of the N09 Swiss motorway is now subject to major maintenance, renewal and improvement works. To overcome the difficulties caused by traffic overload between the Vennes and Belmont junctions, it is planned to transform the existent emergency lane into a lane suitable for transit at peak hours (temporary PUN). Lombardi Ltd., leader of the joint venture LIG-A, is charged with the project management and most of the tunnel and geotechnical studies for the section TP2 (km 7'610 to 11'800). This section, located in a highly urbanized area, includes major bridges Chandelar (L ≈ 245 m) and Paudèze (L ≈ 410 m), the Belmont tunnels (L ≈ 400 m), the Vennes junction, 4 overpasses and 3 underpasses. All the works will be performed under traffic of 65’000 vehicles / day with 4 busy lanes during peak hours. To do this, major civil works including the Belmont tunnels enlargement and the strengthening and enlargement of the two major bridges of the section are necessary. The Belmont tunnels will be enlarged using a rigid portal structure which ensures protection and a separation area between traffic and civil works. The portal, installed all along the tunnel, accommodates two reduced size lanes (2 x 3.50 m) for regular traffic during the enlargement of the vault's tunnel. This construction method, proposed and adapted for the Belmont tunnel, presents a pioneer in Switzerland and is a significant technical challenge. It is also a great opportunity for various Swiss tunnels that have to be rehabilitated and expanded under traffic in future.