The Western section includes a four-lane divided highway that begins at Autoroute 20 in Vaudreuil-Dorion, including the redesign of Autoroutes 20, 30, and 540. The highway is 35 km long, and connects with Route 138 (boulevard René-Lévesque) at the boundary of Châteauguay and Mercier. This section of the project also includes work on the following highways.

• Autoroute 530
  The town of Salaberry-de-Valleyfield will be linked to Autoroute 30 from Route 201, at the intersection of the existing Autoroute 30, to the intersection of rue Perron in the Saint-Timothée District. This 7 km long four-lane divided highway will be equipped with two interchanges, one at boulevard Pie XII and the other at Route 201.
• Route 236 (Chemin Saint-Louis)
  The existing highway will be relocated to the west of Rivière Saint-Louis in the Beauharnois-Melocheville industrial park. This will be a two-lane regional road.

Bridges

The completion of Autoroute 30 will involve the construction of several structures, specifically intended to maintain the existing road links and involving the redesign of certain interchanges.

The Western section also includes two major structures that will make it possible to cross two large waterways:

• The bridge crossing the Beauharnois Canal – spanning close to 2.5 km, with a vertical clearance in excess of 38 metres;
• The bridge spanning the St. Lawrence River – close to 2 km in length.

The total investment in these bridges represents more than 40% of the cost of the Western section, and must satisfy certain criteria that have been previously negotiated with the federal government and with the St. Lawrence Seaway Management Corporation.