In 1932, a more northern route following the mainline of the Canadian Pacific Railway known as the Central Trans-Provincial Highway and designated as Route 'B' was chosen as the future alignment of the Trans-Canada Highway. In 1941, British Columbia transitioned from lettered to numbered highways, with the Lower Mainland section of Route 'A' and all of Route 'B' becoming Highway 1, while the remainder of Route 'A' became Highway 3. Post-World War II, the BC government began to upgrade its highway system and on November 2, 1949, the Hope-Princeton Highway through Allison Pass and Sunday Summit was opened, reducing the highway distance from approximately to . In 1954, a new highway was constructed from Trail to Salmo and was designated as Highway 3A. Highway 3A and Highway 6 shared a common alignment from Salmo to Nelson, meeting with Highway 3. On November 7, 1957, the $4 million West Arm Bridge (also known as the Nelson Bridge) was opened across the West Arm of Kootenay Lake in Nelson, replacing ferry service.