The Connaught Tunnel, built between 1913 and 1916, is 5.02 miles long. At the time, it was the longest tunnel in Canada. The Tunnel was opened on December 16, 1916. Prior to construction of the Connaught Tunnel, the Canadian Pacific mainline twisted around the base of the mountains through Rogers Pass.

The tunnel is 20 feet wide, cement-lined and named for the Duke of Connaught, who was Governor-General of Canada. Construction of the tunnel eliminated 200 degrees of curves, clipped 4.52 miles off the transcontinental mileage and reduced hazards due to a 30-foot average yearly snowfalls. There were some problems at first, such as inadequate ventilation, wet rails causing wheels to slip and dangerous loose rocks. The original dual track was reduced to a single track to increase clearance and make maintenance easier and safer. The Connaught Tunnel contributed to development of the railway as a more reliable east to west transportation link which could be used throughout the year.