Big Hill - The Spiral Tunnels

The Spiral Tunnels

The Big Hill "temporary" line was to remain the main line for twenty-five years, until the famous Spiral Tunnels were opened on September 1, 1909.

The improvement project was started in 1906, under the supervision of John Edward Schwitzer, the senior engineer of CPR’s western lines. The first proposal had been to extend the length of the climb, and thus reduce the gradient, by bypassing the town of Field at a higher level, on the south side of the Kicking Horse river valley. This idea had quickly been abandoned because of the severe risk of avalanches and landslips on the valley side. Also under consideration was the extension of the route in a loop northwards, using both sides of the valley of the Yoho river to increase the distance, but again the valley sides were found to be prone to avalanches. It was the experience of severe disruption and delay caused by avalanches on other parts of the line (such as at the Rogers Pass station, which was destroyed by an avalanche in 1899) that persuaded Schwitzer that the expensive solution of digging spiral tunnels was the only practical way forward.

The route decided upon called for two tunnels driven in three-quarter circles into the valley walls. The higher tunnel, "number one," was about one thousand yards in length and ran under Cathedral Mountain, to the south of the original track. When the new line emerged from this tunnel it had doubled back, running beneath itself and fifty feet lower. It then descended the valley side in almost the opposite direction to its previous course before crossing the Kicking Horse River and entering Mount Ogden to the north. This lower tunnel, "number two," was a few yards shorter than "number one" and the descent was again about fifty feet. From the exit of this tunnel the line continued down the valley in the original direction, towards Field. The constructions and extra track would effectively double the length of the climb and reduce the ruling gradient to 2.2%. The new distance between Field and Wapta Lake, where the track levels out, is 11+1⁄₂ miles (19 km).

The contract was awarded to the Vancouver engineering firm of MacDonnell, Gzowski and Company and work started in 1907. The labor force amounted to about a thousand and the cost was about 1.5 million Canadian dollars.

Even after the opening of the spiral tunnels, Field Hill remained a significant challenge and it was necessary to retain the powerful locomotives at Field locomotive depot.