When British Columbia joined Confederation in 1871, it was on the condition that Prime Minister John A. Macdonald would build a railway to link the province to the rest of the country. Building a railway across such a large continent was a major undertaking and one of the most serious obstacles was the Rocky Mountains. Several passes were considered for the route and despite its rugged terrain, Kicking Horse Pass was chosen because of its proximity to the US border and its shorter distance to the Pacific Coast.
The steep grade in Kicking Horse Pass posed a serious challenge. Under government pressure to complete the railway, and given the engineering challenges that came along with the geography, Canadian Pacific was not in a position to carve a gradual descent.
The solution for a more gradual grade came from J.E.Schwitzer, one of the railway’s Assistant Chief Engineers. He modeled the Spiral Tunnels after a system used in Switzerland. In 1909 the Spiral Tunnels were completed and after 25 years of use, the Big Hill grade was abandoned. With a gentler grade, descents became safer and slower, spur lines and rear pushers were no longer necessary, and scheduling delays and operating costs were reduced. Although the Spiral Tunnels were a great improvement for the grade, rockfall, mudslides and avalanches are some of the challenges we still face today in this area where nature reigns supreme.
You can safely watch trains and learn more about the Spiral Tunnels and Kicking Horse Pass National Historic Site of Canada. On average, 25 to 30 trains pass through the Spiral Tunnels daily, though not on a regular schedule. The Upper Spiral Tunnel in Cathedral Mountain can be seen from the pull-off 2.3 km up the Yoho Valley Road
http://www.pc.gc.ca/pn-np/bc/yoho/natcul/spiral...
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Photo: http://www.takemytrip.com/09albertabc/08n_19a.htm#spiral