The North County Model Railroad Society (NCMRS) helix provides a way to get members’ HO Scale trains from lower-level tracks to upper-level tracks, giving much more running distance to the layout.
The NCMRS four circle helix is double-tracked so several trains can move up or down between levels. Each track is approximately 88 actual feet long or 17.5 miles of real train track. Elevation changes by 20 inches in scale or 1760 feet with a 1.95 percent grade.
There are several examples below of how a helix or loop has been used in actual railroad construction.
Railroad construction engineers determined early on that a grade or elevation change of more than two percent was going to be inefficient and dangerous for steam and later for diesel-powered trains. So, in the late 1800s, loops, spirals, and helixes were designed to meet this challenge.
A loop is created when the circle of a higher track crosses over the circle of a lower track. The lower track then usually goes into a tunnel while the upper track crosses above. A helix is simply a series of elevating circles like a spiral where the tracks never cross.
Brusio Spiral Viaduct; Bernina Railway;
The Brusio Spiral Viaduct is a single-track nine-arched stone spiral railway viaduct on the Bernina railway in Switzerland. It was first opened in July 1908. It is just south of Brusio, and approximately 34 miles from St. Moritz in Switzerland.
The spiral viaduct, still in use today is 360 feet long, has a horizontal radius of curvature of 230 feet, a longitudinal slope (grade) of 7 percent. The spiral is made up of nine spans, every 33 feet in length.
The Big Hill
Canadian Pacific Railroad, British Columbia, Canada
The Big Hill Spiral opened for running in1884 on the Canadian Pacific Railway mainline in British Columbia, Canada. It is situated in the rugged Canadian Rockies west of the Continental Divide of the Americas and Kicking Horse Pass. The original Big Hill open-spiral was replaced by spiral tunnels in 1909. The tunnels are still in use today.
The railway tracks of The Big Hill climb 1,070 feet along a distance of 10 miles climbing to the top of the Continental Divide, a grade of 4.5%. Unfortunately, the first train to attempt The Big Hill in 1884 derailed, killing three workers.
The Tehachapi Loop, Union Pacific Railroad, Tehachapi Pass, the Tehachapi Mountains, Kern County, California
The Tehachapi Loop is 3,779 feet long. Now part of the Union Pacific Railroad running through Tehachapi Pass in Kern County in central California, the line connects Bakersfield and the San Joaquin Valley to Mojave in the Mojave Desert. Construction of the loop began in 1874, and the line opened in 1876. There is a siding on the loop to accommodate multiple trains.
Rising at a constant 2 percent grade, the track gains 77 feet in elevation and makes a 1,210-foot diameter loop. Any train that is at least 20 cars passes over itself going around the loop.
Between 1875 and 1876 about 3,000 Chinese workers equipped with hand tools, picks, shovels, horse-drawn carts and blasting powder cut through solid and decomposed granite to create the loop.
The loop averages now about 36 freight trains each day; passenger services such as Amtrak’s San Joaquin are normally banned from using the loop.
Georgetown Loop; Georgetown, Breckenridge and Leadville Railway;
Clear Creek in the Rocky Mountains west of Denver, Colorado
The Georgetown Loop Railroad is a 3 ft narrow gauge United States Heritage Railroad located in the Rocky Mountains in Clear Creek County, Colorado. The Georgetown Loop was built by the Georgetown, Breckenridge, and Leadville Railway in 1884.
Now a tourist activity, the train runs between the communities of Georgetown and Silver Plume, a distance of 2 miles. Including the loop, the trip is 4.5 miles long and climbs an elevation of 640 feet through mountainous terrain along with trestles, cuts, fills, and a loop where the maximum grade is 4 percent.
Originally part of the larger line of the Colorado Central Railroad constructed in the 1870s and 1880s, in the wake of the Colorado Gold Rush, this line was used extensively during the silver boom of the 1880s to haul silver ore from the mines at Silver Plume. In 1893, the Colorado and Southern Railway took over the line and operated it for passengers and freight until 1938.
The line was dismantled in 1939, then restored in the 1980s to operate during summer months as a tourist railroad.
Today’s hefty locomotives, often in multiples, are powerful enough to exceed the 2 to 4 percent grade pushing the limit towards 10 percent and above. The Red Marble Grade in North Carolina, part of the Great Smokey Mountain Railroad until it discontinued service in 2019, has a 7 percent grade.