A horseshoe curve is a class of climbing curve in a roadbed which reverses turn direction (inflection) twice on either side of a single tight curve that varies through an angle of about 180 degrees or more.
Such curves are more commonly found in a railway line of travel but are also used in roads. The characteristic U shape, or even slight balloon shape, of such a curve resembles a horseshoe, hence the name. On roadways such curves, if the hard curve is tight enough, are typically called hairpin turns.
A horseshoe curve is a means to lengthen an ascending or descending grade and thereby reduce the maximum gradient. Grade or gradient is defined as the rise divided by the run (length) or distance, so in principle such curves add to length for the same altitude gain, just as would a climbing spiral around one or more peaks, or a climbing traverse (cutting) wrapping around an end of a ridge.
If the straight route between two points would be too steep to climb, a more circuitous route will increase the distance traveled, allowing the difference in altitude to be averaged over a longer track (or road) length. Unlike a spiral, a horseshoe curve does not involve the track crossing over itself, and the full horseshoe involves both relatively straight sections, curve deflections in both directions and tightly curved segment; while a spiral generally has a more uniform curvature. Obviously, a horseshoe also gives rise to a severe change in direction requiring another corrective curve to regain displacement in the overall direction of travel, while a spiral generally does not.
A horseshoe curve is sometimes used where the route bridges a deep gully. Deviating from a straight-line route along the edge of the gully may allow it to be crossed at a better location.
Horseshoe curves are common on railway lines in steeply graded or hilly country, where means must be found to achieve acceptable grades and minimize construction costs. As with spirals, the main limitation in laying out a horseshoe is keeping its radius as large as possible, as sharp curves limit train speed, and through increased friction, are harder on rails, requiring more frequent replacement of outer tracks.
Horseshoe curves were used extensively on the many narrow gauge railroads in the Colorado Rocky Mountains, now mostly abandoned, for example:
The Denver & Rio Grande Western Railroad, often shortened to Rio Grande, D&RG or D&RGW, formerly the Denver & Rio Grande Railroad, was an American Class I railroad company. The railroad started as a 3 ft narrow-gauge line running south from Denver, Colorado in 1870. It served mainly as a transcontinental bridge line between Denver, and Salt Lake City, Utah. The Rio Grande was also a major origin of coal and mineral traffic.
A mountain railway is a railway that operates in a mountainous region. It may operate through the mountains by following mountain valleys and tunneling beneath mountain passes, or it may climb a mountain to provide transport to and from the summit.
The Big Hill on the Canadian Pacific Railway main line in British Columbia, Canada, was the most difficult piece of railway track on the Canadian Pacific Railway's route. It was situated in the rugged Canadian Rockies west of the Continental Divide of the Americas and Kicking Horse Pass. Even though the Big Hill was replaced by the Spiral Tunnels in 1909, the area has long been a challenge to the operation of trains and remains so to this day.
A spiral is a technique employed by railways to ascend steep hills.
The Denver, South Park, and Pacific Railroad was a historic 3 ft narrow gauge railroad that operated in Colorado in the western United States in the late 19th century. The railroad opened up the first rail routes to a large section of the central Colorado mining district in the decades of the mineral boom. The railroad took its name from the fact that its main line from Denver ascended the Platte Canyon and traversed South Park. Founded in 1872 by Colorado Governor John Evans, the company was purchased by the Union Pacific Railway in 1880, though it continued to be operated independently. The line went bankrupt in 1889 and was reorganized under the new moniker the Denver, Leadville and Gunnison Railway. When the Union Pacific went bankrupt in 1893, the DL&G lines went into receivership and were eventually sold to the Colorado and Southern Railway. In the first half of the 20th century, nearly all the company's original lines were dismantled or converted into 4 ft 8 1⁄2 instandard gauge. The last train to run the old DSP&P tracks was from Como, Colorado on April 11, 1937. A section of the standard gauge line between Leadville and Climax is still operated as a passenger excursion railroad called the Leadville, Colorado and Southern Railroad. At its peak the Denver, South Park and Pacific Railroad had 335 miles (539 km) of narrow gauge line, making it the largest narrow gauge railroad in the state of Colorado.
A double-track railway usually involves running one track in each direction, compared to a single-track railway where trains in both directions share the same track.
The Georgetown Loop Railroad is a 3 ft narrow gauge United States heritage railroad located in the Rocky Mountains in Clear Creek County, adjacent to Interstate 70 in Colorado.
The Pittsburg and Shawmut Railroad, also known as the Shawmut Line, was a short line railroad company operating passenger and freight service on standard gauge track in central and southwestern Pennsylvania. Since 2004, it has been operated as part of the Buffalo and Pittsburgh Railroad, which is owned by Genesee & Wyoming Inc.
The Pittsburg, Shawmut & Northern Railroad also known as the Shawmut Line, was a Class I railroad company operating passenger and freight service on standard gauge track in central Pennsylvania and western New York. The line was financially troubled for its entire life span and declared bankruptcy after just six years of operation. It would spend the remaining 42 year of its existence in receivership or trusteeship, one of the longest bankruptcy proceedings in American railroading history.
The Cumbres & Toltec Scenic Railroad, often abbreviated as the C&TSRR, is a 3 ft narrow-gauge heritage railroad running for 64 miles (103 km) of track between Antonito, Colorado and Chama, New Mexico, United States. The railroad gets its name from two geographical features along the route, the 10,015-foot (3,053 m)-high Cumbres Pass and the Toltec Gorge. Originally part of the Denver and Rio Grande Western Railroad's narrow-gauge network, the line has been jointly owned by the states of Colorado and New Mexico since 1970.
The Roaring Camp & Big Trees Narrow Gauge Railroad is a 3 ft narrow-gauge tourist railroad in California that starts from the Roaring Camp depot in Felton, California and runs up steep grades through redwood forests to the top of nearby Bear Mountain, a distance of 3.25 miles (5.23 km).
The Uintah Railway was a small 3 ft narrow gauge railroad company in Utah and Colorado in the United States. It was constructed to carry Gilsonite which provided most of its operating revenues; but it operated as a common carrier from 1904 to 1939, also carrying passengers, mail, express, and other cargoes including sheep and wool. When a public library was built in Dragon in 1910, the Uintah Railway agreed to deliver library books free of charge to and from any borrower along its route. Many area ranchers and miners took advantage of the opportunity.
The Sacramento Northern Railway was an 183-mile (295 km) electric interurban railway that connected Chico in northern California with Oakland via the California capital, Sacramento. In its operation it ran directly on the streets of Oakland, Sacramento, Yuba City, Chico, and Woodland and ran passenger service until 1941 and freight service into the 1960s.
The South Pacific Coast Railroad (SPC) was a 3 ft narrow gauge steam railroad running between Santa Cruz, California and Alameda, with a ferry connection in Alameda to San Francisco. The railroad was created as the Santa Clara Valley Railroad, founded by local strawberry growers as a way to get their crops to market in San Francisco and provide an alternative to the Southern Pacific Railroad. In 1876, James Graham Fair, a Comstock Lode silver baron, bought the line and extended it into the Santa Cruz Mountains to capture the significant lumber traffic coming out of the redwood forests. The narrow-gauge line was originally laid with 52-pound-per-yard (26 kg/m) rail on 8-foot (2.44 m) redwood ties; and was later acquired by the Southern Pacific and converted to 4 ft 8 1⁄2 instandard gauge.
The Colorado and Southern Railway was an American Class I railroad in the western United States that operated independently from 1898 to 1908, then as part of the Chicago, Burlington and Quincy Railroad until it was absorbed into the Burlington Northern Railroad in 1981.
Standard gauge was favored for railway construction in the United States, although a fairly large narrow-gauge system developed in the Rocky Mountains of Colorado and Utah. Isolated narrow-gauge lines were built in many areas to minimize construction costs for industrial transport or resort access, and some of these lines offered common carrier service. Outside Colorado, these isolated lines evolved into regional narrow-gauge systems in Maine, New York, Pennsylvania, Ohio, Iowa, Hawaii, and Alaska.
The Utah Division of the former Denver & Rio Grande Western Railroad (D&RGW) is a rail line that connects Grand Junction, Colorado and Salt Lake City, Utah in the Western United States. It is now incorporated into the Union Pacific Railroad (UP) system as its Green River and Provo Subdivisions, forming a portion of the Denver-Nevada Central Corridor. Daily passenger service is provided by Amtrak's California Zephyr, and the BNSF Railway and Utah Railway have trackage rights over the line.
The Central Corridor is a rail line operated by the Union Pacific Railroad from near Winnemucca, Nevada to Denver, Colorado in the western United States. The line was created after the merger with the Southern Pacific Transportation Company by combining portions of lines built by former competitors. No portion of the line was originally built by the Union Pacific; in fact, some portions were built specifically to compete with the Union Pacific's Overland Route. The line is known for significant feats of engineering while crossing the Wasatch Mountains of Utah and the Rocky Mountains of Colorado. The line features numerous tunnels, the longest and highest of these is the Moffat Tunnel.
The Pittsburgh Line is a rail line that is located in state of the Pennsylvania and it is owned and operated by the Norfolk Southern Railway. The Pittsburgh Line is Norfolk Southern Railway's primary east–west artery in its Pittsburgh Division and Harrisburg Division across Pennsylvania and it is part of the Amtrak-Norfolk Southern combined rail corridor, the Keystone Corridor.
The Alamosa–Durango line or San Juan extension was a railroad line built by the Denver and Rio Grande Western Railroad, following the border between the U.S. states of Colorado and New Mexico, in the Rocky Mountains. The line was originally built as a 3 ft narrow-gauge line between Alamosa, Colorado, and Durango, Colorado. Portions of the route survive to this day: the now standard-gauged segment from Alamosa to Antonito, Colorado, and a narrow-gauge portion from Antonito to Chama, New Mexico.