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A horseshoe curve is a tight curve in a railway or a road, through an angle in excess of 180 degrees. A horseshoe curve is a means to lengthen the passage of an ascending or descending grade, so as to reduce the maximum gradient of ascent or descent. The horseshoe refers to the U shaped bypass of a straight route. The straight route would be too steep to climb, so instead the route takes a more circuitous route. In the case of roads, such curves, if tight enough, are typically called hairpin turns.
The route deviation thus undertaken greatly lengthens the actual distance travelled, and by so doing, it allows the difference in altitude to be averaged over a much longer track length. This is similar to the way a spiral works. However, a horseshoe curve does not involve the track crossing over itself, and the three main curves are only a part of a horseshoe, whereas a spiral is generally a continuous curvature. Another reason for a horseshoe curve is where the straight-ahead route involves bridging a deep gully. The deviation might allow the gully to be crossed at a more favourable location to one side.
Horseshoe curves are a common feature of railway lines in steeply graded or hilly country, where effective means have to be found to achieve an acceptable grade or construction cost of a line. Like spirals, the main limitation of the horseshoe is keeping the radius of the curvatures at or above a desirable minimum. Sharp curvatures will limit the speeds at which trains can run on a line.
[edit] Examples of horseshoe curves
- Horseshoe Curve (Pennsylvania), at Kittanning Gap
- Dunsmuir, California has a pair of horseshoe curves nearby. Map
- Chorro, California near San Luis Obispo.
- Cascade Tunnel has a gully on the western approaches that is an unnamed horseshoe curve.
- Dovrebanen, the main line of the Norwegian railway network, has a horseshoe from Dombås and up to the Dovre platau.
- Raumabanen, Norway, has a double horseshoe with one bridge and two tunnels at Verma downhill from Dombås.
- Flåmsbana, Norway, has a double horseshoe, one inside a tunnel, one in the open, few kilometres below top station.
- The Raurimu Spiral in New Zealand has a horseshoe curve as the first part of the climb. The Turangarere horseshoe curve on the same railway route is another well-known example.
- Kamaishi Line of East Japan Railway Company in Japan, has a horseshoe curve from Kamiarisu Station down to Rikuchū Ōhashi Station ("down" on the elevation and registration of direction of the line).
- The Rhein-Ruhr S-Bahn in Germany has a horseshoe curve in Neviges, Velbert on the route between Essen and Wuppertal, known as the Prince William railway.
- Picton railway station, New South Wales, turns back on itself at about 225 degrees.
[edit] See also
