# Horseshoe curve

The horse shoe shape gives the curve its name.

A horseshoe curve is a reversing curve through a single tight curve in a railway or a road, through an angle of about 180 degrees or more. The U shape, or even slight balloon shape, of such a curve resembles a horseshoe, hence the name. On roads such curves, if 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. If the straight route between two points would be too steep to climb, a more circuitous route will increase the distance travelled, allowing the difference in altitude to be averaged over a longer track (or road) length. This is similar to the function of a spiral. However, a horseshoe curve does not involve the track crossing over itself, and the full horseshoe involves both relatively straight and tightly curved sections, while a spiral generally has a more uniform curvature. Obviously, a horseshoe also gives rise to a severe change in direction, 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.

## Examples

### Europe

Flåmsbana, 1926 shortly after construction
Credit: Anders Beer Wilse
• Dovrebanen, the main line of the Norwegian railway network, has a horseshoe from Dombås at the steep hills to the Dovre plateau.
• Flåmsbana, Norway, has a double horseshoe, one inside a tunnel, one in the open, few kilometres below top station.
• Raumabanen (Rauma Line), Norway, has a double horseshoe through the steep and narrow valley at Verma, one inside a tunnel and one that includes the Kylling Bridge.
• Grybów, Poland has a horseshoe curve 2,5 km west of the town.
• Kalisz, Poland has a double horseshoe curve leading the tracks from a flat plateau down to the valley of the Prosna river.
• Between Jelenia Góra and Szklarska Poręba in Poland there is a five-times, elongated horseshoe curve (50°51′19"N, 15°34′17"E). Map
• 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.
• The horseshoe curve on the West Highland Line in Scotland between Upper Tyndrum and Bridge of Orchy was built because the engineers of the railway couldn't afford to build a viaduct crossing the remote valley.
• In Slovakia there is a significant number of horseshoe curves on the Banská Bystrica to Turčianske Teplice railway track and on the railway from Zvolen to Turčianske Teplice. More than 20 tunnels and couple of horseshoe curves were built to overcome rough terrain and elevation differences.