Raurimu Spiral facts for kids
The Raurimu Spiral is a special railway track in the middle of New Zealand's North Island. It helps trains climb a big hill on the North Island Main Trunk railway (NIMT). This railway connects the cities of Wellington and Auckland. The spiral helps trains go up 139 metres (about 456 feet). It is a very clever piece of engineering. Many people call it an "engineering masterpiece." It is also known as an important historical site for engineers in New Zealand.
Why the Raurimu Spiral Was Needed
When the main railway line was being built, engineers faced a big problem. They needed to cross very steep hills. These hills were between the North Island Volcanic Plateau and the Whanganui River valleys.
The land near the towns of Raurimu and National Park was too steep. A straight railway line there would climb 200 metres (about 656 feet) in only 5 kilometres (about 3 miles). This would be too steep for trains to climb easily. Surveyors looked for other ways in the 1880s. One idea was a 20-kilometre (12-mile) detour. This plan also needed nine huge bridges. Even then, the slope would still be very steep.
How the Raurimu Spiral Was Built
The problem was solved in 1898 by a surveyor working for Robert Holmes. He was an engineer for the Public Works Department. He suggested a railway line that would loop back on itself. It would then spiral around using tunnels and bridges. This design would make the slope much gentler for trains.
This plan was expensive and needed a lot of work. But it was still cheaper than the earlier idea with many bridges. What is amazing is that you cannot see the whole spiral from any one spot. It is said that Holmes imagined the entire layout in his mind.
The railway line goes upwards as it spirals south. It has two short tunnels, one full circle, and three sharp bends. Trains coming from the north pass Raurimu. Then they go around a big left turn. This turn is called a horseshoe curve. It makes the track climb above where the train just was.
After this, there are two sharp turns to the right. The line then goes through two short tunnels. These are the Lower Spiral Tunnel (384 metres long) and the Upper Spiral Tunnel (96 metres long). Trains then complete a full circle. They cross over the Lower Spiral Tunnel, which is 23 metres (75 feet) below them. After this, they continue towards Wellington. About 2 kilometres (1.2 miles) further on, the line has two more sharp bends. One is to the right, and then one is to the left.
After the second of these bends, a train has climbed 132 metres (433 feet). It has travelled 6.8 kilometres (4.2 miles) from Raurimu. But the straight-line distance is only 2 kilometres (1.2 miles). Some of the sharp curves are quite tight.
Railway spirals are common in places like the Alps in Switzerland. But they usually involve long tunnels inside mountains. Holmes' design is clever because it uses the natural shape of the land. This meant no big bridges were needed, only two short tunnels.
There is a story that a train driver once used the emergency brakes at night. He saw the light of his guard's van on a nearby part of the spiral. He thought it was the back of another train right in front of him!
See also
In Spanish: Espiral de Raurimu para niños
