The Bethungra Spiral is a rail spiral

Spiral (railway)

A spiral is a technique employed by railways to ascend steep hills.A railway spiral rises on a steady curve until it has completed a loop, passing over itself as it gains height, allowing the railway to gain vertical elevation in a relatively short horizontal distance...

, built on the Main South railway line

Main Southern railway line, New South Wales

The Main Southern Railway is a major railway in New South Wales, Australia. It runs through the Southern Highlands, Southern Tablelands, South West Slopes and the Riverina regions.- Description of route :...

 of New South Wales

New South Wales

New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...

 in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 at Bethungra

Bethungra, New South Wales

Bethungra is a locality in Junee Shire in the South West Slopes region of New South Wales, Australia situated on the Olympic Way about 13 kilometres northeast of Illabo and 24 kilometres southwest of Cootamundra....

 to ease the gradients when the line was duplicated between 1941 and 1946. Bethungra is between Cootamundra

Cootamundra, New South Wales

Cootamundra is a town and Local Government Area in the South West Slopes region of New South Wales, Australia and within the Riverina. At the 2006 census, Cootamundra had a population of 5,566. It is located on the Olympic Highway at the point where it crosses the Muttama Creek, between Junee and...

 and Junee

Junee, New South Wales

Junee is a medium sized town in the Riverina region of New South Wales, Australia. The town's prosperity and mixed services economy is based on a combination of agriculture, rail transport, light industry and government services, and in particular correctional services...

.

The original line was graded at 1 in 40 for Sydney

Sydney

Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...

 bound trains, which imposed a severe limitation on train loads, and also caused congestion as bank engine

Bank engine

A bank engine or helper engine or pusher engine is a railway locomotive that temporarily assists a train that requires additional power or traction to climb a grade...

s were attached. The spiral makes use of local geography in the shape of a convenient hill which the uphill line spirals around. Two short tunnels are required. The spiral increases the distance traveled by uphill trains by about 2 km. Downhill trains continue to use the original line. The ruling gradient of the new uphill line is now 1 in 66, compensated for curvature.

Normally trains from the south bound for Sydney

Sydney

Sydney is the most populous city in Australia and the state capital of New South Wales. Sydney is located on Australia's south-east coast of the Tasman Sea. As of June 2010, the greater metropolitan area had an approximate population of 4.6 million people...

 use the spiral while trains from Sydney to Melbourne

Melbourne

Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...

use the original steep downhill line.

Geography

Bethungra lies near the base of a mountain range. Bethungra is at an elevation of approximately 310m.

5km south-west of Bethungra, the track is at 280m. The track rises to 320m passing the side of the township of Bethungra. 6km north-east of the Bethungra, the track reaches a plateau at 420m. Any new deviation which attempted to remove the spiral and retain the ruling gradient would require major earthworks, over a span longer than 6km. Fast Sydney-bound passenger trains may only benefit by reducing their travel time by about 3 minutes, while slower freight trains should save much more time.