Bethungra Spiral
The Bethungra Spiral is a rail spiral, built on the Main South railway line of New South Wales in Australia at Bethungra to ease the gradients when the line was duplicated between 1941 and 1946. Bethungra is between Cootamundra and Junee.
The original line was graded at 1 in 40 for Sydney bound trains, which imposed a severe limitation on train loads, and also caused congestion as bank engines 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 use the spiral while trains from Sydney to Melbourne 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.
References
- "Bethungra Spiral (listing NSW5011929)". Australia Heritage Places Inventory. Department of Sustainability, Environment, Water, Population and Communities. Retrieved 2008-08-13.
Coordinates: 34°45′S 147°53′E / 34.75°S 147.88°E