The original single-track line, opened in 1878, 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 and detached. When the line was duplicated in the late 1940s, an 8.9 kilometre spiral deviation was built. The spiral makes use of local geography in the shape of a convenient hill which the uphill track spirals around in order to gain the necessary height over a longer distance, thus giving a lesser gradient. However the fact that the hill is on the 'down' side of the original track necessitated two crossings of the original line by the new northbound track - one a tunnel to take it to the eastern side of the original track in order to then spiral around the hill, and a viaduct beyond the spiral to take the new track back to the left hand side of the original line. The Spiral has two short tunnels - one already mentioned at the beginning of the Spiral, for the 'up' track to cross beneath the original line to reach the 'down' side, and a second tunnel which allows it to pass over itself at a later point in the Spiral, having circled the hill to gain height. The spiral increased the distance travelled by uphill trains by about two kilometres. Downhill trains continue to use the original line. The ruling gradient of the new uphill line is 1 in 66. Due to the extensive blasting required to create 27 metre deep cuttings through granite, the line suffers from rockfalls, with twelve significant falls between 1960 and 1987. In January 1994, the spiral line closed for a four-month rebuild which saw the cuttings widened and regraded to benched 55 degree slopes, as part of the One Nation project.
Heritage listing
The Bethungra Spiral is of high significance, illustrating a means of ascending a significant mountain range with easier grades than the original line. It is a major civil work and an ingenious engineering solution using the technology available at the time of construction. The site has major landscape value. Bethungra Spiral was listed on the New South Wales StateHeritage Register on 2 April 1999 having satisfied the following criteria:
The place possesses uncommon, rare or endangered aspects of the cultural or natural history of New South Wales.
This item is assessed as historically rare. This item is assessed as scientifically rare. This item is assessed as arch. rare.
Description
Starting at the lower left corner of the interactive map, the 'up' track to Cootamundra is the one on the left. It diverges from the 'down' track and has been built at a less steep gradient than the 'down' track and so is able to pass under it then sweeping around the hill, gaining elevation all the while until crossing over itself above the second tunnel. It is now higher than the down track and on its right, and at an overpass further north, crosses back over to the left and eventually the two tracks converge just short of the Olympic Highwaylevel crossing.
The route of the proposed Inland Railway entails a new section of line from Illabo, west of Bethungra, to Stockinbingal, to obviate the need for northbound trains on the Inland Railway to climb the Bethungra Spiral to Cootamundra then drop down to Stockinbingal to continue north towards Forbes then Parkes. It is projected that this section of the Inland Railway will be completed by 2025. The Spiral will remain in use as part of the Melbourne-Sydney line.
Tourism
A traveller who has just passed through Bethungra township on the way to Cootamundra would be unaware of the existence nearby of the Bethungra Spiral, to the right of the Olympic Highway, as there is no signage or safe off-road parking to observe the two tracks at three different elevations. However there is a point at which three railway tracks can be seen at three different heights on the adjacent hillside to the east of the Olympic Highway. The bottom and top tracks are the 'up' track before and after it has crossed the 'down' track and traversed the Spiral, while the middle track is the original single-track line, which is now the 'down' track.
