Cougal Spiral (railway)

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The Cougal Spiral is a feature of the North Coast Railway in Australia that connects New South Wales with Queensland. The railway lines needs to climb at a steady ruling gradient from Kyogle to the summit at a tunnel at the border between the 2 states. The border is also at the watershed.

Climbing almost not stop at the ruling grade of 1 in 66 the line has almost continuous curves of 300 metre radius. Near Cougal, the alignment finally runs out of valley, and has nowhere to go. Fortunately a convenient hill allows the line to circle back on itself so that it climbs 30 without having to make any forward progress. Soon after the Border Tunnel is reached, and the line descends down the other side. The spiral has two short tunnels, one where is passes under itself, plus another through a small spur in the hillside.

The tunnel at the summit is 1600m long. A lower summit, perhaps without the spiral, would be possible with a considerably longer and more expensive summit tunnel, with the possibility of problems with fumes for both the original steam locomotives and the replacement diesel engines.

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