Lapstone Zig Zag

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The Lapstone Zig Zag was a zig zag railway built on the Great Western Railway of New South Wales in Australia around 1872, to overcome an otherwise insurmountable climb. The ruling grade was already very steep at 1 in 33 (3%). The original plan had been to build a 3km tunnel, but this was beyond the resources of the state of New South Wales at the time. The little zig zag still required several short tunnels and some viaducts.

This zig zag soon ran into problems that the length of the top points and bottom points limited the length of trains. A tunnel was built around 1890 to replace the zig zag, but it was built at too steep a grade, and smoke became a problem for uphill trains.

By 1910, the line as a whole was being duplicated (made into double track) and the rathole tunnel was replaced with a gentler alignment with 1 in 60 (1.67%) grades.