Back when a Thirroul tunnel was South Coast rail solution | Illawarra Mercury

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A rail tunnel under the escarpment that would cut out five stations and shave almost 20 minutes off a trip to Sydney sounds like a pipe dream. But it’s not – it was once considered as an option to address the problems of the South Coast line. In 2003 the then Transport NSW commissioned a study looking at ways to “deliver increased capacity, reliability and reduce travel times” on the line. One option was not to change anything, which wouldn’t have delivered much in the way of improvements. The second option was “incremental upgrades”, which included straightening the track between Waterfall and Otford, and between Stanwell Park and Scarborough – which would require the construction of a new viaduct at Stanwell Park. The ambitious option was an 11-kilometre tunnel running from Helensburgh to just north of Coledale, at an estimated cost of $1.4 billion back then (the figure is well over $3 billion these days) and a construction time of eight years. Heading north the tunnel would have cut off 16 minutes travel time, and 19 minutes heading south. There were significant problems with the tunnel option, however. It couldn’t be used for freight and commuter trains due to the length of time needed to vent the diesel fumes, which meant the existing line would have to be maintained for freight trains. There was also the risk of having to tunnel through mine-disturbed areas. While a revised alignment would avoid passing directly through the coal seam area, there remained “a high level of uncertainty as to the extent of coal workings/disturbed ground that will be encountered and this risk cannot be completely removed”. In evaluating the options via a cost-benefit analysis, it was decided the incremental approach provided better value than the tunnel – and would cut travel time by up to 14 minutes. Former Transport Minister Andrew Constance described a tunnel as “pixies at the bottom of the garden stuff” in 2017. But to date, the track straightening options had not been adopted either. The Illawarra Mercury newsroom is funded by our readers. You can subscribe to support our journalism here. Sign up for breaking news emails below …


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