The Big Dipper on the Princes Motorway could have been replaced by a tunnel as part of a planned upgrade.
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Roads and Maritime Services is planning to add an extra lane in both directions along the M1 between Picton Road and Bellambi Creek.
The upgrade also includes a realignment of the curves at both ends of the “Big Dipper”, while also cutting several metres off the crest of each hill.
The $84 million project is jointly funded by the NSW and federal governments, with work slated to begin next year.
A document released as part of Roads and Maritime Services’ response to public submissions highlights some of the other options considered for the upgrade.
This included a tunnel to replace all or part of the route but the required length proved to be too costly.
“Tunnel options over a length of 400 metres were not considered to be economically feasible for this project,” the document stated.
“Three potential tunnel options with maximum grades of three per cent, six per cent and eight per cent were considered.
“While likely traffic efficiency benefits would be high, funding would be outside the available scope. These options were not further progressed.”
A Roads and Maritime Services spokesman added that the difficult terrain also posed a problem for any possible tunnel.
Another option initially considered was a large 1.8-kilometre curve linking Picton Road and Bellambi Creek.
“The option would remove the tight curves on the existing section of road improving road safety and traffic efficiency,” the document states.
It would also be built away from the existing motorway, removing concerns of worker safety.
But the high cost of earthworks, the need for 40-metre cuttings and the increased environmental impact of construction led to Roads and Maritime Services dropping this as an option.
An upgrade from Bellambi Creek to Bulli Tops will be constructed at a later stage.
