A "Sea Cliff Bridge style" train line over the water at Stanwell Park is an option being considered by the NSW government.
It would be a way of providing a long-term improvement to the South Coast line, on which trains can slow down considerably as they make their way through the escarpment.
At a public meeting at Thirroul to discuss the parking problems caused by last October's revision of the train timetable, Heathcote MP Lee Evans said he had included a revamp of the South Coast train line into the government's forward estimates and added that "it made the cut".
After the meeting, Mr Evans said the government was looking at ways to deal with the "pinch points" caused by the twin tunnels at Stanwell Park.
He said the suggestion of creating a straighter route would be too expensive as it would mean drilling tunnels through the escarpment, effectively doubling the cost of any project to well over $1 billion.
Instead, the solution Mr Evans put forward involved opening a second train line around the Stanwell Park area, to bypass the two-tunnel pinch point.
"What I'm talking about, it hasn't been done, and that's why others are a bit iffy about it, is a Sea Cliff Bridge style of line where it comes out from Stanwell Park, goes around it all and then joins up again," Mr Evans said.
He said the bridge could cater for one line, with the other still going through the tunnel. Or both could be moved over the water.
Mr Evans estimated it would cost $600 million to lay down new rail lines and build the bridge, a far cheaper option than "spending $1 billion drilling through the escarpment and then having to spend an extra $400-500 million to build the rail lines".