Finishing the Maldon-Dombarton line would improve the South Coast rail line more than a rail bridge off Stanwell Park, said a University of Wollongong academic.
On Wednesday, the Mercury broke the news of Heathcote MP Lee Evans's proposal to build a "Sea Cliff Bridge style" rail line over the water at Stanwell Park.
Mr Evans said the line would reduce pressure on the "pinch points" caused by the two tunnels at Stanwell Park.
Rail expert and UOW academic Philip Laird said he was pleased the government was thinking about how to fix the South Coast line and reduce travel times to Sydney but added that all the options needed to be considered.
This included the Maldon-Dombarton line and two options canvassed by previous governments - a direct connection between Waterfall and Thirroul and a realignment of the track to get rid of S-bends at Helensburgh.
He said smaller benefits could also be gained from simple moves such as tighter timetabling.
"Last month, I was on one going north and it stopped at Helensburgh for four minutes simply because it can't leave ahead of the timetabled time," Mr Laird said.
"It shows you the amount of padding in the existing timetables."
While Mr Laird said all options needed to be considered, he felt the completion of the Maldon-Dombarton rail link offered the most benefit given that its price tag would be close to the $600 million Mr Evans suggested the Sea Cliff rail bridge would cost.
It would take most freight off the South Coast line, leaving it for the use of passenger trains.
"Maldon-Dombarton would allow for more passenger trains and faster passenger trains and it was disappointing to see that there wasn't anything in the state budget this week for it," Mr Laird said.
"Port Kembla wants to expand and the recent reservations expressed by Roads and Maritime Services and other agencies show that to expand the port, we really need better rail infrastructure feeding that port.
"We don't only deserve better, we need better if Port Kembla is to be able to expand and our city is able to take advantage of the employment opportunities in Sydney. We must have a better rail system with more passenger trains and faster passenger trains."
Meanwhile, Transport Minister Gladys Berejiklian would not confirm or deny whether the government was considering the Sea Cliff rail line.
She did state that other efforts were in train to improve the South Coast service.
"The budget handed down this week includes $71 million next financial year to boost reliability and safety for Illawarra rail customers," Mrs Berejiklian said.
"I am also pleased that work is progressing on delivery of a new state-of-the-art intercity train fleet."
Mrs Berejiklian added there was not enough money in the current budget for bigger ticket items, such as a new South Coast rail line.
"We have been clear about the delivery of other new major infrastructure projects - they are simply not possible unless the government gets a mandate to lease 49 per cent of the state's poles and wires - unlocking a huge $20 billion for much-needed infrastructure," Mrs Berejiklian said.