The first step has been taken towards boosting capacity on the overcrowded T4 Illawarra and T8 Airport rail lines by having services as frequently as every two minutes during the peak.
Two contracts totalling $600 million have been awarded for construction work, to be followed by the installation of digitalised signalling.
The More Trains, More Services project, which was promised before the 2019 state election, will be staged over "three to four years".
Transport Minister Andrew Constance and Sydney Trains chief executive Howard Collins announced the first two contracts, which will provide 550 new jobs, at Sutherland station on Thursday.
T4 Illawarra Line
A 20 per cent increase in peak services, including an extra three services an hour in the peak for key hubs like Hurstville and Sutherland.
[When the promise was made in 2018, the government said there would an extra five trains an hour].
Additional capacity to carry 3600 more customers in the peak
T8 Airport Line
More services, including a 60 per cent increase at the International, Domestic, Mascot and Green Square stations during the morning peak, meaning trains on average every three to four minutes instead of every six minutes today
Additional capacity to carry 2400 more customers in the peak
South Coast Line
During peak times, all New Intercity Fleet trains will operate as 10 car trains instead of eight, proving a new level of comfort, convenience and reliability for customers
An extra off peak service each hour between Wollongong and the Sydney CBD, meaning a train every 30 minutes on average
Mr Constance said the improvements would make the T4 and T8 lines "in essence, like a turn up and go Metro service involving the Tangara fleet and the new inter-city fleet".
Mr Collins said, 'This is almost as exciting as the Metro opening".
"Our busiest corridors pre-Covid, were the line between Central and Hurstville and beyond down to the South Coast, and the T8 Airport line.
"We are now introducing capacity of potentially a train every two minutes.
"We will deliver 'turn up and go' using the existing rolling stock.
Mr Collins said the project was "probably as significant as Bradfield's electrification of the metropolitan network".
"What we are seeing is something other cities have done," he said.
"London Underground increased capacity by one third, not by building lines but by increasing the capacity of the network.
"This is like building another couple of lines.
"We need to do our homework first - capacity of sidings , power supplies, those things which need be done first have now been authorised and we are getting on with it.
"The next thing is to introduce and get those contracts going for digital signalling systems.
"It's a three to four year strategy.
"While still running the marathon of operating the railway, we still have to carry out the open heart surgery of getting this work done."
As part of the works, all Tangara trains will be maintained at the Mortdale sheds.