On Sunday NSW Premier Gladys Berejiklian the T4 Illawarra and airport lines will be the first to benefit from a $880 million program to introduce digital signalling.

Getting rid of the reliance on trackside lights in favour of digital signals would mean trains can travel closer together – resulting in an extra five trains an hour during the morning and evening peaks.

“The T4 Illawarra Line and T8 Airport Line are the first beneficiaries of these signalling upgrades, which will be rolled out across the network – significantly boosting capacity and reliability for all train customers,” Premier Gladys Berejiklian said.

However, any improvements on those lines won’t be seen for several years, with upgrades coming on line from the early 2020s.

The T4 Illawarra line runs between Waterfall and the city and becomes the South Coast line at Helensburgh.

A Transport for NSW spokeswoman said the South Coast line would see some positive effects from these signalling upgrades.

“The next stage of More Trains, More Services will focus on delivering improvements for T4 Eastern Suburbs and Illawarra Line, T8 Airport and South Line and South Coast Line customers,” the spokeswoman said.

“We’ve delivered a number of improvements for South Coast customers but we know that more needs to be done.

“That’s why the program will focus on upgrading key infrastructure that will allow more services to operate on the South Coast line.

“The program will investigate upgrades to the T4 and T8 lines including new high-tech signalling, power supply and train station improvements.”

The spokeswoman could not say how many extra services could be introduced on the South Coast line.

“Details around how many extra services will be delivered will be finalised as the program progresses, and will be shared with customers well in advance of any changes,” the Transport for NSW spokeswoman said.