At present the rail line between those stations is largely one track, which means trains running regularly in both directions is not an option

Last weekend saw the start of investigative work for what will become the Toolijooa crossing loop - a four-kilometre stretch of rail line.

A crossing loop is a stretch of rail line that leaves the main line for a short distance, allowing trains to travel in both directions.

The $125 million loop was an election promise made by Kiama MP Gareth Ward at the 2019 NSW election.

"In the future this will mean more frequent services for South Coast customers, as trains will be able to pass each other between Kiama and Bomaderry," Mr Ward said.

"These upgrades will support the capacity for a service every 30 minutes in peak hours and every 60 minutes in the off-peak, potentially doubling the frequency and providing more connections to Wollongong and Sydney."

At this stage, Transport for NSW have not announced any plans to increase the number of services to Bomaderry.

There is no clear start date for construction of the passing loop, with Transport for NSW stating it would begin in the "early 2020s"

The investigative work includes drilling boreholes in the rail corridor, pit excavations, geotechnical surveying and locating underground utilities.

The work will take five weeks to complete.

In addition, an extra platform is also planned at Bomaderry station that will allow a train to arrive before another departs.

It is unclear exactly where the second platform would be located, due to a railway siding to the east of the existing single platform.

The South Coast rail corridor from Sydney to Bomaderry is one of four being investigated for a faster rail connection, with a business case being developed.

Kiama is the latest South Coast station to get an upgrade to accommodate new trains.

When they are introduced on the South Coast line in 2022, the New Intercity Fleet will run as 10-carriage trains during peak periods.

So that the longer trains can fit, Transport for NSW is extending a number of South Coast platforms.

This includes Kiama station, which will see both platforms extended by eight metres.

Gates and stairs will be relocated to the newly created section of the platforms.

The work will also include improved lighting and tactile markings on the platform.

Preliminary investigations are expected to start this week ahead of the main construction work.

The other South Coast platforms in line for an upgrade under the More Trains, More Services program are Thirroul, Bellambi, Coniston and Port Kembla.

We depend on subscription revenue to support our journalism. If you are able, please subscribe here. If you are already a subscriber, thank you for your support.