Most commuters travelling from stations west of Bankstown will be able to use direct services to get to Sydney's CBD and avoid having to switch trains if a "preferred option" for a shake up of the rail network to accommodate a new metro rail line is adopted.

The conversion of a 13.5-kilometre stretch of rail line through Sydney's south-west from Sydenham to Bankstown to allow it to carry single-deck metro trains by 2024 means major changes are in store for the existing suburban railway west of Bankstown.

The NSW transport agency's preferred option is for trains on the existing T3 Bankstown Line to run from Liverpool via Regents Park to get to the CBD. At present, the Bankstown Line operates as two branches with trains running from Liverpool and Lidcombe to the CBD via Bankstown.

The proposed changes to the existing railway west of Bankstown will be 'complex' to introduce. Credit:Simon Alekna

While describing it as the best of three options canvassed, transport experts say it will put more pressure on a "rail bottleneck" between Lidcombe and Homebush, which is nearing capacity in terms of the number of trains it can handle during peak periods.