Driverless trains might save the NSW government on wages but it turns out the old passenger trains that have relied on humans to ply Sydney's railway lines for decades can still go places their replacements can't – curved platforms at train stations.

One of the challenges confronting engineers labouring on Australia's largest public transport project is the need to straighten curved platforms at 11 existing stations from Sydenham to Bankstown to cater for new single-deck metro trains. They will run on Sydney's new metro line that will stretch from Rouse Hill in the northwest to Bankstown via Chatswood, the CBD and Sydenham in the south.

Curved platforms such as the one at Dulwich Hill in the inner west present challenges for builders of Sydney's new metro line. Credit:Christopher Pearce

"One of the things that has taxed us is that they are significantly curved platforms," Sydney Metro program development director Luke Franzmann told about 500 people at an industry briefing on Friday. "That is something we want to test with industry."

Unlike the double-decker trains such as the S-Sets and Tangaras that ply the existing Bankstown Line, the driverless metro trains will need to stop at exact positions on platforms to allow for barriers to open for passengers.