Designed to withstand blasts, fires and power outages, a new nerve centre for Sydney's ageing rail network could not come soon enough for a system frequently crippled by train delays.

But confidential government documents, obtained by the Herald using freedom of information laws, show the fortress-like rail operations centre being built in the city's inner south has been dogged by delays, increased costs and "leadership and governance issues".

The new rail operations centre near Green Square station in Sydney's inner south was meant to open last year. Credit:Nick Moir

They reveal the project's cost has now blown out by $20 million to $296 million, even after it was scaled back last year in an attempt to avoid budget overruns.

And a "health check review" by the state's transport agency shows a revised timetable to complete the technically complex project by the end of next month is a "best-case scenario, not a likely case".