Sydney rail commuters are suffering from more frequent delays caused by a greater reliance on older trains and the network's inability to recover from major incidents quickly enough to prevent disruptions spreading, an internal report reveals.

In a stark assessment of the state of maintenance on the city's rail network, the public operator Sydney Trains also warns its decades-old trains such as the C and K Sets, and Xplorer regional trains, are in a "poor to unacceptable condition".

Sydney Trains' "asset management plan", completed in September and obtained by the Herald using freedom of information laws, presents as a desperate plea for funding to improve the condition of trains, tracks, bridges and other infrastructure.

Sydney Trains' older fleet has been deemed to be in 'poor to unacceptable condition'. Credit:Kate Geraghty

The report says forecast growth in passengers and freight over the next decade will "significantly restrict" the ability to maintain and develop Sydney's 165-year-old rail network without a funding boost and a shake-up of maintenance. Sydney Trains' maintenance backlog blew out by 21 per cent to $434 million last financial year, from $359 million a year earlier.