A delay of two to four minutes to Sydney Trains services risks causing platform crowding at Chatswood station during the morning peak as thousands of commuters switch from new driverless metro trains to get to the city, internal government documents reveal.

Internal modelling forecasts almost 4500 passengers to transfer from single-deck metro trains at Chatswood to Sydney Trains services on the North Shore Line between 8am and 9am – the busiest hour of the morning peak. The $7.3 billion metro line from Rouse Hill in Sydney's north to Chatswood will open to passengers on May 26.

Thousands of extra passengers will pass through Chatswood station every day after the metro line opens on May 26. Credit:Janie Barrett

The total number of passengers switching trains or exiting Chatswood station between 8 and 9am is set to more than double to 16,544 passengers – from 6913 – after the line opens.

The documents obtained by the Herald under freedom of information laws lay bare the challenges integrating the privately operated Metro Northwest train line into the existing network. Chatswood will be the station most under pressure, followed by Epping.