Longer delays to traffic on busy roads through central Sydney will have "significant impacts" on the performance of the city's new $2.9 billion light rail line and the broader road network in the CBD, the state's roads officials have warned.

Just weeks out from the opening of the light rail line, internal documents from NSW's transport agency lay bare the complexity of running 67-metre trams every four minutes through a congested city.

They also show the City of Sydney has privately complained to Transport for NSW about the "appalling" way large numbers of pedestrians cross streets near Central Station – and the light rail line that circles part of it – had been handled during construction.

Pedestrians crowd onto a footpath between the light rail line and Elizabeth Street near Central Station. Credit:Nick Moir

The government is expected to confirm as early as this week the date for the start of tram services from Circular Quay to Randwick, which had been slated for December 7. The opening is contingent on the outcome of the final testing of trams.