Trams on Sydney’s new $2.1 billion light rail line will need greater priority over motorists at traffic lights in the inner city if passengers are to avoid longer delays to their trips, an internal report shows.

The confidential report commissioned by Transport for NSW estimates passengers will spend between seven and nine minutes waiting on the 67-metre trams at red lights along the line between the CBD and the city's south-east during the morning and evening peaks.

"The traffic signal delay results indicate that the locations of highest delays are reasonably consistent for both the AM and PM peak periods with the majority of delays encountered by light rail occurring in the southern CBD and Surry Hills," the report said.

The tram sets on Sydney's $2.1 billion light rail line will be 67 metres long.

The time that trams spend waiting at intersections for red lights to change will be one of the major causes of delays to trips.