The state government has pledged to cut journey times for trams on Sydney's $2.9 billion light rail line over the coming months, following concerns they are much slower than buses.

After carrying about 115,000 passengers in its first 28 hours of operation, the new line between Randwick and Circular Quay faces another major test on Monday during the morning travel peak.

While delays and several incidents marred the opening on Saturday, light rail operator Transdev said trams operated smoothly on Sunday apart from one tram halting services briefly due to a mechanical brake failure while passing through Surry Hills in the inner city.

The government came under fire from Labor over the trams' average travel time of about 50 minutes between Randwick and Circular Quay, which is slower than forecasts several months ago of 38 to 40 minutes. Buses can take about 35 minutes to complete the same route.