Work has started on the $170 million Airport East precinct roads upgrade, which includes replacing the General Holmes Drive rail level crossing with a road underpass to the south.
Roads and Maritime Services (RMS) warned motorists to expect traffic changes in the area.
The project, which was announced in 2016, is designed to improve the movement of rail freight from Port Botany and the traffic flow and access to the airport and port.
Initial work will involve relocating various services across the project area, including electricity, gas, water, sewer and communications.
Major service relocation work will take place along Botany Road and Wentworth Avenue over a period of about 12 weeks.
Service relocation work will take about 12 weeks to complete, weather permitting.
The main feature of the project is replacing the General Holmes Drive rail level crossing with a road underpass between General Holmes Drive, Botany Road and Wentworth Avenue.
Other improvements include changes to the Mill Pond Road intersections with General Holmes Drive and Botany Road.