Drivers will experience less congestion and faster travel times with a fifth lane added.
There are now three lanes dedicated to eastbound traffic on the bridge, meaning drivers will save up to five minutes when travelling between City Road and Hoddle Street.
The Swan Street Bridge was originally completed in 1952 with only two lanes in each direction. The upgrade now adds one eastbound lane on the bridge and one outbound lane along Olympic Boulevard.
Complex work to upgrade the bridge involved 140,000 work hours, 2,000 tonnes of reinforced concrete and 1,600 steel bars
The upgrade will be officially complete in mid-2018, when new pedestrian and cycling paths are added to either side of the bridge.