Motorists should experience a smoother and possibly faster journey over the Sydney Harbour Bridge following a 15-month upgrade to the road at its southern end, including the removal of 14 cash toll booths, the state government says.

The completion of almost the entire project this weekend brings to an end work that was described as "very difficult" due to utilities and train and tram tunnels under the roadway at the southern end of the bridge and the sheer volume of vehicles that use it each day.

From Monday, south-bound motorists who want to drive to the northern end of the CBD via Grosvenor Street are advised to use lanes four or five of the bridge, while those heading towards the western distributor should use also lane five, as well as lane six.

Roads Minister Melinda Pavey said the upgrade to the southern end had been a "very difficult project" because of the major traffic demands on the bridge.