Council's director of infrastructure Warren Sharpe said the upgrade would improve road safety and meet future transport needs.

"The current bridge has narrow lanes and shoulders. It will not cater for future traffic volume and heavy vehicle loads," Mr Sharpe said.

The upgrade will see the bridge strengthened and widened from 6.7 metres to 11 metres to include 2-metre wide shoulders on both sides for safer cycling. The bridge approaches will be realigned and widened to conform to current regional road standards.

"We're in the final design stages and will begin preparatory - clearing, road widening, culvert extensions and service relocation - work before Christmas.

"Commuters can expect significant delays on North Head Drive during work and should use the Princes Highway and Broulee Road alternative where possible," Mr Sharpe said.

Construction of the bridge will begin next year.

Mr Sharpe said Garlandtown Bridge was an important part of the alternative coastal route from Batemans Bay to Moruya.

"The bridge upgrade means this key link can function for people, goods and services should the Princes Highway be cut, as we saw in last summer's bushfires," he said.

The Garlandtown Bridge upgrade is substantially grant funded with $691,709 from the NSW Government's Restart NSW program and $850,000 from the Australian Government's Bridges Renewal Program, and the remainder coming from Council.