Windang Bridge not subject to a heavy vehicle ban, says Transport for NSW

Rocks are being laid at the base of the piers to reduce the erosion of sand that helps hold them in place.

The move has sparked rumours that trucks using the bridge have been told to find alternative routes.

A Transport for NSW spokesman said this was incorrect.

"There are no restrictions for heavy vehicles currently approved to use the bridge," the spokesman said.

"New permits for over-size and over-mass heavy vehicle movements using Windang Bridge will be assessed on their respective merits."

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Over-size vehicles - such as those carrying mining equipment - require a permit to drive on any road in NSW.

The spokesman said the work being carried out was "essential" to keeping the bridge open.

"The placement of rocks around the base of the piers will provide protection to the bridge piles, prevent further scour and reduce ongoing maintenance," he said.

The rocks are being transported under the bridge by barge before being placed below the surface.

The work is expected to take three months.

"Transport for NSW will continue to advise motorists about minor traffic impacts outside of peak periods, including lane closures and additional travel times, while carrying out monitoring of Windang Bridge throughout the project," he said.