Up to 500 people have descended on a park in Sydney's inner west to protest the NSW government's Westconnex road project.

Picnics and music performances were held at the Rozelle park on Sunday afternoon before urban transport experts and Greens representatives, including Grayndler federal candidate Jim Casey, addressed the crowd.

They called on the state and federal governments to stop funding the road, which they say does not provide value for money and will only produce more traffic.

Instead, funding should be redirected to public transport, health and education.

"We've always said Westconnex has all the hallmarks of a dirty project," WestConnex Action Group spokeswoman Amanda Bull said.

"No transparency, escalating costs, corrupted planning processes, contracts signed before approvals are granted and more."

The Greens have committed to working towards blocking federal funding for the 33 kilometre transport project, the largest of its kind in Australia.