The Roads and Traffic Authority has refused to release almost every document dealing with the planned extension of the controversial M4 East motorway despite a resolution of the NSW upper house ordering the production of all material.

On Wednesday night the RTA produced half a box of papers, most of which were already public, but did not explain what happened to six more boxes compiled by its major infrastructure branch.

A spokesman insisted it had provided ‘’all relevant documents to the Legislative Council in compliance with the call for papers'’.

Asked why it had not produced six other boxes of material referred to in RTA correspondence, the spokesman said they were all protected by cabinet secrecy provisions.

The Greens MP Lee Rhiannon said it was absurd to say all RTA documents were cabinet documents, especially as some have already been leaked and published in the media.

She accused the Government of hiding details of the planned route for the motorway and location of access ramps because it fears disclosure will provoke a voter backlash in the Labor seats of Marrickville and Balmain.

‘’They are abusing the cabinet exemptions to sidestep a clear upper house directive,'’ Ms Rhiannon said.