Two lanes on Parramatta Road will be "solely dedicated" for public transport, says the NSW Planning Department, which has approved a motorway tunnel under the maligned corridor.

The approval conditions mean there will be less road space for motorists trying to avoid paying tolls, but public transport travel times should improve.

Planning Minister Rob Stokes announced on Friday he had approved the M4 East motorway section of the WestConnex motorway between Homebush and Haberfield, but imposed what he described as "unprecedented" conditions on the project.

Foremost is the requirement for at least one lane in each direction on Parramatta Road to be exclusively used for public transport.