Some Sydney roads are so clogged that even building multibillion-dollar tunnels underneath will not make them faster to drive on.

At least that is the prediction for one of the city’s most notorious stretches – Pennant Hills Road – under which a new nine-kilometre toll road will be built.

Pennant Hills Road: Peak hour times will lenghten. Credit:Getty-Images

The environmental impact statement for the so-called NorthConnex project, a $3 billion road tunnel to run from the M2 motorway at West Pennant Hills to the M1 motorway, was released on Tuesday by the Department of Planning.

The environmental impact statement predicts that even when road tunnels are built by about 2019 under Pennant Hills Road, the time it will take to drive along the surface road will be about the same as it is now.