Work has started on the $220 million Hobsonville deviation motorway and Brigham Creek extension that will complete the new $400m Upper Harbour motorway.

The new road network provides North Shore with a faster connection with Waitekere city, enabling motorists to travel from Paul Matthews Drive in Albany to the northwestern motorway along a single motorway.

The new motorway will also form the northernmost section of the western ring route between Albany and Manukau city, linking the Upper Harbour, northwestern and southwestern motorways to provide an alternative to the northern motorway across the harbour bridge.

The New Zealand Transport Agency says the 6km Hobsonville deviation will have two lanes in each direction to connect the northwestern motorway at Hobsonville Rd with the Upper Harbour bridge and Greenhithe deviation motorway.

The 3km Brigham Creek project will extend the northwestern motorway through Massey north to a new roundabout with Brigham Creek Rd.

The two-lane extension is expected to reduce congestion on the motorway north of Don Buck Rd.

Called the Green Route, the Brigham project will feature extensive planting of native flaxes along with green walls planted with ferns, grasses, climbers and hanging plants.

Stormwater wetlands will be planted with reeds, flaxes and cabbage trees to maintain and enhance the natural environment.

The agency says the new motorway will better connect the Shore and Waitakere and support economic development in the growing northwest area of Auckland.

The road network includes the Greenhithe deviation and duplication of the Upper Harbour bridge which are already open.

Construction will take four years with the new motorway to be opened in 2012.