The New Zealand Transport Agency (NZTA) is arranging a community open day on 28 August to preview a new motorway, which is part of the Western Ring Route.

The agency is inviting the public to walk or cycle the new SH20-1 Manukau extension motorway before it is opened to traffic.

The walking route will make up 3.5km of the new motorway from Cavendish Drive Interchange to the SH1 underpass.

The new $220m Manukau Extension motorway will be opened progressively between late August and December.

The 4.5km extension, with two lanes in each direction, will connect the couthern and south-western motorways. It will also connect to Auckland International Airport.

The motorway will provide the southern entrance to the Western Ring Route. When completed, the route will provide a 48km alternative to SH1 between Manukau and Albany.

NZTA has warned the public about traffic disruption on local roads as temporary detours will be in place.