The project is to build a 27km four-lane (two in each direction) median-divided motorway from MacKays to Linden (through Transmission Gully), with interchanges connecting the route to MacKays, SH58, eastern Porirua and Kenepuru.
In July 2014, the Transport Agency signed a Public Private Partnership contract with the Wellington Gateway Partnership. Under the terms of the PPP contract, the Wellington Gateway Partnership will design, construct, finance, operate and maintain the new Transmission Gully motorway for the 25 years that will follow the programmed five-year period to build the motorway. The Wellington Gateway Partnership has indicated that the motorway will be open for traffic by 2020.
The proposed highway will assist in remedying the projected capacity problems and current safety/congestion concerns on the existing State Highway 1. It will provide a route that is more resilient to natural disasters (earthquakes, storms, tsunamis etc) than the existing coastal highway. Communities along the existing SH1 will benefit from the reduction of through traffic.