[1] Construction began on 8 September 2014 and completion was originally scheduled for April 2020, but contractual negotiations as well as difficulties resulting from the COVID-19 pandemic caused delays.

This route began construction in 1936 and opened on 4 November 1939,[5] with the section north from Pukerua Bay running along a narrow strip of coastline below the Paekakariki escarpment.

From its northern terminus at Mackays Crossing, the route proceeds a short distance to an interchange providing access to Paekākāriki and Pukerua Bay before rising steeply inland to the Wainui Saddle, and then gently descends through Transmission Gully following the Horokiri Stream to Pāuatahanui, where an interchange with State Highway 58 provides access to and from the Hutt Valley.

The Greater Wellington Regional Council, in preparing its Western Corridor Plan, initially rejected Transmission Gully as unaffordable, preferring to upgrade the existing coastal route, but changed its position after public consultation.

The NZTA proposed other options like the existing highway route at several community meetings, but a full Sandhills Expressway on the old designation won by 2009, although opposed by Jenny Rowan the Green Party Mayor of Kapiti Coast.

[13] On 4 May 2012, after a series of public hearings, the EPA-appointed board of inquiry into the Transmission Gully proposal stated in a draft decision that it would grant resource consents for the project.

On opening day, a Holden VF Commodore police car drove into the northbound truck arrester bed due to driver error.

[4] Supporters claimed that it will improve access to Wellington City, arguing that the existing coastal route is too congested, is accident-prone, and could be damaged in a serious earthquake.

Opponents of upgrading the coastal route said that doing so would cause significant disruption to the communities it passes through, whereas Transmission Gully avoids urban areas.

[28] Others, such as the Green Party and the lobby group Option 3, believed that the money would be better spent on improving Wellington's public transport, particularly the existing rail line.

They argued that the original choice between building Transmission Gully or upgrading the coastal route was a false dichotomy, and that in reality neither option was necessary or desirable.

[citation needed] In May 2012, Julie Anne Genter, the Greens' spokeswoman on transport, described the motorway as incurring costs of $1 billion when the official business case benefits were $600 million, in order to ease congestion for an unlikely projected growth of 1500 vehicles per day.

[32] In March 2021 the road was reported to cost a projected $1.25 billion by its then-expected opening date in September 2021, and would not include a planned extra merge lane at the Linden interchange to relieve congestion.

[34] Land information New Zealand (LINZ) has applied the name gifted by Ngāti Toa Rangatira to the NZ Topo 50 map BP31.