Wellington Needs a New Roading Plan

The Transmission Gully Highway might have been a good idea half a century ago, but Wellington has outgrown it just as surely as it has outgrown the Coastal Highway.
If the goal is an unobstructed road from Peka Peka to Wellington, we should investigate a motorway through the Akatarawa Valley combined with an upgraded Western Hutt Road.
From Waikanae, the route would climb to a saddle about 2.5 km southwest of the summit of the present Akatarawa Road, then follow the Akatarawa Valley to the existing highway near Upper Hutt.
This route has gentle gradients that would allow it to become a true motorway. The steepest section, the climb from Waikanae to the summit, requires a five percent gradient, much flatter than the eight percent gradients of Transmission Gully and the Ngauranga Gorge.
The Western Hutt Road between Petone and Wellington can be upgraded by carving three new northbound lanes into the hillside above the existing road, which would become three southbound lanes and a two-way cycle track wide enough to accommodate proper road maintenance equipment.
The distance from Pekapeka to Wellington via Akatarawa is within a kilometre or so of the distance via the proposed Western Bypass, Paraparaumu, and Transmission Gully.
The existing Akatarawa Valley Road would be retained as a local access road, with no connection to the motorway except Upper Hutt, Cloustonville, and Waikanae. The summit would have a grade-separated intersection providing access to the ridge-top tracks.
(also posted on Stuff)