New Zealand Road history: Newlands Interchange, Wellington

Newlands Interchange - Project Newsletter 1996

It is taken for granted now by drivers and passengers using SH1 Ngauranga Gorge today, but it is notable that the last traffic light controlled intersection on SH1 north of Wellington until Papakowhai (and today until Levin) was not removed until 1998.

At the top of the Ngauranga Gorge on SH1 in Wellington, the Newlands intersection was a legacy of when the Gorge road was upgraded, sealed and widened in the 1930s as part of the Centennial Highway project (which ended in suburban Johnsonville and did not recommence until beyond Plimmerton to Pukerua Bay and along the coast to Paekakariki). Having a traffic light controlled intersection on a six-lane highway that, at the time, operated at a 100 km/h speed limit, created a considerable bottleneck, primarily for the state highway traffic, but also long queues for traffic turning off to Newlands (which would back-up into the fast lane). Queues southbound would extend past the Johnsonville southbound offramp and northbound down to the Ngauranga intersection. Some of this is illustrated in the project newsletter. Contributing to congestion is that trucks from the quarry and industrial sites on the southern side of SH1 Ngauranga Gorge have to go uphill and enter Newlands, by crossing into the fast lane and queuing to turn. This would be eliminated by the project having a slip lane to enter the interchange for an easier turn.

The intersection would also be the site for accidents ranging from multiple nose-to-tails to occasional red-light collisions. One report indicated that the intersection had had 28 injury accidents in the five years from 1991-1996.

In essence, the efficiency and useful capacity of this section of highway was compromised by the intersection. Noting that by the time this project was built, two traffic light controlled intersections on SH1 in Porirua just north of the Johnsonville-Porirua Motorway (at Mungavin Avenue and The Ramp) had already been replaced by grade-separated interchanges, permanently relieving congestion on SH1 through Porirua.

The Newlands Interchange project plans were released in 1993, but construction did not start until December 1996 and it was opened in March 1998. The problem was not funding, as it had a Benefit/Cost Ratio above 6. This consisted of $70m in travel time and vehicle operating cost savings over 25 years and $12m in accident savings over that time. At the time SH1 Ngauranga Gorge had around 60,000 vehicles per day with Newlands Roads at 13,000. Today Ngauranga Gorge still averages around 59,000 vehicles per day.

Delays were due to planning appeals, specifically local concerns about construction disruption from the adjacent motel and opposition from the Rainforest Action Group. This post includes multiple newspaper articles about the project, but also the official information leaflet upfront.

The project was originally costed at $9m but ended up costing $16.3m (the BCR of over 6 reflect the latter cost, the previous cost had a BCR over 11)

Newlands Interchange - Project Newsletter Page 2

Newlands Interchange - Project Newsletter Page 3

Newlands Interchange - Project Newsletter Page 4

The following articles are :

dated 13 July 1996 from the Evening Post, about appeals for planning approval from the Manor Inn Group (largely due to concerns over disruption during construction) and the Rainforest Action Group (which withdrew its appeal).
Dated 8 August 1997 depicting the construction of the project, including an image of how erosion and debris would be addressed.
Undated in 1997 also depicting construction of the project