Why isn’t it just another raised roundabout, like the Dowse interchange at the bottom of Maungaraki hill? Why can’t southbound traffic on SH2 have a direct on-ramp onto the new bridge, instead of a loop back to it?
They’re some of the questions asked about the new design for the Melling Interchange – and now we have answers from Waka Kotahi and traffic engineers.
First thing to note from a briefing to the Hutt Valley Chamber of Commerce on 18 June is that the illustrations released earlier this month depicting a sort of two-leafed clover layout, with the new bridge as a stem, are not detailed designs. Waka Kotahi Director Regional Relationships (Wgtn) Emma Speight and Project Director Matt Hunt said there’s more work to do before the final design is locked in for construction.
Nevertheless, the new look shows clear advantages over what’s there now, and indeed over the layout presented at consent hearings two years ago.
- The right had turn conflict that causes so much delay (and leaves that dangerous tail-back on SH2) is gone. Traffic turning right off the bridge to head north, and traffic turning right off SH2 into the city, will be able to sail past each other without stopping.
- There’s a 4.5-metre wide shared path on the southern side of the bridge and some way up Harbourview for cyclists and pedestrians to access Pharazyn St and the new railway station. For those on foot/two wheels coming off the hill, there’s only one narrower (and traffic-lighted) intersection to negotiate to get to the trains, and the new City Link bridge direct into downtown Lower Hutt.
- It’s a cramped site but the different layout means less extensive cuts into the Western Hills (and thus fewer, expensive, retaining walls). With the interchange moved slightly south and east, and SH2 slightly realigned, it also means more of the construction work can happen ‘off-line’, with less disruption to traffic.
So why not a raised roundabout, like at the Dowse interchange?
The traffic engineers said a roundabout is more walker/cyclist unfriendly, and there was also the problem of how to get cars and people down to the new railway station. There are two sets of traffic lights on the bridge (three if you count the ones at the city end where the bridge lands at the Rutherford St/Queens Dr corner). Phasing of these allows better traffic flow, especially at peaks.
Why the loop-back onto the bridge for traffic southbound on SH2 and from Belmont and Kelson?
The loop allows much more capacity on the bridge and is part of eliminating what was a five-armed intersection. The design also means it’s less likely drivers unfamiliar with the area will head off down the wrong way.
It wasn’t stated at the briefing but presumably it also lessens the risk of a tail-back on the state highway, and will allow a turn at the bridge traffic lights for that traffic to access Pharazyn St/the railway station.
And it also means a greater chance, at some time in the future, of being able to extend the Melling rail line further north. The loop-back rises up to the bridge, making it easier for a rail tunnel to go underneath.
All things considered, for an interchange that has to give clear way for 40,000 vehicles per day to move along SH2 without an intersection/traffic lights, to cater for 20,000vpd using the bridge, and on a site where rail, the earthquake faultline and the Waiwhetu aquifer are factors – in my opinion it looks pretty good.
At the Chamber briefing, concerns were expressed by cycle groups and retailers/businesses about disruption during construction. Make no bones about it – there is going to be considerable delays and hold-ups. A multi-agency working group has been set up specifically to investigate/oversee ways of easing snarl-ups during construction.
But keep your eye on the prize: one-in-440 year flood protection, much better traffic flow for all modes (including cycle paths that link to Te Ara Tupua/the Melling to Ngauranga path) and a city that faces the river, with all sorts of potential for rejuvenation downtown and along the river-front.
The ($420 million-plus) question – when will the interchange be finished?? The Alliance partnership is working through final designs and scheduling of which bits should be done when. A final agreement is due to be signed at the end of the year, with construction starting next year.
Greater Wellington is already underway with stopbank work at the Mills St end.
Do you still have questions?
The Hutt Valley Chamber of Commerce (3rd floor of the building at 15 Daly St) is hosting a ‘drop-in’ session on Thursday 20 June. Drop in any time between 4.307.30pm.
There’s also some great information, plus a ‘video fly-over simulation’ of what the interchange will look like, here – https://teawakairangi.co.nz/our-projects/our-projects/mellingimprovements .
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