Wellington Scoop

Noise barriers 3 metres tall – what the council didn’t mention in its flyover report

Opinion by the Architectural Centre
Much of the noise currently produced by traffic round the Basin Reserve is mitigated for cricketers by the earth berms which create the Basin’s eastern bank. The Transport Agency’s flyover proposal to lift 260 metres of road eight metres above the ground will exacerbate the traffic noise and will concentrate it along the northern area of the Basin.

The city council’s report to last Thursday’s meeting fails to mention the need that the flyover will generate for noise mitigation. It fails to acknowledge the need for noise barriers. Noise barriers will block views, negating much of the report’s positive valuation of the flyover. Yet international best practice suggests that the flyover will need these barriers.

Noise mitigation for motorways, such as the flyover, requires tall and long noise barriers, which have no openings. “A noise barrier should be at least high enough to block the line-of-sight from a house to the engines of vehicles on a road. This line should be assessed from a point 1.5 metres above the floor of an adjacent house to the furthest point one metre above the road surface.”

Noise mitigation will be particularly important because it is the council’s intention to encourage increased density in this area in accordance with the Adelaide Road Framework and the Transport Spine Study. Both aim to encourage increased medium-density, mixed-use apartments. Yet highway noise is notorious for sleep disturbance.

The noise barriers – usually in the realm of 3 metres high – will have to prevent line-of-sight between the noise source and the receiver., and apartment buildings will have the best view of the flyover.

The Virginia Department of Transportation specifies a uniform height of 4.9 metres. The Washington State Department of Transportation suggests 7.6 metres tall.

A noise enclosure, rather than a noise barrier, may be preferable given the proximity of the existing nearby apartments (e.g. the Grandstand Apartments) and the promotion of future apartment living in the area.

Vegetation is not a viable solution, as according to the US Department of Transportation a lot is needed: “Thirty metres of dense vegetation can reduce noise by five decibels.”


  1. Driver, 25. March 2013, 14:47

    Ugh, things just get worse and worse for anyone living near the Basin Reserve.

  2. erentz, 25. March 2013, 15:07

    Someone should put a big plaque on this thing to commemorate the intellectual laziness of all those involved in bringing it about. A useful thing to have for the photo op when a future mayor has the inevitable privilege of knocking it down.

    Mind you it would be a bloody big plaque. This goes back a long way to the laziness surrounding the cop-out that was the original N2A “strategy”. There is a long list of regional councillors, regional mayors, government ministers, NZTA bureaucrats, and of course WCC’s own transport officers and councilors who have had their fingerprints on this.

  3. Rod James, 25. March 2013, 16:37

    Hi, Rod James from the NZTA here.

    The Basin Bridge section of the Wellington Northern Corridor does not include 3m high noise walls. It’s true that some roading projects need to be mitigated like this, but this generally applies to motorways adjacent to residential suburbs, with far higher traffic volumes travelling at high speeds.

    The Basin Bridge is more like an elevated two lane street, with a 50km/h speed limit and two lanes travelling in one direction through the city. I can appreciate that people are concerned about noise, but clearly we are talking about something very different here to a 100km/h multi-lane motorway.

  4. Driver, 25. March 2013, 21:28

    If apartment-dwellers don’t need any protection from the elevated traffic, then why is there a (reported) NZTA plan for cricketers to be given special mitigation?

  5. Elaine Hampton, 25. March 2013, 22:27

    An elevated street is a flyover.
    Why is there mitigation for the cricket ground and not for the apartment dwellers and other residents?
    50 kph is noisy, more so depending on the engine and polluting, especially diesel fuel.
    All that money for an unnecessary two-lane, one-way, flyover, Madness.

  6. Guy Marriage, 25. March 2013, 23:11

    Rod, thanks for your reply – I’m glad to see that you and your team are taking note of the concerns of Wellingtonians.
    However, I think you have a long way to go before succeeding in convincing people that the flyover has no ill-effects. Certainly, there will be noise. Certainly, also, the flyover has been designed for a speed limit higher than 50kph, and therefore cars can, and will, travel at higher speeds. Certainly, noise from an elevated source such as a flyover has the ability to travel a considerable distance. I look forward to seeing a full acoustic mitigation report from your consultants.

  7. KB, 26. March 2013, 10:01

    Rod James, you lack a basic understanding of physics if you think comparing noise generated on an elevated road by cars moving at 50kmh is somehow going to be anywhere near equivalent to cars travelling on a ground level road at the same speed.

  8. NigelTwo, 26. March 2013, 11:46

    A flyover with a “noise enclosure”.
    Oh, I get it now, a tunnel on stilts!

  9. JC2, 26. March 2013, 13:02

    KB – I don’t know if it’s true or not, but it’s not what Rod said.

  10. Kent Duston, 26. March 2013, 22:26

    Rod – I can’t help noticing that these were exactly the same questions about noise mitigation that were asked at the NZTA “information day” last year … you know, the one that you and Jenny Chetwynd busily stayed away from, whilst hiding behind your press releases.

    And as it turned out, your Opus mercenaries provided very similarly vague assurances that were similarly short of actual factual detail, like any acoustical engineering studies.

    Now perhaps NZTA – contrary to its reputation – might actually have done the work and assessed the noise footprint, but frankly, who’s to know? It’s not like you were actually there to answer the questions put to NZTA by the community.

    So here’s the challenge. If you genuinely think that the noise effects are open to mitigation, how about you grow some balls and actually show up and explain how to the local community – the people whose homes will be adversely affected by your pet project. I’m sure the Mt Vic Residents Association or Mt Cook Mobilised would be happy to organise a session.

    In fact, you can give me a call directly and I’ll be happy to arrange a suitable public meeting – you can present your view, and presumably an appropriately qualified acoustical engineer can give their view, and the local community can decide which one they believe.

    Of course, based on your track record I don’t think there’s a snowball’s chance in hell that you’ll have the courage of your (apparent) convictions and actually agree to anything that resembles public accountability.

    The balls (or lack thereof) are in your court.

  11. Curtis Nixon, 27. March 2013, 8:14

    Mitigations – remember Manners Mall was a ‘mitigation’ for the urban motorway extension – and look what happened to that. Don’t trust NZTA – if they can give it today and take it back tomorrow they will.
    Wellington roads for Wellington people. Take them back!

  12. Lindsay, 29. March 2013, 12:25

    We’re waiting for Rod James to respond to the issues which have been raised in the above comments.

  13. Michael Gibson, 18. April 2013, 15:51

    Regarding the “mitigation for the cricket ground” mentioned by Elaine Hampton, John Morrison confirmed to me the other day that he had voted for the flyover because this had been promised. I will ask him for details of the actual undertaking he has had from the NZTA about this.

  14. Michael Gibson, 22. April 2013, 17:44

    John Morrison = deathly silence!! It really is quite important to find out how reliable he thinks the NZTA undertakings are.