Rudman's city: People also need shielding from thunder of motorway

By BRIAN RUDMAN

The rare native trees at the Auckland Regional Botanic Gardens are no doubt grateful for the newly erected $300,000 sound barrier between them and the adjacent motorway.

At last they will be able to hear each other's leaves drop.

But who will pay for similar protection for their human neighbours?

Since the 3.5m by 440m steel wall went up in January, there have been claims from residents across the motorway from the Manurewa park that the barrier bounces noise into their homes.

What I find hard to believe is that instead of trying to have the baffle pulled down, they are not clamouring for a sound barrier of their own - paid for by, well, anyone they can shame into coughing up.

Every time I see a new block of Housing Corporation or private apartments being squeezed into a remaining piece of motorway no man's land, I wonder how we, as a society, can continue to house people in such a way.

But until I saw the noise levels measured as part of the botanic gardens wall inquest I did not realise what a hell those living alongside the motorways have to endure.

Noise readings taken between 3.30 pm and 4.30 pm over two days outside homes across the motorway from the gardens recorded average levels of 73 decibels (dBA). For 10 per cent of the time, the noise exceeded 76dBA, with peaks reaching 95dBA.

These are levels of sounds that if they came from your stereo would have the noise police marching in to confiscate your equipment. It's the sort of volume you'd expect to encounter from the Auckland Philharmonia inside the town hall.

Curiously, while there are rules regulating when cocks can crow and dogs bark, there is nothing in bylaws or national standards regulating the noise pollution emanating from our roads or motorways.

When you are constructing a building or digging a mine, most local authorities would insist you kept the noise down to 75dBA. Daytime industry is generally expected to limit it to 65dBA.

On residential boundaries the rules are stricter, with 55dBA being the daytime norm and 45dBA the night-time level.

Translating dBA into noise levels is a bit complicated, but experts claim that most people would consider that noise levels doubled every 10dBA

We all know from personal experience that noise can drive you batty. Research by Cornell University, New York environmental psychologist Gary Evans backs this up.

He found that low-level but chronic everyday traffic noise can cause stress in children and raise blood pressure, heart rates and levels of stress hormones. And this was comparing children who lived in quiet (below 50dBA) rural areas with similar kids in noisier (60dBA) residential areas.

I couldn't find any evidence of the effect of noise on trees and, to be fair, the botanic garden wall wasn't built for that reason. Director Jack Hobbs says it was an attempt to persuade visitors back to a part of the gardens that most chose to avoid - because of the noise.

And it has worked.

Intriguingly, the complaints about the wall have not come from those directly opposite but from people further afield - some as far as a kilometre away. Mr Hobbs says some have even come from people on the far side of the gardens and presumably on the good side of the protecting wall.

Before and after measurements by Manukau City acousticians and regional council advisers Marshall Day Acoustics show the wall has not added to the woes of its nearest neighbours.

Proving whether the increases in noise those further afield claim are real or, shall we say, psychological, is much more difficult. No "before" measurements were taken, and the ARC is refusing to demolish its wall for the sake of science.

But whether the increase in sound is real or perceived, the present fight is surely the wrong one.

If I was suffering the noise problems these motorway neighbours have to endure, I'd be praising Transit NZ's new enlightened policy of lining motorway sections with noise barriers and loudly demanding a retro-fit along my stretch of hell.