A chip on the roading shoulder

A disintegrating asphalt road surface north of Auckland, has been grabbing the news in recent days. It will probably turn out to be a bad batch, because anyone observing the laying of this material shows that it sets very hard after much roller work and as the product cools down. Hard to believe that there isn’t some roadside test that can be done to new asphalt surfaces before the affected lane is reopened.


It seems not widely known, that local bodies receive subsidies from NZTA for work on their local streets. The rate of subsidy varies but I don’t know of any local body that receives a subsidy of less than 50 percent and many are higher. This subsidy is known as the ‘FAR’ or ‘Financial Assistance Rate’. Two of the determining factors for setting individual council FAR rates, are topography and degree of social deprivation. The Far North receives the highest rate in the country, because of its scores in both of these factors.

But with government money, comes government rules and a few months ago an NZTA worthy reportedly reprimanded local bodies for putting in FAR requests for more asphalt surfacing than he deemed necessary. The alternative is of course chip surfacing. I don’t know the precise cost differential between chip and asphalt, other than the fact that asphalt costs a lot more.

‘No’ to asphalt

With this reprimand in mind, it was somewhat amusing to read another NZTA announcement that the Otaki to Peka Peka stretch of the SH1 redevelopment north of Wellington would be delayed because of a shortage of asphalt! This raises the question as to whether local bodies are being bullied out of asphalt use to provide supplies of that product for main highways.

To the motorist, the most noticeable downside of chip versus asphalt is road noise. Another unheard penalty is rolling resistance. There is considerable energy expended on overcoming rolling resistance and the cost of that energy transfers to your fuel bill. My little bit of physics knowledge tells me that energy can only be dissipated in three ways – heat, light or sound. There is no light generated by a car’s tyres rolling over a chip surface. There is no doubt heat and there is certainly noise.

Electric cars

To a motorist driving at 100kph along a chip-surfaced highway, the road noise is a constant background. More expensive makes of cars are insulated against road noise and I understand that a BMW is a much quieter ride for passengers, than your average Japanese hatchback.

For those living alongside chip-surfaced streets and highways, road noise is a much more disturbing ‘Brrrt’. Brrrt’. ‘Brrrt,’ sound pattern.

Although I haven’t personally experienced this, I recall reading a comment from an electric car owner that the battery power use meter jumps appreciably when the vehicle crosses from asphalt to chip surface.

The fact is that the Otaki to Peka Peka project has a huge 'vanity factor'. Jet black asphalt with pure white markings will impress the PM no end, when she takes her maiden drive.

Objectivity required

I suggest that asphalt use on local roads be determined by an objective test, based around traffic flow and associated speed and housing density – not vanity. If the noise effect of chip is in excess of levels determined acceptable by way of objective test, then asphalt must be FAR-subsidised.