Every city in NZ has potholes, and Palmy is no different. This page explains why potholes occur, what we're doing about them, how you can report them and how we prioritise our roading jobs.
Potholes form when water seeps under the surface of the road surface via small cracks, or by water in the soil coming from underneath.
This weakens the surface of the road, with the weight from cars and trucks breaking those cracks open under pressure. Water makes the risk of potholes forming worse, and they can appear within just a few hours of heavy rain.
Resealing a road is expensive and we prioritise work based on safety.
We need to use your ratepayer money wisely to make sure it stretches to cover everything we need to do for our roads and footpaths.
To increase the lifespan of a road, we only fix the parts that need it to help our budget go further. Each road has an estimated lifespan and we repair potholes to help the road last until it is scheduled for a full road reseal.
We can fix 2000 potholes for the cost of rebuilding a section of road that’s only a couple of hundred metres. We can also repair 50 potholes for the cost of repairing a small patch of road that is only a few metres wide.
We can only afford to fully rebuild one section of road each year as they can cost upwards of $1-2million. We can also only do this in summer when the weather is dry, so during winter we can only make temporary repairs. Winter is also the time of year that most potholes appear because those pieces of road that are not waterproof get water into them which traffic then shakes until it fails.
Resealing a road is a two-stage process that is designed to waterproof sections of road to extend their lifespan.
First we fix the specific areas that are failing or need smoothing over. These are known as pre-seals, which need to cure for a few months to harden and are similar in nature to the minor patch up repairs done to weatherboards before repainting a house. After that, we do the final layer of the road surface – asphalt or chipseal.
We try to do pre-seals about 12 months before the final stage to make sure we get the best surface we can.
Palmy is a great place to live, but we do get some wet winters.
The city is built on a combination of soft river soil and moisture-sensitive blue clays that are not ideal foundations for roads. They also don’t drain very well. Water is a major cause of road failure – a well-drained and waterproof road will last much better than one that is not.
Once water can get into our roads, it becomes much easier for tyres to pluck out loose seal, allowing more rainwater to penetrate, making the road even weaker and more susceptible in a vicious downward spiral that leads to the road falling to bits.
Palmy’s role as a logistics hub is a good thing – trucks mean work. But they also shorten the life expectancy of our residential roads that were made for smaller cars, pedestrians and people on bikes.
Cars and delivery trucks are under 8 tonnes per axle, which is about the limit our residential streets can carry. Anything over, such as 18-wheeler trucks or buses, cause damage to roads unless they are especially designed for that type of load. These roads require a lot more material beneath the road to keep it stable – which is much more expensive than building inner-city or residential streets. That’s why we are turning our focus to building selected roads for freight to navigate around the city, such as Tremaine Ave and the inner ring road.
For comparison, a loaded bus puts the pressure of 2600 cars on the road. The combination of heavy commercial vehicles, poor underlying ground conditions and thin existing road surface is causing deterioration across our network.