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Interesting Facts
- What does Transit New Zealand do?
- How many kilometres of state highways are there?
- What is the total number of vehicle kilometres travelled?
- What is the busiest stretch of road in New Zealand?
- When did New Zealand first have a motorway?
- How much do roads cost?
- What impact does weather and terrain have in the way Transit designs roads?
- Do trucks wear roads out quicker than cars?
- Why are New Zealand roads black?
- Is New Zealand the only country with our sort of roading?
- Why does Transit build roads where it does?
- What is asphalt?
- What is chip?
- Why is there variation in chip?
- What sort of chip seal does Transit use on the roads?
- Is a road with big chip safer than a smoother road?
- How often does a road get repaired?
- How do you accommodate things like fault lines?
- Why are state highways numbered the way they are?
- What is the longest straight road in New Zealand?
- Which is the highest highway in New Zealand?
- What is the longest bridge in New Zealand?
- How many bridges are there on the state highway network?
1. What does Transit New Zealand do?
Transit New Zealand develops, manages and maintains the country's state highways.
2. How many kilometres of state highways are there?
There is nearly 11,000 kilometres of state highway network, 10,894.9 to be precise (5973.8 km in North Island and 4921.1 km in South Island – as of August 2006). This network provides a vital link to 82,000kms of local roads managed by territorial authorities (ie councils). It is a national asset worth $12.511 billion and carries 50% of all New Zealand's traffic. There are 170 kilometres of motorway in the highway network.
3. What is the total number of vehicle kilometres travelled?
There are 19 billion vehicle kilometres travelled on New Zealand state highways. Auckland state highways carry 21% of those kilometres travelled but has only 3% of the state highway network length. However, Auckland has 32% of New Zealand’s population, which means there are a lot of cars on the road there.
4. What is the busiest stretch of road in New Zealand?
State Highway 1 immediately south of Auckland is the busiest road in New Zealand with over 200,000 vehicles a day. The Central Motorway Junction (Spaghetti Junction) in Auckland city is the next busiest with 200,000 vehicles a day.
5. When did New Zealand first have a motorway?
The first section of motorway opened in December 1950. It ran for 3 miles between Takapu Road and Johnsonville and is part of the main approach to Wellington City.
6. How much do roads cost?
In the year 2000/01 it was expected that about $1.8 billion would be spent on state highway and local road construction and maintenance. Most of this comes from taxes and charges paid by road users.
7. What impact does weather and terrain have in the way Transit designs roads?
The terrain adds hugely to the cost of building roads. Once you have done the expensive earthworks for a road it is very expensive to realign it or try to make it higher or lower. It's also expensive to cut through hills or build up roads over wet or coastal areas.
Weather makes a big difference to maintenance costs also. Hot weather can cause bleeding (this can occur when the road surface gets hot and melts), snow and ice can crack the road, and in wet weather water can get under the surface of the road and break it up.
Roads also have a camber (each side of the road slopes away from the centreline at a rate of about 3%) to let stormwater run off as fast as possible.
8. Do trucks wear roads out quicker than cars?
Yes - by the 4th power law. For example, a vehicle weighing 2 tonnes is 16 (24th = 2*2*2*2 = 16) times more damaging to the road than a vehicle weighing 1 tonne (14th = 1*1*1*1 = 1). Heavier vehicles pay for this extra wear through higher road user charges.
9. Why are New Zealand roads black?
New Zealand roads are made from bitumen, not concrete. Bitumen is flexible, copes with different temperatures, suits lower volumes of traffic and is cheaper. Our roads have a chip seal, (the coating of stones on top) some with big chips, some with little chips. Some of the roads in South Africa and Australia are like ours.
10. Is New Zealand the only country with our sort of roading?
South Africa and Australia have similar roads to those in New Zealand. They all have a thin chip seal surface. In New Zealand this is the case especially on our rural roads. This sort of road is cheaper to build and it suits the lower traffic volumes and less intensive development that South Africa, Australia and New Zealand have in common.
11. Why does Transit build roads where it does?
New Zealand's roads have mostly been developed from original bullock tracks. We assume that the quickest way from A to B is a straight line. But if the line (our road) has to go over swamps, across rivers and over hills it will be very expensive to build. Not only that, our ancestors took the line of least resistance. They went round the swamp, round the hill and sometimes alongside the river till they found a good point to cross because that was easier - even if it took longer.
Our roads started being built many years ago when people wanted to go to and from the ports, the goldfields, their farms and elsewhere.
Today's highways carry heavy, sophisticated and expensive vehicles. But the roads we travel on today might well be laid on the foundation that was a bullock track one hundred and fifty years ago.
We've grown up with a traditional pattern of roads, and in New Zealand especially, it's far from being a straight line. That's a reflection of our topography and of the changing patterns of our economic and social development.
People want roads, but right from the beginning they wanted them built for low costs. So there has to be a balance between what is best for the economy of the country, what will satisfy people's needs, improve their safety, and what we can afford to build.
12. What is asphalt?
Asphalt is a mixture of stones and bitumen. You take stones and put them into a mixer with bitumen which glues them together, and they finish up like concrete. The road surface is actually called asphaltic concrete, and it is like concrete, just not quite as brittle. Most of the roads in New Zealand have only very thin layers of asphaltic concrete on top. They are built mainly out of gravel, compacted down with rollers.
Bitumen is a residue made out of a distillation of the same oil that is used for fuels. Most of the bitumen Transit uses is produced at the Marsden Point refinery.
13. What is chip?
The chip is the name for the small sharp edged rock embedded on the top of the road. In the South Island the rock comes from rivers; in the North Island it mostly comes from quarries. You can make chip only out of very good rock - it has to be strong so it doesn't get slippery after it's been on the road surface for a while.
14. Why is there variation in chip?
New Zealand has a huge variety of rock. The South Island has river gravels or greywackes that have washed off the surfaces of the Southern Alps into the rivers. This makes excellent sealing chip in the South Island. In fact South Island roads are more grey than black because this kind of chip has more quartz in it. Chip used in the North Island uses more pure volcanic materials, such as andocites and basalts so North Island roads are blacker.
15. What sort of chip seal does Transit use on the roads?
If a road is re-sealed with big chips on top of big chips on top of big chips, layer after layer, every 10 to 12 years, then eventually the road becomes a pudding of black bitumen with big stones at the bottom. That kind of road is flexible and gets slippery.
The cure for that is to re-seal with alternate layers of small and big chips which fills the gaps and stops the chips falling to the bottom of the mix. The whole mix is a lot stronger, and the bitumen does not rise to the top (called flushing) and become black and slippery on top.
16. Is a road with big chip safer than a smoother road?
No, not at all. What makes a road safe is how much grip (skid resistance) vehicle tyres have on the road. This is a combination of how big the chips are in terms of whether they stick out of the bitumen, and how the surface of the chip looks.
Some of the chips are very, very small, like the relatively soft volcanic andacites. But even though the chip is small it has a high skid resistance. Transit keeps monitoring skid resistance and uses the standards that are used in the United Kingdom. There's no simple rule that 'big chips give you better grip'.
What does matter is the way the road is built. If you keep building a road out of big chips on top of big chips on top of big chips, layer after layer, every 10 to 12 years, then eventually you will probably get a pudding of black bitumen with big stones in it.
17. How often does a road get repaired?
A road gets resurfaced every 10 or 12 years. Transit re-builds a road every 30 to 40 years. If roads are built from asphaltic concrete they only need to be re-furbished every 60 odd years, because all you do is put on a new top. What changes is the amount of traffic on a road, and that's usually always increasing.
18. How do you accommodate things like fault lines?
We can't assume that our roads will stay in place during an earthquake. Transit does pay detailed attention to seismic technology. In fact New Zealand road and bridge builders are world leaders in this area having shared skills in both California and Japan.
The SH73 Otira Viaduct on the West Coast, which was opened at the end of 1999, has been designed for seismic forces 40% higher than the maximum value normally used by Transit.
19. Why are state highways numbered the way they are?
The numbering system on state highways is for internal administrative purposes but it also provides a good way for road users, particularly strangers to an area and tourists, to travel on the state highway system by using route numbers. The numbers are chosen according to what is most suitable and historical precedent.
The more important roads of the state highway network have generally been given single digit numbers while the less important state highways within regional areas are usually given two digit numbers . For example, the Northland and Auckland highways are numbered 10,11 and so on to 19. South of the Auckland Harbour Bridge to Waikato is 20, 21 onwards, and from Waikato to Taupo the numbers are 30, 31 and so on to 39.
When a new state highway is declared Transit looks for the most appropriate number to fit the series.
20. What is the longest straight road in New Zealand?
The longest section of straight state highway is through Culverden on State Highway 7 in the South Island. It starts just south of the intersection with SH70 to Kaikoura, and is approximately 13.7km long.
21. Which is the highest highway in New Zealand?
The highest State Highway in New Zealand (elevation) is SH1 the Desert Road at 1,074 metres. Other high highways are
SH8 Lindis Pass 1,000 metres
SH94 at the Homer Tunnel 945 metres, and
SH60 Takaka Hill Road 791 metres
The highest road (not a state highway) is the road over the Crown Range.
22. What is the longest bridge in New Zealand?
The longest bridge on the state highway network is the Rakaia River bridge on SH1S at RP 381/18.80, Length = 1,757 metres. [RP means route position]
The next longest bridge is the:
- Auckland Harbour Bridge SH1N at RP 414/9.21, Length - 1,580 metres.
- Thorndon Overbridges on SH1N at RP 987/2.24, Length = 1,335 metres.
- Whirokino Trestle Bridge on SH1N at RP 873/11.72, Length = 1,098 metres.
- Waitaki River Bridge on SH1S at RP 569/0.00, Length = 906 metres.
- Hokitika River Bridge on SH6 at RP 471/0.00, Length = 740 metres.
- Haast River Bridge on SH6 at RP 750/0.00, Length = 737 metres.
The longest state highway structure is the Lyttleton Tunnel on SH74 at RP 22/3.72, length = 1,945 metres.
23. How many bridges are there on the state highway network?
A bridge is defined as 3.5 metres across, which includes some large culverts. There is a total of 3,983 bridges on the state highway network, accounting for 139 kilometres of the total highway network length of 10,894 kilometres. There are 177 one-lane bridges, 15 timber bridges and speed restrictions on 12. Bridges vary in character from rural single lane bridges, dual mode bridges such as the historic Awatere road and rail bridge, spectacular viaducts such as the Otira Viaduct to multi-lane motorway bridges.
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