Pavement Surface
Rigid pavements of cement concrete or bituminous concrete have been generally so expensive that these materials have not been used outside cities; rather than put a strong surface pavement on a relatively poor subgrade, New Zealand engineers have tended to build a very strong subgrade and cover the surface with a light treatment just sufficient to meet the needs of traffic. They have developed the bituminous seal with the large chip. This method produces tyre noise, but it does give at a low cost a strong nonskid membrane protecting the subgrade.
Where the traffic is heavy, or in districts where the supply of chips is not readily available, other types of pavement have been developed. For instance, on the Desert Road, which runs north of Waiouru across the North Island Central Plateau, local material was used to make a bituminous mix which has given very satisfactory smooth riding for many years. On the motorways around Auckland, where the traffic is extremely heavy and tyre pressures are high, an even stronger bituminous pavement has been laid down. On the more congested urban streets and highways the tendency is to put down the high-type concrete or bituminous surface. In cities the most permanent surface used is a bituminous mix on a concrete base. With modern equipment available it is possible to construct either type to a high degree of accuracy and with smooth-riding and long-lasting surfaces. To cope with the weight and thrust of heavy transport buses it has been necessary to provide concrete loading areas at bus stops.
Maintenance
Of equal importance is road maintenance. Even in the worst of weather, maintenance gangs keep open the traffic routes of the country. Modern highways are designed to stand up to the stresses of heavy traffic, but all roads require regular attention. The magnitude of this work may be appreciated by the fact that maintenance cost in recent years is approximately one-third of the total highway expenditure.
Bridging
The story of road engineering in a country such as New Zealand would be incomplete without reference to the bridge engineers. Recent advances in this field have been quite as outstanding as in those of roadway design. Like many of the early roads, some of the first bridges built in the colony are still open to traffic or have just been replaced, as, for example, the Kawarau Bridge (1962) on the Cromwell-Queenstown route. The old bridge (1880) was a suspension one with a 300-ft span. The Wanganui Bridge, which originally had lift spans, was erected in 1869 and still serves the city. Bridges of standardised design in steel and pre-stressed concrete speed up construction by pre-fabrication methods, and decrease the work to be done on the site. Again, new concepts and construction techniques, such as the use of steel piling in various forms, prestressed concrete piles, or bored piles, have enabled structures to be built where timber or ordinary concrete piles would have been inadequate. Construction by cantilevering out from piers has been recently used on a number of major bridges in New Zealand. This is a procedure which can be used on difficult sites.
As in road engineering, bridge design must be related to traffic requirements. In the early days the approaches to a bridge were of minor importance and every effort was made to secure the shortest and cheapest site. Moreover, bridges were designed for smaller loads than those required by modern traffic. Today a bridge is considered part of a highway and must be constructed in conformity with the curves and alignment of the road. But bridge construction is also designed for other purposes, equally important. The extension of overhead motorways into the heart of Wellington and of Auckland will require many major structures over land and rail.
The Future
Highway engineering is one of those branches of engineering which has been associated step by step with the progress of New Zealand. Today much has been achieved, but there remains just as much to be done. The engineer will be required to provide surfaces to carry heavier loads on more and more routes; at the same time manufacturers will be producing more and faster vehicles, which will require more road space.
by Harry Lancelot Hume, B.E., B.SC.(N.Z.), M.E.(YALE), M.I.C.E. Chief Civil Engineer, Ministry of Works, Wellington.
ROAD ENGINEERING
It is often said that engineering in some form or other has been associated with every step of progress which has been made in New Zealand. This statement is certainly true of the present, and one of the branches which is playing an increasingly important role in national development is highway engineering. Usually we think of highway engineering as one of the branches of civil engineering, but in some projects all branches of engineering are involved – civil, mechanical, electrical, and even electronic. For the purpose of this article, highway engineering is assumed to cover work associated with all public roads.
Road or highway engineering has two important aspects. First, it deals with people's reactions and, secondly, it deals with engineering problems. Closely involved in these two aspects are five basic transportation factors: safety, comfort, time, convenience, and economy.
Traffic Factors
In New Zealand the principal authorities responsible for roading works are the Government, the National Roads Board, and municipal and county councils. In the early years of the colony's development the county authorities had to provide some form of communication between farm and market; thus the original county roads were designed primarily for moving stock on the hoof and for light vehicles. Today, however, the farmer no longer moves his stock on the road; he must therefore be able to get a normal truck to his farm so that he can deliver his stock to the freezing works at the main centres. This has brought about a change in the character of country roads, with the result that bridges have had to be strengthened or rebuilt to carry heavier loads and the roads themselves made capable of carrying heavy vehicles, even though the frequency of traffic may be quite low.
National Roads Board
Since its inception the National Roads Board has endeavoured to develop a national system of rural highways to connect the county roads with those in urban areas. This policy has now reached the stage where the main difficulties lie within the cities' boundaries. Until recently, the Board had undertaken little or no work within the cities. When, however, the constitution of the National Roads' Board was amended to include municipal representatives, the Board assumed the responsibility for providing better routes through the municipalities. These roads have always had to accommodate the heaviest vehicles, because many cities are also seaports. Nevertheless, as public transportation now requires large buses with heavy axle loads, many routes have had to be upgraded. Meanwhile, the internal roading system in New Zealand has been improved to such an extent that hindrances to the free movement of traffic are becoming more pronounced only as such highways reach the city boundaries. The solution of the problems, particularly at intersections, is both complex and costly. Some of the work is being done by the cities and some by the National Roads Board, which acknowledges that “through” routes are part of the system. The Auckland Metropolitan Planning Authority has investigated the problem of traffic flow within its limits; in other cities the problem has been so complex and time consuming that overseas consultants have been engaged. Wellington city, for instance, has recently received a master plan for future development from such a firm.
Traffic Flow
In order that planning may be integrated more closely with transport needs the National Roads Board conducts traffic counts on all main routes at regular intervals, when the number of cars, as well as the number and weights of heavy vehicles, is recorded. The bulk of the traffic is local but on some of the major or arterial routes, through traffic is increasing to such an extent that by-pass roads have become desirable. Traffic counts taken on city streets usually show greater density than do those on nearby rural highways. Normally the pattern shows a marked increase as the road enters an urban area and a corresponding decrease as it leaves.
Recent traffic counts taken on the Auckland-Wellington main route give the following figures: at the south end of the Auckland Motorway density reaches 17,000 vehicles per day, falling to 2,800 south of Mercer and increasing again to 6,000 between Ngaruawahia and Hamilton. Between Hamilton and Cambridge the traffic averages 4,500 vehicles per day; on the Desert Road, 500; at Himatangi, 2,800; and north of Paekakariki, 6,100 vehicles per day. The Hutt Road, which connects the Hutt Valley with Wellington city, carries up to 30,000 vehicles per day. This is the densest traffic, outside city limits, on any road in New Zealand.
The traffic density in the South Island is generally much lighter than in the North. On the main route from Picton to Bluff the average varies considerably. Between Picton and Blenheim it is 1,400 vehicles per day; at Kaikoura, 400 vehicles per day; at Waimakariri Bridge, north of Christchurch, it is 6,500; at the Rakaia Bridge, 2,200; and north of Oamaru it drops to 1,000 vehicles per day At Milton, south of Dunedin, the average rises to 1,800 vehicles per day, while between Invercargill and Bluff it drops again to 1,400.
The situation in the larger cities is as follows. In Auckland, on the Great North Road just north of Point Chevalier Road, and also on Broadway in Newmarket, traffic density varies from 25,000 to 30,000 vehicles per day. In Wellington the traffic density south of Ngauranga is about 28,000 vehicles per day, increasing to 33,000 vehicles south of Ngaio Gorge. Waterloo Quay, north of Bunny Street, carries about 25,000 vehicles per day. In Christchurch the traffic in Blenheim Road is about 10,000 vehicles per day and the lower end of Papanui Road about 15,000 vehicles per day. In Dunedin trafic is about 20,000–25,000 vehicels per day along the Anderson's Bay Road, south of Cumberland Street, while the Main South Road in Caversham carries 10,000–12,000 vehicles per day.
Development of Roading
At the present time many new routes are being constructed which will give access to large areas of land for closer settlement. The West Taupo access road will open up fertile farming areas at present being broken in by the Departments of Lands and Survey and Maori Affairs. The Waipapa road scheme, which will connect est Taupo, via the west bank of the Waikato River, with Te Awamutu, will become a new main route between Auckland and Wellington. In the State forest area between Taupo and Rotorua hundreds of miles of roads have been built to serve the logging trucks which feed the paper mills at Murupara and Whakatane. In the South Island a particularly difficult problem is the completion of the Haast Pass road which will link Westland with Otago and so provide New Zeland with a wonderful tourist attraction. Along the Haast route, as in so many other districts, the bridging of numerous rivers and streams is not the least of the problems facing road engineers.
Road-building Materials
The best use of road-building material in New Zealand depends to a great extet on an understanding of the country's geology and petrology. Certain areas are volcanic in origin and provide good roading materials such as basalt or, as in the case of Taranaki, andesite, a softer rock. The scoria of the Auckland area is an asset. In the centre of the North Island, around Tongariro National Park, the brown ash is very poor and fails completely when wet. The rhyolite ignimbrite and pumice of the Waikato Valley are familiar to most travellers, but these have limitations. In general, the North Island is deficient in good roading materials, and the plastic clays and volcanic ash in the Auckland Province make remedal measures most expensive. Some areas, such as Hawke's Bay, Canterbury, and Southland, are fortunate to have excellent greywacke gravels, the reslt of the denudation of the main ranges. Although these gravels are most useful for road bilding tey require special consolidation to stand up to the stresses of modern traffic. Frost and ice are special winter problems in some places. In varous parts of the country roads have had to be built on poor swamp foundations, as, for instance, near Bluff, to the north of Wellington near Paraparaumu, and in the Waikato and Bay of Plenty districts.
In both islands there are high mountain ranges which binder road communications. There are no low alpine passes suitable for road crossings on the Southern Alps between the Lewis Pass and the Haast Pass, a distance of 180 miles. In the North Island the only low crossings are the Manawatu Gorge and the Waioeka Gorge. Throughout the country ribs from these ranges or foothills set the highway engineer an exacting problem.