ROAD PLANNING AND MAKING
By E. A. H. McDonald (Visitor)
Presented at a Joint General Meeting of the Durban Branch of the Engineers' Association (S.A.), the Natal Institute of Engineers and the Natal Branch of the Institution of Certificated Mechanical and Electrical Engineers, South Africa, 6th August 1964.
ABSTRACT
The paper covers the more interesting activities of the Natal Roads Department.
National and Provincial Roads and freeways, their classification and standards of construction are referred to. Certain aspects of the Natal provincial road policy are discussed. The annual expenditure on roads in Natal is given. Legislation applicable to Natal roads is mentioned.
Here are indeed few people who will not concede that a country's transportation system is probably the main feature which distinguishes a progressive country from a backward one. It is a fact that efficient transportation is a sine qua non without which no country can develop to compete with others in today's keen competition for economic survival.
The motor vehicle of today and modern highways are complementary. Without the well-planned road, the safe road spanning valleys and cutting through ridges, the road with the wide smooth sur-face, easy curves and gradient and adequate bridges and culverts, the motor vehicle is not an economic solution to the transport problem. It is said in the United States of America that it costs more not to have good roads than it does to have them, but even there they are faced, as we are, with the economic fact that 'available resources which can be used in different ways are limited about various desirable aims'.
The first problem then is planning. Where should the roads be built to serve the first needs first; to what standard should they be built; how can the available resources be allocated most advantageously? I have been said that whereas in the case of national roads the standards used are acceptable, those applied to provincial roads are not satisfactory and that the policy of the roads department regarding its standards should, therefore, be reviewed.
The question that arises, therefore, is whether this administration is building roads of not sufficiently high a standard. As an answer and in vindication of the policy of the Department I propose giving the method used in coming to a decision on the standard to be applied and also the practical implications involved in the implementation of the decision.
Primarily the criterion for a road to qualify for being black-top standard is its present traffic density and Its future traffic potential. In assessing these, regard has to be had not only to its numerical count but also nature, weight and purpose of the traffic which is using the road under consideration.
Once a decision has been reached that a road merits improvement to black-top standard, the next step is the determination of the standards, both geometric and structural, that should be adopted. The geometric standards of a road deal with the dimensions of the visible features of the road such as alignment, sight distance, width, slopes, grades and so on, as distinct from the structural design, which amongst other things, has reference to the thickness, composition of materials, and load-carrying capacity.
It should be realised that available finances do not permit the construction of the ideal in road design. It is, however, suggested that when the economy is necessary, it be practised on some feature of the road design other than on the geometric features.
The roadway section can always be improved and widened at a reasonable cost; the paving surface can be widened and strengthened at any future date when finance will permit; but the geometric features of alignment, grade and sight distance, when once moulded to the landscape and tied down to paving surfaces and rights of way, are most difficult and expensive to correct. It is essential, therefore, that in decisions on geometric standards a generous factor of safety should be allowed to cater for possible future requirements. It must, however, be pointed out that, although it is desirable to have high geometric standards, these standards will be dictated to a large degree by topographical features and economic considerations.
The standards decided upon can, and do, vary from a 30-mile per hour to a 60-mile per hour design speed, and these are illustrated practically by the low design speed of the Muden-Greytown road built on its old location and the high design speed of the Dundee- Vryheid road. It would, however, be a retrogressive step to adopt a low standard in all cases.
Another aspect affecting the road policy of the province is the question of cost-benefit. Considerations
of traffic safety alone demand that certain minimum standards of alignment, grade and visibility be adhered to and only prohibitive costs should cause the adoption of lower standards.
Once a road design has attained an adequate safety standard, It should be examined to ascertain whether further Improvement is justified. For this purpose, the technique of cost-benefit analysis is used in which the saving in time and vehicle operating costs are balanced against the cost of any improvement.
These factors are readily evaluated once the probable traffic density has been assessed, and, if the capitalised value of such saving exceeds the cost of the proposed Improvement, there is justification for such Improvement. Let me illustrate by an example:
Survey shows that a road carrying 500 vehicles per day can by deviation be shortened by one mile. Taking the cost of vehicle operation at the conservative figure of 10d. per. mile the annual saving enjoyed by the general public is ￡7 600. This sum represents the interest and redemption of the capital of ￡95 000 borrowed over 20 years at 5 %. If, therefore, the deviation can be earned out for less than that figure it is economically warranted, even though time savings, reduced maintenance costs and other benefits have been disregarded, This example is, of course, an over-simplification of the technique of cost-benefit analysis but it serves to illustrate the method of approach.
Although up to the present only some 14% of the Province s road system has been black-topped, approximately 75% of all provincial rural motor traffic in the province is carried on these black-topped roads. Natal, which is the smallest province in the Republic, is renowned for its scenery, Its holiday resorts, both on the Indian Ocean coasts and in the Drakensberg mountain range and, if I may be permitted to say, for its roads. The Province spends some 16 million rands annually on its 7 900 miles of road, 8 million rands on national road construction and million rands on maintenance and betterment of the entire road system. The construction of new roads is simplified to a great extent by two government ordinances.
Firstly, the Government incorporated a clause in the title deeds of land sold for farming giving it the power to expropriate 100 ft strip of land for road or railway construction wl.th further powers to compulsorily purchase land of widths up to 250 feet. No compensation is therefore paid to the landowner for strips of land less than 100 ft wide but he is compensated for the loss of improvements such as crops, buildings, irrigation, drainage, and so on, which are destroyed through the construction of a road.
As farms in Natal are usually between 500 and 3 000 acres in extent, the farmer is prepared to give up a narrow strip of his land to gain access to an Improved road, except in the case of freeways. Indeed, the value of his property increases when served by an all-weather road whether it be freeway or expressway.
Access to main roads is also controlled by ordinance in that no access may be made to the main road without the permission of the Chief Roads Engineer and the Chief Engineer may alter any existing access at his cost to a more suitable position. As I have mentioned, access is denied completely except at interchanges in the case of freeways.
The effect of this ordinance is to speed up new construction since once the road design has been drawn up, the compensation to the farmer is fixed by mutual agreement between the Chief Engineer and the landowner. The question of public enquiry never arises. In the event of disagreement regarding compensation, the case is brought before a statutory body for arbitration.
Secondly, the maximum axle load is fixed by law at 18 000 lb hence the design of the pavement is based on a wheel I ad of 9 000 lb. This law is not difficult to enforce and the transportation companies overcome the difficulty by modifying their vehicles to incorporate an extra axle if the laden weight is excessive, Occasionally this requirement cannot be met in the case of industrial equipment requiring transportation and in such cases, special transport permits are issued by the Chief Engineer.
Bridges are designed to full British Ministry of Transport loading, as a bridge failure under heavy loading is much more serious than isolated pavement failures.
I am very pleased to say that because the people of Natal take pride in their roads they are prepared to accept this ordinance for the benefit of the community and are happy to see the road system developing so that cases of the dispute are few and far between.
Broadly speaking, the roads in the province are divided into two groups: (a) National and (b) Provincial. National roads are the inter-city and interprovincial main roads such as the Durban-Johannesburg, Durban-Cape Town and Durban-Bloemfontein roads. There are approximately 550 miles of National roads within the province. These are constructed and maintained by the province to a specification laid down by the National Transport Commission, which is also responsible for the financing of such construction and maintenance. The roads are usually 24 ft wide, black-topped carriageways with 8 ft shoulders and are designed to a minimum 50 mile per hour speed standard with a maximum gradient of 5%. The design is naturally based on traffic studies and dual carriageways are provided on the sections with high traffic densities. Also, provision is made in the design for future improvement of all national roads to dual carriageway, limited access standards.
The bridges are normally designed to allow for doubling the deck width. In some instances, the abutments of bridges are constructed to allow for these possible future requirements. Fly-over and rail-over-road structures are often built incorporating two spans for future development.
Provincial roads, which are financed by the Provincial Council, can be sub-divided into two groups.
Under group one are the inter-town roads built to the same standards as national roads and with sections of the dual carriageway where traffic densities are high. There are approximately 540 miles of roads in this group.
In group two, totalling approximately 7 000 miles, are the minor roads or farm-to-market roads usually of gravel surfaced construction. These roads are being improved in priority, depending on traffic counts, to 22 ft wide black-top standard with the elimination of all railway level crossings and a design speed of 50 miles per hour with a maximum gradient of 7%.
Now some comments on freeways which are currently being constructed in Natal.
I think it can be said that South Africa can be justifiably proud of its achievements and its steady and healthy development over a comparatively short period. Its economy may be regarded as buoyant and as stable as international conditions will permit. Let us examine the road and transportation system as part of its economy.
Transportation, whether by road, rail, air or water, is an integral part of the social and economic systems of a country, and it can be said that the rapid development of a country is only possible if its transportation system is highly efficient and modern. A feature of 20th-century progress has been the development of road traffic. In the United States of America in particular, this mode of transport has outstripped in other forms and has necessitated, particularly since World War II, a forced growth and development of r ad systems of fantastic magnitude. It is probably true that the superhighway or freeway is not the final answer to the road traffic problem, but it certainly is an indispensable part of the solution.
The phenomenon of a rapid change-over to road transport has, as we know, occurred in our own country and despite the considerable progress made In post-war years in providing inter-provincial or national roads, It has not been possible as yet to keep up with the demands of traffic, more particularly in the larger urban areas. However, extensive plans are now underway which, in the next decade should result in a great improvement in our road' system.
In planning adequate roads, particularly freeways we have been fortunate in being able to draw extensively on overseas, particularly North American, experience, practice and research. Provided this data is applied intelligently it can be used extensively on our road systems.
It is, incidentally, interesting to note the effects of tradition and history on a country's roads. In Great Britain, these have been at least partly responsible for the present old-fashioned and inadequate road design, whereas in the United States they have had little or no adverse effect on the road system which has and is developing unhampered to an advanced stage of efficiency.
Natal became a partner in the business of constructing inter-provincial roads in 1935 with the formation of the National Road Board, now the National Transport Commission. Some of the declared roads had been surfaced at this stage, including the main arteries converging on Durban, the centre of greatest activity in the province. They linked the urban and semi-urban areas along the routes, forming sections of road with intermittent bottlenecks at each (of the towns or local authority areas.
These bottlenecks, the comparatively low geometric standards and the almost total lack of access control reduced the traffic to speeds of 35 to 40 m.p.h. With the growth of traffic, the problem of improving the standards arose, but little actual construction took place until after the war when construction to expressway standard was carried out on portions of the national roads.
Route 3 showed the greatest rate of growth largely as a result of township development following the provision of a dual carriageway, 4-lane road, increasing from 8 000 vehicles per day (V.P.D.) in 1954 at Westville to 19 000 V.P.D. in 1962, with peak volumes of up to 37 000 V.P.D. and 3 600 vehicles/carriageway/ hour. The previous reasonably adequate intersections at grade became accident "black spots" and in 1955 it was decided to convert the road to freeway standard in stages as far as Pinetown.
Subsequently, partly as a result of a change in policy, and partly owing to the improvement in the finances of the national road fund, it was decided to construct Route 3 from Durban to Mooi River, Route 2 from Durban to the Illovo River and Route 14 to the Umhloti River to freeway standard.
As an experiment, the new Route 14 from Tongaat as far as Chaka's Rock has been constructed as a single carriageway to extend eventually as far as new Guelderland.
The main features of freeways are their high geometric standards based on driver behaviour and vehicle performance, and the complete elimination of all direct conflicts by elimination of at-grade crossings using grade separations, interchanges and access or service roads.
One of the major considerations of a freeway is the spacing of interchanges. For economic reasons, these should be spaced as far apart as possible but from a service point of view, the spacing has its limits.
This problem is also affected by the adequacy or otherwise of the existing road system as well as the extent of development of adjoining land. On Route 3, between Durban and Pietermaritzburg, the average spacing in Westville and Pinetown is 1 1/4 miles and thereafter two miles plus, whereas between Pietermaritzburg and Mooi River the average spacing is 4 miles. On Route 14 it Will be two to three miles and on Route 2 about two miles.
Dealing specifically with the Department's organisation the Province is divided into five districts controlled by District Engineers each with a compete staff organisation and an individual annual financial allocation under their direction. The entire organisation is under the Chief Engineer, who directs the work of the Department following the five-year development plan.
The allocation of finance voted by the Provincial Council for roads is apportioned by him to the various divisions of the Department. Financial allocation is based on a budget prepared by the Chief Engineer and is made up as follows:
For national road construction and maintenance, the allocation is derived from fuel tax. In the case of provincial road construction, it is met from capital funds with a 20-year redemption period for roads and 40 years for bridges. Certain construction is also carried out and financed from revenue.
The expenditure on maintenance of the roads is met entirely from revenue derived from annual vehicle licence fees based on the weight of the vehicle and a central government subsidy.
The Traffic Engineering Section organises and records the traffic statistics for the Province. It undertakes traffic studies and loadometer surveys. It is advised of all road accidents by the police and it controls the signposting and traffic marking of roads. From his records and statistics, the Traffic Engineer can advise the Chief Engineer and other sections of pre-planning priorities and design standards.
Traffic censuses are carried out annually on all road in the Province, there are about 700 counting points, with the duration of the counts varying from 12 hours in one day to continuous 24-hour counts taken for every day of the year. The counter used is the pneumatic type mechanical recorder, which stamps the time and the traffic volume on a recorded tape.
The results of these counts are analysed annually and adjusted to annual average daily traffic, from which a traffic volume map is produced for the Province. Growth of traffic is then estimated using the information from the above map to calculate the vehicle miles. This is then plotted on a graph against time. The number of vehicles registered in the Province is plotted similarly and also sales of fuel. The latter method gives a good indication of traffic growth because the miles per gallon run by vehicles has not changed appreciably in the past 10 years and is likely to remain fairly constant. Consideration of the trends of each of these items enables a reasonable prediction of future traffic growth to be made.
It is interesting to note from these graphs that between the World Wars the growth of traffic was 5% compound per year. Over the last few years, there has been a marked increase in road traffic, probably due to the growth of population and the economic position of the country with the result that traffic has been increasing at between 7% and 8% per annum on the major roads and 6% per annum on other roads. These figures have been accepted for design purposes in Natal.
Loadometer surveys are carried out with police assistance at selected points where, in some cases, permanent weighbridges have been constructed or at lay-byes where portable loadodometers are used.
Accident records are sent to the Traffic Section by the police and are analysed and plotted on strip maps of the roads. These maps are a graphical representation of the road's features with the road shown as a straight line and the alignment featuring the bridges, intersections and so on. In this way the "black spots" become apparent and these are subsequently investigated by the Traffic Engineer who advises what steps should be taken to effect an improvement in road safety.
The geometric design is based on traffic studies either on count alone or on origin and destination surveys, as the case may demand. Roads are usually designed for a 20-year life, therefore the traffic volume is calculated on the present traffic expanded at a compound rate of 7% or 6% (whichever may apply) over 20 years and the average volume of this period is taken as the design volume.
In conclusion, I would emphasize that the paper gives a broad picture only of the activities of the
Roads Department. As considerable time would be taken up by covering the whole field I have tried to deal with only the more interesting activities of that Department.