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1.6.1 Introduction

As illustrated in Figure 1.1, there are many disciplines in addition to geometric design itself that impact on the final design that is to be built.

In countries that are well-endowed with wide-ranging professional skills, the geometric designer can focus on his or her field of interest with the ancillary information being pro- vided by others. It would, if only in order to be able to ask the right questions and then to interpret the answers’ impact on the design be necessary to have some knowledge of the supporting disciplines. In other countries that are less fortunate, it may be necessary for the geometric designer to become involved in these disciplines as well.

These supporting disciplines are discussed further below.

1.6.2 Systems analysis

All the geometric designer is really doing is seeking an answer to a problem. The first step, thus, is to define the problem. It is remarkable how often a design is produced without much thought being given to the underlying problem. The client may suggest that the problem is that a road is required between two points. If this is the brief provided to the designer, it is to be trusted that the client had at least undertaken a process that led to this conclusion being drawn. Unfortunately, this may not always prove to have been the case.

For example, industries may be set up in areas where their input materials are at hand. On the other hand, if their processes are labour intensive, it may be worthwhile for them to be located adjacent to their potential labour force. As a further alternative, it may financially be more attractive if they were to be located in close proximity to their markets.

These three alternatives result in totally different transportation problems to be resolved. Should the workers be required to commute to the industrial area? If so, should this be by public transport and, if so, should the mode be rail or road? If the industries concerned are to be relocated to the location of the potential source of labour, this would require the movement of materials rather than of people. Raw materials may have to be shipped in and finished products shipped out. Rail transport may thus be more suitable than transport by road. The third alternative would require the movement of both people and raw materials, whereas the final movement of products to the market would be relatively straightforward.

Systems analysis needs to be brought to bear on the transportation problem to be solved. It comprises a hierarchy of steps, as follows.

10 Geometric design of roads handbook

• Problem definition

• Identification of possible solutions

• Selection of a solution appropriate to the problem being addressed • Implementation of the proposed solution

• Monitoring the outcome of this implementation

Implementation may lead to the emergence of a new problem or monitoring to identify one previously hidden by the old problem. This completes the loop leading to a further round of systems analysis. Without knowledge of systems analysis and the ability to apply its prin- ciples, the likelihood of a successful design being developed is reduced.

1.6.3 Project analysis

One of the steps in the systems analysis process is the selection of the problem solution to be implemented. It is a fact of engineering life that problems having only one unique solution do not exist outside the classroom. There could be many solutions that are patently wrong or unimplementable but, equally, there could be many solutions that, to some greater or lesser extent, address the problem. However many adequate solutions are found, only one can be implemented. Which then is the most adequate solution? Economic analysis offers one way of comparing competing solutions and utility analysis another. Without these analytical tools, the application of systems analysis would not be possible.

Economic analysis involves a determination of the economic benefits accruing from pro- viding the road in comparison with the cost of providing it. Three methodologies could be brought to bear on this form of analysis.

• Rate of return • The benefit/cost ratio • Net present worth

The first mentioned would be employed by a national or state government that has to pro- vide a variety of competing services to the population, such as education, health care and transportation, ensuring an equitable allocation of its limited budget. It would also be used by transport economists in allocating financial resource to competing modes of transport or to competing roads such as between A and B vis-à-vis between C and D.

Geometric designers, however, typically have to decide between competing routes that provide the same service, that is, only one of which is going to be selected for design and construction. Either the benefit/cost ratio or the net present worth method could be used for this purpose. Regardless of which method is used, the ultimately ranking of the competing routes would be identical.

Design and construction costs are incurred during a relatively short period of time whereas maintenance and road user costs accrue over the lifetime of the road. In addition to being familiar with the two possible forms of analysis, it is necessary to be aware of the process of discounting future costs to a common baseline year.

Utility analysis comes into play where roads have a social as opposed to an economic value. Roads that serve as links to schools, hospitals or recreational areas would fall into this category. Utility analysis provides a formalised allocation of nonmonetary values to each of the facilities served by the various possible routes under consideration. Typically, roads have a combination of economic worth and social value. Both would have to be borne in mind in the final decision of the route to be designed and built.

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1.6.4 transportation planning

Convenience simply means that people can move between origin and destination with- out having to suffer inordinate levels of congestion and correspondingly long travel times, which include having to cope with over-saturated intersections. Questions that have to be answered are thus:

• ‘How many people would require or wish to move from A to B, C to D, etc.?’ • ‘Where are A, B, C, D, etc. relative to each other?’

• ‘What would the preferred mode of travel be – car, bus, train etc?’ • ‘What would the average occupancy of each vehicle on the network be?’

Origin–destination surveys and other high-level predictive techniques will ultimately pro- vide the geometric designer with information on traffic volumes that have to be accommo- dated on the roads in the network including the road of immediate interest. These techniques fall in the realms of transportation planning. The geometric designer should have some understanding of transportation planning and the techniques it employs to verify the valid- ity of its findings and its application to road geometry.

1.6.5 Capacity analysis

Roads are never designed to accommodate only the traffic that is anticipated to currently use it. They have to provide some or other acceptable level of service in a future year, typically at the end of the design life of the road. The cross-section of the road is predicated on the volume of traffic anticipated for that future year. The cross-section can be anything from a multi-lane freeway to a two-lane two-way road and, in very limited circumstances, may be only one lane wide with passing bays. It is necessary for the designer to carry out capacity and level of service analyses to determine the cross-section that has to be provided.

Furthermore, roads carrying large volumes of traffic moving at high speeds generally have higher geometric standards than those applied to lower order roads. Level of service and speed inputs thus also have a bearing on more than just the cross-section.

Because urban intersections are usually closely spaced, the efficiency of urban networks is dependent on the capacity and level of service provided by these intersections. A turning vehicle can cause considerable delay to the vehicles following it so that, even where only one vehicle wishes to turn across opposing traffic, it may be advisable to provide a turning lane. The deter- mination of the required length of turning lane becomes an application of traffic flow theory.