It seems appropriate to describe in short the interpretation of the theme adopted in this paper. The basic components of the theme:- 1. road safety measures 2. choice 3. governing principles are defined as follows: Definition 1 A road safety measure is any measure which influences road safety. This includes measures that are not intended to influence road safety and even measures with an adverse effect on road safety. Definition 2 Choice is a decision, determining the comparative preferability of one alternative above another. This applies both to the determination of an optimum when the only distinguishing features of the alternatives are their parameter values, and to a ranking process when the alternatives are essentially different and independent of one another.· The comparison of a single measure with the existing situation is a special case of this "ranking". Definition 3 A governing principle is a criterion for decision making. Ifthe social system in question requires a rational method of decision-making the criterion must be expressed as some function of the relevant characteristics of the system. The relevant characteristics and consequently the "criterion function" generally have different values for alternative measures. The order of preferability of the alternative measures is determined by the order of the associated values of the criterion function. Sections 2 and 3 discuss the possibilities and limitations of benefit-cost relationships as an aid towards taking rational decisions in a rather abstract way, i.e. not specifically associated with road safety measures. Section 4 comprises a critical commentary on the preceding sections; some complications which may arise and are not discussed in preceding sections are briefly mentioned. Section 5 gives examples of applications of the method to road safety measures to illustrate its practical value for decision making. 2. The relevant characteristics Incomplex social oreconomic systems there are generally a great many variables and parameters characterizing the state of the system. These are the characteristics of the system. The objective of a specific measure is to influence some of the characteristics. Generally some will have to be changed to achieve the measure. And a side effect of ·the measure may be to alter yet other characteristics. Together these three groups are the relevant characteristics associated with the measure. They can be divided into two categories with regard to decision making. a) Cost: The investment required to make the measure operational; b) Benefit: The results obtained with respect to general objectives. The investment required is drawn from the resources of the system characteristics such as available manpower, energy, land, money etc. Generally the cost can be evaluated in money. The benefits are of a different nature depending primarily on the objectives of the measure. In the case of measures \Vith an economic objective the benefits can also generally be evaluated in money. Measures with a social objective, such as the improvement of social security or public health and the protection of human rights, have benefits of a different kind. Attempts are made nevertheless to evaluate these benefits in terms of money. No doubt there are economic advantages associated with an .increase in public health or social security, but these are only a minor part of the scene. The fundamental importance of such measures lies primarily in the domain of humanitarian values, the evaluation ofwhich according to some arbitrary economic scale seems very unlikely to Q.e generally_ accepted. Apparently decisions related to measures with social objectives will have to involve benefits and costs in different dimensions. Relevant characteristics of a road safety measure are the frequency and seriousness of road accidents. In view of the definition of road safety measures given in the introduction, these characteristics may occur as side effects of measures intended to serve other objectives. Traffic measures, such as traffic control and reconstruction of road networks, primarily intended to influence capacity, travel speed, congestion and other economic objectives, may in particular have such side effects. Similarly, measures to improve road safety generally also have economic effects. If several relevant characteristics are influenced by a measure, it is unrealistic to evaluate the benefit only in terms of its objective. An evaluation including all relevant characteristics is a complex operation. If a more restricted definition of road safety measures was chosen, i.e. if only measures having no other relevant characteristics than road safety were considered, one would expect that all the benefits ofalternative measures might be evaluated in the same dimension, e.g. some scale in which accident data are presented, thus avoiding the complications mentioned above. (Author/publisher)
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