1.23
the issue of PLB's. In order to provide comparative infor- mation on the effect of PLB's a network similar to that
operating today was introduced into one of the options. The Option B network was selected for this purpose since it permitted the examination of continued PLB operation in the context of maximum availability of street capacity.
The development and evaluation of the alternatives was seen as a process from which a set of conclusions would be reached and a recommended strategy developed. It was not anticipated that one of the options, as originally specified, would include all of the features that would be recommended at the conclusion of the study.
Evaluation of the Alternative Systems
1.24
Evaluation consists of assessing the effects of each alternative in terms of predetermined quantitative features such as costs, benefits and capacity relative to demand. The process itself can be thought of as a mechanical one since all of the inputs are specified beforehand. However `interpretation of the results of the evaluation process and
the selection of a preferred plan or strategy involves. the judgement of those responsible for planning and decision making. This arises because of uncertainty about the appropriate value to be placed on some of the inputs used in the evaluation process, because some results may be weighted differently to others by the decision maker and because other factors may be taken into account that are either very difficult to quantify or impossible to express in numerical terms.
1.25
In order to distinguish as much as possible between these different aspects of evaluation and selection the two processes have been separated to the greatest extent possible. The remainder of this section and Chapter 2 are predominantly concerned with evaluation. Chapter 3 is predominantly concerned with other factors and issues considered in
selecting a preferred strategy. It is not entirely academic to note however that the judgement of the Study Team and the
12