The preferred route option is unlikely to be superior in every respect. The final selection process is one of judging between a number of disparate factors.
Appraisal Summary Tables (ASTs) summarise the significant consequences of a road investment proposal and are set out simply and concisely using the five Government over-arching objectives for transport as headings. Presenting the information in this way provides decision takers with a clear and reliable basis for their decisions, without giving prominence to any one type of impact or to benefits expressed in monetary terms compared with those that cannot be monetised.
The Appraisal Summary Tables provide a formal and comprehensive assessment according to the principles:
- all significant impacts are measured
- wherever possible, the assessments reflect the numbers affected (drivers, residents, sites and so on) as well as the impact on each
- ensure transparency; assessments are carried out in a structured way, using specified information
- simple judgements of overall impact are avoided
- assessment of any specific subsidiary objective is, as far as possible, comparable between proposals
Putting these principles into practice is difficult to achieve. It is not possible to specify quantitative measures for all objectives, and summary assessments take three different forms:
- Where current appraisal practise is to estimate monetary values, these are used, presented as present values - this applies to safety, journey times and vehicle operating costs, and scheme cost objectives
- Where reliable quantified assessments can be made, these are used - this applies to the noise and local air quality objectives; and
- Where quantified assessments cannot be made, or where they are very broad brush, a textual scale is used - this applies to all the other objectives.
It is important to note that summary assessments are not generally comparable between objectives. The summary assessments enable those making the decisions to compare the impacts of one option with those same impacts which would result from other options. But because the various impacts measured in the Appraisal Summary Tables are very different from each other, they cannot be combined into a single measure of an option's overall performance.