Definition – A scenario is a description of possible actions or events in the future, such as a possible future set of demographic and economic conditions.
Relevance to SUMP – When developing a strategy, the planning authority should consider the changing context for mobility in the future. One problem when developing a SUMP for a long timeframe (e.g. 15 years) is that the context becomes less certain. The principal uncertainties typically relate to changes in economic and demographic factors, such as changes in population, household size and income levels. The direction and pace of technological change is a further uncertainty. Developing a range of scenarios based on population and economic projections enables planners to undertake an appraisal of the performance of alternative mobility strategies under different future conditions. Scenario appraisal normally involves consideration of a “business as usual” baseline case. This assumes that future economic and transport trends follow those of the past and that no changes in mobility policy take place.
Source: Cambridge Dictionaries (online); KonSULT (online)