In the case of a single intervention, forecasts are ideally required for the year of opening (see below) and a second 'forecast' year, some years after opening. In the case of a strategy or plan, forecasts are ideally required for at least the year of opening of each of the main elements of the option and for the future 'forecast year'. However, it may not always be practical to conduct forecasts for the opening years of every one of the main elements of an option. In such cases an appropriate common year should be chosen so that streams of costs and benefits can reasonably be inferred from a variety of different starting points.
